Fruit Manufacturing

FOOD ENGINEERING SERIES Fruit Manufacturing Scientific Basis, Engineering Properties, and Deteriorative Reactions of Technological Importance JORGE E. LOZANO

FRUIT MANUFACTURING Scientific Basis, Engineering Properties, and Deteriorative Reactions of Technological Importance

FOOD ENGINEERING SERIES Series Editor Gustavo V. Barbosa-Ca´novas, Washington State University Advisory Board Jose Miguel Aguilera, Pontifica Universidad Catolica de Chile Pedro Fito, Universidad Politecnica Richard W. Hartel, University of Wisconsin Jozef Kokini, Rutgers University Michael McCarthy, University of California at Davis Martin Okos, Purdue University Micha Peleg, University of Massachusetts Leo Pyle, University of Reading Shafiur Rahman, Hort Research M. Anandha Rao, Cornell University Yrjo¨ — Roos, University College Cork Walter L. Spiess, Bundesforschungsanstalt Jorge Welti-Chanes, Universidad de las Ame´ricas-Puebla Food Engineering Titles Jose M. Aguilera and David W. Stanley, Microstructural Principles of Food Processing and Engineering, Second Edition (1999) Stella M. Alzamora, Mar´ıa S. Tapia, and Aurelio Lo´ pez-Malo, Minimally Processed Fruits and Vegetables: Fundamental Aspects and Applications (2000) Gustavo V. Barbosa-Ca´novas and Humberto Vega-Mercado, Dehydration of Foods (1996) Gustavo V. Barbosa-Ca´novas, Pedro Fito, and Enrique Ortega-Rodriguez, Food Engineering 2000 (1997) Gustavo V. Barbosa-Ca´novas, Enrique Ortega-Rivas, Pablo Juliano, and Hong Yan, Food Powders: Physical Properties, Processing, and Functionality (2005) P.J. Fryer, D.L. Pyle, and C.D. Reilly, Chemical Engineering for the Food Industry (1997) A.G. Abdul Ghani Al-Baali and Mohammed M. Farid, Sterilization of Food in Retort Pouches (2006) Richard W. Hartel, Crystallization in Foods (2001) Marc E.G. Hendrickx and Dietrich Knorr, Ultra High Pressure Treatments of Food (2002) S.D. Holdsworth, Thermal Processing of Packaged Foods (1997) Lothar Leistner and Grahame Gould, Hurdle Technologies: Combination Treatments for Food Stability, Safety, and Quality (2002) Michael J. Lewis and Neil J. Heppell, Continuous Thermal Processing of Foods: Pasteurization and UHT Sterilization (2000) Jorge E. Lozano, Fruit Manufacturing: Scientific basis, engineering properties, and deteriorative reactions of technological importance (2006) R.B. Miller, Electronic Irradiation of Foods: An Introduction to the Technology (2005) Rosana G. Moreira, M. Elena Castell-Perez, and Maria A. Barrufet, Deep-Fat Frying: Fundamentals and Applications (1999) Rosana G. Moreira, Automatic Control for Food Processing Systems (2001) M. Anandha Rao, Rheology of Fluid and Semisolid Foods: Principles and Applications (1999) Javier Raso-Pueyo and Volker Heinz, Pulsed Electric Field Technology for the Food Industry: Fundamentals and Applications (2006) George D. Saravacos and Athanasios E. Kostaropoulos, Handbook of Food Processing Equipment (2002)

FRUIT MANUFACTURING Scientific Basis, Engineering Properties, and Deteriorative Reactions of Technological Importance Jorge E. Lozano PLAPIQUI (UNS-CONICET) Bahia Blanca, Argentina

Dr. Jorge E. Lozano PLAPIQUI (UNS-CONICET) Camino La Carrindanga KM.7 C.C.: 717 8000 Bahia Blanca Argentina [email protected] Color illustration: Santiago Lozano, Amblagar Studio, www.amblagar.com Library of Congress Control Number: 2005936521 ISBN-10: 0-387-30614-5 e-ISBN 0-387-30616-1 ISBN-13: 978-0387-30614-8 Printed on acid-free paper. ß 2006 Springer ScienceþBusiness Media, LLC All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer ScienceþBusiness Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed in the United States of America. 987654321 springer.com

PREFACE The fruit processing industry is one of the major businesses in the world. While basic principles of fruit processing have shown only minor changes over the last few years, major improvements are now continuously occurring, and more efficient equipment capable of converting huge quantities of fruits into pulp, juice, dehydrated, frozen, refrigerated products, etc. make possible the preservation of products for year-round consumption. The fruit processing and storage, even under the most industrially available ‘‘mild conditions,’’ involves physical and chemical changes that negatively modify the quality. These negative or deteri- orative changes include enzymatic and nonenzymatic browning, off-flavor, discoloration, shrinking, case hardening, and some other chemical, thermophysical, and rheological alter- ations that modify the nutritive value and original taste, color, and appearance of fruits. The ability of the industry to provide a nutritious and healthy fruit product to the consumer is highly dependent on the knowledge of the quality modifications that occur during the processing. This book emphasizes the products rather than the processes, procedures, or plant operations. It presents the influence in fruit products’ quality of the different processing methods, from freezing to high temperature techniques. Origin of deterioration, kinetics of negative reactions, and methods for inhibition and control of the same are discussed. Prob- able changes in thermodynamical, thermophysical, and rheological properties and parameters during processing of fruits at a wide range of soluble solids, temperatures, and pressure are also summarized. This book is intended to provide professionals involved in development and operations of the fruit industry, with the necessary information for the understanding of the deteriorative effects on the fruit quality during processing. v

CONTENTS 1. Overview of the Fruit Processing Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Classification of Fruits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.3 World Production and Commercial Applications of Fruits . . . . . . . . . . . . . . . . 1 1.4 History of Fruit Products’ Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.5 Harvest of Fruits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.5.1 Chemical Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.6 Postharvest Handling of Fruits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.6.1 Postharvest Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.6.2 Cooling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.7 Controlled Atmosphere Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.8 Modified Atmosphere Packaging of Fruits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.8.1 Factors Affecting Fruit Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.8.2 Factors Influencing the Exact Modified Atmosphere Within a Sealed Pack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.9 Technology of Semiprocessed Fruit Products . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.9.1 Preservation of Semiprocessed Fruit Products . . . . . . . . . . . . . . . . . . . . . 17 2. Processing of Fruits: Ambient and Low Temperature Processing . . . . . . . . . . . . . . . . . 21 2.1 Fruit Products and Manufacturing Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2 Fruit Juice and Pulp Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.1 Front-End Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2.1.1 Reception Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2.1.2 Final Grading, and Inspection and Sorting . . . . . . . . . . . . . . . 28 2.2.2 Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.2.2.1 Citrus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.2.2.2 Pomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.2.2.3 Pressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.2.2.4 Other Extraction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.2.3 Clarification and Fining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2.3.1 Partial Concentrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2.4 Use of Enzymes in the Fruit Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.2.4.1 Other Enzymes in Juice Production . . . . . . . . . . . . . . . . . . . . . . 37 2.2.4.2 Pectinase Activity Determination . . . . . . . . . . . . . . . . . . . . . . . . 38 2.2.4.3 pH Dependence on the Pectic Enzymes Activities . . . . . . . . . . 39 2.2.4.4 Enzymatic Hydrolysis of Starch in Fruit Juices . . . . . . . . . . . . 40 2.2.5 Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.2.5.1 Pressure Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.2.5.2 Filter Aid and Precoating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 vii

viii Contents 2.2.6 2.2.5.3 Types of Pressure Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.2.5.4 Vacuum Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Membrane Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.2.6.1 Stationary Permeate Flux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.2.6.2 Permeate Flux as a Function of Time . . . . . . . . . . . . . . . . . . . . 50 2.2.6.3 Influence of VCR on the Permeate Flux . . . . . . . . . . . . . . . . . 51 3. Processing of Fruits: Elevated Temperature, Nonthermal 55 and Miscellaneous Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.1 Pasteurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.1.1 Batch Pasteurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.1.2 HTST (Short Time) Pasteurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.1.3 UHT Pasteurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.1.4 Nonthermal Pasteurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.2 Sterilization of Food by High Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.2.1 High-Pressure Equipment and the System . . . . . . . . . . . . . . . . . . . . . . . . 58 3.3 Concentration by Evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3.3.1 Batch Pan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.3.2 Rising Film Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.3.3 Falling Film Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.3.4 Scraped-Surface Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.3.5 Multiple Effect Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.3.5.1 Thermocompression (TC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.3.5.2 Mechanical Vapor Recompression (MVR) . . . . . . . . . . . . . . . 62 3.4 Dehydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.4.1 Spray Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.4.2 Powder Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.5 Miscellaneous Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.5.1 Size Enlargement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.5.1.1 Instantizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.5.1.2 Agglomeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 3.5.1.3 Agglomeration Process and Equipment . . . . . . . . . . . . . . . . . . 70 3.5.1.4 Agglomeration Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.5.1.5 Selective Agglomeration (Spherical Agglomeration) . . . . . . . . 4. Thermodynamical, Thermophysical, and Rheological Properties of Fruits 73 and Fruit Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.2 Thermophysical Properties’ Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.3 Fruits and Fruit Products’ Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.3.1 Fruit and Fruit Products’ Properties During Freezing . . . . . . . . . . . . . . 75 4.3.2 Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.4 Experimental Data and Prediction Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 4.4.1 Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 4.4.1.1 Porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 4.4.1.2 Density Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.4.1.3 Empirical Equations and Theoretical Density Models . . . . . .

Contents ix 4.4.2 Specific Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.4.3 4.4.2.1 Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.4.4 4.4.2.2 Prediction Models and Empirical Equations . . . . . . . . . . . . . . 80 4.4.5 Thermal Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.4.3.1 Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.4.6 4.4.3.2 Prediction Models and Empirical Equations . . . . . . . . . . . . . . 83 Thermal Diffusivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.4.4.1 Measurement Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 4.4.4.2 Empirical Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 4.4.5.1 Measurement Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 4.4.5.2 Newtonian Fruit Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 4.4.5.3 Non-Newtonian Fruit Products . . . . . . . . . . . . . . . . . . . . . . . . . 91 4.4.5.4 Effect of Temperature and Pressure on the Viscosity 92 of Foodstuffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Boiling Point Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Color, Turbidity, and Other Sensorial and Structural Properties of Fruits and Fruit Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.2 Measurement of Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.2.1 Absorbance Spectrophotometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.2.1.1 Spectrophotometer Components . . . . . . . . . . . . . . . . . . . . . . . . 101 5.2.1.2 Improved Spectrophotometers . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.2.1.3 Turbidity and Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.2.1.4 Reflection Spectrophotometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.2.1.5 Tristimulus and Special Colorimeters . . . . . . . . . . . . . . . . . . . . 104 5.2.1.6 CIELAB Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 5.2.1.8 Measurement of Tristimulus Values . . . . . . . . . . . . . . . . . . . . . . 108 5.2.1.9 Application of Colorimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 5.3 Food Dispersions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.3.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.3.2 Food Dispersion Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.3.3 Particle Size, Shape, and Size Distribution . . . . . . . . . . . . . . . . . . . . . . . . 112 5.3.3.1 Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5.3.3.2 Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.3.3.3 Photon Correlation Technique . . . . . . . . . . . . . . . . . . . . . . . . . . 115 5.3.4 Cloudy Fruit Juice Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 5.4 Fruit Aroma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5.4.1 Activity Coefficients of Fruit Juice Aroma . . . . . . . . . . . . . . . . . . . . . . . . 118 5.4.2 Experimental Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 5.4.3 Thermodynamic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 5.4.3.1 Wilson Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 5.4.3.2 NRTL Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.4.3.3 UNIQUAC Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.4.3.4 UNIFAC Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.4.4 Fruit Aroma Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

x Contents 5.4.5 Fruit Shrinkage During Dehydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.4.5.1 Shrinkage coefficient, sb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 5.4.6 Structural Damage During Freezing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 6. Chemical Composition of Fruits and its Technological Importance . . . . . . . . . . . . . . . 133 6.1 Proximate Composition of Fruit and Fruit Products . . . . . . . . . . . . . . . . . . . . . 133 6.1.1 Proteins and Amino acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 6.1.2 Organic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 6.1.3 Carbohydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 6.1.3.1 Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 6.1.3.2 Pectin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.1.4 Lipids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.1.5 Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.1.6 Vitamins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 6.1.7 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 6.1.8 Aroma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 6.1.9 Color compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Anthocyanidins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Flavones and Flavonols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Flavonones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Catechins and Leucoanthocyanidins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.2 Influence of Processing and Storage on the Composition of Fruits . . . . . . . . . 150 6.2.1 Vitamin Destruction During Processing and Storage . . . . . . . . . . . . . . . 150 6.2.2 Effect of Storage on Metal Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.2.2.1 Influence of Storage on Fruit Juice Aroma . . . . . . . . . . . . . . . 152 6.2.3 Fruit Juice Change in Amino Acid Content During Storage . . . . . . . . 153 6.2.4 Effect of Storage on Fruit Sugars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 6.2.5 Effect of Processing and Storage on Fruit Pigments . . . . . . . . . . . . . . . 157 6.2.6 Changes in Organic Acid Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 6.2.7 Changes in Phenolic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 7. Fruit Products, Deterioration by Browning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 7.1.1 Different Mechanisms of Deterioration . . . . . . . . . . . . . . . . . . . . . . . . . . 163 7.2 Enzymatic Browning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 7.2.1 Phenolic Compounds and Oxidases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 7.2.2 Kinetics of Enzymatic Browning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 7.2.2.1 Effect of the Temperature in the Color Change . . . . . . . . . . . 167 7.3 Nonenzymatic Browning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 7.3.1 Maillard Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.3.1.1 Tristimulus Parameters and Absorbance as a Measurement of Browning in Fruit Juices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 7.3.1.2 Kinetics of Nonenzymatic Browning (NEB) . . . . . . . . . . . . . . 170 7.3.1.3 Effect of Soluble Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 7.3.1.4 Effect of Reducing to Total Sugars’ Ratio (R/T) . . . . . . . . . . 171 7.3.1.5 Effect of the Fructose to Glucose Ratio (F/G) . . . . . . . . . . . . 171 7.3.1.6 Effect of Amino Acids (AA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

Contents xi 7.3.2 7.3.1.7 Effect of the Content of Organic Acids . . . . . . . . . . . . . . . . . . . 173 7.3.1.8 Effect of Other Minor Components . . . . . . . . . . . . . . . . . . . . . . 173 7.3.1.9 Effect of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 5-HMF Formation During Storage and Processing of Fruit Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 8. Inhibition and Control of Browning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.2 Inhibition and Control of Enzymatic Browning . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.2.1 Thermal Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 8.2.1.1 Elevated Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 8.2.1.2 Refrigeration Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 8.2.2 Chemical Inhibition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 8.2.3 Effect of the Ascorbic Acid (AA) Content in Color Change . . . . . . . . . 192 8.2.4 Nonconventional Chemical Inhibition of EB . . . . . . . . . . . . . . . . . . . . . . 193 8.2.4.1 Honey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 8.2.4.2 Aromatic Carboxylic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.2.4.3 Proteases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.2.5 Miscellaneous Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.2.5.1 Irradiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 8.2.5.2 Ultrafiltration (UF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 8.2.5.3 High-pressure treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 8.3 Inhibition and Control of Nonenzymatic Browning (NEB) . . . . . . . . . . . . . . . . 197 8.3.1 Preventive Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 8.3.1.1 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 8.3.1.2 Process Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 8.3.1.3 Ion Exchange Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 8.3.2 Restorative Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 8.3.2.1 Effect of Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 8.3.2.2 Use of PVPP (Polyvinyl Polypyrrolidone) . . . . . . . . . . . . . . . . . 209 8.3.3 Miscellaneous Methods for Inhibition and Control of Nonenzymatic Browning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 8.3.3.1 Color Reduction by Combined Methods . . . . . . . . . . . . . . . . . 209 8.3.3.2 Use of Chemical Inhibitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 8.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217

CHAPTER 1 OVERVIEW OF THE FRUIT PROCESSING INDUSTRY 1.1. INTRODUCTION The Latin word fruor, meaning ‘‘I delight in,’’ is the source of the word fruit. Fruits are essential in the human diet as they contain compounds of nutritional importance, including vitamins that are not synthesized by the human body. Fruits are defined as the reproductive organs arising from the development of floral tissues with or without fertilization (Fig. 1.1). 1.2. CLASSIFICATION OF FRUITS It is common to classify fruits as temperate fruits, subtropical fruits, and tropical fruits depending on the region where they grow (Kader and Barret, 1996). A more specific classi- fication is given in Table 1.1. Commonly the term fruit is often restricted to succulent (fleshy) edible fruits of woody plants like apples, melons, and such small fruits as strawberries and blueberries. As the ovary matures, its wall develops to form pericarp. Pericarp is divided into three layers: exocarp (outer), mesocarp (middle), and endocarp (inner). In fleshy fruits the pulpy layer is usually the mesocarp (as in peaches and grapes). The seed or seeds, which in some cases constitute the entire edible portion of the fruit, lie immediately within the pericarp (Koning, 1994). For example, the hard husk of coconut is the pericarp and the edible part inside is the seed. While in typical cases the fruit is confined to the ripened ovary, in apples it includes ovary plus receptacle. On the other hand, strawberry is an aggregation of small fruits and pineapple is a development of the entire inflorescence. Dehiscent and indehiscent dry fruits, and some other fruits like pumpkin and cucumber are classified as vegetables. Their processing is specifically not considered in this book. Cereals, sunflower, peanuts, and beans are also beyond the interest of this work. With this in mind, the simplified classification of fruits shown (Table 1.1) will be of interest when considering different processing methods. 1.3. WORLD PRODUCTION AND COMMERCIAL APPLICATIONS OF FRUITS Table 1.2 lists world production and major commercial applications of selected fruits. In 2003 world fruit production reached nearly 380 million metric tons (MT). World fruit production grew at an average of 0.86% per year for the period 2000–2003 (FAOSTAT, 2005) and rose 1.6% in 2004, according to the latest crop production data collated by the United Nations’ Food and Agriculture Organization (FAO). This marks the fourth consecutive annual increase in 1

2 Fruit Manufacturing Cashew Strawberry apple Mangosteen Fig Grape Pedicel Receptacle AcMceesssoocrayrtipssue tiAscscueessory Pomegranate seed intrSaPlleoapctcuuelnamtratlissue ArilPedunclePericarp Outer layer of Endodermal the testa intralocular Peduncle tissue Pineapple Orange Apple Tomato Peach Figure 1.1. The origin of selected fruits from plant floral tissue. Reprinted, with permission, from the Annual Review of Plant Physiology, Vol. 27 (copyright) 1976 by Annual Reviews. international fruit production levels. The FAO data reveal bananas as the most commonly produced fruit in the world, with output inching upward from 103,000 MT to 70.63 million MT in 2004. It was followed by grapes, with production rising from over 3 million MT to 65.5 million in 2004. Oranges are the third most widely grown fruit in the world, with output in 2004 rising roughly from 2.4 million MT to just over 63 million MT. Apple production rose from almost 270,000 MT to just over 59 million MT in 2004. 1.4. HISTORY OF FRUIT PRODUCTS’ DEVELOPMENT People have been trying to improve the quantity and quality of their food and drink for centuries. As soon as the first humans decided to settle in one place and grow their own food, they started to improve its quality and increase its quantity. The following are the remarkable milestones associated to fruit and fruit processing:

1 . Overview of the Fruit Processing Industry 3 Table 1.1. Classification of edible fleshy fruits based on: (1) the structure of the flower where the fruit belongs; (2) the number of ovaries included; and (3) the number of carpels in each ovary. One carpel Drupe Peach One single ovary Plum Coconut True berry Blueberry Gooseberry Single Grape Multiple Squash More than one Hesperidium All citrus carpel fruits Pepo Apple Squash Watermelon Aggregate of single False berries Raspberry fruits Blackberry Peduncle and Derived from accessory tissues Pineapple different parts of (inflorescence) Fig the flower Strawberry Receptacle YEAR MILESTONE -4000 The Egyptians master viticulture and the art of wine making. -2000 Egyptians and Sumerians learn fermentation. Although people had been eating naturally fermented foods since the Neolithic Age, the process was never under- -1000 stood. -300 The Greeks develop grafting techniques, leading to the creation of orchards and 0 groves. 1000 In the Roman Empire, drying process was used for preservation. In addition, 1276 honey was sometimes used as a preserving agent for fruit. 1400 Pliny the Elder in his Natural History describes 20 varieties of apples 1650 The first whiskey distillery was established in Ireland. 1676 Modern candy is created in Europe when cooks dip fruits and berries into melted 1850 sugar. Fre`re Jean Oudart and Dom Pierre Pe´rignon, abbeys of Saint Pierre aux Monts de Chaˆlons and d’ Hautvillers became the fathers of naturally sparkling wine (Champagne) The Compagnie de Limonadiers of Paris was granted a monopoly for the sale of lemonade soft drinks Soft drinks are invented by mixing fruit juice with other ingredients such as sugar, carbonated water and citric acid.

4 Fruit Manufacturing Table 1.2. World production and commercial applications of selected fruits (based on Hui, 1991). 1998 world production Major commercial Fruit Scientific name (106 ton/year) applications Apples Pyrus malus 56,060 Brandy, cakes, cider, citric acid, cookies, confections, dried, essence, filling, jelly, Apricots Prunus armeniaca 2,670 juice, marmalade, pectin, preserves, 2,325 sauce, and vinegar Avocados Persea americana 58,618 Bananas M. Caveindeishii, — Brandy, cakes, citric acid, confections, dried, essence, filling, jelly, juice, Black berries M. Paradisiaca — marmalade, preserves, and pure´e Rubus alleghaniensis — Crushed and Pure´e Boysen berries Rubus 1,550 Cookies, crushed, pure´e, dried, Breadfruits Artocarpus altilis 47,695 and frozen Brandy, cakes, canned, cocktail, cookies, Cherries, sour Prunus cerasus — 285 crushed, essence, jam, jelly, juice, nectar, pie, Cherries, sweet Prunus avium 654 pie filling, preserves, pure´e, snack bars, — strained pure´e, syrup, and wine Coconuts Livistona chinensis — Brandy, cakes, canned, cereals, cocktail, 1,178 confections, cookies, essence, jam, jelly, Crabapples Malus pumila juice, nectar, pie, pie filling, preserves, Cranberries Vaccinium — strained pure´e, syrup, and wine 5,072 Chunks and pure´e Currants macrocarpum 57,397 Brined, cakes, canned, citric acid, cookies, Ribes vulgare, rubrum diet spread, frozen, jam, preserves, pure´e, 2.1 and wine Elder berries Sambuca nigra Brined, cakes, canned, cocktail, confections, Figs Ficus carica cookies, frozen, nectar, pie, pie filling, preserves, and pure´e Goose berries Ribes hirtellum Brandy, cakes, canned, chunks, cocktail, confections, cookies, crushed, dried, frozen, Grapefruits Citrus paradisi, jam, juice, nectar, pie, pure´e, snack bars, Grapes pommelo strained pure´e, and syrup Jelly, pectin, and pickles V. rotundifolia Canned, confections, crushed, glace´, jam, jelly, V. vinifera juice, pure´e, sauce, strained pure´e, and syrup Vitis labrusca Canned, diet spread, and pure´e. Canned, cookies, crushed, essence, glace´, Guavas Psidium guajava jam, and pure´e Brandy, cocktail, frozen, glace´, jelly, juice, nectar, and pure´e Cakes, canned, cereals, cocktail, confections, cookies, crushed, diet spread, dried, frozen, Glico, leather, preserves, pure´e, and snack bars Canned, cocktail, confections, jelly, juice, nectar, pie, pie filling, preserves, and wine Canned, chunks, confections, crushed, rozen, Glico, juice, and marmalade Cocktail, jam, jelly, juice, sauce, Grapes, and wine Champagne, cocktail, crushed, diet spread, jam, juice, sauce, vinegar, and wine Crushed, diet spread, jam, jelly, leather, pure´e, and snack bars (continued )

1 . Overview of the Fruit Processing Industry 5 Table 1.2. (Continued ) 1998 world production Major commercial Fruit Scientific name (106 ton/year) applications Honeydew Cucumic melo — Crushed, diet spread, jam, jelly, leather, melons 852 pure´e, and snack bars Actidia chinensis 9,335 Kiwifruits Fortunella margarita Canned, cocktail, crushed, and dried Kumquats Citrus lemon — Jam Lemons Citric acid, cocktail, essence, frozen, 23,455 Limes Citrus aurantifolia — Glico, juice, marmalade, and pectin 13,757 Citric acid, cocktail, crushed, essence, Longans Euphoria 66,212 Loquats Eriobotrya japonica frozen, juice, marmalade, and pectin Lychees Litchi chinensis 4,801 Citric acid and crushed Mangoes Mangifera indica — Cocktail and pure´e Nectarines Prunum nectarina 11,065 Canned and dried Crushed and pure´e Olives Olea europala 14,379 Canned, cocktail, confections, cookies, Oranges Citrus quarantium, 1,960 crushed, diet spread, frozen, jam, and pure´e sinensis Brined and canned — Cereals, champagne, confections, cookies, Papayas Carica papaya 12,100 crushed, diet spread, essence, frozen, Glico, Passion fruit Passiflora 8,008 juice, marmalade, pectin, and wine — Crushed, juice, leather, pure´e, and snack bars Peaches Prunus persica 334 Crushed, juice, nectar, pure´e, and strained 326 pure´e Pears Pyrus cominunis Brandy, brined, cakes, canned, cereals, — chunks, cocktail, confections, cookies, Persimmons D. virginiana 2,600 crushed, diet spread, dried, essence, frozen, 6.0 jam, juice, leather, pickles, pie, pie filling, Persimmons Diospyros kaki preserves, pure´e, sauce, snack bars, strained Pineapples Ananas cormosus pure´e, syrup, and wine Brandy, canned, cereals, chunks, cocktail, Plums and Prunus domestica confections, cookies, crushed, diet spread, dried, and frozen Prunes Brandy, chunks, crushed, jam, juice, marmalade, pectin, pie, pie filling, preserves, Pomegranates Punica granatum and syrup Chunks and crushed Quinces Cydonia vulgaris Cakes, canned, cereals, chunks, cocktail, confections, cookies, crushed, diet spread, Raspberries Rubus idueus or frozen, glace´, jam, leather, preserves, jelly, R. stigosus pectin, preserves, pure´e, vinegar, and wine Cereals, cocktail, confections, crushed, Sapotes Pouteria sapota diet spread, juice, pure´e, and strained pure´e Strawberries Fragaria chiloensis Jam, juice, leather, pure´e, snack bars, and strained pure´e Tangerines Citrus reticulata Jam, jelly, juice, pickles, preserves, pure´e, strained pure´e, and wine Cakes, canned, cereals, confections, cookies, crushed, diet spread, essence, frozen, jam, jelly, uice, nectar, pickles, pie filling, preserves, snack bars, strained pure´e, and syrup Crushed, juice, and pure´e Brandy, cakes, cereals, confections, cookies, crushed, frozen, and juice Cocktail, frozen, glace´, juice, and pure´e

6 Fruit Manufacturing 1861 Louis Pasteur develops his technique of pasteurization, in which he protects food by heating it to kill dangerous microbes, removing the air and sealing it in a 1870 container. 1906 The Navel orange is introduced into the United States from Brazil. 1913 Modern freeze-drying techniques are mastered in France. 1920 Home refrigerators are invented in the United States. 1940 American Charles Birdseye invents the process of deep freezing foods. Microwave technology is developed, which leads to the invention of the micro- 1957 wave oven. 1958 The first aluminum cans were used. ‘‘Basic Four’’ food guide introduced by USDA: milk, meat, vegetable and fruit, 1965 and bread and cereal groups. 1970 Soft drinks in cans dispensed from vending machines. 1990 Plastic bottles are used for soft drinks. Irradiation approved by the FDA and USDA for use on selected foods, including 1992 papaya. 2005 USDA releases the new Food Guide Pyramid, USDA releases the new Food Guide Pyramid, providing a graphics based quan- titative guide to food consumption. 1.5. HARVEST OF FRUITS Harvesting at the correct time is essential to the production of quality fruits (O’Brien et al., 1983). The correct time to pick fruit depends upon several factors, including variety, location, weather, ease of removal from the tree, and purpose to which the fruit will be put. Oranges change with respect to both sugar and acid as they ripen on the tree: sugar increases and acid decreases. The ratio of sugar to acid determines the taste and acceptability of the fruit and the juice. For this reason, in some countries there are laws that prohibit picking until a certain sugar–acid ratio has been reached. These and other measurements indicate when the fruit is ready for harvesting and subsequent processing. A large amount of the harvesting of most fruit crops is still done by hand; this labor may represent about half of the cost of growing the fruit. Mechanical harvesting is currently one of the most active fields of research for the agricultural engineer. For proper harvesting: . the fruit should be picked by hand and placed carefully in the harvesting basket, in order to avoid any mechanical damage; . the harvesting basket and the hands of the harvester should be clean; . the fruit should be picked when it is ready to be processed into a quality product. Moreover, the proximity of the processing plant to the source of supply for fresh raw materials presents several advantages, including the possibility to pick at the best suitable moment, reduce losses by handling/transportation, minimize raw material transport costs, and simplify methods for raw material transport. After harvesting, the organoleptic and nutritional properties of fruits deteriorate in different degrees. Causes of deterioration include the growth and activity of micro- organisms, the activities of the natural food enzymes, the action of insects and rodents, changes in temperature and water content, and the effect of oxygen and light. Usual storage

1 . Overview of the Fruit Processing Industry 7 life of fruits is between 1 and 7 days at 218C if proper measures are not taken (Kader and Barret, 1996). Many quality measurements can be made before a fruit crop is picked in order to determine if proper maturity or degree of ripeness has developed: . Color can be checked with instruments (see Chapter 4) or by comparing the color of fruit on the tree with standard picture charts. . Texture may be measured by compression by hand or by simple type of plungers. . Percentage of soluble solids, which are largely sugars, is generally expressed in degrees Brix, which relates specific gravity of a solution to an equivalent concentration of pure sucrose. The concentration of soluble solids in the juice can be estimated with a refractometer or a hydrometer. The refractometer measures the ability of a solution to bend or refract a light beam, which is proportional to the solution’s concentration. A hydrometer is a weighted spindle with a graduated neck, which floats in the juice at a height related to the juice density. . The acid content of fruit changes with maturity and affects flavor. Acid concen- tration can be measured by a simple chemical titration on the fruit juice. For many fruits the tartness and flavor are affected by the ratio of sugar to acid. In describing the taste of tartness of several fruits and fruit juices, the term sugar to acid ratio or Brix to acid ratio is commonly used. The higher the Brix the greater the sugar concentration in the juice, the higher the Brix to acid ratio the sweeter and less tart is the juice. Once the fruit is harvested any natural resistance to microorganisms is lost. Fruits are living tissues and they continue to respire even after they have been harvested. In case of aerobic respiration, refrigeration is not enough to retard ripening and foods may not develop desired flavor/texture. Moreover, it may be harmful for tropical or subtropical fruits. To ensure maximum storage life, fruits should be harvested when mature, but not yet fully ripe or overripe (Claypool, 1983). Ripe fruit should be avoided because it will continue to ripen in storage. If harvested before they have matured, fruits will be more susceptible to storage disorders. Firmness and the level of soluble solids in the fruit are good indicators of maturity in determining picking time. Fruits are very susceptible to bruising and other forms of mechanical damage, and therefore should not be handled more than necessary. Fruits are normally transported and stored in bulk boxes (bins) kept in the orchard. Bins should not be allowed to sit for extended periods in direct sunlight, nor for more than a few hours before cooling is started (Hanson, 1976). 1.5.1. Chemical Treatments Harvested fruits are often treated with chemicals to inhibit storage disorders. Dip or spray treatments with calcium chloride plus a scald inhibitor mixed with a surfactant and fungicides are commonly used to prevent scald and a group of disorders such as bitter pit. If necessary, a surfactant is used to provide complete wetting of the fruit. Many chemicals destroy microorganisms or stop their growth but most of these are not permitted in foods; those that are permitted as food preservatives are listed in Table 1.3. Chemical food preservatives are those substances that are added in very low quantities

8 Fruit Manufacturing Table 1.3. Selected chemicals permitted as food preservatives. Agent Acceptable daily intake Commonly used (mg/kg body weight) levels (%) Citric acid No limit No limit Acetic acid No limit No limit Sodium diacetate 15 0.3–0.5 Sodium benzoate 5 0.03–0.2 Sodium propionate 10 0.1–0.3 Potassium sorbate 25 0.05–0.2 Methyl paraben 10 0.05–0.1 Sodium nitrite 0.2 0.01–0.02 Sulfur dioxide* 0.7 0.005–0.2 Source: Dauthy, 1995. *Sulfite containing additives have been used extensively as antibrowning agents to keep vegetables and fruits fresh looking. Because sulfites have been linked to allergic reactions, the Food and Drug Administration (FDA) prohibited the use of sulfite preservatives in fresh vegetables and fruits (Langdon, 1987). (up to 0.2%) and do not alter the organoleptic and physicochemical properties of the foods or change only very little. Preservation of food products containing chemical food preservatives is usually based on the combined or synergistic activity of several additives, intrinsic product parameters (e.g., composition, acidity, water activity) and extrinsic factors (e.g., processing temperature, storage atmosphere, and temperature). 1.6. POSTHARVEST HANDLING OF FRUITS Fruits continue to live and respire even after they are picked (Biale and Young, 1981). A major economic loss occurs during transportation and/or storage of fresh fruits due to the effect of respiration. A conventional attempt to reduce such degradation has been to refrigerate the fruits, thereby reducing the rate of respiration. Even if fruits are to be stored for only a short period, it is still very important that the field heat be removed from them as soon as possible. The higher the holding temperature, the greater the softening and respir- ation rate, and the sooner the quality becomes unacceptable. Apples, for instance, respire and degrade twice as fast at 4.58C as at 08C. At 168C they will respire and degrade more than six times faster. The optimum storage temperature for fruits depends also on the variety. On the other hand, fruits require humidity to preserve, which may be reached by adding water vapor to the air in the storage room with one or more humidifiers. Maintaining the humidity within this range will also reduce weight loss. Humidity near the saturation point will promote the growth of bacteria and fungi. Table 1.4 lists the recommended storage temperature and relative humidity for selected fruits. If chilled fruits are suddenly transferred into warm air, water vapor in the air will condense on them. This ‘‘sweating’’ also occurs when the doors of a cold storage room are opened, allowing warm, moist air to enter. Sweating causes wetting, which facilitates the growth of microorganisms. If molds are found to be growing in the storage room, the interior surfaces, refrigeration coils, fans, and ducts must be disinfected.

1 . Overview of the Fruit Processing Industry 9 Table 1.4. Recommended storage temperature and relative humidity for selected fruits. Fruit Temperature(8C) Relative humidity(%) Storage life (weeks) Apples À1.0/4.0 90–95 5–52 Apricots À0.5/0.0 90–95 1–3 Bananas 13/14 90–95 — Berries (other than cranberries) 2/4 90–95 1–5 Figs À0.5/0.0 85–90 1–2 Grapefruits 10–15 85–90 6–8 Grapes, vinifera À1/À0.5 90–95 4–31 Kiwis À0.5/0.0 90–95 14–25 Oranges 3–9 85–90 8–12 Passion fruit 7–10 85–90 3–5 Peaches À0.5/0.0 90–95 2–4 Pears À1.5/À0.5 90–95 2–7 Pineapples 7/13 85–90 2–5 Plums and prunes À0.5/0.0 90–95 2–4 Source: Hardenburg et al. (1986) and Hanson (1976). 1.6.1. Postharvest Cooling Proper postharvest cooling is advisable to: . suppress enzymatic degradation (softening) and respiratory activity; . slow down or inhibit water loss (wilting); . slow down or inhibit the growth of decay-producing microorganisms (molds and bacteria); . reduce the production of ethylene (a ripening agent) or minimize the commodity’s reaction to ethylene. 1.6.2. Cooling Methods To reduce the cooling load fruits should be harvested as much as possible during the cool hours of the day. Allowing the fruits to sit outside overnight in bulk boxes will generally not lower their temperature. Moreover, bulk storage may cause the fruit temperature to increase. It is recommended to cool the fruits quickly and thoroughly. There are many methods of cooling fruit products before storage or shipment, including room cooling, forced-air cooling, vacuum cooling, hydrocooling, package icing, and top icing. One of the common and least expensive methods for cooling fruits is room cooling (Raghavan et al., 1996). . Room cooling is accomplished by stacking bulk boxes, or bins, inside a refrigerated room where the heat is allowed to dissipate slowly. Cooling is achieved by moving room air around the containers. An airflow rate of 5---10 m3 minÀ1 is necessary to cool fruits. Moreover a high relative humidity (90–95%) is necessary to avoid fruit dehydration. Although time of cooling may be too long with this method, it requires minimum handling and labor. The time of cooling may vary from several days to more than 2 weeks for the fruits to reach approximately the same temperature as the air in a cold storage room. After cooling is completed, the facility can be used for short-term storage. Bins should be spaced

10 Fruit Manufacturing between the containers and walls must be from 25 to 60 cm, and between the bins and ceiling, 45 to 60 cm. Normally, more refrigeration is required to cool down fruits than to maintain fruits at a cool temperature. . Forced-air cooling. The rate of heat transfer from fruits in the middle of the box may be insufficient to overcome the temperature rise produced by natural respiration. In such a case, forced-air movement is necessary and adequate space for proper air circulation between rows of stacked bins should be allowed. Cooling is carried out by exposing the bulk boxes in a storage room to a higher air pressure on one side than the other, by means of fans that draw refrigerated air through the container vents (Fraser, 1991). Pressure difference increases the cooling rate up to 4 times more than room cooling. Relative humidity needs to be checked to avoid substantial water loss and fruit shrinkage. Water loss increases with the cooling air velocity. As the key to forced-air cooling is the moving of cold air through the containers vents, location and size of vents need to be carefully calculated. While few or small vents slow the flow of cooling air, too many vents may produce container collapse. Some of the forced-air cooling alternatives are: (i) cold wall (where cold air is driven from a false wall, or air plenum, to cold room by fans); (ii) forced-air tunnel (an exhaust fan is placed at the end of the aisle of two rows of bins; the aisle’s top and ends are covered with plastic or canvas, creating a tunnel); and (iii) serpentine cooling (a serpentine system, which is a modification of the cold wall method, is designed for bulk bin cooling). Figure 1.2 shows a typical cold wall alternative for the forced-air cooling of fruit bins. Hydrocooling is one of the quickest methods for removing field heat from fruits. This process can be used on most commodities that are not sensitive to wetting and generally requires large volumes of chilled water to flood the fruit (Raghavan et al., 1996). Cold well or stream water may be used as a source of hydrocooling fluid, after it has been checked for purity. Fruits in boxes are placed on a conveyor that pushes the boxes through a cooling tunnel. Large quantities of chilled water are sprayed directly on the tops of the boxes. Water flows down through the product and is collected in a tank or sump underneath the tunnel. Cooling units Fans Cold wall Fruit bins Figure 1.2. Cold wall alternative for the forced-air cooling of fruit bins.

1 . Overview of the Fruit Processing Industry 11 . It may be possible to apply fungicides and scald inhibitors during hydrocooling. Water removes heat about 5 times faster than air, but is less energy efficient. Mechanical refrigeration is the most efficient method of cooling water; however, ice in water will also provide a source of coolant. If hydrocooling water is re-circulated, it should be chlorinated to minimize disease problems. The temperature of water for hydrocooling must be kept as near to 08C as possible. To save time and energy, fruits are seldom hydrocooled to lower than 78C. Slower methods, such as forced-air or room cooling, are usually employed complementarily. The rate at which fruits may be hydrocooled depends on fruit size. Figure 1.3 shows a compact hydrocooling equipment using water as the refrigerant. It can be approximated that the size of the refrigeration systems needed for hydrocooling is 10 tons of refrigeration capacity for each ton of fruits cooled per hour. Hydrocooling may prevent recently harvested fruits from wilting, shrinking, and losing flavor. Top or liquid icing. This may be used on a variety of commodities and is particularly effective on dense and palletized packages that are difficult to cool with forced air. Because of its residual effect ice methods work well with high-respiration commodities such as sweet corn, and are not recommended for fruits. Alternative cooling methods. Alternatives to the above-mentioned cooling methods, particularly to smaller volumes of commodities, are: . Harvest time: Harvest should be made during mornings or, when possible, night time, when commodities and air temperatures are usually coolest. . Refrigeration with well water: Temperatures are usually lower than 158C. . Altitude: If easily accessible, higher elevations can provide cooling. . Cellars/caves: Generally maintain fairly constant, cooler-than-air temperatures. . Shade: If refrigeration is not available, at least keep commodities from warming up. Figure 1.3. Hydrocooling system (from Boyette et al. (1990). Published by North Carolina Cooperative Extension Service, with permission).

12 Fruit Manufacturing Initial fruit temperature Temperature Still air Hydrocooling Forced-air Room temperature cooling Time (relative) Figure 1.4. Comparison of relative cooling rate of different cooling systems. Refrigerated trucks are not designed to cool fresh commodities. They can only maintain the temperature of previously cooled products. While Fig. 1.4 compares the relative cooling rate of different cooling systems, Table 1.5 lists recommended cooling methods for selected fruits. 1.7. CONTROLLED ATMOSPHERE STORAGE Controlled atmosphere (CA) storage prolongs fruit life by lowering the oxygen concentration and increasing the carbon dioxide concentration in the storage atmosphere. The effects of CA are based on the often-observed slowing of plant respiration in low O2 environments. There is about 21% O2 in air (Table 1.6). As the concentration of O2 falls below about 10%, fruit Table 1.5. Recommended cooling methods for selected fruits. Commodity Recommended cooling methods* Normal storage life Apples Room cooling, forced-air cooling, hydrocooling 1–12 months Blueberries Room cooling, forced-air cooling 2 weeks Peaches Forced air cooling, hydrocooling 2–4 weeks Strawberries Room cooling, forced-air cooling 5–7 days Watermelons Room cooling 2–3 weeks Adapted from Wilson et al. (1999).

1 . Overview of the Fruit Processing Industry 13 Table 1.6. Average air composition. Air components* Symbol Volume (dry air) Nitrogen (%) N2 78.08 Oxygen (%) O2 20.95 Argon (%) Ar 0.93 Carbon dioxide (ppm) CO2 350 Neon (ppm) Ne 18.2 Helium (ppm) He 5.24 Methane (ppm) CH4 2 Krypton (ppm) Kr 1.1 Hydrogen (ppm) H2 0.5 Nitrous oxide (ppm) N2O 0.3 Xenon (ppm) Xe 0.08 Carbon monoxide (ppm) CO 0.05 – 0.2 Ozone (ppm) O3 0.02–0.03 *Dry atmosphere below 80 Km (ppm ¼ parts per million). respiration starts to slow. This suppression of respiration continues until O2 reaches about 2–4% for most fruits. Depending on product and temperature, if O2 gets lower than 2–4%, fermentative metabolism replaces normal aerobic metabolism; and off-flavors, off-odors, and undesirable volatiles are produced. Similarly, as CO2 increases above the 0.03% found in air, a suppression of respiration results for some commodities. Reduced O2 and elevated CO2 together can reduce respiration more than either alone. These concentrations of oxygen and carbon dioxide also reduce the ability of the ethylene produced by ripening fruits to further accelerate fruit ripening (Kader, 1986). CA storage facilities are specially constructed, airtight cold storage rooms with auxiliary equipment to monitor and maintain specific gaseous atmospheres. Oxygen, carbon dioxide, and ethylene levels should be monitored daily and controlled within narrow limits. Recom- mendations for CA storage conditions change as a result of ongoing research. Optimum conditions depend on several factors, including variety and growing conditions. In general CA methods are much too expensive for applying to process fruit. Table 1.7 lists recom- mended oxygen and carbon dioxide storage condition for various fruits (Kader, 1985; Raghavan et al., 1996). It must be considered that higher storage temperatures lead to higher respiration rates, and gas concentrations recommended in Table 1.7 will not be successful. 1.8. MODIFIED ATMOSPHERE PACKAGING OF FRUITS Vegetables and fruits differ from other foodstuffs in that they continue to respire even when placed in a modified atmosphere. Due to the respiration, there is a danger that CO2 will increase to levels harmful to the packed commodities. On the other hand, respiration con- sumes oxygen and there is a danger of anaerobiosis. If fruits are packed in a sealed imper- meable package, O2 is rapidly used up, CO2 builds up, anaerobic respiration will take place, and off-flavors and odors will develop. There is also the risk of the growth of anaerobic food- poisoning organisms such as Clostridium botulinum. On the other hand, if the packaging film is completely permeable the fruit would not benefit from modified atmosphere. Furthermore,

14 Fruit Manufacturing Table 1.7. O2 and CO2 condition for several fruits’ storage (optimal temperatures are listed in Table 1.4). Fruit O2 concentration (%) CO2 concentration (%) Apples 2–3 1–2 Apricots 2–3 1–2 Bananas 2–5 2–5 Berries (other than cranberries) 5 –10 15 –20 Figs 5 –10 15 –20 Grapefruits 3 –10 5 –10 Grapes, vinifera 2 –5 1–3 Kiwis 2 5 Oranges 5 –10 0 –5 Peaches 1–2 5 Pears 2–3 0 –1 Pineapples 5 10 Plums and prunes 1–2 0 –5 Adapted from del Valle and Palma (1997). when fruits are cut, sliced, shredded, or otherwise processed, their respiration rates increase. This is probably due to the increased surface area exposed to the atmosphere after cutting that allows oxygen to diffuse into the interior cells more rapidly, thereby increasing metabolic activity of injured cells. Fruit packaging has progressed in the past several years. Appropriate packaging mater- ials have been developed for most of the more common fresh-cut products. Technical challenges still exist in fruit packaging. A number of special packaging materials intended for vegetables and fruits have been developed such as smart films, microporous films, and microperforated films. 1.8.1. Factors Affecting Fruit Respiration The ability of modified atmosphere packaging (MAP) to extend the shelf life of foods has been recognized for many years. MAP may be defined as the packaging of a perishable product in an atmosphere, which has been modified so that its composition is different from that of air. In MAP of respiring foods, e.g., fresh fruits, once the atmosphere has been changed to the desired level, the respiration rate of the produce should equal the diffusion of gases across the packaging material in order to achieve an equilibrium atmosphere in the package. The potential advantages and disadvantages of MAP have been reviewed by Farber (1991). The main effects of MAP on fruits are to: . lower the rate of fruit respiration (slow down ripening and senescence); . slow down the rate of ethylene production, which is a natural plant hormone involved in the control of ripening; . retard the growth of molds, extending the storage/shelf life of the fresh fruit. If the packaging film is semipermeable O2 and CO2 can diffuse through it, and an equilibrium concentration of both gases is established when the rate of diffusion through the package is equal to the rate of respiration.

1 . Overview of the Fruit Processing Industry 15 The main disadvantages are: . cost increase . need of temperature control . different gas formulations for each product type . special equipment and personnel training . product safety. MAP technology is largely used for minimally processed fruits. MAP combined with low-temperature storage is a common method to improve the storage stability of ready-to-use products. The three main gases used commercially in MAP are oxygen, nitrogen, and carbon dioxide. The gases and their concentrations should be tailored for each individual product. The required combinations of temperature, oxygen, and carbon dioxide levels vary with fruit type, variety, origin, and season. Carbon dioxide is important because of its biostatic activity against many spoilage organisms that grow at refrigeration temperatures. Oxygen inhibits the growth of anaerobic pathogens, but in many cases does not directly extend shelf life. Nitrogen is used as a filler gas to prevent pack collapse, which may occur in high CO2-containing atmospheres. Modified atmospheres may be produced naturally by respiration (passive MA) and by the application of gas flushing techniques (equilibrium MA) (Fig. 1.5). A sliced fruit is still alive and it continues respiring. Therefore it creates an MA within the pack with a reduced level of oxygen and an increased level of carbon dioxide. During passive MA gases’ equilibrium due to package film permeability will be reached at a certain relatively long time (a week or longer). When the estimated final equilibrium concentration of gases is Active MAP % CO2 or O2 (relative) CO2 Passive MAP O2 Active MAP Time after packaging Figure 1.5. CO2 and O2 concentration evolution during passive and active MAP of packaged fruit products (adapted from Zagory and Kader, 1988).

16 Fruit Manufacturing artificially created immediately after packaging (by air purge and replacing) respiration rate is more quickly controlled. For respiring products, the permeability characteristics of the film determine the equi- librium gas concentration achieved in the package to a large degree. The actual equilibrium MA attained within a package will also depend on factors such as the prepared form of the fruit studied, the rate of respiration at storage temperature, the pack volume and fill weight, and the surface areas for gas exchange. 1.8.2. Factors Influencing the Exact Modified Atmosphere Within a Sealed Pack Respiration depends not only on the variety of fruit but also on the stage of maturity of fruit when harvested. Storage temperature influences respiration rate of the product, affects the rate of diffusion of O2 and CO2 through the package film, and affects the rate of spoilage. The temperature must be kept both constant and low #48C. In the second place, the fitted atmosphere within the pack is influenced by gaseous environment inside the pack. The initial gas mix must be corrected and tailored to the individual products. As previously indicated, too high levels of CO2 will still reduce the respiration rate and inhibit the growth of bacteria, but physiological damage of the product may take place. Too low levels of O2 may still reduce the respiration rate, but if they are too low anaerobic respiration will take place. The package must be made from a suitable material. PVC and LDPE are the most commonly used films. Among other factors affecting MAP, antifogging agents added to film, weight of product, volume of gas, and area of film must be considered. Lipton (1975) proposed a helpful approach to selecting the required ratio of O2 to CO2 permeability of a polymeric film, which was expressed as: PCO2 ¼ PoOu2t À POin2 , (1:1) PO2 PiCnO2 À PCouOt2 where OiPn2,CouOt2aarnedthPeOp2aartriealthperepsesrumreeaobf igliatsyescoinefsfidiceieanntds of CO2 and O2 respectively, and P in,out and P outside CO2 package, respectively. Table 1.8 gives permeability coefficients of different polymeric films to oxygen and carbon dioxide. EXAMPLE Using Eq. (1.1) and Table 1.4 select the appropriate film to create an atmosphere containing 2% O2 and 5% CO2. Partial pressure of atmospheric gases at normal conditions is PCouOt2 ¼ 0:001 atm and PoOu2t ¼ 0:21 atm, respectively. Then, from Eq. (1.1): PCO2 ¼ 0:21 À 0:02 ¼ 3:8 PO2 0:05 From Table 1.8, both HDPE and PP have permeability ratio to oxygen and carbon dioxide close to the required calculated value. It is worth noting that the actual ratio for a particular film is not constant, but depends on the temperature. In general, the ratio increases as the temperature decreases.

1 . Overview of the Fruit Processing Industry 17 Table 1.8. Permeability coefficient of selected polymer films. Film material Permeability coefficient [mL (STP) cm cmÀ2 sÀ1 cmHgÀ1] O2 CO2 Low-density polyethylene (LDPE) 55 352 High-density polyethylene (HDPE) 10.6 35 Polypropylene (PP) 23 92 Polystyrene 11 88 Polyethylene terephthalate (PET) 0.22 1.53 Adapted from Robertson, 1993. In summary, handling of fruits requires care during harvesting, transportation and handling operation within the processing plant. Temperature and relative humidity need to be properly maintained. Refrigeration is required for prolonged storage or transportation for long distances. 1.9. TECHNOLOGY OF SEMIPROCESSED FRUIT PRODUCTS The semiprocessed fruit products are manufactured in order to be delivered to industry processing plant, to be manufactured in finished products such as jams, jellies, syrups, fruits in syrup, etc. The following categories of semiprocessed fruit are defined: . Fruit pulps: Obtained by mechanical treatment (or, less often, by thermal treatment) of fruit followed by their preservation. Either whole fruit, halves, or big pieces are used, which enables easy identification of the species. Pulps can be classified as boiled or nonboiled. . Fruit pure´es-marks: Obtained by thermal and mechanical treatment operations by which all nonedible parts (cores, peels, etc.) are removed. Pure´es-marks are also classified as boiled or nonboiled. . Semiprocessed juices: Products obtained by cold pressure, or eventually by other treatments (diffusion, extraction, etc.) followed by preservation. 1.9.1. Preservation of Semiprocessed Fruit Products Preservation can be achieved by chemical means, freezing, or pasteurization. The choice of preservation process for each individual case depends on the semiprocessed product type and the shelf life needed. Chemical preservation may be carried out with sulfur dioxide, sodium benzoate, formic acid, and, on a small scale, with sorbic acid and sorbates. Preservation with sulfur dioxide is a common process because of its advantages: universal antiseptic action and very economic application. The preservation with sulfur dioxide, although linked to allergic reactions, is mainly used in pulps and pure´es. Sodium benzoate is also in use in pulps and pure´es-marks. Preservation with sodium benzoate does not firm up the texture and does not modify fruit color. The disadvantages are that it is not a universal antiseptic, and needs an acidie medium to act. Moreover, sodium benzoate is difficult to remove. Practical dosage level for 12 months’ preservation was

18 Fruit Manufacturing recommended in the range 0.18 – 0.20% sodium benzoate, depending on the product to be preserved. Sodium benzoate is used as a solution in warm water; the dissolution water level has to be at maximum 10% reported to that of semiprocessed product weight. Formic acid, an antiseptic effective against yeasts, may be used for semi-processed fruit juices at a dosage level of 0.2% pure formic acid (100%). Formic acid does not influence color and is easily removed by boiling. Because of a potential effect of pectic substance degradation, formic acid is less used in pulps and pure´es-marks preservation. Sorbic acid can be used for preservation of semiprocessed fruit products at a dosage level of 0.1% maximum. Advantages of sorbates are that they are completely harmless and without any influence on the organoleptic properties of semiprocessed fruit products. Heat treatment. As fruits have a low pH, preservation of semiprocessed fruit products by heat treatment step at maximum temperature of 1008C, can be done (pasteurization). This treatment results in a more hygienic process, thereby assuring long-term preservation. How- ever, air-tight containers are needed and pectic substances could deteriorate if the thermal treatment is too long. Freezing. Freezing is applied to semiprocessed fruit products with a very high quality and cost. This can be done with or without sugar addition. The obvious advantages of this process are the absence of added substances, a very good preservation of quality of fruit constituents (pectic substances, vitamins, etc.), and good preservation of organoleptic properties. Freezing is done at about À20 to À308C and storage at À10 to À188C. REFERENCES Biale, J.B. and Young, R.E. (1981). Respiration and ripening in fruits—retrospect and prospect. In Recent Advances in the Biochemistry of Fruits and Vegetables, Friend, J. and Rhodes, M.J.C. (eds.). Academic Press, NY, pp. 1–39. Boyette, M.D., Estes, E.A. and Rubin, A.R. (1990). Hydrocooling. Published by North Carolina Cooperative Extension Service 10/92.2M. TAH.220544 AG-414–4. www.bae.ncsu.edu/programs/extension/publicat/ postharv. Claypool, L.L. (1983). Biological and cultural aspects of production and marketing of fruits. In Principles and Practices for Harvesting and Handling Fruits and Nuts. O’Brien, M., Cargill, B.F. and Friedly, B.B. (eds.). AVI Publishing Company, Inc., Westport, CT, pp. 15–42. Coombe, B.G. (1976). The development of fleshy fruits. Ann. Rev. Plant Physiol. 27: 507. Dauthy, M.E. (1995). Fruit and Vegetable processing. FAO AGRICULTURAL SERVICES BULLETIN No. 119 Food and Agriculture Organization of the United Nations, Rome. In: http://www.fao.org/documents. del Valle, J.M. and Palma M.T. (1997). Preservacio´ n II. Atmo´ sferas controladas y modificadas. In Temas en Tecnolog´ıas de Alimentos. Vol. 1. J.M. Aguilera Ed. CYTED-IPN MEXICO. FAOSTAT Data (2005). FAO Statistical Databases. www.fas.usda.gov/http/Presentations./ Farber, J.M. (1991). Microbiological aspects of modified-atmosphere packaging technology—a review. J. Food Protection 9: 58–70. Fraser, H.W. (1991). Forced-air rapid cooling of fresh Ontario fruits and vegetables. Ministry of Agriculture and Food, Toronto, Ontario, AGDEX 202–736. Hanson, L.P. (1976). Commercial processing of fruits. Noyes Data Corporation, London, p. 302. Hardenburg, R.E., Watada, A.E. and Wang, C.Y. (1986). The commercial storage of fruits, vegetables, and florist and nursery stocks. USDA, Agric. Handbook, 66, p. 130. Hui, Y.H. (1991). Data sourcebook for Food Scientists and Technologists. VCH Publishers, New York. Kader, A.A. (1985). Modified atmospheres: an indexed reference list with emphasis on horticultural commodities, supplement no. 4. University of California, Davis, Postharvest Hort. Series No. 3, 31 pp. Kader, A.A. (1986). Biochemical and physiological basis for effects of controlled and modified atmospheres on fruits and vegetables. Food Technol. 40(5): 99–103.

1 . Overview of the Fruit Processing Industry 19 Kader and Barret (1996). Classification, composition of fruits, and postharvest maintenance of quality. In Processing Fruits: Science and Technology. V. 1 Biology, Principles, and Applications, Somogyi, L.P., Ramaswamy, H.S. and Hui, Y.H. (eds.). Technomic Publishing Company, Inc., pp. 1–25. Koning, R.E. (1994). Plant Physiology Information Website. http://plantphys. info/index. html. Langdon, T.T. (1987). Prevention of browning in fresh prepared potatoes without the use of sulfiting agents. Food Technol. 41(5): 64–67. Lipton, W.J. (1975). Controlled atmospheres for fresh vegetables and fruits- why and when. In Postharvest Biology and Handling of Fruit and Vegetables, Haard, N.F. and Salunke, D.K. (eds.). AVI Publishing Company, Inc., Westport, CT, p. 130. Nagy, S., Chen C.S. and Shaw, P.E. (Eds.) (1993). Fruit Processing Technology. Agscience, Inc., Auburndale, FL. O’Brien, M., Cargill, B.F. and Fridley, R.B. (1983). Principles and Practices for Harvesting and Handling of Fruits and Nuts. AVI Publishing Company, Inc., Westport, CT, 636 pp. Raghavan, G.S.V., Alvo, P., Garie´py and Vigneault, C. (1996). Refrigerated and controlled modified atmosphere storage. In Processing Fruits: Science and Technology. V. 1 Biology, Principles, and Applications. Somogyi, L.P., Ramaswamy, H.S. and Hui, Y.H. (eds.). Technomic Publishing Company, Inc., pp. 135–167. Robertson, G. (1993). Food Packaging. Principles and Practice. Marcel Dekker, Inc., NY, pp. 472–473. Wilson, L.G., Boyette, M.D. and Estes, E.A. (1999). Postharvest handling and cooling of fresh fruits, vegetables, and flowers for small farms. Part II. Cooling7/99 HIL-800 NC cooperative extension service publication AG-414–1, and USDA Agricultural Handbook No. 66. Zagory, D. and Kader, A.A. (1988). Modified atmosphere packaging of fresh produce. Food Technol. 42(9): 70–74, 76–77.

CHAPTER 2 PROCESSING OF FRUITS: AMBIENT AND LOW TEMPERATURE PROCESSING 2.1. FRUIT PRODUCTS AND MANUFACTURING PROCESSES World trade of fruit and vegetable juice averaged nearly US$4,000 million last decade (FAOSTAT, 2005). By far the largest volume of processed apples and oranges, the two most important fruit commodities, is in the form of juices, and a great part of the present chapter is devoted to describing the processing of these liquid foods. There are however many other products obtained from fruits, including canned, dried, and frozen fruit; pulps; pure´es; and marmalades. Table 2.1 lists final products and processes applied on selected fruits. In addition, developments in aseptic processing have brought new dimensions and markets to the juice industry. Juices are a product for direct consumption and are obtained by the extraction of cellular juice from fruits; this operation can be done by pressing or diffusion. Fruit juices are categorized as those without pulp (‘‘clarified’’ or ‘‘not clarified’’) and those with pulp (‘‘pulps,’’ ‘‘pure´es,’’ and ‘‘nectars’’). Other classifications include ‘‘natural juice’’ products obtained from one fruit, and ‘‘mixed juice’’ products obtained from the mixing of two or three juices of different fruit species or by adding sugar. Juices obtained by removal of a major part of their water content by vacuum evaporation or fractional freezing are defined as ‘‘concen- trated juices.’’ Fruit composition is mainly water (75–90%), which is mainly found in vacuoles, giving turgor (textural rigidity) to the fruit tissue. Juice is the liquid extracted from the cells of mature fruits. Fruit cell wall is made of cellulose, hemicellulose, pectic substances, and proteins. The primary cell wall, composed of crystalline cellulose microfibrils, is made up of polymers of b-D-glucose linked by b-1-4-glycosidic linkages and cellulose embedded in an amorphous matrix of pectin and hemicelluloses. The definition of a mature fruit varies with each type. Typically, sugar and organic acid levels, and their ratio indicate maturity stage. The extracted liquid is composed of water, soluble solids (sugars and organic acids), aroma and flavor compounds, vitamins and minerals, pectic substances, pigments, and, to a very small degree, proteins and fats. The various sugars, such as fructose, glucose, and sucrose, combined with a large number of organic acids (most important being citric, malic, and tartaric), help give the fruit its characteristic sweetness and tartness. During ripening of fruits, a general decrease in acidity and starch as well as an increase in sugars is seen. Moreover, formation of odors, breakdown of chlorophyll, and hydrolysis of pectic substances also occur. It must be noted that plant tissues continue to ripen after harvest. Finally, senescence occurs, at a rate accelerated by the increase in ethylene. 21

22 Fruit Manufacturing Product Table 2.1. Principal fruit products and manufacturing processes. Canned Fruit Process description Frozen Apples Canned apple is the product prepared from fresh apples of one variety, which are not Frozen Apple sauce overripe, and whose fruit is packed with or without any of the following ingredi- ents: water, salt, spices, nutritive sweetening ingredients, and any other ingredients Cranberry permissible under regulations. The product is then heat processed to ensure sauce preservation in hermetically sealed containers Fruit salads Canned apple sauce is the product prepared from comminuted or chopped apples, Apples which may or may not be peeled and cored, and to which may have been added Apricots thereto one or more of the optional ingredients specified by regulations. The product is heated and, in accordance with good manufacturing practices, bruised Berries apple particles, peel, seed, core material, and other coarse, hard, or extraneous Cherries materials are removed. The product is processed by heat, either before or after Grapefruit sealing, so as to ensure preservation. The soluble solids’ content is $ 98Brix Lemon Canned cranberry sauce is the jellied or semijellied cranberry product prepared from clean, sound, matured cranberries, and contains sweetening ingredients and water. Pectin may be added to compensate for deficiency of the natural pectin content of the cranberries. The mixture is concentrated and sufficiently processed by heat to ensure preservation of the product. Final soluble solid is ffi 35–45% Canned fruits for salad consist of carefully selected apricots, cherries, yellow clingstone peaches, pears, pineapple, and grapes. The product is packed in a suitable liquid medium with or without the addition of sweetening ingredients, or other permissible ingredients. The product is heat processed and is processed to ensure preservation of the product in hermetically sealed containers Frozen apples are prepared from fresh apples of one variety, not overripe, which are peeled, cored, trimmed, sliced, sorted, washed, and properly drained before filling into containers. Sweetening ingredient and any other ingredient permissible under regu- lations may be used. The product is frozen in accordance with good commercial practice and maintained at temperatures necessary for the preservation of the product Frozen apricots are prepared from fresh fruit of one variety, which are not overripe, which are sorted, washed, and may be trimmed to ensure a clean and wholesome product. The apricots are properly drained of excess water before placing into containers. The addition of sweetening ingredients, including syrup containing pureed apricots, suitable antioxidant ingredients, and or any other ingredients permissible under regulations is allowed Frozen berries are prepared from properly ripened fresh fruit berries, are stemmed and cleaned, may be packed with or without packing media, and are frozen and stored at temperatures necessary for the preservation of the product. The same is applicable to frozen blueberries. Frozen cranberries do not need stemming before freezing Frozen sweet cherries are prepared from fresh fruit of one variety, which are not overripe, fruit of any commercial variety of sweet cherries, which are sorted, washed, and drained. The addition of nutritive sweetening ingredients is allowed. The product is frozen in accordance with good commercial practice and maintained at temperatures necessary for the preservation of the product Frozen grapefruit is prepared from fresh fruit of one variety, which are not overripe. After the fruit has been washed and peeled, and separated into segments by removing the core, seeds, and membrane it is packed with or without packing additives. The product is frozen and stored at temperatures necessary for the preservation of the product Frozen lemon concentrate is the product prepared from lemon juice (from fresh, sound, ripe, and thoroughly cleansed fruit) and lemonade ingredients (sweeteners; lemon oil, its extracts, or emulsions) and water in sufficient quantities to stand- ardize the product. The product contains $48.08Brix (corrected for acidity). Such juices may be fresh or frozen, or fresh concentrated or frozen concentrated; processed in accordance with good commercial practice and is frozen and maintained at temperatures sufficient for the preservation of the product (continued )

2 . Processing of Fruits 23 Product Fruit Table 2.1. (Continued ) Melon Process description Peaches Melon balls are spheres of melon flesh prepared from balls of suitable varieties of Pineapple sound, fresh melons. The balls are prepared and washed in a manner to assure a Plums clean and wholesome product. The product may be packed with the addition of a suitable fruit and or vegetable garnish; nutritive or non-nutritive sweetening Dried Apples ingredients, including syrup and any other ingredient permissible under regulations. It must be frozen in accordance with good commercial practice and Apricots maintained at temperatures necessary for preservation Figs Frozen peaches are prepared from fresh peaches of one variety, which are not Peaches overripe, peaches are peeled, pitted, washed, cut, and trimmed to assure a clean and Pears wholesome product. The peaches may be packed with the addition of a sweetening Raisins ingredient, including syrup and/or syrup containing pureed peaches and any other permissible ingredients. The product must be frozen in accordance with good Prunes commercial practice and maintained at temperatures necessary for the preservation Frozen pineapple is prepared from the properly ripened pineapple fruit, which is peeled, cored, trimmed, and washed; is packed with or without packing media; and is frozen and stored at temperatures necessary for the preservation of the product Frozen plums are prepared from clean, sound, fresh fruit of any commercial variety of plums, which are sorted, washed, drained, and pitted; which may be packed with or without the addition of a nutritive sweetening ingredient; and which are frozen in accordance with good commercial practice and maintained at temperatures necessary for the preservation of the product Dried apples are prepared from fresh apples of one variety, which are not overripe, by washing, sorting, trimming, peeling, coring, and cutting into segments. The pre- pared apple segments are properly dried to remove the greater portion of moisture to produce a semidry texture. The product may be sulfured sufficiently to retard discoloration. The sulfur dioxide content of the finished product should not exceed 1,000 parts per million. No other additives are allowed Dehydrated low-moisture apricots are prepared from fresh fruits of one variety, which are not overripe, which are cut, chopped, or otherwise prepared into various sizes and shapes; are prepared to assure a clean, sound, wholesome product; are processed by dehydration whereby practically all of the moisture is removed to produce a very dry texture; and are placed in a container, which has low moisture. The product is packaged to assure dryness retention and should be sulfured at a level sufficient to retain a characteristic color Dried figs are prepared from clean and sound fruits and are sorted and thoroughly cleaned to assure a clean, sound, wholesome product. The figs may or may not be sulfured, or otherwise bleached Dried peaches are the halved and pitted fruit from which most of moisture has been removed. The dried fruit is processed to cleanse and it may be sulfured sufficiently to retain color Dried pears are made with the halved fruit, which may or may not be cored, from which the external stems and calyx cups have been removed. Before packing, the dried fruit may be sulfured sufficiently to color Processed raisins are dried grapes of vinifera varieties, such raisins as Thompson Seedless Sultanian, Muscat of Alexandria, Muscatel Gordo Blanco, Sultana, or White Corinth. The processed raisins are from fresh fruit, which are not overripe. Grapes are properly stemmed and cap stemmed, seeded, sorted or cleaned, or both, and are washed in water to assure a wholesome product Dehydrated prunes are prepared from clean and sound prunes, which are pitted and prepared into various sizes and shapes, washed, and processed by dehydration to produce a very dry texture. The product is then packaged to assure retention of the dryness characteristic of the product. A safe preservative may be added (continued )

24 Fruit Manufacturing Table 2.1. (Continued ) Product Fruit Process description Juices Grape Frozen concentrated sweetened grape juice is prepared from concentrated Juices unfermented single-strength grape juice from fresh fruit, which are not overripe, Apple frozen with or without aging, or grape juice depectinization, and is then concentrated. Others concentrate Single-strength grape juice or natural grape essence, or a combination of single- strength grape juice and natural grape essence may be mixed to the concentrate Canned apple and may or may not be packed with the addition of ingredients like sweeteners, juice edible fruit acid, and ascorbic acid. The product is then frozen in accordance with good commercial practice Canned grape juice Frozen concentrated apple juice is prepared from the concentrated unfermented, liquid obtained from apple juice during the first pressing of properly prepared, Lemon single- clean, mature, fresh apples by good commercial processes. The juice is clarified strength and concentrated to at least 22.98Brix. The apple juice concentrate so prepared, with or without the addition of ingredients permissible under regulations, is Lemon packed and frozen in accordance with good commercial practice and maintained concentrate at temperatures necessary for the preservation Tangerine Canned apple juice is the unfermented juice obtained from sound, ripe apples, with or without parts. No water may be added directly to the finished product. Marmalade However, concentrated apple juice is allowed. Apple essence may be restored to a level that provides a natural apple juice flavor Canned grape juice is the unfermented liquid obtained from the juice of properly matured fresh grapes. Such grape juice is prepared without concentration, without dilution, is packed with or without the addition of sweetening ingredients, and is sufficiently processed by heat to assure preservation of the product in hermetically sealed containers Canned lemon juice is the undiluted, unconcentrated, unfermented juice obtained from sound, mature lemons of one or more of the high-acid varieties. The fruit is prepared by washing prior to extraction of the juice to assure a clean product. The product is sufficiently processed with heat to assure preservation in hermetically sealed containers The fruit is prepared by sorting and by washing prior to extraction of the juice. The concentrated lemon juice is prepared and concentrated in accordance with good commercial practice. It may or may not require processing by heat, subsequent refrigeration, or freezing to assure preservation of the product. The finished product may contain added pulp, lemon oil to standardize flavor, and or permissible chemical preservatives. Concentrated tangerine juice is the tangerine concentrated product obtained from sound, mature fruit. The fruit is prepared by sorting and by washing prior to extraction of the juice. The concentrated tangerine juice is processed in accordance with good commercial practice, and may or may not require processing by heat or subsequent refrigeration to assure preservation of the product. Cold-pressed oil to standardize flavor and permissible chemical preservatives may be added Orange marmalade is the semisolid or gel-like product prepared from orange fruit ingredients together with ingredients like sweeteners, food acids, food pectin, lemon juice, or lemon peel. Soluble solids of finished marmalade is $65% Source: Hui (1991); Nagy et al. (1992); Somogyi et al. (1996). 2.2. FRUIT JUICE AND PULP PROCESSING Fruit processing plants can vary from a simple facility for single juice extraction and canning, to a complex manufacturing facility, which has ultrafiltration and reverse osmosis equipment, cold storage, and waste treatment plant. A simplified characteristic flow diagram of a juice

2 . Processing of Fruits 25 processing line is shown in Fig. 2.1. Processed products can be either single strength or bulk concentrate, and are available either as clarified or cloudy juice. Production of fruit juices can be divided into four basic principal stages: . Front-end operation . Juice extraction Fruit Grape, berries Washing (brushing, spraying, etc.) Steming, destoning, peeling Blanching If necessary Extraction Milling, chopping, crushing Seeds´removing (berries) Enzymatic treatment Puree (maceration, liquefaction) Centrifugation Pressing Turbid juice Enzymatic treatment Flocculation Heat treatment UF Clarification Centrifugation filtration Clear juice Cloudy juice Concentration step Final product Figure 2.1. Typical fruit juice (clear or cloudy) and pure´e-processing line steps.

26 Fruit Manufacturing . Juice clarification and refining . Juice pasteurization and concentration. Figure 2.2a and b shows descriptive sketches of alternative processing steps for cloudy and/or clarified apple juice concentrate elaboration. Reception line Pressing (from silos) Milling/pulping Enzymatic mashing Screening Aroma Cloudy Supernatant (Sp) stripping Sediment UF Clarification (Sd) (a) Vacuum filtration Centrifugation (Sd) (Sp) (UF) Ultrafiltration Fining (UF) Storage Other Concentration (b) Figure 2.2. Typical apple juice processing plant. (a) From fruit to cloudy juice; (b) From cloudy juice to concentrate.

2 . Processing of Fruits 27 2.2.1. Front-End Operations This stage includes those operations related with the reception and classification of fruits in the manufacturing plant: 2.2.1.1. Reception Line . Weighing of incoming fruit: Origin and variety are usually recorded in this step. . Unloading of fruits into silos system: Harvesting containers known as bins are com- monly used worldwide for transportation of fruits from the orchard to the processing plant. Standard bins are 1:21 Â 1:21 Â 1:0 m in size. Up to 30 or more bins may be placed in a single truck. Once in the plant, bin dumping–unloading can be performed at least in three different ways, depending on the fruit (Fig. 2.3). . Sampling and laboratory testing: Table 2.2 lists the recommended fruit controls at the reception in processing plant, including assay of soluble solids, yield, Brix-acid ratio, etc. Other special tests are Magnus–Taylor pressure tester for pears and apples, and background color for peaches. . Washing of fruit: The harvested fruit is washed to remove soil, microorganisms, and pesticide residues. Spoiled fruits should be discarded before washing in order to avoid contaminating the washing tools and/or equipment and the contamination of other fruits during washing. Washing efficiency can be estimated by the total number of microorganisms present on fruit surface before and after washing. Apples require heavy spray applications and rotary brush wash to remove any rot. Many fruits such as mechanically harvested berries are air cleaned on mesh conveyors or vibrators • Hinged sides: Tilt when Good for cherries, partly empty apricots, and peaches • Bin tippers: Good for apples, pears, grapes, etc. Bins Flotation • Flotation unloaders: Bins Good for fruits with density < 1 (apples) Figure 2.3. Unloading of fruits into silos systems. Reprinted from the Encyclopedia of Food Science and Nutrition. Lozano J.E., Separation and Clarification, pp. 5187–5196 (copyright) 2003, with permission from Elsevier.

28 Fruit Manufacturing Table 2.2. Recommended fruit controls at reception. Checks per lot Checks for every 10 lots Once during harvest season Color Density Ascorbic acid Taste Water content Mineral substances Texture Total sugars, reducing sugars Tannic substances Flavor Total acidity Pectic substances Soluble solids (Brix) Variety Sanitary evaluation passing over an air jet. Washers are conveyor belts or roller conveyors with water sprays, reel (cylinder) type with internal spray (Fig. 2.4), brushes and/or rubber rolls with or without studs. Vibratory-type washers are very effective for berries and small fruits. Brushes are effective in eliminating rotten portions of fruits, thus preventing problems with micotoxins (patulin in apples). Some usual practices in fruit washing are: . Addition of detergents or 1.5%-HCl solution in washing water to remove traces of insecticides and fungicides; . Use of warm water (about 508C) in the prewashing phase; . Higher water pressure in spray/shower washers. Washing must be done before the fruit is cut in order to avoid losing high-nutritive value soluble substances (vitamins, minerals, sugars, etc.). 2.2.1.2. Final Grading, and Inspection and Sorting Fruit sorting covers two main separate processing operations: (1) Removal of damaged fruit and any foreign substance; and (2) Qualitative sorting based on organoleptic criteria and maturity stage. The most important initial sorting is performed for variety and maturity. However, for some fruits and in special processing technologies, it is advisable to carry out a manual dimensional Fruit in Water in Water spray Figure 2.4. Sketch of a reel washer with internal spray. Reprinted from the Encyclopedia of Food Science and Nutrition, Lozano J.E., Separation and Clarification, pp. 5187–5196 (copyright) 2003, with permission from Elsevier.

2 . Processing of Fruits 29 Sorting method Table 2.3. Fruit sorting methods. By size By weight Description By texture firmness By color Rollers (cherries), diverging belts, reels with holes Apples and citrus sorters. Sort into 20 or more weight grades Bounce system (cranberries) Citrus color sorter measures green to yellow ratio sorting (grading). Sorting may be performed by different ways, such as those listed in Table 2.3 (Fellows, 1988): . Aligning: Feeding into some processes (peeling, trimming, etc.) needs the fruit to be placed in a single line. This may be performed with accelerating belts or water flumes. . Peeling (skin removal): Although manual peeling is still used for certain large veget- ables, the method is very expensive. When required, fruits are usually peeled with one of the methods (Woodroof, 1986; Fellows, 1988) listed in Table 2.4. In general, loss increases with surface to volume ratio and decreases with fruit size. Mechanical methods are the worst, with up to 30% loss, while chemical (caustic) methods reduce loss to #10%. . Trimming: This is usually a manual operation that precedes cutting, in order to eliminate few defective pieces. . Cutting: Many special cutters are available, including sector cutters for apples, berry slicers, dicers, etc. . Pitting and coring: This operation usually occurs after sorting and peeling. In peaches, pitters cut away some flesh. Automatic cherry pitters have also been developed. . Belt conveyor: Transport fruits to juice extractors (citrus), crusher and mills (pomes), or stem and seed remover (grapes and berries). Method Table 2.4. Peeling methods. Mechanical peeling Description Steam peeling Chemical peeling . By abrasion: It is used in batch with rotating abrasive base and water wash. This method is inefficient, with excessive losses. Hot gas peeling Freeze–thaw peeling . Abrasive roll peelers: This is a continuous method that combines rolls and brushes. . Blade type: The fruit rotates and mechanized knives separate the peel. . Live knife: Incorporates hydraulic control of the knife pressure. Good for apples and pears. . Pressure steam peeling make the peel blow off with pressure drop coming out of peeling chamber. May be combined with dry caustic peeling system. . Caustic peeling is extremely common. The simplest type involves immersion on a pocketed paddle wheel, with hot NaOH (20%), followed by scrubbing and washing. Tomatoes, peaches, and apples are peeled by this method. KOH is preferred because or its tissue penetration and disposal properties. . When hot gas contacts a vegetable on the belt or roller conveyor, the skin is blown off by the steam formed. It is generally not used in fruits. . Fruit is frozen in a low temperature medium (À408C) for few seconds and then warmed in water (408C). As a result of freezing the immediate subpeel cells are disrupted, releasing pectinases, which free the peel. Peeling loss is reduced to a minimum.

30 Fruit Manufacturing 2.2.2. Extraction The method of separating most of water and soluble solids (juicing) depends on the fruit variety. 2.2.2.1. Citrus . There are three main types of extractors manufactured by different companies (Ramas- wamy and Abbatemarco, 1996): (1) The FMC citrus juice extractor, in which juice is extracted from the whole fruit without first cutting the fruit into half. Outlet streams carry juice peel, center part, and oil emulsion. (2) The Brown extractor, in which the fruit is cut into half. Outlet streams are juice of high yield and quality, and rag and peel. (3) The Rotary press, in which the fruit is cut in half and the juice extracted in rotary cylinders. More than 75% of the world’s processors use FMC technology,this process is described in more detail here. When the upper and lower cups start to come closer to each other, the upper and lower cutters cut two holes in the fruit (Fig. 2.5a). As the upper and lower cups continue to come together, the peel is separated from the fruit (Fig. 2.5b). The peeled fruit moves into the strainer tube where the juice is instantaneously separated from the seeds and the rest of the fruit (Fig. 2.5c). 2.2.2.2. Pomes There are few problems in reducing the size of fresh ‘‘hard’’ apples or pears. After washing, pome fruits are milled. The fruit to be milled is continuously fed into the milling device. For the disintegration fixed positioned or rotating grinding knives may be used. Depending on the product quality different types of knives need to be selected. The types of fruit mills generally used are: Figure 2.5. FMC citrus juice extractor (with permission).

2 . Processing of Fruits 31 Figure 2.6. Fruit grinding mill. . Fruit grinding mill: The milling tool is a rotating disk with radially arranged grinding knives. The speed of the disk is variable, permitting to produce the required particle size (Fig. 2.6). . Rasp or grater mill: It consists of a revolving metal cylinder with adjustable toothed blades, which rotate toward a set of parallel metal knifes or plates. . Fixed blade hammer mills: The rotor with fixed blades rotates within a perforated screen. Hammer mills may be horizontal, sloping, or vertical shaft mounting (Fig. 2.7). Mills must not produce too much fines as these will contribute to pressing and later high pulp content in the juice. The particles should all be about the same size. Grater mills are found to be more efficient with firm fruits, while hammer mills are more suited for mature or softer fruits, provided speed is properly adjusted. Fruit Rotating hammer Mesh Pulp Figure 2.7. Hammer mill.

32 Fruit Manufacturing 2.2.2.3. Pressing Most systems for extracting juices from apples and similar fruit pulps use some method of pressing juice through cloth of various thicknesses, in which pomace is retained. These systems, called filter presses, include (Lozano, 2003): (i) rack and cloth press, (ii) horizontal pack press, (iii) continuous belt press, and (iv) screw press. (1) In a rack and cloth press the milled fruit pulp is placed in a nylon, Dacron, or polypro- pylene cloth to form a ‘‘cheese,’’ with the help of a cheese form. Layers of up to 10-cm thick pulp cheeses, separated by racks made of hardwood or plastic, are stacked up to 1 m or more in height depending on maturity of the fruit and size of racks (Fig. 2.8). Rack and cloth presses are efficient but very labor intensive as they require operation, cleaning, and repairing. Maximum yield may be obtained by use of a series of two to three pressure heads located around a central pivot, using pressures up to 200 atm. (2) Cage presses are horizontal presses with enclosed cages of several cubic meters in which pressing takes place. Pomace is pumped into the cage without contact with air, thereby reducing oxidation (Fig. 2.9a). The cage is filled with a complex filter systems consisting of grooved flexible rods filled with sleeves of press cloth material. During the pressing step (Fig. 2.9b), the juice passes from the pulp, through press cloth sleeves, along grooves in the flexible rods, and out to collecting channels at the ends of the cage and the piston. The drum may be rotated, thereby breaking up the pulp and adding more water. This permits a second pressing with more juice extraction. The whole process may be automated. Although some cleaning labor is saved, rods and sleeves require a considerable amount of Press Racks Pulp cheese Expressed juice Figure 2.8. Sketch of a rack and cloth press. Reprinted from the Encyclopedia of Food Science and Nutrition, Lozano J.E., Separation and Clarification, pp. 5187–5196 (copyright) 2003, with permission from Elsevier.

2 . Processing of Fruits 33 Pulp in Juice out Figure 2.9. Hydraulic press: (a) loading, (b) pressing. maintenance. These presses may slow down the operating cycle for production of stable cloudy nonoxidized juice. (3) Continuous belt press: Based on the Ensink design for paper pulp pressing this type of presses offers a truly continuous operation (Fig. 2.10). In belt presses, a layer of mash (pulp) is pumped onto the belt entering the machine. The press aid may be added for improved yield. (4) Screw presses: A typical screw press consists of a stainless steel cylindrical screen, enclosing a large bore screw with narrow clearance between screw and cylinder. Adjust- able back-pressure is usually provided at the end of the chamber. Breaker bars must be incorporated to disrupt the compressing mash. Capacity for screw presses of 41-cm diameter is up to 15,000 kg/h (Bump, 1989). Pulp Mesh Bagasse Juice Figure 2.10. Sketch of a typical fruit belt press.

34 Fruit Manufacturing 2.2.2.4. Other Extraction Methods . Centrifugation: Both cone and basket centrifuges have been used in producing fruit juice. Both systems have resulted in high levels of suspended solids and a high investment cost for a given yield. Horizontal decanters are presently used for juice clarification. . Diffusion extraction: This was adapted from the method used for the extraction of sugar from sugar beet. Extraction is a typical countercurrent-type process. It is desir- able to retain the same driving force DC (concentration of soluble components in solids versus concentration of soluble components in liquids). In order to maintain a constant DC throughout the extraction process, it is necessary to carry out a continuous weighing of ingoing apple slice and control the water flow to the counterflow extractor, by means of a relatively simple control loop (Fig. 2.11). The diffusion extraction process is influenced by a number of variables, including tempera- ture, thickness, water, and fruit variety. Slices from extractors pass through a conventional press system, and the very dilute juice is returned to the extractors. It is seen that the extra juice yield from diffusion extraction compensates the extra energy cost involved for concen- tration. . Addition of press aids: Hydraulic pressing does not usually require addition of press aids, unless exceptionally overmature fruit is used. For continuous screw presses however it is usually necessary to add 1% (w/w) or more of cellulose. Mixing of cellulose and fruit occurs in the mill and subsequent pumping to press. Pumping is commonly performed with a Moyno-type moving cavity food pump. Warm water inlet Fruit Fruit pulp in pulp out Juice Figure 2.11. Sketch of fruit juice diffusion extraction process.

2 . Processing of Fruits 35 2.2.3. Clarification and Fining The conventional route to concentration is to strip aroma, then depectinize juice with enzymes, centrifuge to remove heavy sediments and filter through pressure precoat filters and polish filters (Figure 2.2a). The juice is then usually concentrated through a multistage vacuum concentrator. This process involves a slight decrease in concentration of juice during the stripping step (usually up to 10% volume is removed). Stripping usually precedes depectinization, as pectin methyl esterase releases significant quantities of methanol, which spoils the essence. The use of enzymes for clarification is described later in this chapter. When a more concentrated juice is clarified (ffi20 8Brix) the volume to handle is reduced practically in a half. However, viscosity increased with concentration, which may slow flocculation and filtration. If a cloudy product is required, the juice is pasteurized immediately after pressing to denature any residual enzymes. Centrifugation then removes large pieces of debris, leaving most of the small particles in suspension. 2.2.3.1. Partial Concentrates Fruit juices, both clarified or opalescent, may be concentrated up to 4 fold (ffi50 8Brix) with natural pectin gelling with little effort. At this point in the concentration process little heat damage is detected. This concentrate can be canned and frozen. For clear juice these suspended particles have to be removed (McLellan, 1996). It may seem simple merely to filter them out, but unfortunately some soluble pectin remains in the juice, making it too viscous to filter quickly. A dose of commercial enzyme is the accepted way of removing unwanted pectin. Depectinization has two effects: it degrades the viscous soluble pectins and it also causes the aggregation of cloudy particles. Pectin forms a protective coat around proteins in suspension. In an acidic environment (apple juice typically has a pH of 3.5) pectin molecules carry a negative charge. This causes them to repel one another. Pectinolytic enzymes degrade pectin and expose part of the positively charged protein beneath. As the electrostatic repul- sion between cloudy particles is reduced, they clump together. These larger particles will eventually settle, but to improve the process flocculating agents (fining) such as gelatin, tannin, or bentonite (a type of clay) can be added. Some fining agents adsorb the enzyme onto their surface, so it is important not to add them before the enzyme has done its job. Fining agents (Table 2.5) work either by sticking to particles, thereby making them heavy enough to sink; or by using charged ions to cause particles to stick to each other, thereby making them settle to the bottom. Although this method of conventional clarification was widely used in the clarified juice industry, this technology has been practically replaced by mechanical processes such as ultrafiltration and centrifugal decanters. Yeasts and other microbes, which may have contaminated the juice, may also be precipitated by fining. What is left is a transparent, but by no means, clear juice. A second centrifugation and a subsequent filtration are needed to produce the clear juice that many consumers prefer. Another potential contributor to the haziness of juice is starch. This is particularly so if unripe apples have been used. Unripe apples may contain up to 15% starch. Although the first centrifugation—before the juice reaches the clarification tank—removes most of the starch, about 5% usually remains. This can be broken down using an amylase (amyloglucosidase) active at the pH of apple juice, added at the same time as the pectinase.

36 Fruit Manufacturing Name Table 2.5. Fruit juice clarification agents. Sparkolloid Gelatin Description Kieselsol Sparkolloid is a natural albuminous protein extracted from kelp and sold as a Bentonite very fine powder Isinglass It is in general a mixture of gelatins and silicon dioxide, with animal collagen being the active ingredient Filters or Polishers Pectic Enzymes Kieselsol is a liquid in which small silica particles have been suspended. It is usually used in tandem with gelatin. The dosage is 1 ml/g of gelatins. This fining aids in pulling proteins out of suspension Bentonite is sold as a powder and as course granules. It is refined clay. A better way is to add the same amount to a liter of hot water, stir well, and let stand for 36–48 h. In this time the clay swells and becomes almost a gelatin Produced from sturgeon swim bladders, isinglass is sold either as a fine white powder or as dry hard fragments. It is a protein extracted from the bladders of these fish. This product is also available as a prepared liquid called ‘‘super-clear’’ With a fine porosity pad, filters are very effective in removing particles (yeast cells, proteins, etc.) Almost all fruits contain pectin, some more than others. When added as directed, it eliminates pectin haze. There is no other way to prevent this condition, and if it is in a juice, the haze will never clear on its own For juice processing both depectinization and destarching are essential. This is because most apple juice is concentrated by evaporating up to 75% of the water content before storage. This makes the juice easier to transport and store, and the concentrate’s high sugar content acts as a natural preservative. Unfortunately, heat treatment also drives off the juice’s pleasant aroma, so it is necessary to gently heat the juice and collect the volatile smell and flavor compounds, so that they can be put back again when the juice is reconstituted. Heating can cause residual pectin or starch in the juice to gel or form a haze, hence the necessity of enzyme treatment. Increased haze formation occurs when fining with gelatin and bentonite is not performed. Optimization of fining and ultrafiltration steps can help retard or prevent postbottling haze development. 2.2.4. Use of Enzymes in the Fruit Industry Commercial pectic enzymes (pectinases) and other enzymes are now an integral part of fruit juice technology (Grampp, 1976). They are used to help extract, clarify, and modify juices from many fruits, including berries, stone and citrus fruits, grapes, apples, pears, and even vegetables. When a cloudy juice or nectar is preferred (for example, with oranges, pineapples, or apricots) there is no need to clarify the liquid, and enzymes are used to enhance extraction or perform other modifications. The available commercial pectinase preparations used in fruit processing generally contain a mixture of pectinesterase (PE), polygalacturonase (PG), and pectinlyase (PL) enzymes (Dietrich et al., 1991). Enzymatic juice extraction from apples was introduced 25 years ago, and now some 3–5 million tons of apples are processed into juice annually throughout the world. The methods employed for apple juice are generally the same as those for other fruits (Table 2.6). As previously mentioned, after fruits like apples have been washed and sorted, they are crushed in a mill. Peels and cores from apple slice or sauce production may also be used

2 . Processing of Fruits 37 Table 2.6. Application of pectolytic enzymes to fruit and vegetable processing. Enzymatic process Examples of application Clarification of fruit juices Apple juice, depectinized juices can also be concentrated without gelling Enzyme treatment of pulp and developing turbidity Maceration of fruit and vegetables Soft fruits, red grapes, citrus, and apples; for better release of juice (disintegration by cell separation) (and colored material); enzyme treatment of pulp of olives, palm fruit, and coconut flesh to increase oil yield Liquefaction of fruit and vegetables Special applications to citrus fruits Used to obtain nectar bases and in baby foods Used to obtain products with increased soluble solids’ content (pectinases and cellulases combined) Used for the preparation of clouding agents from citrus peel, cleaning of peels before use in candy and marmalade production, recovery of oil from citrus peel, depectinization of citrus pulp wash (Source: Rombouts and Pilnik, 1978). together with whole apples. Although pectinases are often added at this stage, better results are achieved if the apple pulp is first stirred in a holding tank for 15–20 minutes so that enzyme inhibitors (polyphenols) are oxidized (by naturally occurring polyphenols oxidized in the fruit). The pulp is then heated to an appropriate temperature before enzyme treatment. For apples 308C is the optimal temperature, whereas stone fruits and berries generally require higher temperatures—around 508C. This compares with 60–658C required if pectinase is not used (here the juice is liberated by plasmolysis of the plant cells). Prepress treatment with pectinases takes anything from 15 min to 2 h depending upon the exact nature of the enzyme and how much is used, the reaction temperature, and the variety of apple chosen. Some varieties such as Golden Delicious are notoriously difficult to breakdown. During incubation the pectinase degrades soluble pectin in the pulp, making the juice flow more freely. The enzyme also helps to breakdown insoluble pectin, which impede juice extraction. Enzyme treatment is considered to be complete once the viscosity of the juice has returned to its original level or less. It is important that the pulp is not broken down too much as it would then be difficult to press. Pressing is done using the previously described equipment. Juice yields can be increased by up to 20%, depending upon the age and variety of fruit used and whether preoxidation was employed. Enzyme treatment is particularly effective with mature apples and those from cold storage. 2.2.4.1. Other Enzymes in Juice Production . Cellulases: The addition of cellulases during extraction at 508C improves the release of color compounds from the skins of fruit. This is particularly useful for treating blackcurrants and red grapes. Increasingly cellulases are being used at the time of the initial pectinase addition to totally liquefy the plant tissue. This makes it possible to filter juice straight from the pulp without any need for pressing. . Arabanase: The polysaccharide araban (a polymer of the pentose arabinose) may appear as a haze in fruit juice a few weeks after it has been concentrated. Although commercial pectinase preparations often contain arabanase, certain fruits (like pears)

38 Fruit Manufacturing are rich in araban and may require the addition of extra arabanase to the clarification tank. . Glucose oxidase (from the fungi Aspergillus niger or Penicillium spp.): Catalyzes the breakdown of glucose to produce gluconic acid and hydrogen peroxide. This reaction utilizes molecular oxygen. Glucose oxidase (coupled with catalase to remove the hydrogen peroxide) is therefore used to remove the oxygen from the head space above bottled drinks, thereby reducing the nonenzymatic browning due to oxidation, which might otherwise occur. 2.2.4.2. Pectinase Activity Determination Complete pectin breakdown in apple juices can be ensured only if all the three types of pectinolytic enzymes (PG, PE, PL) are present in the correct proportion. Apple juice proces- sor in general lacks reliable methods for checking the different enzyme activities. Application and success of a pectinase product also depend on the substrate where they act. The problems in evaluation of pectinolytic activities are caused by the difficulty in standardizing fruit substrate. Acidity, pH, and the presence of inhibitors or promoters of the enzymatic reaction depend upon the variety of apple processed. Figure 2.12 shows the residual polygalacturonase activity of two commercial enzymes after 30 min of heating at different temperatures. They start to become inactivated at temperatures higher than 508C, which is a very well defined breaking point, if the enzyme 1 PG-PECTINOL A1 100 2 PG-R HAPECT D5S 3 PL-R HAPECT D5S 80 Relative Residual Activities (%) 60 21 40 3 20 0 50 60 70 40 Temperature (ЊC) Figure 2.12. Enzymatic residual activities after thermal treatment 30 min at different temperatures) of enzyme solutions in 0.1 M citrate/0.2 M phosphate buffers at optimum pH). Reprinted from Food Chem. 31(½), Ceci, L. and Lozano, J.E. Determination of enzymatic activities of commercial pectinases, 237–241. (copyright) 2003, with permission from Elsevier.

2 . Processing of Fruits 39 were to rapidly loses its activity. The rate of PG activity decrease could be divided into two periods (Fig. 2.12). The first period was characterized as a thermolabile fraction. The second can be defined as the thermoresistant fraction of the enzyme. Sakai et al. (1993) and Liu and Luh (1978) reported that the optimal temperature for PG activity was in the range 30–508C. Both authors indicated that for temperatures greater than 508C inactivation was notable after a short period of heating. Moreover, the optimal temperature is also a function of the type of substrate to be treated (Ben-Shalom et al., 1986). Inactivation curve of lyase activity (PL) is also shown in Fig. 2.12. As in the case of PG activities, 508C can be easily identified as the breaking point where PL rapidly inactivates. Alkorta et al. (1996) found that PL from Penicillum italicum was active after 1 h at 508C but resulted in complete inactivation for the same period at 608C. The commercial enzymes proved to be more heat tolerant than purified fractions (Liu and Luh 1978). This phenom- enon was attributable to the heat protective action of impurities. 2.2.4.3. pH Dependence on the Pectic Enzymes Activities Figure 2.13 shows the behavior of PG and PE activities of RHD5 enzyme versus pH. The resulting optimum pH was approximately 4.6. However, the curve for lyase activity as a RÖHAPECT D5S 100 80 RELATIVE ACTIVITIES (%) 60 PG PL 40 PE 20 0 4.0 6.0 pH Figure 2.13. Effects of pH on the enzymatic activities of Ro¨ hapect D5S (Ceci and Lozano, 1998). Reprinted from Food Chem. 31(½), Ceci, L. and Lozano, J.E. Determination of enzymatic activities of commercial pectinases, 237–241. (copyright) 2003, with permission from Elsevier.

40 Fruit Manufacturing function of pH was much broader, and it was difficult to identify a single optimal value. In this case, an optimal range of pH 5–6 may be defined. As a result, as much as 40% of PG and PE inactivation can be expected during the enzymatic clarification of the relatively acidic Granny Smith juice. It was found that a shift in the optimal pH toward the acid zone (Spagna et al., 1993) or a broadening of the optimal activities’ range (Ates and Pekyardimci, 1995) can be obtained after enzyme immobilization on appropriate supports. In general pectinolytic enzymes (PG and PE) show a rapid decrease in activity at about pH 5 and become practically inactivated near neutrality. However, this problem becomes irrelevant because pH values of fruit juices are lower than pH 5. It was found that a shift in the optimal pH toward the acid zone (Spagna et al., 1993) or a broadening of the optimal activities’ range (Ates and Pekyardimci, 1995) can be obtained after enzyme immobilization on appropriate supports As fruit juice clarification is usually done at 45–50C, special care must be taken to avoid excessive inactivation when lyase activity is considered important. It is known (Dietrich et al., 1991) that commercial enzyme preparations cause a certain degree of side activities other than those required (Ceci and Lozano, 1998). 2.2.4.4. Enzymatic Hydrolysis of Starch in Fruit Juices Starch can be a problem for juice processors. Polymeric carbohydrates like starch and arabans can be difficult to filter and cause postprocess cloudiness. In the case of a positive starch test, the following problems may occur: slow filtration, membrane fouling, gelling after concentration, and postconcentration haze. Apple juice is one of the juices that can contain considerable amounts of starch, particularly at the beginning of the season. Unripe apples contain as much as 15% starch (Reed, 1975). As the apple matures on the tree, the starch hydrolyzes into sugars. The starch content of apple juice may be high in years when there were relatively low temperatures during the growing season. Besides the generalized application of commercial amylase enzymes in the juice industry, there is a lack of information on apple starch characteristics and extent of gelatinization during juice pasteurization. Starch must be degraded by adding starch-splitting enzymes, together with the pec- tinase during depectinization of the juice. First starch must be gelatinized, by heating the juice to 778C. When an aqueous suspension of starch is heated the hydrogen bonds weaken; water is absorbed; and the starch granules swell, rupture, and gelatinize (Zobel, 1984). The juice must then be cooled to <508C to avoid enzyme inactivation. Starch is generally insoluble in water at room temperature. Because of this, it is stored in cells as small granules. Starch granules (Fig. 2.14) are quite resistant to penetration by both water and hydro- lytic enzymes due to the formation of hydrogen bonds within the same molecule and with other neighboring molecules. When the starch granule is not broken down completely, a short-chained dextrin is left. This can lead to a condition known as retrograding. When starch retrogrades, the short-chained dextrin recrystallizes into a form that is no longer susceptible to enzyme attack, regardless of heating. Figure 2.15 shows a SEM photomicrograph of haze sediment obtained from a pasteurized apple juice sample.