oldose amono s N-substituteds 2H2O sugar compound sA glycosylamines Amadori B rearrangement s I - amono - I - deoxy - 2 ketose (1,2-enol form) -3H2O C D -2H2O Schiff base of HMF or s + a-amono acid E furfuralss - amino comp’d feductones s Strecker degradation + H2O s s HMF or s furfural s -2H s +2H s fissino CO2 products aldehyde dehydro (acetol, reductones pyruvaldehyde diacetyl etc.) F with or FF F without + amino + amino + amino amino comp’d comp’d comp’d compd. ss G ss aldols and G G aldimines N-free aldimines aldimines G polymers or G + amino comp’d. ketimines G G s s ss s MELANOIDINS (brown nitrogenous polymers and copolymery Figure 1. Hodge 1953. Maillard Browning Pathway COLOUR 51
Features of Maill ard reaction Presence of reducing sugars and amino compounds (proteins, amino acids) Requires dry heat and high temperature – baking, frying, toasting Rapid at pH>7.0, slower at pH<6.0 Colour: colourless → yellow → brown → dark brown Benefits: contributes to flavours in bread, crusts, milk chocolates, caramels, fudges and toffees Drawbacks: loss of amino acids: lysine, histidine, arginine; (production of mutagenic heterocyclic amines) Melting point process is acid or base catalysed and generally requires The melting point is the temperature at which the sol- temperatures >120°C. Above melting point, melted id crystalline and liquid phases of a substance are in dry sugar takes on an amber colour and develops an thermodynamic equilibrium at normal pressure. All appealing flavour and aroma. This amorphous sub- solids, except the amorphous forms, have a definite stance resulting from the breakdown of sugar is known melting point. Pure, crystalline solids melt over a nar- as caramel. Under heat, caramelisation transforms sug- row range of temperatures, whereas mixtures melt ars from colourless, sweet compounds into substances over a broad temperature range. The melting points ranging in colour from pale yellow to dark brown and can be used to identify compounds. Table 1 shows the in flavour from mild, caramel-type to burnt and bitter. melting points of some mono-, di- and trisaccharides. If heating is continued caramelised sugars break down into black carbon. Caramelisation occurs in food, when Caramelisation food surfaces are heated strongly, e.g. the baking and Caramelisation is defined as the thermal degradation roasting processes, the processing of foods with high of sugars leading to the formation of caramel aroma sugar content such as jams and certain fruit juices, or and brown-coloured products (caramel colours). The in wine production. COLOUR 52
Mono- di- and Chemical formula Melting point °C trisaccharides Fructose C6H1206 103-105 Glucose C6H1206 146 Sucrose C12H22011 186 ± 4 Maltose C12H22011 160-165 Lactose C12H22011 223 Ribose C5H1005 86-87 Mannose C6H1206 133 Raffinose C18H32016 118-120 Table 1. Melting points for some mono-, di- and trisaccharides. Source: Sugar Technologists Manual, Z. Bubnik, P. Kadlec, D. Urban, M. Bruhns. When sugar is heated the added heat energy can over- come the intermolecular forces and sugar melts to form a liquid. There is no temperature change during the phase change. If the melted sugar is further heated, the sugar is caramelised before it is hot enough to turn to vapour. COLOUR 53
Index 55-53 16-19 Browning reaction 24-26 Bulking 27-30 Crystallisation 48-49 Effect of sugar and sweeteners on pectin gel formation 11-15 Fermentation feedstocks 31-34 Interaction with other tastes and fl avours 20-24 Particle size 40-42 Solubility Sucrose hydrolysis 4-10 Sweetness 35-39 Viscosity 43-47 Water activity and its implications in sugar-rich foods 54
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