356 DAIRY CHEMISTRY AND BIOCHEMISTRY 68 62 60 5.6 period at130°Cmin) Figure 9.7 The ph of samples of milk after heating for various periods at 130C with air(O) O,(O)or N,(A)in the headspace above the milk; t, coagulation time (from Sweetsur and white. 1975). 9.3.3 Maillard browning The mechanism and consequences of the maillard reaction were discussed in Chapter 2. The reaction is most significant in severely heat-treated products, especially in-container sterilized milks. However, it may also occur to a significant extent in milk powders stored under conditions of high humidity and high temperature, resulting in a decrease in the solubility of the powder. If cheese contains a high level of residual lactose or galactose (due to the use of a starter unable to utilize galactose; Chapter 10), it is susceptible to Maillard browning, especially during cooking on pizza, e. g Mozzarella(Pizza)cheese. Browning may also occur in grated cheese during storage if the cheese contains residual sugars; in this case, the water activity of the cheese(aw s0.6)is favourable for the Maillard reaction. Poorly washed casein and especially whey protein concentrates (which contain 30-60% lactose)may undergo Maillard browning when used as ingredients in heat-treated foods 1. The final polymerization products(melanoidins)are brown and hence dairy products which have undergone Maillard browning are discoloured and aesthetically unacceptable356 DAIRY CHEMISTRY AND BIOCHEMISTRY r E .- L 0 5.6 0 10 20 30 40 Heating period at 130°C (min) Figure 9.7 The pH of samples of milk after heating for various periods at 130°C with air (O), 0, (0) or N, (A) in the headspace above the milk; T, coagulation time (from Sweetsur and White, 1975). 9.3.3 Maillard browning The mechanism and consequences of the Maillard reaction were discussed in Chapter 2. The reaction is most significant in severely heat-treated products, especially in-container sterilized milks. However, it may also occur to a significant extent in milk powders stored under conditions of high humidity and high temperature, resulting in a decrease in the solubility of the powder. If cheese contains a high level of residual lactose or galactose (due to the use of a starter unable to utilize galactose; Chapter lo), it is susceptible to Maillard browning, especially during cooking on pizza, e.g. Mozzarella (Pizza) cheese. Browning may also occur in grated cheese during storage if the cheese contains residual sugars; in this case, the water activity of the cheese (a, - 0.6) is favourable for the Maillard reaction. Poorly washed casein and especially whey protein concentrates (which contain 30-60% lactose) may undergo Maillard browning when used as ingredients in heat-treated foods. Maillard browning in milk products is undesirable because: 1. The final polymerization products (melanoidins) are brown and hence dairy products which have undergone Maillard browning are discoloured and aesthetically unacceptable