Dairy Chemistry And Biochemistry

356 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.