Dairy Chemistry And Biochemistry

54 DAIRY CHEMISTRY AND BIOCHEMISTRY

Figure 2.28 Repeating unit of xanthan gum.

fermentation substrates, especially sucrose in molasses or glucose produced

from starch. Except in special circumstances, the processes can be regarded

as the cheapest method of whey disposal.

2.5 Lactose and the Maillard reaction

As a reducing sugar, lactose can participate in the Maillard reaction, leading
to non-enzymatic browning. The Maillard reaction involves interaction
between a carbonyl (in this case, lactose) and an amino group (in foods,
principally the E-NH, group of lysine in proteins) to form a glycosamine
(lactosamine) (Figure 2.29). The glycosamine may undergo an Amadori
rearrangement to form a l-amino-2-keto sugar (Amadori compound) (Fig-
ure 2.30). The reaction is base-catalysed and is probably first order. While
the Maillard reaction has desirable consequences in many foods, e.g. coffee,
bread crust, toast, french fried potato products, its consequences in milk
products are negative, e.g. brown colour, off-flavours, slight loss of nutritive
value (lysine), loss of solubility in milk powders (although it appears to