Lactose is the main carbohydrate of milk. It is formed by the
union of one molecule of D-galactose (engaged by its semiacetyl
function) and one molecule of D-glucose (committed
by its hydroxyl 4 position). It has a β-galactoside 1,4 bond
(which is hydrolyzed by a β-galactosidase) and is a 4-Dglucopyranosyl-β-D-galactopyranose.
Although lactose is a
sugar, it does not have a sweet flavor. Its concentration
varies slightly in milk (4.5 to 5.2 g / 100 g) contrary to the
concentration of fat, that of lactose cannot be easily
modified by feeding and true step of a dairy race to another.
It is used as substrate during the fermentation of milk by
lactic acid bacteria, differing in the fermented products
such as yoghurt and cheese. It plays a role in fermented
milk production. The amount of lactic acid produced by
lactic acid bacteria in a fermented milk product depends
not only on the bacterium itself (the bacterial strain more
less active) and operating parameters, but also on the
available amount of lactose bacteria. The buffer milk power
also plays an important role as we shall see later