Determining Lactose Content in Milk Via an Enzymatic Method

β-D-galactopyranosyl-(1 -4) D-glucose, more commonly known as lactose, is a disaccharide which constitutes 2 – 8% of milk. In the method in this application note β-galactosidase is added to milk, cleaving lactose into glucose and galactose. At pH 7.8, glucose is phosphorylated by glucokinase, and releases protons that induce a change in pH. The pH change varies as a function of the lactose content of the sample and is measured by using a differential pH analyzer.