EFFECT OF MILK CONSTITUENTS ON THE HYDROLYSIS OF LACTOSE BY LACTASE FROM Kluyveromyces fragilis

Lactase activity in cold milk and whey is controlled by the ionic environment; maximum activity occurred in the presence of manganous ions. Of the major cations present in milk, sodium and calcium were inhibitory while potassium and magnesium were activating. Milk proteins strongly activated lactase in potassium phosphate buffer and the effect was enhanced in the presence of manganous ions; however the activation was masked by the milk salts in dairy products. Lactase activity in whey heated to 85°C was about 50% higher than in unheated whey, but no changes were observed in heated milk. There was no evidence for a thermolabile lactase inhibitor among the whey proteins.