PROPERTIES OF BETA-GALACTOSIDASE OF SACCHAROMYCES-LACTIS IN MILK AND MILK-PRODUCTS

Lactase (β-galactosidase) from Saccharomyces lactis was tested on skim milks and wheys to determine optimum conditions for converting lactose to monosugars. Emphasis was on parameters of interest to processors. Lactase effectively can hydrolyze lactose in skim milk, whey, and a 41% total solids concentrate of skim milk; the hydrolysis rate for milk concentrates is 15% lower than that of unconcentrated skim milk. The optimum pH for lactose hydrolysis is 6.5, which is close to the pH of milk. Heating lactase for 1 min results in 97% inactivation at 60 C and complete inactivation at 70 C. Some inactivation occurs at 40 C over 1-h incubation. Lactose can be hydrolyzed in 22 h at 5 C as effectively as in 2 h at 31 C. Potassium, magnesium, and manganese ions accelerated slightly lactase activity in fluid milks while sodium and calcium ions inhibited the reaction significantly. © 1978, American Dairy Science Association. All rights reserved.