Abstract
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 1min results in 97% inactivation at 60C and complete inactivation at 70C. Some inactivation occurs at 40C over 1-h incubation. Lactose can be hydrolyzed in 22h at 5C as effectively as in 2h at 31C. Potassium, magnesium, and manganese ions accelerated slightly lactase activity in fluid milks while sodium and calcium ions inhibited the reaction significantly.
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