Properties of β-Galactosidase of Saccharomyces Lactis in Milk and Milk Products

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Abstract
Lactase (.beta.-galactosidase) [EC 3.2.1.23] from S. lactis was tested on skim milks and wheys to determine optimum conditions for converting lactose to mono-sugars. 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.degree. C and complete inactivation at 70.degree. C. Some inactivation occurs at 40.degree. C over 1-h incubation. Lactose can be hydrolyzed in 22 h at 5.degree. C as effectively as in 2 h at 31.degree. C. K, Mg and Mn ions accelerated slightly lactase activity in fluid milks while Na and Ca ions inhibited the reaction significantly.