Estimation of Lactose Hydrolysis by Freezing Point Measurement in Milk and Whey Substrates Treated with Lactases from Various Microorganisms

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Abstract
β-Galactosidase concentrates obtained from several microorganisms were used to hydrolyze skim milk, low fat (2%) milk, sweet whey, acid whey, acid whey permeate, and acid whey concentrate. Among acid substrates, the freezing point depression for each 1% lactose hydrolyzed was the greatest with the lactase from Aspergillus niger (0.0501°H); among neutral substrates, the depression was greater in sweet whey (0.0495°H) and lesser in low fat milk (0.0445°H). All data were statistically significant. The average freezing point depression for each 1% lactose hydrolyzed was 0.0468°H (range 0.0436-0.0501°H). Oligosaccharides formed in the lactose hydrolysis, inconsistent freezing point readings of the cryoscope at the low freezing points measured, and protease contamination in some lactases may affect the precision of freezing point determination. Hydration and volume of non-protein components in commercial enzymes, unstable color complex formed by lactose in methylamine solution, and difficulty in the use of methylamine solution might cause variations in determination of lactose by the analytical procedure. These factors can be eliminated or minimized. This method is the simplest and quickest estimation of lactose hydrolysis, and it offers great accuracy and consistency

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