Lactose hydrolysing ability of sonicated cultures of Lactobacillus delbrueckii ssp bulgaricus 11842

The lactose-hydrolysing ability of Lactobacillus delbrueckii ssp. bulgaricu s strain 11842 (LB 11842) was tested after cultivation in MRS broth under v arying conditions. After sonication for an optimum time determined to be 4 min to disrupt the cells, cultures were added to various substrates, includ ing pH 7 buffered 2.5 and 5% lactose test solution, skim milk, or a 30% lac tose or whey permeate solutions. Freezing point changes were used to measur e the progress of hydrolysis at a wide range of temperatures. Cultures adde d to the lactose test solutions resulted in 20% and 63% of the lactose bein g hydrolysed after 3 h at 7 and 51 degreesC, respectively. Values for hydro lysis in skim milk were slightly higher. Enzyme activity was not hindered i n 30% lactose or 30% whey permeate solution and the hydrolysis rate was acc eptable at a low temperature (7 degreesC) in skim milk.