β- galactosidase, commonly named lactase, is one of the most important enzymes used in dairy processing; it
catalyses the hydrolysis of lactose to its constituent monosaccharide’s glucose and galactose. The aim of the
present study was focused on the isolation of novel yeast strains and formulation of medium for optimal β-
galactosidase activity. β- galactosidase activities of isolated strains were carried out by ONPG assay. The effect of
pH, temperature, lactose concentration and various nitrogen sources on β-galactosidase enzyme production in a
semi-synthetic medium was analysed. β- galactosidase enzyme was detected by SDS-PAGE method. The β-
galactosidase appeared as a single protein band in SDS-PAGE gel with a molecular mass of approximately 70 K
Da. The probiotic yeast isolate produced blue colour colonies on X-Gal plates indicates β-galactosidase positive.
The optimum pH and temperature for the β-galactosidase production was found to be pH-5 (96.8 U/ml) and 35°C
(53U/ml). The concentration of β-galactosidase enzyme increased linearly with increasing lactose concentration up
to 7 % (58.8 U/ml) and by utilising peptone as nitrogen source had the most significant effect on β-galactosidase
enzyme production (49.1 U/ml). The results suggest that this yeast strain isolated from curd having β-galactosidase
activity may be suitable for both the hydrolysis of lactose and for the production of galacto-oligosaccharides in
milk processing
