Purification and biochemical properties of a galactooligosaccharide producing β-galactosidase from Bullera singularis

A β-galactosidase, catalyzing lactose hydrolysis and galactooligosaccharide (GalOS) synthesis from lactose, was extracted from the yeast, Bullera singularis KCTC 7534. The crude enzyme had a high transgalactosylation activity resulting in the oligosaccharide conversion of over 34% using pure lactose and cheese whey permeate as substrates. The enzyme was purified by two chromatographic steps giving 96-fold purification with a yield of 16%. The molecular weight of the purified enzyme (specific activity of 56 U mg−1) was approx. 53 000 Da. The hydrolytic activity was the highest at pH 5 and 50 °C, and was stable to 45 °C for 2 h. Enzyme activity was inhibited by 10 mM Ag3+ and 10 mM SDS. The Km for lactose hydrolysis was 0.58 m and the maximum reaction velocity (Vmax) was 4 mm min−1. GalOS, including tri- and tetra-saccharides were produced with a conversion yield of 50%, corresponding to 90 g GalOS l−1 from 180 g lactose l−1 by the purified enzyme.

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