Lactobacillus plantarum 70810 from Chinese paocai as a potential source of β-galactosidase for prebiotic galactooligosaccharides synthesis

Abstract

A novel food-grade strain Lactobacillus plantarum 70810 producing β-galactosidase with high transgalactosylation activity was isolated from Chinese paocai. The galactooligosaccharides (GOS) were synthesized by using this enzyme with a maximum yield of 44.3 % (w/w) from 400 g/L lactose at 45 °C for 10 h. The β-galactosidase from this strain was purified to homogeneity by ammonium sulfate precipitation, anion exchange chromatography and gel filtration chromatography. It was a heterodimer arrangement of approximately 105 kDa composed of two subunits of 35 and 72 kDa. The optimal pH of the purified β-galactosidase was 8.0 for both o-nitrophenyl-β-d-galactopyranoside (oNPG) and lactose hydrolysis, and optimal temperature was 60 °C and 55 °C, respectively. Its K m and V max values for oNPG and lactose were 0.89 ± 0.05 mM, 194 ± 3.0 μmoL/min/mg protein, and 9.88 ± 0.16 mM, 15.88 ± 0.21 μmoL/min/mg protein, respectively. This enzyme was slightly inhibited by the hydrolysis products, that is, glucose and galactose. Since the β-galactosidase from L. plantarum 70810 exhibited higher transgalactosylation activity, strong affinity for lactose and low end-product inhibition, it was suggested to be a potential candidate for the synthesis of prebiotic GOS.