Abstract: This study aimed to obtain a lactic acid bacterial strain producing β-galactosidase with high transglycosylation activity in order to provide a novel source of β-galactosidase for efficient synthesis of galacto-oligosaccharides (GOS). Lactic acid bacterial strains were isolated from traditional cheese samples collected from pastoral households in Yili, Xinjiang autonomous region. Primary screening on MRS plates with added 5-bromo-4-chloro-3-indolyl-β-D-galactoside (X-Gal) using lactose as the sole carbon source was performed based on calcium dissolution zone size, and secondary screening was carried out by thin layer chromatography (TLC) analysis of the lactose hydrolysates obtained with β-galactosidases produced by the selected strains. The isolate with the highest transglycosylation activity was identified by physiological and biochemical characteristics, together with sequence analysis of the 16S rRNA gene. The optimal temperature, pH and lactose concentration for the synthesis of GOS using lactose as substrate were investigated, and GOS produced under optimal reaction conditions were quantified by TLC and high performance liquid chromatography (HPLC). Six lactic acid bacterial strains producing β-galactosidases with transglycosylation activity were isolated, among which β-galactosidase produced by Lactobacillus plantarum YLBGNL-S7 showed the highest transglycosylation activity. An initial lactose mass concentration of 300 mg/mL, a reaction temperature of 50 ℃, an initial pH of 6.0 and a reaction time of 4 h were determined as the optimum conditions for GOS synthesis with β-galactosidase produced by YLBGNL-S7, which resulted in a GOS yield of 43.40%. The GOS mixture contained 18.29% diaccharides and 12.95% trisaccharides. These results demonstrated that L. plantarum YLBGNL-S7 is a novel promising source of β-galactosidase with good potential for prebiotic GOS synthesis.

Key words: β-galactosidase, transglycosylation activity, galacto-oligosaccharides, Lactobacillus plantarum, cheese