Biochemical characterization of a β-galactosidase from Lactiplantibacillus plantarum YLBGNL-S7 and utilization of its permeabilized whole-cell catalyst for in situ galactooligosaccharide synthesis during yogurt making

Recently, lactic acid bacteria (LAB)-derived β-galactosidases have attracted much attention for their enzyme's high transglycosylation activity, GRAS status, and a tendency to form galactooligosaccharides (GOS) with a good prebiotic effect. However, their intracellular nature and the lack of a cost-effective method for the preparation of a food-grade catalyst hampers their application in the dairy industry. In this study, a β-galactosidase LpLacLM from Lactiplantibacillus plantarum YLBGNL-S7 was characterized. In addition, the permeabilized whole cells of L. plantarum YLBGNL-S7, containing approximately 3.79 × 10 −5 kat g −1 of β-galactosidase activity, were prepared via lyophilization. The permeabilized whole cells could efficiently hydrolyze lactose and achieve maximum GOS yields of 31.71 g/100 g and 14.21 g/100 g at initial lactose concentrations of 30 g/100 mL and 5 g/100 mL, respectively. Moreover, the preincubation of reconstituted whole milk with 5.0 × 10 −8 kat mL −1 of the permeabilized whole-cell catalyst at 50 °C for 3 h before the inoculation of traditional starters led to an 86.74% reduction in lactose and the production of 6.62 g L −1 GOS in the yogurt. Through this study, we demonstrated a novel method to prepare permeabilized whole cells for LAB-derived β-galactosidases and verified the feasibility of using this permeabilized whole-cell catalyst for in situ GOS synthesis during yogurt making. • A β-galactosidase from Lactiplantibacillus plantarum YLBGNL-S7 was characterized. • Permeabilized LAB cells with high β-gal activity were prepared by lyophilization. • The β-gal whole-cell catalyst is efficient for lactose hydrolysis and GOS forming. • The β-gal whole-cell catalyst could be employed for GOS-enriched yogurt making.