Screening and characterization of β-galactosidase activity in lactic acid bacteria for the valorization of acid whey

β-Galactosidase is an enzyme produced by some strains of lactic acid bacteria (LAB) commonly found in dairy products; however, industrial demand for these enzymes is still low. Acid whey (AW), a lactose-rich byproduct, has large output from cottage cheese and remains unexploited. The purpose of this study was to understand the production mechanism of β-galactosidase from LAB using AW as a culture medium. First, bioinformatics analysis was conducted on 15 species of LAB. Then, 24 strains were selected and inoculated in de Man, Rogosa, and Sharpe (MRS) broth and in AW medium to compare the bacterial kinetic growth and β-galactosidase production. Bacterial growth and total protein activity were measured using spectrophotometric techniques. β-Galactosidase activity was determined by 2 methods: following the hydrolysis of o-nitrophenyl-β-d-galactopyranoside and of 5-bromo-4-chloro-3-indoyl-β-d-galactopyranoside (X-gal) in tryptic soy agar plates. The relative expression of the β-galactosidase gene was performed using real-time quantitative PCR. Despite generally lower growth in AW, 18 strains showed higher β-galactosidase activity when grown in AW compared with MRS medium. The highest β-galactosidase activity in AW was in Lactobacillus helveticus strain OSU-PECh-4A, which showed almost 5 times higher activity than average. Analysis of 6 selected strains for expression of the bgal-620 gene found higher overexpression in AW than in MRS, regardless of specific β-galactosidase activity. Strains of LAB such as OSU-PECh-4A could valorize AW through the production of β-galactosidase (as an aid to lactose digestion) and production of prebiotic galactooligosaccharides.