Effect of process parameters on the β-galactosidase hydrolysis of lactose and galactooligosaccharide formation in concentrated skim milk

•Hydrolytic and transgalactosylation activity of β-galactosidase was examined at 7 °C.•Activity of β-galactosidase from K. lactis was more effective than B. linchenformis.•K. lactis was used in concentrated skim milk (35–40% w/w) for lactose hydrolysis.•Low lactose milk (˃95% DH) with benefits of GOS was achieved at 9.53 U/mL of enzyme.