Effect of different β-galactosidases on galactooligosaccharides formation in lactose-hydrolysed milk

Galactooligosaccharides (GOS) are prebiotic compounds that can be produced in milk through transgalactosylation reactions catalyzed by β-galactosidase. This study quantified GOS formation in UHT milk after lactose hydrolysis using three commercial β-galactosidases from Kluyveromyces lactis at enzyme dosages of 0.3, 0.75, and 1.5 g L −1 , and compared the results with 11 commercial lactose-hydrolysed milks. In experimental samples, total GOS ranged from 470 to 2055 mg (100 mL) −1 , whereas commercial products contained 120–660 mg (100 mL) −1 . The optimal formulation for lactose-free, GOS-enriched milk was obtained using Bonlacta™ at 0.75 g L −1 , yielding 1527 mg (100 mL) −1 GOS and residual lactose of 0.038 g (100 mL) −1 . Maximum GOS production (2055 mg (100 mL) −1 ) and about 95% lactose hydrolysis were achieved with Bonlacta at 0.3 g L −1 . Approximately 7% of sugars had a degree of polymerization ≥3, indicating enhanced prebiotic potential. These results highlight differences among β-galactosidases and the need for targeted technological strategies to produce functional milk products.