Evaluation of oligosaccharide synthesis from lactose and lactulose using β-galactosidases from Kluyveromyces isolated from artisanal cheeses.

The β-galactosidase activity of 15 Kluyveromyces strains isolated from cheese belonging to Kluyveromyces lactis and Kluyveromyces marxianus species was tested for the production of oligosaccharides derived from lactose (GOS) and lactulose (OsLu). All Kluyveromyces crude cell extracts (CEEs) produced GOS, such as 6-galactobiose and 3'-, 4'-, and 6'-galactosyl-lactose. At 4 h of reaction, the main trisaccharide formed was 6'-galactosyl-lactose (20 g/100 g of total carbohydrates). The formation of OsLu was also observed by all CEEs tested, with 6-galactobiose, 6'-galactosyl-lactulose, and 1-galactosyl-lactulose being found in all of the reaction mixtures. The synthesis of trisaccharides predominated over other oligosaccharides. K. marxianus strain O3 produced the highest yields of GOS and OsLu after 4 h of reaction, reaching 42 g/100 g of total carbohydrates (corresponding to 80% lactose hydrolysis) and 45 g/100 g of total carbohydrates (corresponding to 87% lactulose hydrolysis), respectively. Therefore, the present study contributes to a better insight into dairy Kluyveromyces β-galactosidases and shows the feasibility of these enzymes to transglycosylate lactose and lactulose, producing high yields of prebiotic oligosaccharides.