Synthesis of Galacto-oligosaccharides in Milk by Using Bifidobacterium bifidum β-galactosidases (Saphera 2600L and Nola Fit 5500) Immobilized on Chitosan Beads

The lactose intolerance—as a limiting factor for dairy milk consumption—has a high prevalence worldwide. Dairy milk and milk-derived products are major sources of multiple inorganic compounds and nutrients and thus are considered to be functional foods. β-galactosidases are able to hydrolyze lactose and are therefore widely applied for the production of lactose-free products. In addition, they are capable of the synthesis of galacto-oligosaccharides (GOSs); thus, the dairy industry has a special interest in applying them for the enrichment of dairy products with prebiotic GOSs. In this work, we studied two commercially available β-galactosidase products: Saphera 2600L and Nola Fit 5500. Both enzyme solutions contain a recombinant β-galactosidase of Bifidobacterium bifidum and have already been authorized for food industrial application, but the information about their hydrolytic and/or synthetic activities is only limited. After immobilization on chitosan beads, the enzymes were used for lactose hydrolysis and simultaneous synthesis of GOSs, by performing the reactions in pasteurized milk (skim milk). Both immobilized β-galactosidase exhibited elevated lactose hydrolysis (v max increased from ~ 1 to ~ 4 mM/min) and GOS synthesis as compared to the free enzymes. The enzyme-coated beads were efficiently re-used at least 15 cycles; the residual lactose concentration was < 2 mg/ml after each cycle. After treatment, GOSs were present in ≤ 9% of the total sugar content, indicating that the prepared low-lactose milks were enriched in prebiotic GOSs. The application of immobilized Saphera 2600L and Nola Fit 5500 β-galactosidases may be implemented for the large-scale production of GOS-enriched low-lactose milk. Graphical Abstract