Oligosaccharide production using β-galactosidase from Lactobacillus bulgaricus and Kluyveromyces lactis in sweetened reconstituted nonfat dry milk

Abstract

β-Galactosidase (B-gal) is a vital enzyme used in the food industry to reduce lactose from dairy ingredients through hydrolysis and to synthesize galacto-oligosaccharides (GOS), a known bifidogenic prebiotic, from galactose moieties through transgalactosylation. To favor transgalactosylation, high carbohydrate concentrations must be available to accept the galactose moiety. Because many dairy products rely on sweeteners for flavor and texture, B-gal from generally recognized as safe status Lactobacillus bulgaricus strains LB11 and YB1, Lactobacillus helveticus B548, or Kluyveromyces lactis in the commercial product Lactozyme 2600L (KL B-gal) were used to determine if transgalactosylation can be driven in reconstituted nonfat dry milk (NDM, 10%, wt/wt) with commercial sweeteners compared with unsweetened NDM at 50°C for 18 h. Sucrose (14.4%, wt/wt), corn syrup solids (14.4%, wt/wt), or a mixture of sucrose (9.9%, wt/wt) and corn syrup solids (4.5%, wt/wt) were dissolved with NDM (n = 3), then heated with stirring for 30 min at 70°C for batch pasteurization. For Lactobacillus strains, whole cells were inoculated at 7 log cfu/mL, or the same quantity of cells was lysed before adding to the milk and carbohydrate mixtures, or 1.85 U of KL B-gal was used. The sucrose mixture released the highest glucose from all B-gal preparations, with LB11 lysate releasing the highest (245.57 ± 25.16 mM). High-performance anion-exchange chromatography with pulsed amperometric detection was used to visualize the presence of oligosaccharides with degrees of polymerization of 3 to 7. Oligosaccharides from YB1 lysate treated sucrose mixtures also increased the anaerobic growth of Bifidobacterium breve 2141 at 37°C compared with untreated or KL B-gal–treated sucrose mixtures. β-Galactosidase treatment of sucrose in nonfat milk with and without corn syrup can be a source of prebiotic oligosaccharides, although more work is needed to determine the composition of the oligosaccharides.