Galacto-oligosaccharide production by Lactobacillus delbrueckii ssp. bulgaricus whole cells and lysates

β-Galactosidase is currently applied in foods for reduction of lactose but can also be used for its transgalactosylation activity to synthesize galacto-oligosaccharides (GOS) as prebiotics. The ability of GRAS-status Lactobacillus delbrueckii strains to exhibit such activities would benefit consumers given their extensive history with dairy products. The objective of this study was to characterize the production of GOS in 6 L. delbrueckii strains for their ability to synthesize GOS in 50 mM sodium phosphate (pH 6.5) with a high lactose concentration of 788.8 mM at 50°C. Lactobacillus delbrueckii ssp. bulgaricus B548, LB11, and YB1 lysates released the most glucose at 112.8 ± 6.2 mM, 150.4 ± 11.7 mM, and 190.2 ± 12.2 mM, respectively. However, the ratio of free glucose to galactose released by B548 lysate (1.4 ± 0.3) was lower than that of LB11 (2.8 ± 0.6) and YB1 (2.5 ± 0.6) lysates, so the latter strains were screened at different initial lactose concentrations. The GOS yield from YB1 was not dependent on initial lactose concentration, averaging 54.3 ± 0.6% across starting lactose concentrations. However, optimal LB11 transgalatosylation had an initial concentration of 394.4 mM lactose instead of 788.8 mM, resulting in a GOS yield of 56.8% instead of 47.3%. In all cases for LB11, the lysates had greater free glucose, galactose, and GOS yield than whole cells. The ability of 2 Lactobacillus delbrueckii ssp. bulgaricus strains to produce GOS from common lactose-containing ingredients can have a range of applications in the dairy industry.