This work investigates the feasibility of manufacturing yogurts with three prebiotics: fructooligosaccharides (FOS), galactooligosaccharides (GOS) or lactulose added at two concentrations (2 and 4%, w/v). Physicochemical and microbial characterization was conducted on the effect of prebiotics on acidification, viability of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, lactose and prebiotic consumption and production of organic acids during fermentation (up to 6 hours) and cold storage (for 28 days). The main findings revealed that GOS and FOS remained unaltered throughout fermentation and cold storage, while the viability of starter culture was similar to that observed in the control yogurt. Yogurts manufactured with 4% lactulose showed a significant decrease of lactulose content associated with a lower decrease of lactose relative to the control. This effect was associated to a significant increase (2.2 log10 cfu/mL) in L. delbrueckii ssp. bulgaricus and a relatively lower decrease (1.0 log10 cfu/mL) in S. thermophilus at the end of cold storage.

The production, biochemical characterization and carbohydrate specificity of LacA βgalactosidase (locus lp_3469) belonging to the Glycoside Hydrolase family 42 from the probiotic organism Lactobacillus plantarum WCFS1 is addressed. The β-Dgalactosidase activity was maximal in the pH range of 4.0-7.0 and 30-37 ºC. High hydrolysis capacity towards the β (1 → 4) linkages between galactose and glucose (lactose) or fructose (lactulose) was found. High efficiency towards galactosylderivatives formation was observed when lactose and glycerol, xylitol or erythritol were used. Galactosyl-derivatives of xylitol were characterized for the first time as 3-O-β-Dgalactopyranosyl-xylitol and 1-O-β-D-galactopyranosyl-xylitol displaying the great preference of LacA β-galactosidase for the transfer of galactosyl residues from lactose to the C1 or C3 hydroxyl group of xylitol. These results indicate the feasibility of using LacA β-galactosidase for the synthesis of different galactosyl-polyols, which could be promising candidates for beneficial and appealing functional and technological applications such as novel prebiotics or hypocaloric sweeteners.

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