Galacto-oligosaccharides (GOS) have interest in the food industry due to their recognized functional
properties. In this work, we studied the effect of a commercial b-galactosidase enzyme from Kluyveromyces
lactis (YNL-2, GODO) and Lactobacillus acidophilus La-5, on GOS formation during the manufacture
and storage of drinkable and stirred yogurts. In a preliminary step, GOS synthesis and lactose
hydrolysis by b-galactosidase was evaluated at different initial lactose concentrations and doses of
enzyme. The GOS formation was favored with increasing of lactose concentration and enzyme doses,
while the hydrolysis dominated at lower level of lactose. In turn, the presence of GOS was already evident
at 45 min of fermentation in yogurts with addition of b-galactosidase. Mean concentrations were 0.36
and 0.62 g/100 g for fresh drinkable and stirred yogurts, respectively. No changes in the GOS levels were
observed through storage, indicating that they were stable in the products. The probiotic bacteria added
were not able to produce GOS. The diminution of lactose was significant in yogurts with b-galactosidase;
contents of residual lactose were around 1.3 g/100 g. We obtained different varieties of reduced-lactose
yogurts enriched in galacto-oligosaccharides. The presence of probiotic and prebiotic would increase the
functional properties of yogurts.