Kinetics of lactose hydrolysis and galactooligosaccharides formation in beverages based on goat's milk and its permeate.

The aim of this work was the analysis of galactooligosaccharides (GOS) formation in a model mixture of goat's milk and its permeate from microfiltration and further concentration by ultrafiltration based on the hydrolysis and transgalactosylation of lactose under various temperature and time regimes. These reactions were catalyzed by a β-galactosidase from Kluyveromyces lactis. Simultaneous hydrolysis and transgalactosylation of the milk lactose was carried out at 37, 40, and 43 °C for 6 h. The maximum GOS content in the mixture was obtained at 37 °C after 20 min. It was 6.9% of the total sugars and the degree of lactose hydrolysis was 13.3%. This was about 10% more GOS than in milk. The mixture containing GOS had a faster maximum acidification rate, 33% greater than before transgalactosylation.