On the Enzyme Specificity for the Synthesis of Prebiotic Galactooligosaccharides

Abstract

β-Galactosidases catalyze transgalactosylation reactions in which lactose as well as the glucose and galactose released by hydrolysis serve as galactosyl acceptors yielding a series of galactooligosaccharides (GOS). GOS constitute the major part of oligosaccharides in human milk and are responsible of the formation of a Bifidus microbiota in the intestine of milk-fed babies. The bioactive properties of GOS depend on their chemical composition, structure, and polymerization degree. We have analyzed the product specificity of various β-galactosidases, namely, those from Kluyveromyces lactis, Bacillus circulans, and Aspergillus oryzae. The major products synthesized by B. circulans β-galactosidase contained only β-(1 → 4) bonds, whereas the enzyme from K. lactis synthesized GOS with major presence of β-(1 → 6) linkages. The A. oryzae β-galactosidase formed preferentially β-(1 → 6) bonds, with minor proportion of β-(1 → 3). B. circulans and K. lactis β-galactosidases produce nearly 45–50 % (w/w) GOS, whereas the A. oryzae enzyme produces less than 30 % (w/w). Another difference between the three enzymes was the polymerization degree of products; in particular, for a GOS mixture enriched in disaccharides, K. lactis and A. oryzae β-galactosidases are the best choices. In contrast, the B. circulans enzyme would be preferable for a GOS product with a high trisaccharides and tetrasaccharides content.