Estimation of selectivities in transglycosylation systems with multiple transglycosylation products

Abstract

Transglycosylation can be used to produce oligosaccharides that act as prebiotics. The maximum yield of the oligosaccharides depends on the selectivities for transglycosylation, not only over primary hydrolysis of the original donor molecule, but also over secondary hydrolysis of the oligosaccharides. A recent approach to determining these selectivities only considered systems in which there is a single transglycosylation product. The current work extends this approach, determining selectivities for cases involving multiple transglycosylation products. A model is used to analyze literature data for the production of galactooligosaccharides through the transgalactosylation of lactose, catalyzed by β-galactosidases of Bacillus circulans and Aspergillus oryzae. In the case studies, the selectivity for using oligosaccharides rather than lactose as the galactosyl acceptor ranged from 1.0 (i.e. not selective) to 2.4. Selectivities for transgalactosylating lactose with lactose over primary hydrolysis of lactose ranged from 113 to 919. The selectivities for producing oligosaccharides over secondary hydrolysis of the oligosaccharides decreased with increase in the initial lactose concentration; the values obtained ranged from 6 to 159. Knowledge of these selectivities is useful for guiding the improvement of enzymes for transglycosylation processes.