Selectivities of the β-galactosidase of Bacillus circulans in the production of galactooligosaccharides, lactulose and lactosucrose

There has been recent interest in using the β-galactosidase of Bacillus circulans to produce prebiotic oligosaccharides, including galactooligosaccharides (GOS), lactulose and lactosucrose. The types and amounts of the transgalactosylation products produced depend on the selectivities of the enzyme for the various transgalactosylation and hydrolysis reactions that occur. To date, the selectivities of the β-galactosidase of B. circulans for these reactions have not been adequately characterized. In the current work, we undertake four case studies using literature data for systems in which different product mixtures are produced (i) GOS; (ii) GOS and disaccharides; (iii) GOS and lactulose; and (iv) GOS and lactosucrose. We analyze this data to obtain quantitative estimates of the relevant selectivities. We show that, in the production of GOS, the isoform β-Gal-A is significantly less selective against hydrolysis reactions than the other β-galactosidase isoforms. In the production of lactulose, the β-galactosidase of B. circulans gives high lactulose yields, despite having a 19- to 33-fold preference for producing GOS over lactulose. In the production of lactosucrose, the β-galactosidase of B. circulans also prefers to produce GOS.