Model-based estimation of selectivities of the β-galactosidase of Aspergillus oryzae in the production of lactulose and fructosyl-galactooligosaccharides

There has been recent interest in using the β-galactosidase of Aspergillus oryzae to produce lactulose and fructosyl-galactooligosaccharides, for use as prebiotics. The success of the enzymatic process depends on the selectivities of the enzyme for the various transgalactosylation and hydrolysis reactions that occur in these systems, but the methods that have been used to date to express these selectivities are not adequate. In the current work, we demonstrate a method for determining the selectivity of the β-galactosidase of A. oryzae in two case studies done with literature data: (1) the production of lactulose from a mixture of lactose and fructose and (2) the production of fructosyl-galactooligosaccharides (fGOS) from lactulose. In the first case study, we demonstrate that the enzyme has a 4- to 5-fold preference for producing GOS over lactulose when an equimolar mixture of fructose to lactose is used, but that the selectivity for producing lactulose increases as the initial fructose to lactose molar ratio increases. In the second case study, we show that the enzyme has about a 1.5-fold preference for producing fGOS4 and fGOS5 over the initial transgalactosylation product, fGOS3. The selectivities that we determine in our work will be important parameters for time-based models used to guide the development and optimization of processes for the production of lactulose and fructosyl-galactooligosaccharides as prebiotics.