Synthesis of galactitol galactoside using transgalactosylation activity of β-galactosidase from Aspergillus oryzae

Abstract

In recent years, there is an increasing awareness considering the beneficial effects of functional foods on human health. Accordingly, due attention is given to the research in the field of obtaining new products featuring improved physiological and physico-chemical characterstics. β-Galactosidase, although primarily regarded as hydrolytic enzyme, proved to be a promising tool in prebiotic synthesis. Under specific conditions, β-galactosidase catalyzes transfer of galactose moiety to free hydroxyl group containing compound, yielding different compounds of tremendous prebiotic potential such as galacto-oligosaccharides, lactulose and lactitol, as well as their structural analogues. The aim of this study was to obtain a novel product galactitol galactoside through transgalactosylation reaction using β-galactosidase from Aspergillus oryzae. The importance of using sugar alcohols, namely glactitol in the study, was the possibility of obtaining a diverse mixture of potential prebiotics (galactooligosaccharides and alcohol-galactoside) and thus enabling its more favorable functional features. Given the complexity of these reactions, owing to the several potential galactosyl acceptors, and consequently several potential reaction pathways, key reaction parameters have been optimized using the response surface methodology ensuring the insight into different parameter influences, as well as their mutual interactions on product yield and productivity. In terms of achieving high product yields, model predicted optimal lactose concentration 200 mM, the molar ratio of galactitol and lactose 7:1, the concentration of NaCl 1M, and the reaction time 4.69 h. From the aspect of productivity, the optimum enzyme concentration was found to be 0.2 mg/ml, while the values for other factors coincide. In subsequent experiments, under previously defined optimal conditions, the maximum galactitol galactoside yield was 35 g/l, and productivity 82 g/g enzyme. Finally, the β-galactosidase immobilized onto amino modified nonporous silica nanoparticles was successfully employed in the same reaction.