Optimisation of the synthesis of high galacto-oligosaccharides (GOS) from lactose with β-galactosidase from Kluyveromyces lactis

A rational optimisation for the synthesis of galacto-oligosaccharides (GOS) catalysed by a commercial β-galactosidase from Kluyveromyces lactis, Lactozym Pure 6500 L, is shown. The study of the main reaction parameters – temperature, enzyme concentration, pH, initial lactose concentration and reaction time – using surface response methodology, was demonstrated to be an accurate tool to optimise empirical production of the most desired galacto-oligosaccharides (tri-GOS and tetra-GOS) with a higher presumed prebiotic effect. The optimal value for the yield towards these high-GOS predicted by the model was 12.18% at 40 °C, 5 U mL−1 enzyme concentration, pH 7.0, 250 g L−1 initial lactose concentration and 3 h of reaction. The pH was found to be a critical parameter affecting the transgalactosylation/hydrolysis enzyme activity ratio, and was used to tune the relative production of tri- or tetra-GOS.