High purity galacto-oligosaccharides: Optimal process design and prebiotic effect

Prebiotic unpurified commercial galacto-oligosaccharides (GOS) often contain significant amounts of glucose, galactose and lactose. Current purification processes remove these digestible components, especially lactose with a high risk of affecting functionality.

In the current study a high purity GOS (HP-GOS) was prepared by treating GOS with β-galactosidase to hydrolyze the remaining lactose into glucose and galactose. Subsequently mono sugars were removed by sequential simulated moving bed (SSMB) chromatography. To this end, a design of experiments (DOE) approach was applied to determine the dry matter content and β-galactosidase concentration that optimally support lactose hydrolysis in such a way that the detrimental effects on GOS composition are minimized to preserve its original oligosaccharide composition. The HP-GOS product obtained using the identified optimal settings for lactose hydrolysis contained more than 75% of the original DP2 GOS fraction while the fraction with a DP above 2 was unaffected by the purification. Using fecal fermentations, it was demonstrated that the GOS parts of the HP-GOS and the parent GOS have comparable effects on gut microbiota composition. Both GOS products equally increased the relative abundances of Bifidobacterium. Furthermore, there were no differences in alpha diversity and in the distribution of the different bifidobacterial species. Based on these outcomes it was concluded that the lactose hydrolysis step of the purification process did not influence gut microbiota modulating effects of GOS.