Research noteComparison of the galacto-oligosaccharide forming activity of different β-galactosidases

Galacto-oligosaccharides (GOS) were synthesised by enzymatic transgalactosylation in UF-skimmed milk permeate fortified with lactose (40% w/w) using β-galactosidases (β-GAL) derived from Aspergillus aculeatus, Aspergillus oryzae, Kluyveromyces lactis and Bacillus circulans. GOS yields were assessed arithmetically after photometric determination of the sugar profile. GOS composition was characterised by HPAEC-PAD/MS analysis. The GOS yields, expressed as a percentage of the initial lactose content, were 41%, 21%, 13% and 11% with β-GALs from B. circulans, A. oryzae, A. aculeatus and K. lactis, respectively, under optimal conditions. Thus, the B. circulans enzyme revealed the highest affinity to transgalactosylation relative to hydrolysis. HPAEC-PAD/MS results showed similarities in GOS composition, especially with β-GAL from A. oryzae, A. aculeatus and K. lactis with a preference towards β-galactosyl residues β(1-6). GOS generated are mainly di-, tri- and a few tetra-saccharides. Only the B. circulans β-GAL formed above all penta-saccharides, mainly via β1-4 glycosidic linkages.