Resistance of β-lactoglobulin-bound lactose to the hydrolysis by β-galactosidase

An in vitro study was conducted to investigate the sensitivity of lactose-β-lactoglobulin conjugates to β-galactosidase from Kluyveromyces lactis. The hydrolysis was monitored by ion exchange chromatography. Compared to free lactose or lactulose, which were rapidly hydrolysed, protein-bound lactose was not hydrolysed by β-galactosidase even after an extended hydrolysis time. Tryptic digestion of the conjugates before addition of β-galactosidase improved the substrate accessibility and led to the release of about 50% of the linked lactose. The results strongly suggest that the resistance of protein bound lactose is linked to the globular and compact structure of lactose-β-lactoglobulin conjugates.