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

An in vitro study was conducted to investigate the sensitivity of lactose-b-lactoglobulin conjugates to b-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 b-galactosidase even after an extended hydrolysis time. Tryptic digestion of the conjugates before addition of b-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 compactstructure of lactose-b-lactoglobulin conjugates.