Characterisation of the potential of β-lactoglobulin and α-lactalbumin as sources of bioactive peptides affecting incretin function: In silico and in vitro comparative studies

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are gut-derived peptides and potentiate insulin secretion after meal. Dipeptidyl peptidase-4 (DPP-IV) is the principal enzyme responsible for their rapid inactivation in vivo. The insulinotropic effect of whey proteins is believed to include delay of GIP and GLP-1 inactivation by DPP-IV. The published sequences of peptidic DPP-IV inhibitors were used to suggest a consensus sequence. Then, the release of potential DPP-IV inhibitors after in silico hydrolysis of β-lactoglobulin (β-LG) and α-lactabumin (α-LA) was investigated and the DPP-IV inhibitory activity of the hydrolysates prepared in vitro using digestive proteases was assayed. Both the in silico and the in vitro analyses suggested that bovine β-LG was a better source than α-LA of DPP-IV inhibitors. The IC50 value of β-LG hydrolysate was half that calculated for α-LA, but the maximal inhibitory effect did not differ significantly between the two proteins.