Opioid peptides derived from in-vitro proteolysis of bovine whey proteins

The formation of opioid peptides by in-vitro proteolysis of whey proteins was investigated. Bovine β-lactoglobulin (β-LG) or α-lactalbumin (α-LA) were predigested with pepsin and subsequently treated with either trypsin (Try) or trypsin+chymotrypsin (Try+Chy). For separation and identification of the peptides. HPLC chromatography, protein sequencing and amino acid analysis were used. Identified peptides were synthesized by Peninsula Laboratories Europe Ltd. UK. Binding to rat brain homogenates was tested against 3H-naloxone. The effects of the peptides on smooth muscle were tested in coaxially stimulated guinea pig ileum in vitro. Digestion of β-LG with pepsin plus Try, or Try+Chy yielded Tyr-Leu-Leu-Phe (β-lactorphin). Proteolysis of α-LA with pepsin alone produced Tyr-Gly-Leu-Phe (α-lactorphin) although a higher degree of hydrolysis was achieved by addition of Try. Among hydrolysates of whey proteins at least α-lactorphin exerted a weak but continuous opioid property both in terms of receptor binding and smooth muscle effects.