The in vivo formation of biologically active caseinopeptides was studied. It was proved that bioactive peptides were released in the small intestine of minipigs in the course of luminal digestion of diets containing bovine casein. An opioid peptide and a phosphopeptide were isolated from jejunal chyme and were chemically characterized. The opioid peptide has been identified as a fragment of /?-casein (60-70). This peptide, named /?-casomorphin-ll, displayed substantial opioid activity in an opiate receptor-binding assay. The caseinophosphopeptide has been shown to be a fragment of a sl -casein (66-74). Casein-derived phosphopeptides exhibit a potent ability to form soluble complexes with Ca and trace elements. Evidence exists that casomorphins and caseinophosphopeptides participate in the regulation of nutrient entry.
Bioactive peptides have been identified as digestion products of several food proteins. All the bioactive sequences are hidden in an inactive state inside the polypeptide chain of the larger protein. Milk proteins are a rich source of biologically active peptides such as exorphins (casomorphins), phosphopeptides and immunopeptides. Such peptides are released during intestinal digestion of caseins and whey proteins. They may be involved in regulation of nutrient entry and influence the postprandial metabolism via stimulation of the secretion of hormones. Furthermore, they may exert a stimulating effect on the immune system. These findings offer new aspects for evaluating the nutritive value of food proteins. Moreover, bioactive peptides have already found interesting applications as dietary supplements and as pharmaceutical preparations.
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