Bioactive peptides encrypted in milk proteins: proteolytic activation and thropho-functional properties

The bioactivities of peptides encrypted in major milk proteins are latent u ntil released and activated by enzymatic proteolysis, e.g. during gastroint estinal digestion or food processing. The proteolytic system of lactic acid bacteria can contribute to the liberation of bioactive peptides. In vitro, the purified cell wall proteinase of Lactococcus lactis was shown to liber ate oligopeptides from beta- and alpha-caseins which contain amino acid seq uences present in casomorphins, casokinines, and immunopeptides. The furthe r degradation of these peptides by endopeptidases and exopeptidases of lact ic acid bacteria could lead to the liberation of bioactive peptides in ferm ented milk products. However, the sequences of practically all known biolog ically active peptides can also be cleaved by peptidases from lactic acid b acteria. Activated peptides are potential modulators of various regulatory processes in the body: Opioid peptides are opioid receptor ligands which ca n modulate absorption processes in the intestinal tract, angiotensin-I-conv erting enzyme (ACE)-inhibitory peptides are hemodynamic regulators and exer t an antihypertensive effect, immunomodulating casein peptides stimulate th e activities of cells of the immune system, antimicrobial peptides kill sen sitive microorganisms, antithrombotic peptides inhibit aggregation of plate lets and caseinophosphopeptides may function as carriers for different mine rals, especially calcium. Bioactive peptides can interact with target sites at the luminal side of the intestinal tract. Furthermore, they can be abso rbed and then reach peripheral organs. Food-derived bioactive peptides are claimed to be health enhancing components which can be used for functional food and pharmaceutical preparations.