Under selective pressure throughout evolution, milk has been instrumental as a nourishing diet in the survival of mammalian offspring. The proteins of milk have diverse biological functions beyond serving solely as nutritional sources of amino acids. A dynamic proteolytic system that contains protein substrates, proteases, protease activators, and protease inhibitors is delivered through milk. The selectivity, specificity and activity of this system can be studied at the level of complexity necessary to appreciate its diverse values for health, yet deciphering such a complex delivery system is challenging. Integrated approaches are needed to investigate this delivery system from various perspectives to capture the diverse mechanisms of action and overall value of milk. With a broad collaborative effort, we have examined the proteolysis of human milk as a function of pH. By using LC-MS/MS peptidomic techniques, profiles of endogenous human milk peptides before and after incubation at various pH levels have been mapped. Over 7000 peptides were identified in this study. Specifically, eighty-five peptides derived from eight milk proteins were consistently found independent of pH alterations. Four peptides derived from three proteins were released only at pH 4 (typical infant gastric pH). The results documented that the proteolysis of milk proteins into specific peptides is pH dependent. These findings are building a better understanding of milk as a uniquely complex delivery system with previously unidentified targets of action within infants.

Peptidomic profiling of human milk by mass spectrometry revealed pH-specific milk proteolysis

255th National Meeting (2018)

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