Enzymatic production and degradation of cheese-derived non-proteolytic aminoacyl derivatives

Gamma-glutamyl-amino acids, lactoyl-amino acids and pyroglutamyl-amino acids, collectively named Non-Proteolytic Aminoacyl Derivatives (NPADs) are unusual aminoacyl derivatives of non-proteolytic origins found in consistent amount in several cheeses. Although their enzymatic origin arising from lactic acid bacteria has been demonstrated, the exact enzymes originating them, the ones eventually degrading them and also their resistance to digestive enzymes in the human gastrointestinal tract and in the blood serum after eventual absorption are still unknown. In this paper, pure enzymes and biological media were tested on NPAD and their aminoacidic precursors, for identifying the conditions favoring bioproduction and biodegradation of these compounds. Pure gamma-glutamyl-phenylalanine and its precursor (glutamic acid and phenylalanine), also in the isotopically labeled forms, were tested with Parmigiano-Reggiano extracts, blood serum and different pure enzymes, including typical digestion enzymes (pepsin, trypsin and chymotrypsin), gamma-glutamyl transpeptidase and carboxypeptidase. The data suggested that their production in cheese, and also their partial degradation, might be due to the action of peptidases and gamma-glutamyl transpeptidase. Anyway, under simulated gastrointestinal digestion and in blood serum these compounds turned out to be perfectly stable, suggesting a potential to be absorbed as such and possibly being transported to the body tissues.