Salted fermented soybean paste (miso), soybean sauce (shoyu), and Japanese rice wine (sake) are used as seasonings for traditional Japanese dishes. These products still play important roles in the dietary habits of Japanese, while consumption of these products has decreased approximately to 30-50% of consumption since 1975. These products are produced by a fungi (Aspergillus oryzae) starter, referred to koji. A. oryzae produces a strong amylase and also protease including both endoproteinases and exopeptidases. Thus, these products contain short chain peptides in addition to free amino acids. However, little was known of their structure and biological functions due to difficulty in isolation. Recent advances in LC-MS/MS coupled with derivatization techniques allow identification of peptides in such complicated food matrices. In addition to “normal peptides”, aspartic isopeptides with β-peptide bonds and pyroglutamyl (pE) peptides have been identified. These peptides can be generated from the peptide with aspartyl and glutaminyl residues with amino terminal during aging process. Thus, only negligible amounts of these peptides can be taken by consumption of boiled or steamed soybean, barley, and rice, start materials of the seasonings. Some aspartic isopeptides exert an anti-fatigue effect in an animal model. Some hydrophobic pE peptides ameliorate hepatitis and colitis in animal models (pEL) and also normalize disturbance of gut microorganism flora, referred to as dysbiosis in rodent models (pEL and pENI). Oral administration of pEL increase secretion of endogenous antimicrobial peptide, α-defensin, which can be associated with normalization of dysbiosis. Furthermore, pEL, pEI, pEY, and pEP suppress high fat diet-induced obesity. These peptides exert significant activities by oral administration with small doses at 0.1-1 mg/kg body weight, which can be obtained by consumption of the daily Japanese traditional dishes. Thus, the peptides in these products can impact health of people taking traditional Japanese dishes.

Dr. Kenji Sato

Professor, Kyoto University

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