Background The Japanese traditional cuisine, Washoku, considered to be responsible for increased longevity among the Japanese, comprises various foods fermented with the non-pathogenic fungus Aspergillus oryzae (koji). We have recently revealed that koji contains an abundant amount of glycosylceramide. Intestinal microbes have significant effect on health. However, the effects of koji glycosylceramide on intestinal microbes have not been studied.Materials and methodsGlycosylceramide was extracted and purified from koji. C57BL/6N mice were fed a diet containing 1 % purified koji glycosylceramide for 1 week. Nutritional parameters and faecal lipid constituents were analyzed. The intestinal microbial flora of mice on this diet was investigated.ResultsIngested koji glycosylceramide was neither digested by intestinal enzymes nor was it detected in the faeces, suggesting that koji glycosylceramide was digested by the intestinal microbial flora. Intestinal microbial flora that digested koji glycosylceramide had an increased ratio of Blautia coccoides. Stimulation of B. coccoides growth by pure koji glycosylceramide was confirmed in vitro.ConclusionsKoji functions as a prebiotic for B. coccoides through glycosylceramide. Since there are many reports of the effects of B. coccoides on health, an increase in intestinal B. coccoides by koji glycosylceramide might be the connection between Japanese cuisine, intestinal microbial flora, and longevity.

Koji, rice fermented with Aspergillus, is used for saccharification of starch contained in crops during the manufacturing of many of Japanese traditional foods and drinks. Japanese people have long eaten koji, and many beneficial substances have been reported to be contained in koji. However, there has been no report on the existence or content of galactosylceramide in koji. To address this issue, we analyzed the chemical composition of the sugar moiety of monohexosylceramide contained in koji, and elucidate that 30.3% of yellow koji is galactosylceramide, 69.7% of that is glucosylceramide, 19.2% of white koji is galactosylceramide, and 80.8% of that is glucosylceramide. This is the first report of the existence and content of galactosylceramide in koji.

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