Antibacterial effect of an antimicrobial substance from yellowish black koji causing a fermentation delay in shochu brewing
2020
Setoguchi, S. ((Kagoshima University, Kagoshima (Japan). The United Graduate School of Agricultural Sciences), (Kirishima Shuzou Co., Ltd., Miyakonojo, Miyazaki (Japan))) | Sho, C. | Iijima, R. | Futagami, T. | Kawano, K. | Iwai, K. | Tamaki, H.
We obtained the black koji fungus Aspergillus luchuensis MEM-C which produces a large amount of yellow pigment during the course of mutation breeding. In this study, we performed a brewing test of sweet potato shochu using rice koji prepared with MEM-C strain (hereafter yellowish black koji). The use of yellowish black koji delayed the fermentation of the primary mash and significantly inhibited the growth of the yeast Saccharomyces cerevisiae, indicating that the MEM-C strain secretes an antimicrobial substance. To identify the antimicrobial substance, we performed a fractional extraction from yellowish black koji and a subsequent antimicrobial activity test. Results showed that the extract fraction 3 of the yellowish black koji (hereinafter Fraction 3) exhibited an antifungal activity against S. cerevisiae strains such as shochu yeast, sake yeast, whiskey yeast, baker's yeast and laboratory yeast as well as various fungi including Pichia farinose, Candida kefyr, Kluyveromyces marxianus, but not A. luchuensis itself and bacteria. Furthermore, the basic property of Fraction 3 indicated that the antimicrobial substance is a low polarity compound containing a sugar group with a molecular weight range from 50 to 100 kDa.
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