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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