Induction of mutation in Monascus purpureus isolated from Thai fermented food to develop low citrinin-producing strain for application in the red koji industry

Red koji is produced from cultivating rice with Monascus strains that contain various types of fungal secondary metabolites, such as red pigments and monacolin K. Monascus strain also produces citrinin-a mycotoxin. In this study, Monascus purpureus KUPM5 isolated from the Thai fermented food, sufu, was mutagenized to reduce its citrinin production using UV irradiation, NTG treatment, and a combination of UV and NTG. Screening of the mutants using plate bioassay based on the inhibitory effect against Bacillus subtilis enables the selection of 10 mutants. The mutant strains KS301U and KS302U showed an 80% reduction in citrinin production in red koji compared with the wild type (wt), and maintained the ability to produce red pigments similar to the wild type. Activities of enzymes, α-amylase, protease, and lipase, from red koji extract produced by the mutant strain KS302U, were higher than those of the wt, whereas those of the mutant strain KS301U were similar to those of the wt. Consequently, strains KS301U and KS302U were successfully selected as strains suitable for producing red koji and fermented food.