Solid-State Cultivation of Multiple Industrial Strains of Koji Mold on Different Thai Unpolished Rice Cultivars: Biotransformation of Phenolic Compounds and Their Effects on Antioxidant Activity
TLDR Koji mold on unpolished Thai-colored rice boosts antioxidant activity more than on other rice types.
This study investigated the biotransformation of polyphenolic compounds in Thai-colored rice using four industrial koji mold strains. The molds, including Aspergillus oryzae and A. sojae, were cultivated on unpolished Thai-colored rice (Riceberry and Sangyod), unpolished Thai white rice (RD43), and polished Japanese white rice (Koshihikari). Results showed that koji molds grew on all rice types, with methanol extracts from rice kojis displaying a 2-fold or greater increase in total phenolic content and DPPH antioxidant activity compared to steamed rice. Notably, Riceberry and Sangyod koji samples had increased levels of various phenolic compounds, such as quercetin and ferulic acid. The study concluded that Aspergillus solid-state cultivation on unpolished Thai-colored rice resulted in higher functionalization than on unpolished Thai white rice and polished Japanese white rice.