Antioxidant activity and active compounds of rice koji fermented with Aspergillus candidus

Abstract

Antioxidant activity of ethyl acetate extracts from rice koji (EAERK) fermented with Aspergillus candidus CCRC 31543 was evaluated, and the antioxidant components in koji were isolated and identified. EAERK (200 μg/ml) showed a 90% inhibitory effect on peroxidation of linoleic as determined by the thiocyanate method. EAERK also showed a marked antioxidant activity on the oxidation of lard determined by using the Rancimat method. EAERK had a strong scavenging effect on the DPPH radical. Silica gel column chromatography was used to separate EAERK into eight fractions (A–H). Fractions C–F possessed significant antioxidant activity and showed more than 88% inhibition of peroxidation of linoleic acid. Fraction C was crystallized and purified to obtain compound 1. Fractions D–F were combined and re-separated by means of column chromatography and the subfraction that exhibited strong antioxidant activity was crystallized to yield purified compound 2. Compounds 1 and 2 were shown to be ergosterol and terphenyllin, respectively, on the basis of UV-vis spectral, MS and NMR analyses. Ergosterol showed no antioxidant activity on the peroxidation of linoleic acid. However, the antioxidant activity of terphenyllin was equal to that of BHA at 200 μg/ml.