Antioxidant properties and total phenolics of Thua Nao (a Thai fermented soybean) as affected by Bacillus-fermentation

Abstract

The present study aims to investigate antioxidant activity and phenolic contents of Thai thua nao. Methanolic extracts of cooked non-fermented soybeans (CNF) and thua nao-fermented soybeans prepared by naturally occurring bacteria (TNMX) and Bacillus subtilis TN51 (TNB51) were prepared and used to determine antioxidant activities by β-carotene-linoleic acid system and DPPH-radical scavenging assay. Total phenolic contents of thua nao samples (both TNMX and TNB51) were significantly higher than those of the CNF samples (with an increase around 21 and 35%, respectively). A correlation between larger amount of total phenolics and higher antioxidant activity as determined by the β-carotene-linoleic acid model was observed in these extracts. All these results indicate that production process and bacterial fermentation are responsible for improvement of total phenolics and antioxidant activity. The potential use of B. subtilis TN51 appears to be a suitable fermenting strain to promote antioxidant property in cooked soybean. © 2011 Dajanta K, et al.