This suggestion is supported by a report from Srinivasan et al. (2007), which indicates that ferulic acid is a potent antioxidant compound and a highly effective scavenger of free radicals. The substantial content of citric acid in the mix-cultured rice bran extract compared
to other extracts tested (Table 3) may also be attributed to the high antioxidant activity of this extract. Citric acid is a well-known secondary antioxidant which functions as a synergist to primary antioxidants such as phenols and also oxygen scavengers. On the other hand, the overall antioxidant capacity in an extract is not necessarily indicated by the potent antioxidant compounds present (Leong and Shui, 2002). The extracts were complex mixtures of many compounds which
can show different results by different methods of antioxidant assays. The concentration of compounds should also be taken into account, as it is well known that antioxidant compounds,
such as phenolic acids, have concentration-dependent antioxidant or pro-oxidant activities (Yoshino and Murakami, 1998).