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Abstract
Functional foods have been increasingly popular in Japan and are widely claimed to be beneficial for health. Among many kinds of such food, one distinct type is fermented food employing osmophilic or osmo-tolerant yeasts under high concentration of salt or sugar. We are the first to investigate the antioxidant activities of a strain of sugar-tolerant yeast isolated from high-sugar fermented food. In search of novel natural antioxidants, we screened 17 strains of yeast, including 7 sugar-tolerant strains, 4 salt-tolerant strains and 6 conventional strains, based on DPPH-scavenging (2,2-diphenyl-1-picrylhydrazyl) capacity of their ethyl acetate extracts. A sugar-tolerant strain of Zygosaccharomyces rouxii (MAFF 237555) yielded a maximum amount of extract which exhibited the strongest activity of 66.3% at 2 mg ml−1. The yeast was cultured under various conditions at different pH and different glucose concentrations for different numbers of incubating days and the antioxidant activity of each solvent extract was determined using different assay methods of DPPH, FRAP (Ferric reducing/antioxidant power), NBT (nitro blue tetrazolium) and the capacity for inhibiting linoleic acid oxidation, in comparison with natural and synthetic standard compounds. In most cases, while the activity of the extract was lower than that of BHA, it was higher than or comparable to that of ascorbic acid or α-tocopherol, tested under the same concentration range of 1 mg ml−1 to 5 mg ml−1. The results suggested that the yeast had a wide spectrum of moderately strong antioxidant activity and it could be utilized as a source of natural antioxidant.