Fermentation Time and Extraction Solvents Influenced in vitro Antioxidant Property of Soluble Extracts of Mao-tofu Fermented with Mucor sp.

Mao-tofu fermented for 3, 5, 7 and 9 days by a strain of Mucor sp. was extracted with five solvents including 20, 40 or 60% (v/v) ethanol solutions and pH 4.5 or 6.5 water to investigate the impacts of fermentation time and extraction solvent on the in vitro antioxidant property of the extracts. Extraction yield and degree of hydrolysis of the protein fractions in the extracts were measured. Antioxidant properties of the extracts namely scavenging activity on 2,2-diphenyl-1-picrylhydrazyl radical and 2,2’-azino-bis(3-ethyl- benzothiazoline-6-sulfonic acid), iron (III)-reducing activity and iron (II)-chelating activity were evaluated in vitro. The results showed that longer fermentation time of Mao-tofu gave the extracts a higher extraction yield, higher degree of hydrolysis of the protein fractions and higher antioxidant activity. The extract prepared with 60% ethanol solution behaved the highest antioxidant activity while that prepared with pH 4.5 water showed the lowest activity. Five extracts from Mao-tofu fermented for 9 days were analyzed by size exclusion chromatography and the molecular weights of their main protein fractions were found to be from 0.2 to 6.0 kDa. Amino acids analysis showed that total content of six hydrophobic amino acids among the five extracts showed no difference, while ethanol solution extracts had more Arg, Cys and Met but less Ala, Gly and His than that of water extract. Present result revealed that the soluble extracts of Mao-tofu had an improved in vitro antioxidant activity than soybean proteins and both fermentation time of Mucor sp. and solvent types influenced the in vitro antioxidant activity of the extracts.