Antioxidant capacity of fermented soybeans and their protective effect on protein oxidation in largemouth bass (Micropterus salmoides) during repeated freezing-thawing (FT) treatments

The effect of fermented soybeans from three different origin places (Hunan, Guangdong, and Sichuan in China) on protein oxidation and freshness of largemouth bass ( Micropterus salmoides ) was investigated during repeated freezing-thawing (FT) cycles. The Hunan fermented soybean exhibited the best antioxidant capacity according to the capacity of Fe 3+ reducing power, DPPH radical scavenging activity, super oxide radical scavenging assay, hydroxyl radical scavenging assay, and reduced glutathione (GSH). As expected, 0.1% fermented soybean significantly (P < 0.05) delayed protein oxidation including the decline of reactive and total sulphydryls, Ca 2+ -ATPase activity, and freshness as well as the increase of total volatile base nitrogen (TVB-N) during repeated freezing-thawing cycles treatments. It was concluded that the fermented soybean was not only a seasoning, but also an antioxidant in prepared fishes.