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 Fe3+ 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, Ca2+-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.