Abstract:This research was evaluated the antioxidant activity of fish miso, a newly developed fermented fish paste prepared from horse mackerel meat and the fermentation of traditional Japanese koji inoculated with Aspergillusoryzae. The antioxidant activities in different in vitro models, including DPPH, hydroxyl, nitric oxide and carbon-centered radical-scavenging activity (RSA), and reducing power ability (RPA), were investigated during the fermentation period along with 2 different storage conditions. The antioxidant activity of matured fish miso was also evaluated using a linoleic acid oxidation model system by monitoring hydrogen peroxide formation and oxygen absorption. The RSA against all the types of radicals measured by electron spin resonance showed an increase over prolonged fermentation periods and during storage at high temperatures. However, the RPA showed a rapid increase during the early stages of fermentation. The SDS-PAGE profile of fish miso peptides during the early stages of fermentation indicated the occurrence of hydrolysis, suggesting the involvement of low-molecular-weight peptides in the RSA and reducing power of fish miso. Partial purification of these peptides by using an online-HPLC-DPPH flow injection analysis system and further characterization by thin layer chromatography and molecular weight distribution clearly indicated that low-molecular-weight peptides (<500 Da) were potent antioxidants. These data suggest that the antioxidant activity of fish miso could be substantially improved by fermenting Aspergillus (koji) mold. This approach provides a novel strategy to enhance the value of trash fish, such as horse mackerel.