To identify antioxidants for improving rough skin, we aimed to analyze the amino acid composition of fish mucus and antioxidant activity of the mucus component. Specifically, we aimed to examine the antioxidant properties of dialyzed mucus components secreted from mackerel, which can be used as raw materials for producing cosmetics. The amino acid composition of hydrolyzed mucus was examined by ultra-high-performance liquid chromatography after dialyzing mucus. In addition, the antioxidant

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... ity of the mucus was evaluated via oxygen radical absorption capacity and Trolox equivalent antioxidant capacity assays. The amino acid composition differed between the low-molecular-weight and high-molecular-weight fractions. Moreover, the low-molecular-weight fraction of farmed mackerel mucus exhibited antioxidant activity with high specificity. The results suggest that antioxidant peptides or free amino acids are present in the low-molecular-weight fraction of farmed mackerel mucus.