Identification of Creatinine, the Antioxidant in the Non-absorbed Fraction of Dried Bonito Stock (Katsuodashi)

Abstract

It has been reported that dried bonito (katsuobushi) shows antioxidant activity. In our previous study, we found that both absorbed (ABF) and non-absorbed (NAF) fractions of the hot-water extract (dried bonito stock or katsuodashi) from katsuobushi fractionated by a Porapak^TM Q (a porous polymer) column were determined to be equally antioxygenic by the diphenylpicrylhydrazyl (DPPH) method ; the phenol compounds were determined to be the main participants in the antioxidant activity in the ABF. Here, we investigated the compounds responsible for the antioxidant activity in the NAF. The NAF was separated by gel filtration, resulting in three fractions with radical scavenging activity. The fraction with the most prominent activity was purified by reversed-phase high performance liquid chromatography ; ¹H-NMR, ¹³C-NMR and mass spectrometry analyses identified the active compound as creatinine. IC₅₀ of creatinine for quenching the DPPH radical was 18mg/100ml.