Antioxidants produced by Eurotium herbariorum of filamentous fungi used for the manufacture of karebushi, dried bonito (katsuobushi)

Abstract

Extracts prepared by culturing ten filamentous fungi from Aspergillus and Eurotium species isolated from dried bonito (katsuobushi) were examined for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity. The extracts prepared by culturing E. herbariorum NE-1 and NE-4, which are used in the molding process for the manufacture of karebushi (a kind of katsuobushi), were shown to have higher activity than the others. Five antioxidants were isolated from the extracts and identified as isodihydroauroglaucin (IDAG), auroglaucin (AG), dihydroauroglaucin (DAG), tetrahydroauroglaucin (TAG), and flavoglaucin (FG) by 1H-NMR, 13C-NMR, and EI-MS analyses. Compared with α-tocopherol, the isolated antioxidants exhibited high antioxidative activity for the radical scavenging capacity of DPPH and superoxide, but low activity for inhibiting the autoxidation of docosahexaenoic acid (DHA). The isolated antioxidants were produced by the Eurotium species, but not by the Aspergillus species. DAG and TAG exhibited higher radical scavenging capacity than the other antioxidants and were abundantly contained in the extracts of E. herbariorum NE-1 and NE-4.