Isolation of Aromatic Compounds Produced by Eurotium herbariorum NU-2 from Karebushi, a Katsuobushi, and their DPPH-Radical Scavenging Activities

Aromatic compounds were isolated from an extract of Eurotium herbariorum NU-2, which is used in the process of manufacturing karebushi (a katsuobushi). The seventeen compounds were identified as anthraquinone derivatives (A1-A6), eurotinone derivatives (B1, B2), indole-containing diketopiperazine derivatives (C1-C6), and benzaldehyde derivatives (D1-D3). 2-Methyleurotinone (B1), isoechinulin A (C6), tetrahydroauroglaucin (D1), isodihydroauroglaucin (D2), and flavoglaucin (D3) exhibited significantly higher DPPH (1, 1-diphenyl-2-picrylhydrazyl) scavenging activity compared to α-tocopherol, a standard radical scavenger (P < 0.05). Asperflavin (A4), isoechinulin B (C1), neoechinulin B (C2), and variecolorin O (C4) had similar activity to α-tocopherol. The extract of E. herbariorum NU-2 exhibited high radical scavenging activity compared to other filamentous fungi from katsuobushi, and also contained higher levels of isoechinulin B (C1), echinulin (C5), tetrahydroauroglaucin (D1), and flavoglaucin (D3). The concentration of tetrahydroauroglaucin (D1) in the filamentous fungus extract was highly correlated with the radical scavenging activity.