title: Antioxidants in heat-processed koji and the production mechanisms.
abstract: We previously developed antioxidative heat-processed (HP)-koji via two-step heating (55 °C/2days → 75 °C/3 days) of white-koji. In this study, we isolated antioxidants in HP-koji and investigated their formation mechanisms. The antioxidants were identified to be 5-hydroxymethyl furfural (HMF) and 5-(α-D-glucopyranosyloxymethyl)-2-furfural (GMF) based on nuclear magnetic resonance spectral analysis. HMF and GMF were not present in intact koji, but were formed by heating at 75 °C. As production of these antioxidants was more effective by two-step heating than by constant heating at 55 °C or 75 °C, we presumed that the antioxidant precursors are derived enzymatically at 55°C and that the antioxidants are formed subsequently by thermal reaction at 75 °C. The heating assay of saccharide solutions revealed glucose and isomaltose as HMF and GMF precursors, respectively, and thus the novel finding of GMF formation from isomaltose. Finally, HMF and GMF were effectively formed by two-step heating from glucose and isomaltose present in koji.
authors.affiliation: Division of Shochu Fermentation Technology, Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan.
authors.forename: Kayu
authors.initials: K
authors.lastname: Okutsu
authors.affiliation: Division of Shochu Fermentation Technology, Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Yoshizaki
authors.affiliation: Division of Shochu Fermentation Technology, Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan.
authors.forename: Natsumi
authors.initials: N
authors.lastname: Ikeda
authors.affiliation: Division of Shochu Fermentation Technology, Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Kusano
authors.affiliation: Department of Horticultural Science, Faculty of Agriculture, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Hashimoto
authors.affiliation: Division of Shochu Fermentation Technology, Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-0065, Japan. Electronic address: takamine@chem.agri.kagoshima-u.ac.jp.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takamine
mesh_terms: D000975:Antioxidants / Q000032:analysis*; D001230:Aspergillus; D005285:Fermentation; D005504:Food Analysis; D005511:Food Handling; D055951:Functional Food; D005662:Furaldehyde / Q000031:analogs & derivatives / Q000032:analysis; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging
chemical_list: D000975:Antioxidants; C008046:5-hydroxymethylfurfural; D005662:Furaldehyde
keywords: 5-Hydroxymethyl furfural; Antioxidant activity; Isomaltose; Rice koji