title: Development of a heat-processing method for koji to enhance its antioxidant activity.
abstract: We developed a heat-processing method to enhance the antioxidant activity of koji. The superoxide anion scavenging activity (SOSA) and oxygen radical absorbance capacity (ORAC) of heat-processed koji (HP-koji) at 55 °C for 7 days were 4.9 times and 4.2 times, respectively, those of unheated koji. These results showed that heat processing effectively enhances the antioxidant activity of koji. Analysis of the antioxidant activities of koji subjected to a range of temperatures (45-75 °C) revealed that the SOSA is enhanced by heating at higher temperatures, which might be catalyzed by Maillard reaction, whereas the ORAC was enhanced by heating at lower temperatures, which might be catalyzed by an enzymatic reaction. Assuming these enhancements in antioxidant activities are contributed by both Maillard and enzyme reactions, we hypothesized that the antioxidant activity of HP-koji could be more effectively amplified by heating at a higher temperature after the progression of the enzymatic reaction at a moderate temperature. Therefore, we evaluated the effect of heating of koji in a stepwise manner, first at 55 °C for 2 days and then at 75 °C for 5days. The antioxidant activities of stepwise-heated HP-koji were higher than those of koji heated at either 55 °C or 75 °C. The SOSA and ORAC of stepwise-heated HP-koji were 94 times and 6 times, respectively, those of unheated koji. This result suggests that enzymatic reaction followed by Maillard reaction can effectively enhance the antioxidant activity of HP-koji. Thus, we developed a novel heat-processing method to enhance the antioxidant activity of koji.
authors.affiliation: Division of Shochu Fermentation Technology, Education and Research Center for Fermentation Studies, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima City 890-0065, Japan.
authors.forename: Kayu
authors.initials: K
authors.lastname: Okutsu
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Yoshizaki
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takamine
authors.forename: Hisanori
authors.initials: H
authors.lastname: Tamaki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Ito
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sameshima
mesh_terms: D000975:Antioxidants; D001230:Aspergillus / Q000737:chemistry / Q000502:physiology*; D005511:Food Handling / Q000379:methods*; D006358:Hot Temperature; D015416:Maillard Reaction; D009584:Nitrogen / Q000032:analysis; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D013997:Time Factors
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D013481:Superoxides; D009584:Nitrogen