Effect of heat treatment on total phenolic and anthocyanin contents as well as antioxidant activity of the extract from Aspergillus awamori-fermented black soybeans, a healthy food ingredient

Aspergillus awamori-fermented black soybeans, a healthy food ingredient, were subjected to heating at 40-100 degrees C for 30 min. After heat treatment, the methanol extract of the fermented black soybeans was examined for antioxidant activity including the 2,2-diphenyl-1-picrylhydrozyl radical-scavenging effect and the Fe2+-chelating ability. It was found that antioxidant activity exerted by the methanol extract was stable with heating at a temperature up to 80 degrees C for 30 min. The extract showed a reduced antioxidant activity after heating the fermented black soybeans at 100 degrees C for 30 min. However, it showed approximately 70% and 40%, respectively, of the original 2,2-diphenyl-1-picryl-hydrozyl radical-scavenging effect and the Fe2+-chelating ability. Heating also reduced the total phenolic and anthocyanin content in the fermented black soybeans, but this reduction did not coincide closely with the reduction of antioxidant activity observed.