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

Abstract

Aspergillus awamori-fermented black soybeans, a healthy food ingredient, were subjected to heating at 40–100°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-picryl-hydrozyl 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°C for 30 min. The extract showed a reduced antioxidant activity after heating the fermented black soybeans at 100°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.

Keywords::

• Fermented black soybean
• antioxidant activity
• anthocyanin
• total phenolics

Acknowledgement

This research was financially supported by The National Science Council, ROC (Taiwan) (NSC 95-2313-B-002-017).