Influence of preheating on antioxidant activity of the water extract from black soybean and color and sensory properties of black soybean decoction.

BACKGROUND

Our previous study indicated that black soybean (BS) tea (BST) made from preheated BS showed a significant protective effect against CCl4 -induced liver damage in Sprague Dawley rats due to BS's antioxidant activity. In this study, we investigated three different preheating methods on the antioxidant activity of water extract from BS (WBS) (Glycine max (L.) Merrill), as well as on the color and sensory properties of BST.

RESULTS

WBS baked at 130 °C for 5 min showed high total phenol, flavonoid and anthocyanin contents among three preheating methods, as well as high DPPH radical-scavenging activity, ferrous ion chelating ability and reducing power. BST baked at 130 °C for 5 min had higher polyphenol oxidase activity and L*, a* and b* values but lower peroxidase activity then BST made from unheated BS. Sensory evaluation indicated that BST made from baked BS produced better aroma and flavor than the tea made from unheated BS or a commercial preheated BS.

CONCLUSIONS

An appropriate preheating process improved the amount of extractable antioxidant and the antioxidant activity in WBS. BST baked at 130 °C for 5 min had good flavor properties, as well as high amount of antioxidant.