Effect of steam explosion on phenolic compounds and antioxidant capacity in adzuki beans.

Steam explosion as an efficient pretreatment technology is gradually applied to the food processing industry. At present, steam explosion was used to pretreat adzuki beans at the pressure of 0.25-1.0 Mpa for 30 and 90 s, respectively. The content of total polyphenols (TP) including free polyphenols (FP) and bound polyphenols (BP) in adzuki beans and their antioxidant activity were determined.The results showed that steam explosion can form large cavities and intercellular spaces, which was beneficial to release of polyphenols. After steam explosion, the contents of FP, BP and TP increased. Accordingly, the antioxidant capacity of FP and BP also increased, which demonstrated that there was a positively correlation between the polyphenol content and antioxidant capacity with coefficients of ABTS > FRAP > DPPH. Compounds of FP and BP were further identified by HPLC and showed that protocatechin was the main ingredient in FP and BP, protocatechin in FP was higher. Isoquercetin only exists in FP, but caffeic acid only in BP. After steam explosion, an increase in the contents of protocatechin, catechin and epicatechin was detected in FP and BP. The yield of phenolic compounds and antioxidant capacity were increased at the pressure of 0.25-0.75Mpa, however it is decrease at 1.0 Mpa. In all, at the pressure of 0.75 Mpa for 90 s is the optimal condition for polyphenol separation in adzuki beans.A proper and reasonable steam explosion can effectively increase the release of phenolics and enhance the antioxidant capacity in adzuki beans. This article is protected by copyright. All rights reserved.