pH-dependent antioxidant stability of black rice anthocyanin complexed with cycloamylose

Abstract

This study investigated the effects of cycloamylose (CA) as a complexing agent on the antioxidant activity and stability of anthocyanin extracted from black rice (BRA) at various pHs (2, 4, 6, and 8) and compared the results with those of beta-cyclodextrin (beta CD). The CA (DP 6-31) produced from Dodamssal rice starch had an anti-copigmentation effect for BRA and the discoloration effect increased with the complexing agent concentration, which supported the intramolecular interaction between them. With heat treatment, the CA-BRA complex had a greater antioxidant stability than did free BRA at pHs 4, 6, and 8 in a concentration-dependent manner. In particular, BRA complexed with 1% CA at pH 4 had an approximately 2.0-fold lower degradation rate (k(d)) than that of free BRA. This improvement in the thermal stability was comparable to or slightly better than that of 5% beta CD. CA significantly improved the photostability of BRA at all pHs tested, similarly to beta CD. CA might protect the moiety of BRA functional groups that are involved in antioxidant activity and susceptible to heat and light. The results demonstrated that CA could be an effective complexing agent for BRA and the stable CA-BRA complex could be used as a promising functional material for the various industries.