The effects of different enzymes on the liberation of bound phenolics from rice bran dietary fibre and their antioxidant activities

Bound phenolics are the main phytochemicals and important contributors to the health benefits of whole grains. The commonly used chemical methods for bound phenolic release are not appropriate for processing of food materials. The effects of cellulase and feruloyl esterase on releasing bound phenolics from rice bran dietary fibre (RBDF) and the auxiliary effects of autoclaving pretreatment were investigated in the present study to find a method to effectively increase bioaccessible phenolics in RBDF. The results showed that cellulase (CT) and feruloyl esterase (FT) alone and combined application (CFT) released limited bound phenolics. Autoclaving pretreatment could enhance the release of bound phenolics by enzymatic treatments significantly with 1.74, 5.56 and 1.76 folds increases when compared with the above mentioned enzymolysis, respectively. Moreover, the total quantity of phenolic compounds released from RBDF via combined enzymolysis of cellulase and feruloyl esterase with autoclaving pretreatment (A-CFT) were comparable with that via alkaline hydrolysis previously reported. The predominant phenolic compounds released by A-CFT from RBDF were vanillin and ferulic acid, while ferulic and p-couramic acids accounted for 99.30% of the sum of phenolics released by alkaline hydrolysis. The DPPH scavenging, FRAP and ORAC antioxidant activities of the enzymatic hydrolysates were positive correlated with their total phenolic contents. The phenolics released by A-CFT showed lower antioxidant activity than those by alkaline hydrolysis, which may ascribe to the difference in phenolic profiles between methods. This study provides a new approach for processing whole grain and the by-products for functional foods materials with higher phenolic bioaccessibility.