Enhancement of the antioxidant activity of orange and lime juices by flavonoid enzymatic de-glycosylation

Pure flavonoid glycosides and those present in orange (Citrus sinensis) and lime (Citrus latifolia) juices were structurally modified by enzymatic de-glycosylation to obtain functional derivatives with higher antioxidant activity. The enzymatic reactions were carried out using commercial rhamnosidases (hesperidinase and naringinase) and beta-D-glucosidase. An experimental design and statistical tools for the data analysis were employed for each enzyme to evaluate the independent variables (pH and temperature) that significantly affected the enzyme activity (dependent variable), and the antioxidant activity was evaluated before and after bioconversion using DPPH center dot and FRAP assays. Aliquots of controls and enzyme-treated samples were taken at different times and analyzed by UPLC-MS. The antioxidant activity of both treated juices was higher than that of the untreated juices, confirming that the bioconversion reaction conditions used were efficient and produced an increment in the antioxidant activity. After the 4 h-hesperidinase reaction 60% of the hesperidin was converted into hesperetin in the orange juice. The antioxidant capacities of the glycosylated standards were also increased by the enzyme treatment. The results presented herein are a step forward in the use of alpha-L-rhamnosidases to produce functional beverages by way of de-glycosylation reactions of their flavonoid glycosides. (C) 2013 Elsevier Ltd. All rights reserved.