Effective Antioxidant Activities of Anthocyanins as Affected by the pH of Antioxidant Assays

Paradorn Ngamdee, Sudarat Jiamyangyuen

Abstract


Effect of pH on antioxidant activities of anthocyanins was studied. Five different anthocyanin levels were five black glutinous rice bran crude extracts (BBC), MS, SK, PY, PC, and KK, from Thailand. The antioxidant activities of BBCs were evaluated using two in vitro antioxidant assays conducted at different pH, DPPH (pH 5.5) and FRAP (pH 3.6). Total anthocyanin content (TAC) of KK (23 g/kg) was the highest followed by PC (13 g/kg), PY and SK (11 g/kg), and MS (10 g/kg). The pH of the assays affected the effectiveness of anthocyanins as the KK showed comparable DPPH scavenging activity to other BBCs but exhibited significantly greater FRAP scavenger. To eliminate interferences of other active components in the BBC, anthocyanin-rich isolate (ARI) was isolated from the selected BBC. The ARI contained 90% cyanidin-3-glucoside as analyzed by HPLC. The ARI was dissolved in five different buffer solutions (pH 1, 3, 5, 7, and 9) and incubated for 1 h, 3 days, and 1 week before the evaluation of antioxidant activities. All ARI-containing buffer solutions exhibited comparable DPPH scavenging activity. However, the ones at pH 5 and 7 solutions were less reactive than others as tested with FRAP assay. The results indicated that anthocyanin is a strong antioxidant in an acidic environment. However, derivatives. These results suggest that the application of anthocyanins as natural antioxidants in products, such as food and cosmetic, is not limited by the pH.


Keywords


Anthocyanins, pH, Antioxidant, DPPH, FRAP

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