Analytical Sciences

New Electrochemical Evaluation of the Antioxidant Capacity of Beverages with Polyoxometalates as Redox Probes

Tadaharu UEDA,* Takashi OKUMURA,* Yukino TANAKA,* Saki AKASE,* Tomoko SHIMAMURA,** and Hiroyuki UKEDA**

*Department of Applied Chemistry, Faculty of Science, Kochi University, Kochi 780-8520, Japan
**Department of Agriculture, Faculty of Agriculture, Kochi University, Kochi 783-8502, Japan

A new method was developed to evaluate antioxidant activity based on the redox properties of polyoxometalates, which are partially reduced by antioxidants to generate a limiting potential. The polyoxometalates [PMo₁₂O₄₀]³⁻, [PVW₁₁O₄₀]⁴⁻ and [SV₂W₁₀O₄₀]4− formed in situ were used as electrochemical probes for the new evaluation method, and their formation conditions were optimized to evaluate the antioxidant activities of gallic acid, ellagic acid, catechin, quercetin, morin, trans-ferulic acid, sesamol, α-tocopherol, δ-tocopherol and L-ascorbic acid. The observed difference between initial potential and limiting potential (ΔE) were compared with spectrophotometrically evaluated antioxidant activities. In addition, the antioxidant capacities of five beverages (Japanese green tea, concentrated catechin-containing green tea, grapefruit juice, red wine and Japanese sake) were evaluated.

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