Eco-Friendly Voltammetric Techniques for Assessing Antioxidant Properties in Dietary Supplements

Dietary supplements often promote their antioxidant content as an indicator of quality on the packaging. This study evaluated the redox potential and total antioxidant capacity of various dietary supplements, using different analytical methods to obtain the complexity of antioxidant measurements. A green approach for detecting total antioxidant capacity in dietary products utilized modern electrochemical techniques, including differential pulse voltammetry (DPV) and cyclic voltammetry (CV). These rapid “green” methods measure the redox potential of samples, providing information about the electron-donating ability of antioxidants without the use of harmful chemicals or sample treatments, with minimal environmental impact. ABTS and FRAP measurements were expressed as vitamin C equivalents to allow comparison with CV measurements and actual vitamin C content. This approach enabled indirect comparison of activities obtained using different standard substances through conversion to standard equivalents. The results revealed that the claims made on product labels and packaging often overestimated the antioxidant content and did not match the measured total antioxidant capacities obtained in the current study. Measured vitamin C levels in 10 samples fell within the declared ranges (0–950 mg), but six products contained 4.85% to 49.18% less, and two had significantly higher levels (4.20% and 32.22%) than their declared (p < 0.05). Total antioxidant capacity varied from the labeled values. Similar trends were observed across methods, except for DPPH. FRAP values were correlated with ABTS and CV (r = 0.797 and r = 0.757, respectively). The DPV method provided a more detailed assessment of the redox activity of selected products based on distinct oxidation peaks. The study highlights the importance of mandatory testing and quantification of antioxidants, as well as the need for regulation of antioxidant properties through normative standards.