Use of cyclic voltammetry to determine the antioxidant capacity of berry fruits: correlation with spectrophotometric assays

Background of the study - Among fruits, berry fruits contain a very large complex of chemical compounds that are responsible for their antioxidant properties. As far as we know there is no data available from cyclic voltammetry studies of berry fruits. Objectives - The first objective of the present work was to investigate the electrochemical properties of antioxidants present in four types of berry fruits: strawberries, blackberries, blueberries and red raspberries. The second objective was to establish the correlation between antioxidant capacities obtained from cyclic voltammograms with those obtained using spectrophotometric techniques. Methods - Evaluation of antioxidant activity of 15 berry samples (strawberry, blackberry, blueberry and raspberry) has been carried out using cyclic voltammetry (CV). CVs were taken in the potential range between 0 mV and 800 mV with a scan rate of 100 mV s(-1). Results - A pronounced anodic current peak observed between 0.524 V and 0.540 V in all analyzed berry samples can be ascribed to anthocyanins, which are the major contributors to the antioxidant capacity of investigated berries. Results obtained from CVs were compared with those obtained by using DPPH, ARTS, FRAP and RP assays. ACI parameters were determined for each berry sample by assigning all the assays an equal weight. According to obtained results, the highest ACI had blueberry samples, followed by blackberry, raspberry and strawberry samples. Also, high positive correlations were found between antioxidant capacities deduced from CVs with those obtained using FRAP (R-2 =0.8630, p=0.0006), RP (R-2 =0.7426, p=0.0004), DPPH (R-2 =0.7680, p=0.0001) and ARTS (R-2 =0.8710, p=0.000002). In addition, high positive correlations were also found between total phenols, flavonoids, anthocyanins and CV antioxidant capacity (R-2 =0.8091, p = 0.0005; R-2 = 0.8341, p = 0.0002; R-2 = 0.7163, p =0.0007), respectively. Conclusion - Obtained results showed that the cyclic voltammetry is a suitable method for the determination of the reducing capacity based on the electrochemical properties of compounds under the test.