Electrochemical behaviour of polyphenol rich fruit juices using disposable screen-printed carbon electrodes: Towards a rapid sensor for antioxidant capacity and individual antioxidants

The analysis of antioxidants in different foodstuffs and especially fruits has become an active area of research which has lead to numerous antioxidant-assays being recently developed. Many antioxidants exhibit inherent electroactivity, and hence employing electrochemical methods could be a viable approach for evaluating the overall antioxidant capacity of a fresh produce matrix without the need for added reactive species. This work shows the possibility of using square wave voltammetry (SWV) and other electrochemical methods with disposable screen-printed carbon electrodes, to quantify and assess antioxidant activity and abundance of specific antioxidants, mainly polyphenols in selected soft fruit juices. Freshly squeezed black currant and strawberry juices of different cultivars and maturity stages were chosen according to known differences in their antioxidant profile. As a result of the increasing applied potential (0–1000 mV vs. Ag/AgCl) the electroactive compounds present in the juices were oxidised leading to a characteristic voltammetric profile for each of the samples analysed. Generally, black currant juices had greater oxidation peaks at lower potentials (<400 mV) which were indicators of higher antioxidant capacities. The relationship between sensor cumulative responses at different applied potentials and total or individual antioxidants, as determined by conventional spectrophotometric methods (FRAP, Folin–Ciocalteu) and HPLC (individual anthocyanins and ascorbate), respectively, are discussed in the context of the development of a rapid sensor for antioxidants.