This paper (purchase required) reports an electroanalytical approach for measuring apple juice or apple cider in white wine.
After addition of LiClO4 as electrolyte and deoxygenation, reference samples were analysed using a screen-printed carbon electrode modified with gold nanoparticles (cyclic voltammetry).
The authors report that cyclic voltammograms (CVs) of white wine samples displayed consistency regardless of their grape variety, mono-, bi- or multi-varietal status as well as geographical origin. In contrast, CVs of apple juice and apple cider exhibited similarities but were distinct from those of white wine. They were particularly characterized by the presence of a cathodic peak at about -0.50 V, attributed to sugars and organic acids, predominantly malic acid.
The authors then exported these reference, cyclic voltammograms into data points and classified them using chemometric analysis. Principal Component Analysis effectively grouped samples into two clusters: white wine and apple juice/ apple cider. Class-modelling demonstrated the ability to detect adulteration in white wine samples, with a detection threshold of 5% v/v or lower, contingent upon the adulterant type (apple juice or apple cider). Partial Least Squares regression facilitated approximate quantification of the adulteration level.
They conclude that this approach is both cost-effective and straightforward, involving minimal sample preparation.
