Antioxidant analysis in Vitis labrusca ("fox grape") and related products

Fox grape (Vitis labrusca, "uva fragola" in Italian) is a Vitis species closely related to V. vinifera, but with different characteristic of climactic and terrain compatibility. Moreover, fox grapes also have organoleptic properties different from those of grapevine grapes (they are usually sweeter and lack the "muscat" bouquet); the fermented beverage obtained from the former fruits (commonly called "fragolino" in Italy) cannot legally be labelled as "wine", at least in European Union countries, and cannot be commercialised. While the reasons for this distinction are largely commercial, it is also true that "fox grape wines" have a composition that is quali-quantitatively different from that of "wines"; in particular, the former contain larger amounts of methanol and of tannins. In our previous studies, we have detected and quantified the content of antioxidant compounds such as melatonin, resveratrol, ferulic acid and tryptophan in grapevine fruits and related products (juice, must, wine and grappa). Now, the aim of this study is to evaluate whether the differences in composition between grapevine and fox grape and the respective related products also extend to the mentioned antioxidant compounds, and if so, to which degree. The antioxidant content of fox grapes and "fragolino wine" were evaluated by means of a validated HPLC-F method that exploits the native fluorescence of the analytes to avoid complicated derivatisation procedures. The sample pre-treatment includes a freeze-thaw cycle followed by filtration and an advanced miniaturised procedure based on microextraction by packed sorbent (MEPS).