A chemometric approach to identify the grape cultivar employed to produce nutraceutical fruit juice

Apulian farmers have begun to explore the potential of grape juice as an alternative method to increase the profitability and stability of their farming operations. Grape juice obtained from table cultivar rich in polyphenols are considered value-added food products, so producers are interested in identifying an analytical method that permits (1) to quantify the phenolic composition, in order to select the richer variety of antioxidant substance, and (2) to trace the grape cultivar, in order to have a tool to protect their nutraceutical product from imitations. In this work, a chemometric approach, consisting of the comprehensive application of two-way full-factorial MANOVA, hierarchical cluster (HCA), and principal component analyses (PCA), is proposed as tool to differentiate seven table grape varieties (white, ‘Carati,’ ‘Sugraone,’ and ‘Italia’ and colored ‘Michele Palieri,’ ‘Summer Royal,’ ‘Autumn Royal,’ and ‘Crimson Seedless’) actually used to produce grape juice in Apulia. Anthocyanins were the main flavonoids in the colored grapes, and highly significant quantitative differences (Fcultivar × vintage = 25,461; p < 0.001) in their profile were found; moreover, elevated levels of flavonols and flavan-3-ols were also quantified in all the varieties. According to HCA, cultivars were grouped into two clusters: one including ‘Michele Palieri,’ ‘Summer Royal,’ and ‘Autumn Royal,’ mainly characterized by the presence of anthocyanidins acetyl and coumaroyl glucosides, and the other formed by ‘Crimson Seedless,’ ‘Carati,’ ‘Sugraone,’ and ‘Italia,’ with relatively elevated level of procyanidins as well as quercetin and kaempferol derivatives; furthermore, PCA allowed to differentiate either ‘Michele Palieri,’ the only containing epicatechin, from the other colored cultivars, or ‘Italia,’ thanks to its higher content of quercetin-3-O-glucoside, from the other white grapes. Considering these results, the black cultivar ‘Michele Palieri’ has the highest suitability for the production of grape juice with nutraceutical properties.