Phenolic profiles of minor red grape cultivars autochthonous from the Spanish region of La Mancha

Abstract

The phenolic profiles of little known red grape cultivars, namely Garnacho, Moribel and Tinto Fragoso, which are autochthonous from the Spanish region of La Mancha (ca. 600,000 ha of vineyards) have been studied over the consecutive seasons of years 2013 and 2014. The study was separately performed over the skins, the pulp and the seeds, and comprised the following phenolic types: anthocyanins, flavonols, hydroxycinnamic acid derivatives (HCADs), total proanthocyanidins (PAs) and their structural features. The selected grape cultivars belong to the Vine Germplasm Bank created in this region in order to preserve the great diversity of genotypes grown in La Mancha. This study aims to evaluate the enological potential of these minor grape cultivars. Regarding anthocyanins, the three studied cultivars showed the occurrence of the 3-glucosides of the common grape anthocyanidins, with the prevalence of malvidin-based anthocyanins, followed by peonidin derivatives. However, Garnacho showed a characteristic profile in which anthocyanins based on peonidin and malvidin accounted for similar proportions. Among the acylated anthocyanins, the coumaroyl derivatives dominated over the acetylated ones and some minor caffeoyl derivatives were also found. In addition, minor anthocyanidin 3,5-diglucosides were detected, mainly malvidin 3,5-diglucoside, although its coumaroyl derivative was also found in Tinto Fragoso and peonidin 3,5-diglucoside in the case of Garnacho. Tinto Fragoso showed the highest content of anthocyanins in both years. Flavonol profiles were in agreement with those previously described for V. vinifera grapes: the 3-glucosides, the 3-galactosides and the 3-glucuronides of the six common aglycones, namely kaempferol, quercetin, isorhamnetin, myricetin, laricitrin and syringetin. Moreover, high resolution MS and MS/MS evidence of the occurrence of dihexosides of myricetin was found in grapes. The qualitative content of HCADs showed no differences according to grape cultivar and was dominated by caftaric acid. The pulp accumulated most HCADs. The content of PAs in grape skins does not vary according to grape variety and season year, around 8-13 mg/g skin (as catechin). In contrast, the content of PAs in seeds was lower in Moribel (53-58 mg/g, vs. 75-79 mg/g in Garnacho and 81-86 mg/g in Tinto Fragoso), but no differences were found according to season year. The mean degree of polymerization was similar in the three cultivars and two season years: 9-10 for skin PAs and 6-7 for seed PAs. The percentage of prodelphinidins in skin PAs ranged within 17-18% for the three cultivars, whereas the percentage of galloylation in seed PAs was lower in Moribel (13%, vs. 16-17% in the other two cultivars). Finally, the season year of 2014 was characterized by adverse climatic conditions with regards to the development of grapes and the contents of anthocyanins and flavonols were affected showing lower concentrations for the three grape cultivars.