LAUSR

The vine produces de novo compounds with small molecules, called phytoalexins, as defense response to oxidative stress, microbial infections, and UV irradiation. Such bioactive substances are trans-resveratrol and quercetin. In this study, a rapid HPLC method was developed and validated for simultaneous quantification of both phenolic compounds and was applied for their determination in the grape skins of five grapevine varieties with red berries—two of table grape (Muscat Hamburg and Moldova) and three of wine grape varieties (Plevenski kolorit, Storgosia, and Rubin). All chosen varieties have been grown under conventional practices in the Northern wine region of Bulgaria. The determined amount of trans-resveratrol in the red grape skins ranged from 1.348 ± 0.128 mg kg−1 in samples of Muscat Hamburg to 15.472 ± 0.781 mg kg−1 in samples of Moldova. The lowest average values of quercetin amount were found in grape skins of Rubin—0.724 ± 0.078 mg kg−1 and the highest in Moldova—1.182 ± 0.121 mg kg−1. This method is precise, rapid, and cost-effective and therefore can be applied in quality control of the production of these beneficial for human health substances as food supplements and drugs. Furthermore, it can be used for monitoring of the impact of various environment factors on trans-resveratrol and quercetin accumulation in the grape of different varieties, which will be particularly important for wine scientists and makers.