A supplement of ultraviolet-B radiation under field conditions increases phenolic and volatile compounds of Tempranillo grape skins and the resulting wines

Abstract

Ultraviolet-B (UV-B) supplements have been applied to grapevine in controlled environments but not under field conditions, which would be the only way to manipulate UV-B to provide tangible agronomic benefits. Further, the effects of UV-B supplements should be investigated not only in grapes but also resulting wines, to check whether possible beneficial effects incurred by the raw material are conserved in the elaborated product. In this study, a UV-B supplement was applied to Tempranillo grapes under commercial field conditions, to test its effects on (1) the phenolic composition of grape skins and the resulting wines in two different seasons and (2) the volatile organic compounds (VOCs) of the wines. The UV-B supplement was applied mechanically, using a manufactured lamp mounted on a tractor, to make the application method more realistically viable at a crop scale. Flavonols and antioxidant capacity, and to a lesser extent phenolic acids and flavanols, increased in UV-B-supplemented grape skins and their resulting wines, thus enhancing the quality of both components in wine production. In particular, the augmented flavonols could improve the health properties of grapes and wines, while also contributing to wine color stabilization. In addition, six VOCs were found elevated in the wines elaborated with UV-B-supplemented grapes. Following from these results, we discuss whether these changes were more likely attributable to the irradiance peaks of the supplemental UV-B than to the additional UV-B dose applied. In conclusion, we propose the mechanical application of UV-B supplements on grapevine plants at a crop scale as a new agricultural practice with promising utility, such as counteracting deficits of natural UV-B in specific locations or years.