Influence of adjuvants used in viticulture on the final quality of wines

Abstract

The effect of global warming and water stress on Mediterranean vineyards has prompted the search for strategies to counteract the damage associated with sunburn of grapes and leaf dehydration of vines. Exposure promotes biochemical changes in the phytochemical composition of grapes affecting the final quality of wines. Also, the vine may exhibit physiological changes caused by heat-induced stress. To decrease the surface area exposed to the sun, the use of inert materials – like kaolin- applied to leaves, grape steams and berries has become a viable strategy. Kaolin can reflect solar radiation preventing sunburn and reducing the surface temperature of the vine structures. This effect results in less water loss in the plant and avoiding negative changes in the grape’s composition that could affect the desirable qualities of the wine. The amount of kaolin applied is usually between 1 and 5 % and is carried out after flowering when temperatures rises. During the harvest, mainly through mechanical collection, the grapes are often accompanied by other parts of the vine (leaves, stems), so the residual presence of kaolin is possible during subsequent winemaking stages. Its impact on the phenolic profile during fermentation could affect the organoleptic qualities of wine – like color, which is provided by anthocyanins in red wines-. This research explores the influence of added kaolin on the anthocyanins profile of experimental young Malbec red wine. Degradation parameters of anthocyanins from experimental red wine stored with 3 different kaolin percentages (3,5 and 10 % w/v) over 130 days were determined. Total anthocyanins (T-ACN) were quantified by UV-Vis at 520 nm. Degradation of T-ACN followed first-order kinetics. The reaction rate constant (k value) showed that the degradation rate was highest in the experimental red wine with 10 % kaolin (6.263·10-3 d-1), followed by the wine with 5 % (6.064·10-3 d-1), 3 % (4.509·10-3 d-1) and finally, the wine without additive (1.849·10-3 d-1). Half-time of T-ACN was highest in the control red wine (374.8 d), followed by wine with 3 % kaolin (153.7 d), 5 % (114.3 d) and finally, the wine with 10 % of additive (110.6 d). In addition, the  malvidin-3-glucoside/malvidin 3-O-(6-O-p-coumaroyl) glucoside ratio in experimental red wines was monitored using HPLC-DAD.