COMPOSITIONAL AND STRUCTURAL ASPECTS OF SUNBURN INGRAPE BERRIESASPECTS COMPOSITIONNELS ET STRUCTURELS DU SOLEIL EN BOIS DERAISINS

Abstract:  In recent years, sunburn has become a major concern to viticulture throughout the world. Given that grapevines differ in heat tolerance, the incidence of sunburn is likely to vary among different cultivars. Therefore, the objective of this study was to determine if grapevine cultivars varied in tolerating overexposure of sunlight and temperature by analyzing skin characteristics and fruit composition among red (Merlot, Syrah, Cabernet Sauvignon, Grenache, Sangiovese, and Cabernet Franc) and white (Riesling, Chardonnay, and Gewurztraminer) cultivars. Study showed that the symptomatology of sunburn between red and white cultivars varied; in red cultivars, color development was poor whereas brown lesions appeared on the skins of white cultivars. In all cultivars, the exposed surfaces lost their crystalline structure of epicuticular wax resulting in a shiny surface. The wax platelets were transitioned into amorphous masses with rough surface morphology. The flesh cells incurred losses in cell viability. With respect to composition, generally sunburned berries in all cultivars dehydrated, consequently Brix increased, on the other hand, the acids were lost to respiration. The study revealed that the degree of quality deterioration due to sunburn varied and was a function of berry structure and physiology. Keywords: Anthocyanins, organic acids, sugars, tannins, Vitis vinifera

Keywords: Anthocyanins, organic acids, sugars, tannins, Vitis vinifera