Texture characteristics of the grape berry skin and seed (Vitis vinifera L. cv. Kékfrankos) under postveraison water deficit

Abstract

Water deficit has a great impact on grape and wine composition. One aspect of phenolic maturity in red grapevine cultivars is skin phenolic concentration (i.e. anthocyanins). However, extractability of these components is also an important factor during wine making; therefore skin and seed texture properties have a role in this process. Six-year-old Kékfrankos grapevine (Vitis vinifera L.) was submitted to different water regimes (severe, moderate and nil stress) from veraison under greenhouse conditions. Berry quality parameters (sugar and skin phenolic concentration), skin and seed texture properties were measured by a texture analyser at two harvest dates. Water deficit resulted in decreased photosynthetic activity; therefore non-stressed plants produced higher sugar concentration in their berries compared to the stressed vines. Also, water deficit induced increased phenolic concentration in the skin. However, moderate stress treatment showed higher anthocyanin, catechin and total polyphenol concentration than in the severely stressed berries. A significant increase of skin thickness of the stressed berries was observed during ripening; however, no clear relationship was found between skin thickness and its phenolic concentration. Skin break force as well as skin break energy and skin rigidity presented a significant increase as a result of water shortage. No relationship was found between skin thickness and skin hardness. This result suggests that grape skin mechanical properties are dependent on skin structure rather than its thickness. Similarly, there were significant differences among the treatments in seed mechanical properties; however the effect of water stress disappeared by the second harvest.