Changes in phenolic maturity and texture characteristics of the grape berry under pre-, and post-veraison water deficit

Abstract

Context and purpose of the study – Kékfrankos (Vitis vinifera L.) grapevines grafted on Teleki-Kober 5BB rootstock were submitted to water deficit under greenhouse conditions. The aim of the experiment was to study the effect of pre-, and post-veraison water deficit on grape berry phenolic maturity and texture characteristics.

Material and methods – Plants were planted into 50L white plastic containers in a mixture of perlite (20 %), loamy soil (30 %) and peat (50 %) (v/v). Three regimes of water supply were examined: (1) moderate water deficit from berry set until veraison (WD1), (2) moderate water deficit from veraison until harvest (WD2), (3) no water deficit (C). The water deficit treatments defined by the leaf daily stomatal conductance (between
50-150 H2O mmol m-2s-1). Anthocyanin glucosides and flavonols from berry skin were measured by Shimadzu HPLC system, berry texture characteristics were monitored by TA.XT Plus Texture Analyser. Cell and seed maturity indexes (CMI %, SMI %) and basic parameters (yield, sugar concentration, pH, must acidity) were also investigated.

Results – Pre-veraison treatment resulted in the lowest berry and cluster weight. The highest sugar concentration was found in control berries, and it was followed by the WD1 and WD2 treatments. Berries of the well-watered plants presented the lowest phenolic concentration. Pre-veraison water deficit resulted in a sllighty higher concentration of anthocyanin-glucosides compared to post-veraison water deficit. Water restriction during the ripening period induced higher flavonol (ie. quercetin, kaempferol etc.) concentration related to berry skin fresh weight as well as to the whole berry compared to WD1 treatment. Berry skin hardness (Fsk) was the highest in the case WD2 and the lowest was in WD1. Similar results were obtained in the case of berry skin thickness (Spsk). Seed (SMI %) maturity index presented higher values in the case of WD treatments compared to C. Cell maturity index (CMI %) of WD2 was significantly higher than C and WD1, however no differences were found between C and WD1.