Effect of water deficit on the volatiles profile of Merlot, Pignolo, Tocai friulano and Ribolla gialla wines

Changes in the water status of a plant have an explicit response on grape composition and as a result on wine quality. In this study we evaluated the effect of water deficit on the aroma profile of Merlot, Pignolo, Tocai friulano and Ribolla gialla wines. In 2011 and 2012, field experiments were conducted at the experimental farm of the University of Udine (north-eastern Italy). From berry set to harvest, control plants were weekly irrigated and water deficit plants were not irrigated. At harvest grapes were collected and wine were produced using standardized micro-vinification procedures, respectively for white and red grapes. The analyses of the VOCs profile were performed on a Trace GC Ultra gas chromatograph coupled with a TSQ Quantum Tandem mass spectrometer (Thermo Scientific). Extraction of the free and bound aromatic compounds were completed according to Vrhovsek et al. [1]. Principal component analysis (PCA) showed that wines produced from different varieties had a distinct aroma profile. In all the varieties, water deficit promoted the accumulation of terpenes. Specifically, water deficit increased the concentration of linalool and its oxide (A, B and C), cis and trans- 8-OH-linalool, nerol, geraniol, and 7-OH-geraniol. In 2012, when the water deficit was particularly severe, the effect of water deficit on wine composition was greater. In 2012, 2-aminoacetophenone (2-AAP) was detected in Ribolla gialla wines obtained from water deficit wines. The level of 2-AAP in those wines was over the sensory threshold (1 µg/L). This compound is well known to be responsible of an off-flavour related to untypical aging (UTA). Wines with such a high concentration of 2-AAP are described by sensory panelist with aroma notes of acacia blossom, furniture polish, naphthalene or hybrid grapes. Hence, in Ribolla gialla, severe water deficit may determin a lower wine quality and, eventually, prevent wine commercialization. This study revealed that water deficit can differentially affect wine quality accordingly to the grape variety considered and that, in the context of climatic change, irrigation systems suitable to prevent the most deleterious effect should be considered even in Alpine regions were water availability was historically not considered a major issue.