Diana De Santis

Temperature and water loss affect ADH activity and gene expression in grape berry during postharvest dehydration

Clusters of Aleatico wine grape were picked at 18°Brix and placed at 10, 20, or 30°C, 45% relative humidity (RH) and 1.5m/s of air flow to dehydrate the berries up to 40% of loss of initial fresh weight. Sampling was done at 0%, 10%, 20%, 30%, and 40% weight loss (wl). ADH (alcohol dehydrogenase) gene expression, enzyme activity, and related metabolites were analysed. At 10°C, acetaldehyde increased rapidly and then declined, while ethanol continued to rise. At 20°C, acetaldehyde and ethanol increased significantly with the same pattern and declined at 40%wl. At 30°C, acetaldehyde did not increase but ethanol increased rapidly already at 10%wl. At the latter temperature, a significant increase in acetic acid and ethyl acetate occurred, while at 10°C their values were low. At 30°C, the ADH activity (ethanol to acetaldehyde direction), increased rapidly but acetaldehyde did not rise because of its oxidation to acetic acid, which increased together with ethyl acetate. At 10°C, the ADH activity increased at 20%wl and continued to rise even at 40%wl, meaning that ethanol oxidation was delayed. At 20°C, the behaviour was intermediate to the other temperatures. The relative expression of the VvAdh2 gene was the highest at 10°C already at 10%wl in a synchrony with the ADH activity, indicating a rapid response likely due to low temperature. The expression subsequently declined. At 20 and 30°C, the expression was lower and increased slightly during dehydration in combination with the ADH activity. This imbalance between gene expression and ADH activity at 10°C, as well as the unexpected expression of the carotenoid cleavage dioxygenase 1 (CCD1) gene, opens the discussion on the stress sensitivity and transcription event during postharvest dehydration, and the importance of carefully monitoring temperature during dehydration.

Biochemical Markers for Enological Potentiality in a Grapevine Aromatic Variety under Different Soil Types

Pedoclimatic conditions affect grape and wine quality. In particular, the relationship between soil and grape quality is at the core of the terroir definition. The study focuses on cv. Aleatico, an aromatic and autochthonous grapevine cultivar grown in the northern part of the Latium region (central Italy) in a heterogeneous environment (Protected Denomination of Origin Aleatico di Gradoli). Five subareas were selected to represent the environmental variability. The grape-ripening parameters, along with volatile and phenolic compounds in wines derived from the grapes from these growing areas, were analyzed to assess the relationship between soil traits and biochemical grape and wine parameters. Pedoclimatic analysis was carried out following official protocols for determination of soil texture and calculation of bioclimatic Thermal Index of Winkler. Solid-phase microextraction with gas-chromatographic and standard methods were used to measure volatile and phenolic compounds, respectively. Data were evaluated using descriptive statistical methods (analysis of variance and Pearson’s coefficient) and multivariate statistical analyses (principal component analysis and hierarchical cluster analysis). The results showed a significant ‘soil effect’ on the biochemical composition of the grapes and wines. The soil had a significant effect on grape-ripening parameters, as the soil sand content (%) was highly correlated with concentration of total soluble solids and phenols. Soils with a sandy-loam texture and moderate skeleton content yielded the best wine performance in terms of aroma and phenolic content. The study highlighted the importance of microzonation, even in small winegrape growing areas, for more diverse and competitive wine production. The study enhances knowledge about the relationship between soil and grapevine aromatic varieties. Data indicated that identifying biochemical parameters may be indicators of enological potential according to geographic origin.