Evolution of grape berries during ripening : investigations into the links between their mechanical properties and the extractability of their skin anthocyanins

International audienceAims: The aim of this work was to study the evolution of grape berries during ripening and investigate the possible relationship between the extractability of anthocyanins from grapes and their rheological properties. Methods and results: Cabernet Franc grapes belonging to three different vineyards were harvested weekly from 10 September to 8 October 2007. Their mechanical behavior was measured by compression and puncture tests and the evolution of anthocyanin extractability was monitored during ripening. Significant differences were found in grape textural attributes and anthocyanin content due to the ripening stage and type of vineyard. A multivariate regression model was built to explain the evolution of anthocyanin extractability, by using the mechanical attributes of grape berries as variables. Conclusion: Our results show that differences in the easiness of anthocyanin extraction from grapes could be linked to differences in the mechanical behavior of berries and that the extraction yield of anthocyanins from grapes could be predicted by their rheological properties. To confirm this first hypothesis, further studies with a larger number of vintages and vineyards would be necessary to link the mechanical properties of grape berries, established at macroscopic scale, to the susceptibility of anthocyanin extraction from grape skin. Significance and impact of the study: The need to understand the evolution of the mechanical behavior of winegrapes during ripening and its impact on the release of anthocyanins is important for wine quality control. Understanding the evolution of the material properties of grapes is essential for developing better approaches to improve grape quality and could help winemakers to choose the best time of harvest and the process best adapted to the wine quality desired

Relationships between skin flavonoid content and berry physical-mechanical properties in four red wine grape cultivars (Vitis vinifera L.)

Flavonoids are a class of bioactive compounds extremely important in food and wine industry. The development of rapid methods for their quantification in grape berries is one of the modern challenges in viticulture and enology research. Total flavonoid (TF) amount changes during grape ripening and also berry physicalmechanical properties, as evaluated by instrumental texture analysis, change in the same period. In this work, TF and berry physical-mechanical parameters were linked together through predictive models. Models were developed for each of four red wine grape cultivars: Brancellao, Cabernet Franc, Menc\ueda and Merenzao, and another one considered all cultivars together. These models reached high accuracy and allowed to predict TF in grape berries with a low error (RMSE from 0.15\ub10.07mgg-1 to 0.35\ub10.10mgg-1 in prediction, as evaluated by cross-validation).Berry weight (BW) was the parameter having the largest influence on TF predictions, and also was the only variable having part in all models. BW and chewiness had a similar behavior and when berry weight was excluded, chewiness was able to substitute its role in all models. The other physical-mechanical characteristics displayed a different behavior across cultivars.In conclusion, this work shows that it is possible to predict TF from physical-mechanical predictors in grape berries and that cultivar specific models reach higher accuracy for this purpose than the multi-cultivar model

Influence of wine-grape skin hardness on the kinetics of anthocyanin extraction

The main aim of this work was to study in a model, hydroalcoholic solution containing 12% of ethanol and with a pH of 3.20, the kinetics of anthocyanin extraction from Vitis vinifera L. cv. Nebbiolo berries of different skin hardness. This mechanical property was evaluated as the breaking skin force measured by Texture Analysis, a rapid and low-cost analytical technique. Using a TAxT2i Texture Analyzer, a puncture test was carried out on two groups of berries separated according to their density by flotation in order to obtain more homogenous samples and minimize the effect of different stages of ripening of the berries. Among the berries containing 242 \ub1 8 g/L of reducing sugars in the pulp juice, two groups of berries with different skin hardness were selected: soft (0.26 \ub1 0.04 N) and hard (0.47 \ub1 0.05 N). In our experimental conditions, at the end of maceration, the extracts from the higher skin hardness group showed the higher contents of total anthocyanin: +25 mg/L (+9.4%). The anthocyanin profile of extracts, obtained at different extraction times, showed no significant differences among the distribution of different anthocyanins. Only in the early phases of dissolution, did the extracts reveal a dissimilar anthocyanin profile and in the extracts of hard skins higher percentages of cyanidin and peonidin derivatives were present. Additionally, the evolution of skin mechanical properties from veraison to overripe and the influences of biotype on these parameters at harvest are reported in this work

Transcriptome analysis during ripening of table grape berry cv. Thompson Seedless.

Ripening is one of the key processes associated with the development of major organoleptic characteristics of the fruit. This process has been extensively characterized in climacteric fruit, in contrast with non-climacteric fruit such as grape, where the process is less understood. With the aim of studying changes in gene expression during ripening of non-climacteric fruit, an Illumina based RNA-Seq transcriptome analysis was performed on four developmental stages, between veraison and harvest, on table grapes berries cv Thompson Seedless. Functional analysis showed a transcriptional increase in genes related with degradation processes of chlorophyll, lipids, macromolecules recycling and nucleosomes organization; accompanied by a decrease in genes related with chloroplasts integrity and amino acid synthesis pathways. It was possible to identify several processes described during leaf senescence, particularly close to harvest. Before this point, the results suggest a high transcriptional activity associated with the regulation of gene expression, cytoskeletal organization and cell wall metabolism, which can be related to growth of berries and firmness loss characteristic to this stage of development. This high metabolic activity could be associated with an increase in the transcription of genes related with glycolysis and respiration, unexpected for a non-climacteric fruit ripening