Berry heterogeneity as a possible factor affecting the potential of seed mechanical properties to classify winegrape varieties and estimate flavanols release in wine-like solution.

Seed mechanical properties were instrumentally measured by compression tests in thirty white and red winegrape varieties at harvest. The effect of the berry heterogeneity in a vineyard on these seed texture parameters was also evaluated to improve the understandings of intra-sample variability. Furthermore, the mechanical properties of the seeds were assessed as possible predictors of their phenolic extractability. The results showed that the texture parameters of the seeds are independent of the location of the berry in the vineyard and the soluble solid content at harvest. Density flotation of the berries permits to reduce the intra-sample variability that could hinder the differentiation and/or classification of winegrape varieties according to the seed mechanical attributes. Cluster analysis classified the winegrape varieties studied in three groups according to the seed hardness (low: 32.51-40.80 N, intermediate: 42.84-44.99 N, high: 46.71-57.78 N). The relationships between the seed mechanical properties and the extractable content of phenolic compounds, determined by spectrophotometric and chromatographic reference chemical methods, were evaluated by means of correlation analysis. The existence of significant correlations that were cluster dependent was conducted to develop linear regression calibration models for each varietal cluster separately. The statistical parameters highlighted that total flavonoids, proanthocyanidins and flavanols reactive to vanillin indices can be successfully predicted, from the seed mechanical properties, for the varieties having low and intermediate seed hardness (SEC% ≈20, RPIQ>1.6). For varieties with harder seeds, a satisfactory predictive accuracy seems to require the construction of separate calibration models for each cultivar (Nebbiolo, SEC% ≈20, RPIQ>2.2).