Anthocyanin extractability assessment of grape skins by texture analysis

Aims: The aim of this work was to evaluate the kinetics of anthocyanin extraction in berries of cv Brachetto and Nebbiolo, having the same level of total soluble solids, but with different skin hardness. Methods and results: A puncture test was carried out on berries calibrated according to their density, estimated by flotation in different salt solutions. For each variety, two groups of berries of different skin hardness were selected: soft (< medium value) and hard (> medium value). Spectrophotometric and HPLC methods were used to evaluate the kinetics of anthocyanin extraction in a hydroalcoholic buffer solution. In each of the examined cultivars, the grapes with a higher break skin force produced extracts with a higher content in total anthocyanin. The anthocyanin profile of extracts of Brachetto hard skin is characterized by a higher content of acetyl-glucosides. Conclusion: Texture analysis, which is fast and inexpensive, turned out to be an excellent analytical technique to verify skin hardness measurements. The break skin force proved to be a mechanical parameter able to estimate the extractability of anthocyanins with adequate reliability. Significance and impact of study: The possibility of having an easy way to determine maturity index able to estimate the extractability of phenol compounds with sufficient reliability, can be a valuable tool for the enological community.