In-berry tissue distribution and extraction kinetics of phenolics in novel PIWI red-skinned varieties

Abstract

Although already characterized from an agronomical point of view, the chemical and compositional aspects of new resistant grapevine varieties have limitedly been subjected to in-depth investigation. The aim of this study was to evaluate both the tissue distribution of phenolic compounds and color features, and their extraction kinetics in Termantis and Nermantis. These PIWI varieties, obtained from a cross between Teroldego and Merzling -and subsequently backcrossed- have been recently registered in Italy, and listed in the National Register of grape varieties authorized for wine production.

For each, ten different bunches were hand-destemmed, and twenty berries were randomly picked for each of the biological triplicates used. The composition of seeds and skins of Nermantis and Termantis coming from four different experimental plots were compared to those of several Vitis vinifera cultivars, including Teroldego. Extractions were performed in a buffered simil-must solution at pH 3.4, with incremental ethanol additions to simulate alcoholic fermentation. Over a 15-day period, total phenolic content (Folin–Ciocalteu assay), optical densities, and methylcellulose-precipitable tannins were monitored every 24 hours. BSA-reactive tannins and CIELab color parameters were also measured at the end of maceration. In addition, CIELab parameters, optical densities, and total polyphenol index were evaluated daily during a standardized vinification process conducted on seven different plots for both Nermantis and Termantis.

Only slight differences were observed in total phenolic extraction between Nermantis and Termantis. Both resistant varieties displayed higher total phenolic contents than all Vinifera cultivars, as reported by Cappello et al., (2025), apart from Lagrein, that showed comparable total extraction. Tissue partitioning displayed that phenolic compounds were located in the skins accounting for approximately 64% in both varieties, similarly to Lagrein.

Phenolic extraction kinetics in Nermantis and Termantis were fast, with over 75% of the total content of skins extracted by the fifth day of maceration and a plateau reached by day ninth. During standardized vinification, extraction followed a linear trend, with over 90% of total phenolics released by the fourth day and color intensity peaking on the same day, remaining stable until the end of maceration. Both phenolic and color extraction kinetics were consistent with those observed during simulated maceration.

At the end of vinification, both PIWI varieties wines were rich in polyphenols, with Termantis being significantly higher in total polyphenols and anthocyanins than Nermantis, and both exceeded their parent cultivar Teroldego in total polyphenol concentration.

References

Cappello, N., Gallo, A., Bellini, T., Bruni, F., Agapov, R., Stefanini, M., Bettalli, V., Dorigatti, C., Masuero, D., Mittempergher, A., & Roman, T. (2025). Chromatic characteristics of Nermantis and Termantis wines from traditional and withered grapes • IVES. https://ives-openscience.eu/55794/