Application of protective agents in Nebbiolo vines and effects on grape secondary metabolites

Abstract

Within a context marked by climate change–related abiotic stresses, grapes are more exposed to excessive heat and solar radiation causing sunburn damage with visual and organoleptic alterations in the berries and resulting wines. Sustainable approaches, including the application of foliar protective products in the vineyard, represent potential options for preserving grape quality and protecting wine quality and typicity. This research evaluated the impact of foliar application of anti-stress agents (kaolin 3 %, 6 %, and zeolite) on the polyphenolic and aromatic composition of Nebbiolo grapes for Barolo production, across two consecutive seasons marked by different ripening meteorological conditions. Kaolin and zeolite were applied at different time points after veraison following a two- or three application protocol during two consecutive vintages (2024, 2025).  Quantitative determination of grape aroma precursors was carried out using GC-MS, whereas polyphenols in skins and seeds were analysed by spectrophotometric and HPLC methods. In mild ripening conditions (2024), the 6 % kaolin treatment reduced polyphenol levels, especially anthocyanins in Nebbiolo skins and total polyphenols and flavonoids in seeds, compared to the control. Under stress conditions (2025), no significant differences were observed in skins, but seeds of kaolin and especially zeolite treatments showed higher polyphenol and flavonoid content. Although the similar sugar contents were observed across treatments, zeolite treatments resulted in higher total acidity while kaolin 3 % showed higher malic acid levels. Aroma precursors (norisoprenoids) were highest in the 3 % kaolin treatment, though differences were not significant. Climatic and meteorological conditions play a critical role in determining the effectiveness of protective product applications designed to mitigate climate change impacts. Further research including vinification and sensory evaluation of the resulting wines must be conducted. Such studies will help determine the practical relevance of these protective applications under varying climatic conditions and guide their optimal use in vineyard management.

References

Andriani Asproudi, M., Petrozziello, M., Cavalletto, S., & Guidoni, S. (2016). Grape aroma precursors in cv. Nebbiolo as affected by vine microclimate. Food Chemistry, 211, 947–956. https://doi.org/10.1016/j.foodchem.2016.05.070