Study of the volatile aroma profile of five Italian grape varieties submitted to controlled postharvest withering

Abstract

Wines made with grapes submitted to postharvest dehydration are often referred to as “passito” or “straw wines.” This distinct style of winemaking consists of a process of water loss that allows the berries to undergo a mild water stress and senescence process [1]. Several factors can influence the dehydration kinetics of grapes, some related to the environmental conditions (temperature and relative humidity) and others to the grape characteristics (surface area/volume ratio, skin thickness) [2]. Postharvest dehydration introduces important physicochemical changes and stress to the cell, triggering modifications of genes involved in the formation pathways of many volatile compounds and their precursors [3].

This work aimed to evaluate the aromatic evolution of five Italian grapes varieties (‘Aleatico,’ ‘Corvina,’ ‘Moscato di Scanzo,’ ‘Nebbiolo,’ and ‘Sagrantino’) subjected to controlled postharvest dehydration (T 14-15 °C, RH 40-50%). Grapes at different stages of dehydration (0%-fresh, 10%, 20%, and 30% weight loss) were macerated in a hydroalcoholic solution to extract volatile compounds. Analyses were carried out by GC-MS and SPE/SPME for the identification and quantification of free and glycosidically bound compounds belonging to terpenes, norisoprenoids, volatile phenols, and C6 alcohol classes. Results were normalized according to weight loss in order to eliminate a concentration effect. A variety-dependent behavior was found in terms of both accumulation/degradation of aroma compounds and dehydration kinetic. For Sagrantino, the highest levels of terpenes were observed at 30%, while for norisoprenoids and volatile phenols, at 10%. For Nebbiolo, high levels were found for free and bound norisoprenoids (0% and 20%) and for free and bound C₆ alcohols (10% and 30%). For cv. Corvina and Moscato di Scanzo, the highest levels of free compounds were found in fresh grapes; regarding the bound compounds, a similar behavior was observed with a maximum accumulation at 10% and 20%. In Aleatico, the highest levels were found in free and bound norisoprenoids (10%) and free volatile phenols (10%). In conclusion, postharvest dehydration can be an important factor modulating the aroma profile of grapes. This effect is complex and varies depending on the degree of dehydration and the class of compounds. In most of the cases, free compounds decreased at 30%, indicating that at this level, compounds can start to degrade. Instead, glycosidically bound compounds accumulate at 10 and 20%, which can be a source of aroma potential that later can be released during fermentation and aging.

Acknowledgement

This study is part of the STRAWINE project funded by the Italian Ministero dell’Università e della Ricerca (PRIN project no. 20223K8EJP). Funded by the European Union – NextGenerationEU.

References

[1] Sanmartin, C., et al. “Postharvest Water Loss of Wine Grape: When, What and Why. Metabolites 2021, 11, 318.” (2021).

[2] Barbanti, Davide, et al. “Effect of various thermo-hygrometric conditions on the withering kinetics of grapes used for the production of “Amarone” and “Recioto” wines.” Journal of Food Engineering 85.3 (2008).

[3] Zenoni, Sara, et al. “Disclosing the molecular basis of the postharvest life of berry in different grapevine genotypes.” Plant Physiology 172.3 (2016).