Management of wine aroma using biotechnical tools

The aroma profile of wine is influenced by a myriad of compounds capable of imparting distinct aromas, commonly known as volatile organic compounds (VOCs). These compounds may originate from grapes, emerge during fermentation, or evolve during aging. Among them, yeast-derived VOCs present a particular appeal for the wine industry as they are linked to pleasant fruity and floral scents and characterize the aroma of young wines. These compounds are formed as a consequence of the normal metabolism of yeast during alcoholic fermentation. However, they are strongly influenced by juice composition, and by grape must and fermentation management. The doctoral research project has focused mainly on the impact of different biotechnologies, normally applied in winemaking, on volatile yeast-derived compounds (VOCs), delving into some interventions that can shape the resulting aroma profile. Three main areas were investigated at winemaking conditions with a multifaceted approach, incorporating fermentation trials, gene expression analysis, and different analytical techniques, including Gas Chromatography-Mass Spectrometry/Mass Spectrometry (GC-MS/MS), Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS) and High-Performance Liquid Chromatography-Fluorescence (HPLC-FLD). VOCs are nonetheless the consequence of yeast metabolism, and some non-conventional yeast present specific features affecting the volatile composition. It was demonstrated in different wines styles the metabolic peculiarities of Hanseniaspora. vineae (white, red and sparkling winemaking) and Lachancea thermotolerans (straw wine). Despite its distinctive biochemist, some criticisms emerged at winemaking conditions that were further managed in terms of inoculum and nutrition management, thus meeting expectations both in terms of metabolic outcomes and industrial needs. But the metabolic features are the result of complex networks regulated by signaling and sensing pathways that coordinate cellular metabolisms. Among those that can be managed at winemaking conditions, oxygen and nutrient supplementation during the growth phase increased the expression of genes linked to amino acid and oligopeptides membrane transporters, and in the expression of β-lyases. This resulted in a faster and higher metabolization of aroma precursors in the fermenting musts and in an increased concentration of some VOCs. Lastly, it was studied the impact on must composition and wine aroma of Aspergilopepsins-I supplementation (AP-I), acid endopeptidases industrially employed to achieve protein stability. Along with some amino acids and di/tripeptides increase in treated musts, and despite the positive outcomes in wines of some yeast VOCs, the necessary heat-shock treatment applied degraded some varietal aromas. To overcome the collateral aroma depletion of must heating, it was explored the efficacy of the combination of AP-I with high power ultrasound. At the lowest energy applied ultrasound promoted AP-I activity, with no evident effect on enzyme degradation.