Potentialities of wine yeasts to produce unusual aromas during fermentation
Résumé
A current challenge for the beverage sector, due to the highly competitive worldwide market, is to diversify the range of products and to offer wines and spirits with typicity and character. Wine aroma is a complex mixture of one thousand molecules, with four origins : varietal, pre-fermenta-tive, fermentative and ageing aromas. Secreting hydrolytic enzymes, yeasts contribute to the release of varietal aromas, like thiols. In addition, they are responsible for the synthesis of fermentation aromas. The metabolic pathways involved in the formation of higher alcohols, acetate and ethyl esters, which are the most abundant volatile compounds synthetized by yeasts, have been well characterized. Furthermore , other molecules with a major organoleptic impact can be produced during fermentation. These compounds include terpene derivatives, related to sterol metabolism, benzene derivatives, originating from phenylalanine degradation and lactones coming from β-oxydation of fatty acids. However, little information is available on the yeasts ability to produce these unconventional molecules. This present work aims to provide an overview of the capacities of the yeast species from the enological consortium to produce these unusual aromas. In this study, fermentations were carried out using 41 yeast strains grown on three different musts (Maccabeu, Ugni Blanc, Chardonnay) and a synthetic must, used as control. The profiles of unusual aroma at the end of fermentation were determined by a dedicated Direct Liquid Liquid MicroExtraction (DLLME) GC/MS method, recently developed in the lab. Interestingly, the yeasts are actually able to produce most of the quantified molecules. However, different production profiles were observed depending on the strains, the species. Moreover the cultivars have also a significant impact on the biosynthesis of these aromas. Overall, this study provide new prospects to extend the aromatic palette of wines and to best meet the consumer expectations for wine quality.