Analysing the impact of the nature of the nitrogen source on the formation of volatile compounds to unravel the aroma metabolism of two non-Saccharomyces strains.

Even though non-Saccharomyces yeasts were regarded as spoilage microorganisms for a long time, their abilities to improve and diversify the aromatic profile of wines are now well recognized. Consequently, their use in combination with S. cerevisiae strains during winemaking has attracted substantial attention over the last decade. However, our limited understanding of the metabolism and physiology of these species remains a barrier to promoting efficient exploitation of their full potential. In this study, we further explored the metabolism involved in the production of fermentative volatile compounds of two commercial non-Saccharomyces strains, T. delbrueckii Biodiva™ and M. pulcherrima Flavia®, in comparison with the reference wine yeast S. cerevisiae Lalvin EC1118®. After growing these strains in the presence of 24 different N-compounds, particular attention was paid to the influence of the nitrogen source on the profile of aroma compounds synthesized by these yeasts (higher alcohols and acids, medium-chain fatty acids and their acetate or ethyl esters derivatives). A comprehensive analysis of the dataset showed that these three species were able to produce all the fermentative aromas, regardless of the nitrogen source, demonstrating the key contribution of the central carbon metabolism to the formation of volatile molecules. Nevertheless, we also observed some specific phenotypic traits for each of the strains in their assimilation capacities for the various nitrogen nutrients as well as in their response to the nature of the nitrogen source in terms of the production of volatile molecules. These observations revealed the intricacy and interconnection between the networks involved in nitrogen consumption and aroma production. These differences are likely related to the genetic backgrounds of the strains. Overall, this study expands our understanding of the metabolic processes responsible for the formation of volatile compounds during wine fermentation and their variations according to species and the nature of the nitrogen source. This knowledge provides a new platform for the more efficient exploitation of non-Saccharomyces strains during winemaking, improving the management of the fermentation.