Abstract
The levels of unsaturated fatty acids (UFAs) in grape must significantly influence yeast metabolism and the production of aroma compounds. In this work, cDNA microarray technology was applied to analyze the transcriptional discrepancies of wine yeast (commercial wine yeast Lalvin EC1118) fermenting in synthetic grape must supplemented with different concentrations of a mixture of UFAs (including linoleic acid, oleic acid, and α-linolenic acid). The results showed that the initial addition of a high level of UFAs can significantly enrich the intracellular UFAs when compared to a low addition of UFAs and further increase the cell population and most volatiles, including higher alcohols and esters, except for several fatty acids. Microarray analyses identified that 63 genes were upregulated, and 91 genes were downregulated during the different fermentation stages. The up-regulated genes were involved in yeast growth and proliferation, stress responses and amino acid transportation, while the repressed genes were associated with lipid and sterol biosynthesis, amino acid metabolism, TCA cycle regulation, mitochondrial respiration, and stress responses. Unexpectedly, the genes directly related to the biosynthesis of volatile compounds did not vary substantially between the fermentations with the high and low UFA additions. The beneficial aromatic function of the UFAs was ascribed to the increased biomass and amino acid transportation, considering that the incorporation of the additional UFAs in yeast cells maintains high membrane fluidity and increases the ability of the cells to resist deleterious conditions. Our results highlighted the importance of UFAs in the regulation of aroma biosynthesis during wine fermentation and suggested that the improvement of the resistance of yeast to extreme stresses during alcoholic fermentation is essential to effectively modulate and improve the production of aroma compounds. A potential way to achieve this goal could be the rational increase of the UFA contents in grape must.
Highlights
The production of aroma compounds during wine fermentation is largely influenced by the nutrition status of grape must
The results showed that the ethanol concentration did not differ between treatments, while glycerol was higher in the high UFA fermentation (HUF) (6.34 ± 0.12 vs. 5.93 ± 0.07 g/L in final samples)
The results of the present work indicate that adding high contents of an unsaturated fatty acids (UFAs) mixture into synthetic grape medium increased cell growth and the production of most yeast-derived volatile compounds compared to the low UFA-added culture, including higher alcohols and the corresponding esters, with the exception of several fatty acids
Summary
The production of aroma compounds during wine fermentation is largely influenced by the nutrition status of grape must. Even a small change in the must composition and nutrition concentration, such as sugar concentration, nitrogen source (amino acids), vitamins and fatty acids, could result in a significant impact on the profile of aroma compounds (Bell and Henschke, 2005; Luan et al, 2018). In this context, the effect of assimilable nitrogen sources (YAN) on the formation of volatile compounds has been investigated exhaustively because changes in the YAN content (ammonium salts or amino acids) have a direct and specific effect on the aroma quality of wine (Marks et al, 2003; Mendes-Ferreira et al, 2007). In a study of this synergistic effect, Tween 80, containing 70% oleic acid and 30% palmic acid and stearic acid, was added to improve the content of esters, higher alcohols and volatile fatty acids of wine (Varela et al, 2012)
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