## 1 Introduction  
Grape must is a very complex medium, with at least 200 g/L of sugars and hundreds of other grape metabolites, including amino and non-amino organic acids and fatty acids with concentrations varying from ng/L to g/L [1,2]. It is well-known that the composition of mustas has a vital role in determining the aroma profile that is produced by the fermenting yeast. Even small changes in the must composition could result in a critical effect on the growth and metabolism of wine yeasts, and thus alter the formation of aroma compounds [3]. Numerous studies have been conducted to determine the role of major compounds (such as sugar and amino acid) during wine fermentation [2; 4; 5], however, little information is available on unsaturated fatty acids (UFAs). In fact, as the essential nutrients for yeast to grow under anaerobic conditions, UFAs are crucial for yeast to maintain membrane integrity, as well as the function to adapt well to fermentation stresses [6]. More importantly, UFAs can directly affect the formation of volatile compounds (including medium-chain fatty acids (MCFAs) and esters) by regulating the synthesis of precursor acyl-CoA and the expression of related genes [7; 8; 9]. Grape berries contain 0.15% to 0.24% (wet weight basis) lipids [10]. UFAs are the major components of the total lipids in grape berries, in which linoleic acid (C18:2, LA) is the most abundant, followed by oleic acid (C18:1, OA) and \(\alpha\)-linolenic acid (C18:3, ALA). Their content varied from 0.04 mg/L to 280 mg/L in grape must, and changed with the grape cultivars [11; 12], fermentation technologies, such as grape must clarification and grape-skin maceration [13]. In comparison, the fatty acids of _Saccharomyces cerevisiae_ are mainly made up of OA and palmitoic acid (C16:1), together with the saturated fatty acids (SFAs), palmitic acid (C16:0), and stearic acid (C18:0) [9]. Due to lacking \(\Delta\)12-fatty acid desaturase and \(\omega\)3-fatty acid desaturase, _S. cerevisiae_ cannot produce polyunsaturated fatty acids (PUFAs), such as LA and ALA [9]. However, during wine fermentation, the absence of oxygen suppresses fatty acid desaturation of yeast. An alternative to the biosynthesis is the direct uptake of UFAs from the grape juice. The incorporate exogenous fatty acids into cells can significantly modify the lipid composition of the cells and influence the physiological status and metabolism of yeast [9; 14; 15; 16]. Several studies had investigated the effect of exogenous UFAs on wine aroma biosynthesis; however, the results were not consistent. For example, the addition of OA (31 mg/L) and ergosterol (25 mg/L) increased higher alcohols and acetate esters production, except 1-butanol and 1-pentanol, which exhibited an opposite trend [17]. While [PERSON] et al. found that the presence of LA (50 mg/L) can suppress the ethyl esters and acetate esters production [18]. Recently, [PERSON] et al. reported that increasing the concentration of LA (132 mg/L) was unfavorable for acetate esters formation, but improved the productions of higher alcohols [14]. In one study of a synergistic effect, Tween 80, containing 70% of OA and 30% of palmic acid and stearic acid, was added and improved the esters, higher alcohols and volatile fatty acids of wine [19]. Our previous work indicated that the rational controlling of UFAs contents can improve volatile compounds in synthetic grape medium, such as 2-phenylethanol, butanoic acid, hexanoic acid, isoamyl acetate, and 2-phenylethyll acetate [15]. These inconsistent results could be ascribed to the differences of added UFAs concentration, medium composition, yeast strain and fermentation conditions, while the type of UFAs should not be overlooked because the physiological functions of different UFAs are also different. For example, the ability of PUFAs (LA and ALA) to maintain membrane fluidity is higher when compared to monounsaturated fatty acids (MUFAs, such as OA) and thus showed better protection to cells in harsh conditions [15].