## 4 Discussion
Only one of the fermentation-derived compounds (phenylethyl alcohol) was selected as marker using the SPME dataset, while five (phenylethyl alcohol, cinnamyl alcohol, ethyl benzoate, 3-hydroxy-benzeneethanol and benzenepropanol) were selected using the SPE dataset. It was possibly due to the different selectivity of the extraction methods, since SPME showed very poor affinity to benzenepropanol and 3-hydroxy-benzeneethanol as well as cinnamyl alcohol. The mass peak intensities of cinnamyl alcohol and benzenepropanol were higher in the MBW, while ethyl benzoate, phenylethyl alcohol, and 3-hydroxy-benzeneethanol were higher in the OBW. Among them, phenylethyl alcohol was often reported as a potential aroma compound in wine, which has a rose-like aroma [46; 47]. The profile of fermentation-derived compounds, including alcohols, esters, acids, ketones, and volatile thiols identified in the blueberry wine were similar with those reported in the grape wines. Higher alcohols and esters mainly contribute to the fruity aroma of wine. They can be synthesized by yeast through anabolic pathway from glucose, or catabolic pathway from their corresponding amino acids [48]. As a result, their production in wine is highly dependent on the yeast stain, must YAN, fermentation temperature, and oxygen availability [49]. Since the yeast strain, DAP addition, and fermentation condition were the same in the blueberry winemaking, the differences in fermentation-derived aroma was probably associated with the different YAN of the two cultivars (Table 1), which was also a part of the cultivar characteristics. It was interesting that these fermentation derived compounds were all volatile molecules with the structure of a benzene ring, which might be associated with the metabolization of aromatic amino acids, such as tyrosine, phenylalanine, or tryptophan during fermentation [50; 51], indicating the possible differences of aromatic amino acid composition of the two blueberry varieties. Generally, more of the important features detected in OPLS-DA were berry-derived compounds such as linalool, which has the notes of rosy and fresh fruit, and has a very strong organoleptic contribution in blueberries [15]. Besides linalool, many other terpen were also selected by either one of the two OPLS-DA models, such as \(\alpha\)-terpineol, p-mentha-1(7),8(10)-dien-9-ol, terpinolene, \(\beta\)-citronellol, and p-menth-9-en-3-ol, which was in agreement with previous report that terpen were important aroma compounds in highbush blueberries and their concentration varied with cultivar [11; 15; 52]. Interestingly, we found that OBW contained several berry-derived semi-volatiles such as methyl eugenol, methyl isougenol, (\(E\))-asarone, and (\(Z\))-asarone, which did not exist in MBW (Table 2). Methyl eugenol and methyl isougenol are isomers, which are naturally occurring flavors and fragrances found in a variety of different food sources, including spices (nutme, allspice), herbs (basil, tarragon), and fruit, including bananas and oranges [53; 54]. Methyl eugenol is also one of the plant metabolites used for defense against herbivores and pathogens as well as attracting pollinators [54]. Eugenol, isouegenol, methyl eugenol, and methyl isouegenol share the initial biosynthetic steps with the lignin biochemical pathway [55]. Eugenol and isouegenol can undergo further methylation and require O-methyltransferases for the downstream production of methyl eugenol and methyl isouegenol [56]. In the present study, eugenol and isouegenol were found in both blueberry wines, but methyl eugenol and methyl isouegenol were only found in OBW, indicating the possible O-methyltransferaseness activity difference among the two cultivars, which needs to be confirmed in the future studies. (\(Z\))-Asarone has been found in glycoside form in pineapple wines [57]. It has also been reported as bioactive compounds in some of the medicinal plants such as rhizomes of _Acorus gramineus_[58].