## 2 Results and Discussion
### Volatile Organic Compounds (VOCs)
#### 2.3.1. Varietal Aroma Compounds  
In general, terpenoids with unique aromas and flavors are the main variety of aroma compounds and can add complex flavors and layers to a fruit wine [45]. Eight kinds of terpenids were identified in six strawberry wines, accounting for 42.96-54.92% of the varietal aroma compounds and 2.63-4.07% of the total aroma compounds (Table S1). The relative contents of linalool, \(\alpha\)-terpinol, and trans-nerolidol (1, 6, 10-Dodecatrien-3-ol, 3, 7, 11-trimethyl-, (E)-) were relatively high, accounting for 53.96-74.33%, 8.01-14.43%, and 7.52-26.26% of terpenoids, respectively. Linalool was the primary contributor of fruits and floral aromas to strawberry wines, the OAVs of which were 34.45-52.78 (Table 3). The OAVs of myrtenol in NJ, 50J, 50 PJ, and NM strawberry wines were 1.13-2.95 (Table 3). It has a floral and minty aroma and has been reported as the characteristic aroma of blueberry [36] and blackberry [46]; hence, it was also the characteristic aroma in those wines. Terpenes are affected by many concurrent processes taking place during mash fermentation: their extraction from fruit skins, hydrolysis of bound forms, conversions induced by yeasts, and loss by adsorption onto solids [47]. NM strawberry wine contained the highest level of terpene compounds (122.53 \(\upmu\)g/mL) (Figure 3A) and total terpene OAVs (Table 3), followed by PJ (1064.75 \(\upmu\)g/mL) and 50J (931.98 \(\upmu\)g/mL) strawberry wine (Figure 3A); however, the total OAVs of terpenoids in the 50J strawberry wine were higher than that of PJ (Table 3). The other three samples had levels below 800 \(\upmu\)g/mL. As a result, it might be that the three treatments of fermentation with pulp, thermal maceration, and enzymatic hydrolysis promote the release of terpene precursors from the skins, and then further release these compounds via acidosis or enzymatic hydrolysis during the fermentation process. Figure 3. The total relative concentration of volatile compounds within the different aromatic families: varietal aroma compounds (**A**), fermentative aroma compounds (**B**), and total aroma compounds (**C**). Values identified by the same letters were not significantly different at the 0.05 level (one-way ANOVA–Dunace). However, the contents of terpenes in fermented strawberry wine with skin were not all high, and the contents of PM strawberry wine fermented with skin and pectinase were reduced to 828.44 \(\mathrm{\SIUnitSymbolMicro g}\)/mL. The reasons for these results are worth exploring in the future. The second highest relative content variety aroma component was C6 compounds, accounting for 25.43-40.60% of varietal aroma compounds and 1.48-3.52% of total VOCs (Table S1). The OAVs of two out of three C6 compounds (hexanol and nonanol) were around 0.1, which were the main contributors to the green aroma in berries and wines, and could result from the enzymatic degradation of unsaturated fatty acids in the berries and glycosidic aroma precursors [45]. Their concentration depends on the variety, ripeness stage, treatments prior to fermentation, and temperature/duration of contact with the skins. Similarly to those described for terpenoids, must maceration increased the relative content of this type of compound by 29.43-128.96% in NM strawberry wines compared to other samples (Figure 3A). A significantly higher relative concentration of C6 compounds was found in NM and PM wines (Figure 3A), as a consequence of more oxygen being dissolved in the aqueous medium during the pre-fermentation step, which favored the formation of C6-aldehyde precursors by the LOX/HPL pathway [48]. Red wines produced by thermovinification (pre-fermentation, 20 min at 75 \(\mathrm{\SIUnitSymbolCelsius}\)) exhibited lower amounts of C6-compounds in relation to those fermented at normal temperature as a result of the inactivation of lipoxygenase activity by heat [15], and the same was found in this experiment in 50J wines (Figure 3A).