## 2 Results and Discussion
### Volatile Organic Compounds (VOCs)
#### 2.3.3 Principal Component Analysis (PCA)  
To compare the relative differences in VOCs of strawberry wines obtained using different fermentation methods, a PCA analysis was performed according to OAVs above 0.1 of 34 selected VOCs, as shown in Table 3 (Figure 4). Five principal components were established, and PC1, 2, and 3 contributed 83.99%, which could better reflect the variance of the original data. As the PCA-biplot of the store and loading showed in PC1, 2, and 3 (Figure 4a-c), samples in different methods of fermentation could be separated obviously. The NM and PM strawberry wines fermented with pulp had higher scores in the PC1 negative direction; meanwhile, NJ, 50J, and PJ strawberry wines produced from juice were grouped centrally in the positive half-axis of PC1 (Figure 4a,b). NM and PJ strawberry wines were loaded in the positive vector of PC2. CJ strawberry wines tended to score higher in the negative direction in PC2 (Figure 4a,c). PJ and PM strawberry wines fermented with enzymes were distinguished from other strawberry wines due to having higher scores in the negative half-axis of PC3 (Figure 4b,c).  
Compounds negatively loaded on PC1 were higher alcohols (1-octanol, isoamyl alcohol, and 2-nonanol), C6 compounds (1-hexanol), acids (hexanoic acid), phenylethyls (ethyl benzoate, ethyl phenylpropionate, acetophenone, and phenylethyl alcohol), \(\gamma\)-decanolactone, and several terpenids (geranyl acetone, linalool, and trans-nerol), mainly contributing spicy, whiskey, green, and weak flower aromas. Ethyl esters (ethyl caprylate, ethyl decanoate, ethyl 9-decenoate, ethyl caproate, ethyl laurate, and ethyl enantate), acetates (hexyl acetate and isoamyl acetate), terpen (myrtenol and farnesol), and phenylethyls (ethyl phenylacetate and ethyl phenylpropionate) were positively loaded on PC1, mainly contributing fruity and flowery aromas. Terpenoids (linalool, geranyl acetone, trans-nerol, myrtenol, and \(\alpha\)-terpinol), phenylethyls (ethyl benzoate, ethyl phenylacetate, ethyl phenylpropionate, and ethyl cinnamate), \(\gamma\)-decanolactone, 1-octanol, and 2-nonanol were mainly loaded in positive PC2, contributing plenty of flowers, sweet aromas and some fruity aromas. The key substances to the negative PC2 direction were benzaldehyde, capric aldehyde, caprylic acid, and phenyl ethyl acetate, which primarily contributed to bitter almond, cheese, and fatty aromas. Phenylethyls (phenylethyl acetate, phenylethanol, ethyl benzoate, benzaldehyde, acetophenone, styrene, and ethyl phenylacetate), acids (octanoic acid, hexanoic acid), \(\gamma\)-decanolactone, \(\alpha\)-terpinol, and linalool had positive effects on PC3, contributing rose, fat, sour, cheese, and flower flavors. Methyl salicate, trans-nerolidol, 2-nonanol, methyl caprylate, and farnesol, with peppermint, orange, citrus, and lemon aromas, were negative vectors of PC3.  
In general, the NM and PM wine samples shared more prominent whiskey characteristics, while the NM wine tended to have a floral, fruity, and sweet aroma, and the PM wine tended to have citrus and orange flavors and less northern fruity aromas, such as apple and pear. The overall flavor of CJ strawberry wine was relatively weaker compared to other strawberry wines fermented from juice, focusing on rose, almond, and cheese characteristics. The 50J and PJ strawberry wines had more sweet fruit, flower, and honey aromas than the NJ wine sample, whereas the difference between them was that the 50J wine showed more rose and cheese aromas, and the PJ wine had more orange and lemon characteristics.