## 2 Results and Discussion
### Volatile Organic Compounds (VOCs)
#### 2.3.2 Fermentative Aroma Compounds
[56] reported that ethyl decanoate levels increased when Shiraz wines were produced using prior cryo-maceration. Fatty acids are the main volatile compounds in fruit wine that contribute to the complexity of aroma and balance of taste, and have been described as fruits, cheesy, fatty, and rancid notes. However, high concentrations of acids can lead to negative flavors such as fat and spoilage. Three fatty acid compounds were identified in strawberry wines: hexanoic acid, 2-methyl-hexanoic acid, and octanoic acid. Among them, the contents of hexanoic acid and octanoic acid were high (Table S1), and their OAVs ranged from 0.09 to 1.65 (Table 3). The different treatments utilized gave different results. CJ strawberry wine fermented from juice without any treatment had the highest levels of fatty acids. 50J and NM strawberry wines followed (Figure 3B). It was found that the composition and fermentation conditions of grape juice have a significant impact on the content of fatty acids [57]. Phenylethyl compounds in wine samples come from both parietal aroma and fermentation aroma. By comparing the contents of various components of phenylethyl compounds in wine samples and grapes in the literature, it was found that the contents of these compounds in grapes are much lower than in wine [58; 59], which means that most of them are produced by alcohol fermentation. Therefore, phenylethyl compounds were classified as fermentation aromas in this study. Phenylethyls were the third class of substances with high relative content in strawberry wines, accounting for 9.38-22.68% of total VOCs (Figure 3B, Table S1), besides high alcohols and esters. The contents of phenylethylal, phenylethyl acetate, benzaldehyde, ethyl cinnamate (2-Propenoic acid, 3-phenyl-, ethyl ester), and styrene were relatively high, but the contents of phenylethanol and benzaldehyde were lower than the olfactory threshold, and the contents of phenylethyl acetate, ethyl cinnamate, and styrene were higher than the olfactory threshold (Figure 2, Tables 3 and S1). Thus, these three compounds contributed significant rose, floral, and honey aromas to strawberry wines. The OAV of ethyl cinnamate reached 155.73-516.99, which was reported to be the characteristic ester of strawberry varieties and their wines [60]. The highest relative concentration and OAVs of major phenylethyls were found in 50J strawberry wine (Table 3). Strawberry wines fermented with pectinase were not conducive to the formation of phenylethyls, because PJ and PM strawberry wine reduced the contents of these compounds compared with 50J and NM strawberry wines, except ethyl phenylpropionate and ethyl cinnamate (Figure 3B). Other authors have also described lower concentrations of phenylethyls in red wines obtained by adding pectolytic enzymes [52]. Saccharomyces cerevisiae decomposes aromatic amino acids such as phenylalanine and tyrosine to produce phenylethanol and phenylethyl acetate. It may be that the enzyme operation provides a competitive substrate for cerevisiae to metabolize aromatic amino acids, thus reducing the metabolism of this class of amino acids, resulting in a significant reduction in phenylethanol and phenylethyl acetate. In addition, volatile aroma substances of furans, aldehydes, ketones, other esters, and aromatic species were also detected in the six wine samples, and the contents of these volatile substances were low. They played a complementary and modifying role in the aroma of the strawberry wines.