## 2 Results and Discussion
### Volatile Compounds in Goji Juice  
The types and contents of volatile compounds (Table S1) in the fermented goji juice samples and raw juice were found to be different (Figure 1). In total, 38 compounds were identified in the raw juice, whereas 46, 43, and 53 compounds were detected in the goji juice samples fermented with SLV, SZP, and SZVP, respectively. The volatile compounds in the samples mainly belonged to the following classes: acids (5), alcohols (15), ketones (8), aldehydes (13), esters (6), terpenes (3), phenols (5), and others (7). The acids comprised a class of volatile compounds that increased in abundance after fermentation. Short-chain fatty acids comprising acetic acid, heptanoic acid, and octanoic acid were produced by fermentation with various bacterial strains. In particular, acetic acid was produced via the metabolism of carbohydrates, fats, and amino acids by lactic acid bacteria ([PERSON] et al., 2018). The enrichment of this compound contributed to the aroma of fermented juice ([PERSON] et al., 2018), with a cheesy, fatty, or pungent odor ([PERSON] et al., 2018). The contents of these compounds in the goji juice samples fermented with mixtures of strain were in the order of: SZP (48.55 \(\mu\)g/100 g) \(>\) SZVP (40.13 \(\mu\)g/100 g) \(>\) SLV (32.02 \(\mu\)g/100 g). After fermentation, the concentration of n-hexadecanoic acid increased 5.80-7.47 times compared with the raw juice. However, the threshold for detecting this substance was high, so its contribution to the aroma was not great. Alcohols, such as 1-octanol,linalool, (Z)-3-nonen-1-ol, 1-nonanol, levomenthol, geraniol, and 2,4-decadien-1-ol were produced by different strains during fermentation. In particular, 1-octanol has had an aroma of mushrooms andlinalool had a floral odor ([PERSON] et al., 2018). Dimethyl-silanediol, 1-hexanol, benzyl alcohol, and phenylethyll alcohol were detected in the fermented goji juice samples and raw juice. The benzyl alcohol and phenylethyll alcohol contents were significantly increased after fermentation, where their concentrations followed the order of: SZVP (76.86 \(\mu\)g/100 g) \(>\) SZP (55.87 \(\mu\)g/100 g)SLV (54.71 \(\upmu\)g/100 g). These chemicals have floral odors and the OAVs were greater than 1 [20], indicating their contributions to the overall flavor of the goji juice. Acetoin and (_E_)-1-(2,6,6-trimethyl-1,3-cyclohexadien-1-yl)-2-butten-1-one were only present in the fermented juice. Acetoin can be converted from 2,3-butanedione by diacetyl reductase, and it can also be produced via citrate metabolism [21], where it had a creamy or vanilla odor [22]. Other ketones were present in the fermented goji juice samples and raw juice, where their contents were increased after bacterial fermentation. The concentrations of 6-methyl-5-hepten-2-one and trans-\(\upbeta\)-ionnone were high in the fermented goji juice samples. It was found that 6-methyl-5-hepten-2-one had a green odor and trans-\(\upbeta\)-ionnone had a violet fragrance [23], and these chemicals contributed to the aroma of the fermented goji juice wine [19]. Thus, the increased contents of these chemicals in the present study may positively affect the aroma of the fermented goji juice. The combined concentrations of 6-methyl-5-hepten-2-one and trans-\(\upbeta\)-ionone followed the order of: SLV (67.69 \(\upmu\)g/100 g) \(>\) SZVP (64.66 \(\upmu\)g/100 g) \(>\) SZVP (54.17 \(\upmu\)g/100 g). Nonanal was present in the raw juice but absent after fermentation. The hexanal content was also reduced by fermentation compared with the raw juice, which is consistent with a previous report  
Figure 1: The contents of volatile compounds in the fermented goji juice by different bacteria (\(\upmu\)g/100 g). The heat map was based on the contents of volatile compounds detected in fermented and unfermented goji juice. The scale ranging from 0 (white) to 70 (red) was used to show the contents of volatile matters (\(\upmu\)g) in 100 g goji juice. showing that fermentation reduced the hexanal content in soy milk [24].