## 4 Conclusions  
In this study, we attempted to use the vacuum bag as the fermentation container of _B. napus_. The changing trend of the measured basic biochemical indexes was similar to that of TBA, which shows that this idea is feasible. Further analysis showed that the number of LAB in the VBA was higher than that in TBA during the whole fermentation process. The pH decrease and TTA content growth rates in the early fermentation stage were faster than those in the bottle, most likely because vacuuming in the bag can offer a better environment for LAB fermentation. The combination of CSA and chemical analysis methods, such as LDA, could accurately distinguish the different fermentation stages of VBA and play a role in monitoring the fermentation process.  
In conclusion, low-pressure fermentation using a vacuum bag could replace atmospheric-pressure fermentation using plastic bottles, and CSA could detect the fermentation process. Future research should examine how to improve the packaging form of the bag so that CSA can be placed in the fermented bag but not in contact with the vegetable to realize real-time determination of the fermentation process.  
Figure 7: Data analysis of VBA by CSA detection. **(A)** Images of CSA for VBA at various stages of fermentation; **(B)** LDA data of CSA grouped by fermentation days; **(C)** LDA data of CSA grouped by different fermentation stages; **(D)** PLSR outcome plot of pH for VBA based on the CSA; **(E)** PLSR outcome plot of TTA for VBA based on the CSA; **(F)** PLSR outcome plot of nitrite for VBA based on the CSA. V represented VBA; Numbers (0, 5, 10, 15, 20, 25, 30, 35) represent fermentation time.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods12193573/s1](https://www.mdpi.com/article/10.3390/foods12193573/s1)]([https://www.mdpi.com/article/10.3390/foods12193573/s1](https://www.mdpi.com/article/10.3390/foods12193573/s1)), Table S1: The thermal cycling conditions of PCR. Table S2: Nine kinds of gas-sensitive materials. Table S3: Percentage of main volatile flavor compounds in VBA and TBA fermentation process. Table S4: The basic OTU and species richness information. Table S5: Classification results of CSA data of samples at different fermentation time by LDA. Figure S1: Arrangement order of nine gas-sensitive materials.  
**Author Contributions:** J.L.: conceptualization, methodology, writing, data curation, form analysis, software. M.W.: supervision. Y.H.: supervision. H.S.: project administration, resources. H.L.: project administration, resources, funding acquisition. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Data Availability Statement:** The datasets generated for this study are available on request to the corresponding author.  
**Acknowledgments:** This work was supported by Jiang Xiao Yao Food Technology Co., Ltd., Suzhou, China.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Jiangxiaoyao Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflict of interest.