Physicochemical and Textural Features of the Shuidong Mustard (Brassica juncea) with a 15-Day Microorganism Fermentation Under a Lower Table Salt Usage

In the present study, Shuidong mustard (Brassica juncea) produced in Maoming City, Guangdong Province, was fermented at 25 °C for 15 days, using wild microorganisms and 20 g/kg table salt in water. The results showed that this fermentation endowed Shuidong mustard with acid production via utilizing reduced sugar as the fermentation substrate, causing the fermented Shuidong mustard to have a decreased pH value and increased total titratable acidity. Partly as the result of NaCl usage or fermentation, the fermented Shuidong mustard had enhanced NaCl or ash contents, decreased contents in nitrite/nitrate, vitamin C, total phenols, and total carotenoids, and altered textural features reflected as reduced hardness, chewiness, springiness, and fracturability. Moreover, 90 volatile compounds, including 2-butyl, 3-butenyl, isobutyl, and ethyl isothiocyanates, were detected in the fermented Shuidong mustard after the 15-day fermentation, while 21 members comprised 95% (w/w) of total volatiles. Additionally, the analysis results revealed that the microorganism community of fermented Shuidong mustard was structured at respective phylum, genera, or species levels by Firmicutes and Proteobacteria, or Lactiplantibacillus, Enterobacteriaceae, Lactococcus, and Pediococcus, or Lactiplantibacillus, Enterobacteriaceae, Pediococcus, and Lactococcus. It is thus concluded that this explored fermentation induced both acid production and, more importantly, compositional and textural changes in Shuidong mustard, which had production potential at an industrial scale as part of a healthy diet because these bioactive compounds include isothiocyanates, polyphenols, and carotenoids. Overall, this study focused on the Shuidong mustard fermentation using 20 g/kg table salt to fill a research gap in low-salt fermentation, showing its significance by providing a scientific basis for product development.