###### Abstract  
This study aimed to elaborate on the role of salt concentration on pickled _Brassica napus_ leaf and stem (BLS); it also contributed to the development of low-salt and healthy _Brassica napus_ products in the harvest period. Five sets of pickled BLS samples were prepared, and the physicochemical parameters, free amino acids (FAAs), and the volatile flavor components (VFCs) were analyzed after fermentation. Results showed that some antioxidants, FAAs, and VFCs underwent dynamic changes during fermentation. Nitrite increased with an increase in the salt concentration used for fermentation. Pickled BLS contained a wide range of FAAs; a total of 23 were detected, which might be used as a source of amino acid supplementation. The VFCs were analyzed via headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography and mass spectrometry (GC-MS). A total of 51 VFCs were tentatively identified. The contribution to flavor could be expressed by the relative odor activity value (ROAV). Salt is one of the important factors affecting the quality of vegetable fermentation. Therefore, for large-scale pickled BLS production, a key issue is to balance the low salt concentration and high fermentation quality. Under the action of salt and microorganisms, the fresh BLS fermented via dry pickling, which not only improved its FAAs and VFCs, endowed the production with a unique flavor, but also prolonged the shelf life.  
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peptides and amino acids through fermentation, thereby improving the bioavailability of protein [6; 7]. Compared to other leafy vegetables, BLS is also abundant in protein, making it crucial to investigate the protein content and amino acid profile of fermented pickled BLS. Lactic acid bacteria (LAB) play a major role in the pickling process, contributing to the production of unique flavors and promoting overall health and fitness [8]. LABs are recognized as the most prominent probiotic strains, as some of the species inhabit the small intestine by resisting harsh environmental conditions, such as low pH and high osmotic pressure, etc. [9]. LABs have been widely applied in fermented food. The application of LABs can regulate intestinal flora and enhance immunity, etc. [10; 11]. Furthermore, LABs have been found to improve the polyphenol content, antioxidant capacity, and flavor complexity of fermented products [12; 13; 14]. Salt promotes the growth of LABs in pickles and controls the growth of spoilage microorganisms [15]. More importantly, the concentration and type of salt affect the changes in microbial communities during fermentation [16; 17; 18]. During the fermentation of pickles, many microorganisms promote the production of metabolites. It has been difficult to prove the relationship between salt concentration and metabolites [19]. These metabolites may include sugars, acids, and amino acids, etc., which play a key role in the quality of the final product [20].  
The salt could reduce the nitrite content during pickle fermentation and improve the safety of pickles [21]. On the other hand, the salt concentration could control the quality of pickles [22]. However, excess salt intake increases the risk of blood pressure and cardiovascular disease [23]. The key is to balance the salt concentration and pickle quality. At present, there are few studies on the effect of salt concentrations on vegetables with higher protein content after fermentation; especially, their flavor characteristics and amino acids are worth studying.  
Therefore, the aim of this study was to examine the relationship between the salt concentration for fermentation and characteristics of pickled BLS, including total acidity (TA), soluble sugar, protein, fat, amino acid nitrogen, salinity, glucosinolate, nitrite, and FAAs. In addition, VFCs and some antioxidants were analyzed. The result would help to provide theoretical evidence for improving the comprehensive utilization value of _Brassica napus_.