## 3 Results and Discussion
### Changes in FAAs of Pickled BLS under Different Salt Concentrations  
A total of 23 FAAs were detected in all samples. FAAs were divided into essential amino acids, non-essential amino acids, and semi-essential amino acids, as shown in Table 2. The taste activity value was represented by TAV [51]. TAV was equal to the ratio of the measured substance concentration to its threshold value. According to TAV, high contents of Ala, Cys, Val, Arg, and Gln indicated that these amino acids contributed more to the taste of production. Among them, Ala was an umami amino acid with the largest TAV, which endowed pickled BLS with rich sweetness and umami taste. Cys was an aromatic amino acid, which existed in G1-G5, and TAV was greater than 1, which provided aroma to pickled BLS. The TAV values of Gly, Thr, and Tyr in the five samples were all less than 1, which contributed little to the flavor of pickled BLS. It could be seen from the table that fermented BLS is rich in FAAs, and the content of FAAs in BLS fermented with different salt concentrations was different. From Figure 2, the content distribution of all FAAs could be seen more intuitively. The FAAs with higher content in the five samples were Gln, Pro, and Ala in sequence. Gln was the most important substance that provided umami and could be used as a nutritional supplement [52]. Due to the different salt concentrations used, the detected free amino acid content distribution was different, which is more obvious in G3. Figure 1: Contents of flavonoids and total phenols in pickled BLS with different salt concentrations. G1, G2, G3, G4, and G5 represent the BLS samples pickled with 4%, 5%, 6%, 7%, and 8% salt mass. Figure 2: Stacking chart of FAAs in pickled BLS with different salt concentrations. As an important taste substance, FAAs could provide taste sensations, such as umami, sweetness, and bitterness. According to the classification of taste amino acids and the taste characteristics of amino acids, amino acids were divided into sweet amino acids, umami amino acids, bitter amino acids, and aromatic amino acids. The content distribution of flavor amino acids in BLS is shown in Figure 3. The mass fraction of sweet amino acids was 8.14-15.02 mg/g; it could be seen that pickled BLS as a fermented vegetable mainly imparted sweetness to the product, and the mass fraction of sweet amino acids of G3 (15.02 mg/g) and G1 (11.31 mg/g) was more prominent. The content of bitter amino acids was most prominent in G5; this is not beneficial to the taste of pickled BLS. Since the taste threshold of each amino acid was also different, it could not only be judged from the content. Amino acids are the building blocks for cells and repairing tissues and providing energy for body and brain activity. Amino acids are not only good nutrients, but also play an important role in taste. Changes in FAAs were mainly dominated by protease and peptidase activities influenced by salinity, pH, and temperature, etc. [53]. These factors can also boost the oxidative decomposition of proteins and lipids in pickled BLS and facilitate the accumulation of FAAs and organic acids and the production of various volatile flavor substances [54]. The balance and interactions among different FAAs had an important influence on the pickled BLS flavor [55]. The essential amino acids accounted for up to 13.60% of the entire amino acids detected, making the pickled BLS a good source of amino acids for humans. The total content of FAAs ranged from 32.840 to 60.013 mg/g, and there were significant differences in the total content of FAAs, flavor amino acids, limiting amino acids, and essential amino acids. There were 13 FAAs that contributed greatly to the taste of pickled BLS (TAV > 1), mainly Asp, Glu, His, Arg, Ala, and Cys. G3 had the highest content of total FAAs, as well as the highest Asp, Glu, Gln, and Pro, and its sweetness was also the most prominent. It was possible that more FAAs were released at this salt concentration than at other concentrations.