## 4 Discussion  
Three strains of _L. plantarum_, namely MB1, M22, and 3-14-LJ, were chosen from 708 and inoculated in the _Suanzhuyu_ model and actual systems, respectively. Inoculation was found to accelerate the rate of pH decline in the system, promote protein degradation, and increase the content of TCA soluble peptides, amino acids, and VOCs, particularly esters, in _Suanzhuyu_. Furthermore, electronic tongue results revealed that inoculation could increase the acidity and decrease the bitterness of the product. Inoculation helps maintain  
Figure 3: E-tongue analysis of samples from the model system (**A**) and actual system (**C**). The results of the sour characteristics and the bitterness characteristics of E-tongue in the model and actual system are represented in (**B**,**D**), respectively. Letters “a-e” indicate the significant difference (\(p<0.05\)). For abbreviations, see Table 1.  
the stability of the product and improves quality such as taste. Low pH is crucial for the inhibition of spoilage and pathogenic bacteria [29]. A similar phenomenon that inoculation of LAB could reduce the product's pH, allowing rapid acidification of the product, was also reported in [PERSON]'s study [30]. Furthermore, it was demonstrated that decreasing the pH aids protein hydrolysis and increases the content of TCA-soluble peptides. _Suanyu_ (a traditional Chinese low-salt fermented fish) proteins gradually hydrolyzed, and TCA-soluble peptides and FAAs content increased with decreasing pH during fermentation. The protein concentration was lowest at the end of fermentation, while the peptide content was highest [24]. The same phenomena were observed not only in our study but also in many fermentation products. The increase of TCA-soluble peptides and FAAs content play important roles in taste perception. For example, glutamic acid is one of the most important substances for \"freshness\" [31], while alanine is the main contributor to sweetness [32]. [PERSON]'s study discovered that after LAB inoculation, the content of fresh (Asp, Glu) and sweet (Gly, Ser, Pro, etc.) amino acids increased [33]. The actual _Suanzhaya_ system also showed an increase in SAA and UAA. However, the model system lacked Asp, Ser, and Glu. This might be a result of the single-strain inoculation, which might not accurately reflect the product's true specialty. It has been observed that under low pH stress, LAB could utilize Glu to create gamma-aminobutyric acid (GABA) to alleviate the stress [34]. This could also be because the model system's pH (3.64) is lower than the actual system's pH (4.02). Immunization greatly improved the product's sourness while also significantly lessening its bitterness. This might be a result of the acid that the LAB's carbohydrate metabolism produces, which has been observed in numerous fermented goods [35]. The decrease in bitterness in the inoculated group may be because bitterness is determined not only by BAAs' content but also by some bitter peptides, etc. [14; 36]. The lower ability of degradation of bitter peptides or other bitter substances without LAB may result in a higher bitter taste. Inoculation had a significant effect on the production of esters. In the model system, isoamyl acetate, ethyl caproate, and ethyl caprylate were not detected in either the fresh or the control group, while all three inoculated groups produced higher amounts of these three esters. Similar results were obtained by [PERSON] et al. after inoculation of LAB in the _Suanyu_ model system. Inoculation with _L. plantarum_ M22 was most effective in producing these esters compared with the other two strains [37]. Esters with short-chain acids are represented with a fruity aroma, while esters containing long-chain acids give a fatty odor [38]. Alcohols were also enhanced with inoculation, especially for 3-methyl-1-butanol, 1-hexanol, 1-octen-3-ol, and phenyl ethanol [39]. 1-octen-3-ol, commonly found in aquatic products, has a low odor threshold and can provide mushroom and fruit aromas [40].