## 3 Results and Discussion
### FAA Analysis  
FAA are essential substances that affect the taste of products. [PERSON] et al. showed that intense proteolysis occurred during the dry-cured ham processing, resulting in continuous accumulation of small peptides and FAA [28]. FAA are mainly produced by endogenous enzymes (such as cathepsins/calpains) present in raw meat and by microorganisms to promote the degradation of proteins into smaller molecules (peptides, fatty acids, and aldehydes). [PERSON] indicated that after the longest examined aging time, the FAA content in the loins inoculated with a probiotic strain represented a significant increase of about 25% compared with the control sample [17]. In our previous study, _L. plantarum_ SJ4 also was found to have good proteolytic properties. Therefore, it was necessary to test the FAA of fermented pork loin ham at different times to explore the correlation between FAA and volatile compounds. The results are expressed as a mean (\(n=3\)).  
The FAA content at different fermentation times is shown in Figure 3A. In 0-42 days, except for ILE and MET, the content of the remaining 15 FAA reached the maximum in 35 days. The amino acid levels increased rapidly between days 0-21. The studies of [PERSON] suggested that adding a complex starter helped produce more FAA more quickly. This may be due to the bacterial proteolytic activity of _Lactobacillus_ and _Staphylococcus_[29]. On day 35, the content of TFAA reached 12.422 mg/g. Notably, this was higher than the data of [PERSON] and [PERSON] et al., which might be due to the effect of the starter [30; 31]. This showed that by using a starter, more nutrients could be provided to the fermented pork loin ham. On the day 42, the contents of all amino acids showed a decreasing trend, which was mainly due to microbial metabolism being more intense than production [32]. Some studies showed that the degradation of amino acids increased flavor components [33; 34]. This process might lead to the production of more volatile compound species. Except for day 0, the content of GLU was the highest among all amino acids within 7-42 days, followed by ALA. On the day 35, the content of umami amino acids, including ASP, GLU, GLY, and ALA, reached 4.694 mg/g. Quantitatively the most important FAA were Glu, Ala, and Leu. This FAA profile was mainly consistent with that reported by [PERSON] et al. [35]. In previous E-tongue tests, umami was the more prominent flavor in fermented pork loin ham. However, FAA testing suggested that this umami might be provided by umami amino acids. The content of bitter amino acids was also second only to umami amino acids. [PERSON] et al. speculated that FAA or interactions between compounds played a crucial role in regulating the flavor of the final product [36]. However, [PERSON] et al. showed that the degradation of FAA, especially VAL, LEU, and ILE, enhanced the content of 3-methyl butyric acid and 2-methyl butyric acid, resulting in the defects in ham flavor [37].  
Taste activity value (TAV) is the active taste value, and its value is limited by 1 [38]. When it is lower than 1, the substance contributes little to the taste, and when it is higher than 1, it contributes more to the taste of the sample. The value of the TAV has a positive correlation with the contribution rate of taste. Figure 3B shows that the TAV value in each experimental group was small, but with the increase in time, the TAV showed a trend of first increase and then decrease; its value reached the highest value at day 35. This suggests that the flavor of the fermented pork loin ham may lead to more benefits and better absorption at day 35.