# Effect of Autochthonous Lactic Acid Bacteria-Enhanced Fermentation on the Quality of Suancai
## 3 Results and Discussion
### Changes of the Free Amino Acid in Suancai with Different Starters  
The results of the free amino acid contents in Suancai are displayed in Supplementary Table S1 and there were 17 free amino acids were detected in this study. According to the heatmap, the content of threonine acid (Thr), phenylalanine acid (Phe), alanine acid (Ala), glutamic acid (Glu), and proline acid (Pro) were the main free amino acids in Suancai (Figure 4A). The PLS analysis showed the influence of different strains on the amino acid profiles of Suancai (Figure 4B). The Suancai samples were gathered into different group  
Figure 3: The heatmap and correlation analysis with LABs (**A**), scatter plot (**B**), and total concentration (**C**) of volatile flavor compounds in Suancai fermented with different autochthonous LABs. Different letters represent significant differences (\(p<0.05\)). \({}^{*}p<0.05\), \({}^{**}p<0.01\).  
according to the PCA analysis, indicating that LAB inoculation could affect the profiles of amino acids in Suancai. _Lb. plantarum_, _Leu. Mesenteroides_, and _Lb. brevis_ were significantly correlated to the amino acids (Figure 4C). _Lb. plantarum_ was significantly positive correlated with 10 amino acids. Therefore, the inoculation of _Lb. plantarum_ had the highest content of free amino acids, while LM had the lowest content of amino acids (Figure 4D). _Lb. plantarum_ was reported to generate protein degradation and proteolytic enzymes to produce amino acids [36]. Therefore, the inoculation of _Lb. plantarum_ increased the content of amino acids in Suancai in this study (Supplementary Table S2), which was also observed in previous studies [11; 13]. Amino acid, as the precursor of alcohols, aldehydes, esters, and ketonic acids, participated indirectly in flavor development and contributed directly to the taste of Suancai [27; 37]. As branched-chain amino acids, isoleucine (Ile), leucine (Leu), and valine (Val) can be converted to \(\alpha\)-keto acids by LAB, and then translated into aldehydes and alcohols [38]. Consequently, the contents of Ile, Leu, and Val in CON were lower than that in inoculated group (Figure 4A). Potentially, the LAB increased the content of volatile compounds in Suancai through the converting of the amino acid. LM had the lowest content of amino acid and the highest content of volatile compounds (Figures 3C and 4D). Therefore, the inoculation of _Leu. mesenteroides_ was more beneficial to the convert of amino acid to volatile compounds on account of its slow acidification process obtained a high bacterial diversity.  
Moreover, amino acids contributed to the taste of Suancai. The results of electronic tongue data of Suancai with LABs were displayed in (Figure 5). The taste profiles of Suancai were different with different LABs. After fermentation, Thr was the richest amino acid (Figure 4A). As it is a sweet amino acid [39], Thr could improve the taste of Suancai. LM had the lowest saltiness, sourness, and umami, but had the highest bitterness and astringency (Figure 5), which were an awful taste for Suancai. The sourness, bitterness, astringency, aftertaste-B, aftertaste-A, and richness of the LP and LB had no significant difference. The CON had the highest Asp content. Aspartic acid (Asp) and glutamic acid (Glu) were relevant to umami flavor which considered the basic taste in cooking [40]. Potentially, \(\copyright\) CON had the highest umami taste on account of its high Asp content. These results indicated that LABs could change the FAAs composition to upgrade the taste of Suancai.  
Figure 4: The heatmap (**A**), scatter plot (**B**), correlation analysis with LABs (**C**), and total concentration (**D**) of amino acid in Suancai fermented with different autochthonous LABs. Different letters represent significant differences (\(p<0.05\)). \({}^{**}p<0.01\).