# Effect of Autochthonous Lactic Acid Bacteria-Enhanced Fermentation on the Quality of Suancai
## 3 Results and Discussion
### The Composition of the Bacterial Community in Suancai with Different Starters  
Microorganisms are the most important factor in the quality of fermented foods. High-throughput sequencing has been widely applied to reveal the microbial community in fermented food [4; 5; 9; 13]. In this study, the bacterial community at the phylum, genus, and species were revealed by high-throughput sequencing in Suancai (Figure S1). The number of OTUs taxonomy reached the saturation plateau, indicating that the species in this environment will not increase significantly with the increase of sample size, which means that the sampling is sufficient (Figure S1A). Firmicutes was discovered as the dominant phylum and accounted for more than 80% in all Suancai samples (Figure S1B). Firmicutes were always observed as the dominant phylum in fermented vegetables [1; 2; 24]. The second most dominant phylum was Proteobacteria. At the phylum level, no remarkable differences were found in bacterial abundance. At the genus level, _Lactobacillus_ was the dominant bacterium in all samples, which always predominated in other fermented vegetables foods [7; 25]. Therefore, many species belonging to _Lactobacillus_ were used to improve the quality of fermented vegetables [10; 11; 12]. Some species of _Lactobacillus_ could perform homolactic or heterolactic fermentation to produce lactic acid, acetic acid, ethanol, etc., which can explain the high sensory quality of fermented vegetables because these metabolites had an active influence on the improvement of sensory characteristics [26]. At the species level, a total of 35 species were discovered in all samples and _Lb. plantarum_ was detected as the dominant species in Suancai (Figure 2A). Possibly, _Lb. plantarum_ is a widely distributed LAB and could tolerate low pH [27; 28], indicating that \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Samples 1** & **CON** & **LP** & **LB** & **LM** \\ \hline Chao1 & 20.61 \(\pm\) 5.29 1  & 34.60 \(\pm\) 2.45 1  & 29.38 \(\pm\) 4.20 1  & 31.70 \(\pm\) 13.17 1  \\ Goods coverage & 0.99 \(\pm\) 0.00 1  & 0.99 \(\pm\) 0.00 1  & 0.99 \(\pm\) 0.00 1  \\ Shannon & 0.75 \(\pm\) 0.03 1  & 1.00 \(\pm\) 0.11  & 1.11 \(\pm\) 0.04  & 1.48 \(\pm\) 0.09 1  \\ Observed species & 16.00 \(\pm\) 2.33 1  & 28.57 \(\pm\) 0.76 1  & 24.23 \(\pm\) 3.48 1  & 25.93 \(\pm\) 6.05 1  \\ [PERSON] & 0.22 \(\pm\) 0.01 1  & 0.26 \(\pm\) 0.03 1  & 0.33 \(\pm\) 0.01 1  & 0.49 \(\pm\) 0.02 1  \\ PD whole tree & 1.39 \(\pm\) 0.14 1  & 2.56 \(\pm\) 0.09 1  & 2.14 \(\pm\) 0.26 1  & 0.49 \(\pm\) 0.02 1  \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Alpha index of Suancai fermented with different autochthonous LABs. it can survive in the late fermentation stage of Suancai. Therefore, whichever species of LAB were inoculated, _Lb. plantarum_ was always the dominant bacterium after fermentation of Suancai (Figure 2A). As a kind of homofermatterative LAB, _Lb. plantarum_ was always observed as the dominant species in fermented vegetables [24; 29] and was frequently used in the fermentation of vegetables and fruit juices to improve the quality of products [30; 31]. The results of principal components analysis (PCA) based on the bacterial community are shown in Figure 2B and the variation of two canonical axes explained 10.1% and 86.4%. The inoculated fermentation of starters affected the bacterial community structures of Suancai (Figure 2B). Compared with LB and LM, the bacterial community profiles of the LP were more similar to that of CON (Figure 2B), which may be on account of the _Lb. plantarum_ being observed as the dominant bacterium after fermentation of Suancai. On account of the addition of starters, _Lb. brevis_ and _Leu. mesenteroides_ were observed with high abundance in LB and LM, respectively (Figure 2A,C). Moreover, _Lactococcus lactis_ were observed with a large abundance in LB and LM (Figure 2A) on account of the slower acidification than LP.