## 3 Results and Discussion
### Biochemical Analysis  
The initial pH value of sterile sturgeon fillets was 7.06 \(\pm\) 0.03 (Figure 2C). Overall, all samples showed a trend of pH increase after a slight decreasing at day 6. This is mainly because after the death of live fish, ATP, phosphoreatine and other substances decompose to produce acidic substances such as phosphoric acid. At the same time, glycogen metabolism produces lactic acid, which reduces the pH in fish meat. However, with the increase of storage time, endogenous enzymes and surface microorganisms decompose nitrogen-containing compounds such as protein, producing more alkaline substances, resulting in the increase of pH [31; 37]. However, the pH of each experimental group basically fluctuated due to the low ice storage temperature, the slow decline of fish freshness, the insufficient production of acidic substances metabolized by the body, and the accumulation of alkaline substances. So, the of pH value of _Pseudomonas fluorescens_ group and _Shewanella putrefaciens_ group was higher than that of other bacteria groups at the end of storage, which was 7.35 \(\pm\) 0.02 and 7.31 \(\pm\) 0.05, respectively. Similar studies found that the pH of grass carp fillets also decreased first and then increased at \(-\)3 \({}^{\circ}\)C and 0 \({}^{\circ}\)C [31], which is consistent with our research results.  
Although the TVBN production of different bacteria groups increased slowly at the early period of storage, it was significantly higher than that of the control during storage (Figure 2D). _Pseudomonas fluorescens_ group, _Shewanella putrefaciens_ group, and _Shewanella battica_ group produced a large amount of TVBN rapidly after being stored for 12 days. Meanwhile, _Pseudomonas fluorescens_ group had the maximum production rate of TVBN, which showed a significant difference compared to other groups, and reached 30.80 \(\pm\) 1.98 mg-N 100 g\({}^{-1}\) at the end of storage. The TVBN value of the four other bacterial groups also increased dramatically after being stored for 15 days.  
The TBARS value has been widely used to describe the degree of lipid oxidation. As is shown in Figure 2E, the TBARS value of the control did not change significantly as the storage time extended. Meanwhile, TBARS values of _Pseudomonas fluorescens_ group, and _Shewanella putrefaciens_ group were higher than other bacteria groups at the end of storage, reaching 1.21 \(\pm\) 0.03 and 1.12 \(\pm\) 0.03 mg MDA kg\({}^{-1}\), respectively. The TBARS value of _Pseudomonas mandeli_ group was 0.86 \(\pm\) 0.02 mg MDA kg\({}^{-1}\), which was the minimum value among all bacteria groups at day18.  
Changes of TCA-soluble peptides of different bacteria groups are shown in Figure 2F. The TCA-soluble peptides production of all bacteria groups increased with storage time extended. The TCA-soluble peptides content of _Pseudomonas fluorescens_ group and _Pseudomonas mandeli_ group increased rapidly after being stored for 9 days, and the similar phenomenon was also found in _Shewanella putrefaciens_ group and _Pseudomonas fragi_ group. _Pseudomonas fluorescens_ inoculated group showed the highest amount of TCA-soluble peptides.  
molecules produced by other bacterial species. As for _Shewanella baltica_, biochemical analysis has shown that the spoilage potential was moderate, though it grew at a fast rate as well as _Shewanella putrefaciens_. It was found that _Shewanella_ species could produce off-odor compounds, such as H\({}_{2}\)S, which can react with muscle pigments, and result in a green discoloration [40].