# A Method of Reducing Salt Content in Fermented Soy Sauce Improves Its Flavor and Quality
## 3 Results and Discussion
### Determination of New Fermentation Technology  
In order to determine the amount of salinity, ultrasonic time, mixed yeast addition, and the temperature variation range, the AAN content was taken as the reference basis, and the results are shown in Figure 3.  
This study aimed to develop a reduced-salt soy sauce that will ensure a healthy diet for most people without losing the quality of the soy sauce. As can be seen from Figure 3a, the AAN contents of the five groups with different salt additions gradually increased during the fermentation of the soy sauce in the early fermentation stages and became stable later. However, the increase in the AAN content in the soy sauce when the salinity was 10% showed a significant difference, which indicates that the increase in the salinity increases  
Figure 3: The variation in the amino acid nitrogen contents during fermentation with different (**a**) salinities; (**b**) ultrasonic times; (**c**) mixed yeast additions; (**d**) temperature variation ranges during fermentation. the AAN content to some extent. Therefore, 9%, 10%, and 11% salinity levels were selected for the response surface analysis to determine the optimal salt addition level. The application of ultrasound can significantly improve the accumulation of AAN at the prefermentation stage, but the length of the ultrasonic time also affects the fermentation; too long leads to excessive cracking of the raw materials, affecting the later fermentation. In Figure 3b, it can be seen that the AAN content was significantly different when the ultrasonic time was 10 min. Therefore, 7.5 min, 10 min, and 12.5 min of ultrasound were selected for the response surface analysis to determine the optimal ultrasonic time for the first three days of fermentation. The mixed yeast addition also affected the AAN content of the soy sauce during fermentation. It can be seen from Figure 3c that all five mixed yeast additions had a promoting effect on the AAN content of the soy sauce, increasing the most when the amount of _Z. rouxii_ and _T. halophilus_ added to the mixture was 2.0 \(\times\) 10\({}^{6}\) CFU/g, showing a significant difference. Therefore, the mixed yeast addition amounts of 1.5 \(\times\) 10\({}^{6}\) CFU/g, 2.0 \(\times\) 10\({}^{6}\) CFU/g, and 2.5 \(\times\) 10\({}^{6}\) CFU/g were selected for the response surface analysis to determine the optimal mixed yeast addition amounts. Fermentation temperature plays a crucial role in the fermentation of soy sauce. LS soy sauce is mainly fermented at high temperatures for a short time, resulting in poor flavor and a dark color; HS soy sauce is mainly fermented continuously at low temperature, which provides a rich in flavor but has a long fermentation time, resulting in high selling prices. This SR soy sauce was fermented at 42 \({}^{\circ}\)C for 7 days, cooled to 30 \({}^{\circ}\)C, and then warmed, so the temperature change in the later warmed-up fermentation is essential. Figure 3d shows that the AAN contents of the five different temperatures for the fermentation of soy sauce differed significantly, starting with an initial temperature of 42 \({}^{\circ}\)C for 7 days, followed by cooling to 30 \({}^{\circ}\)C, and then rising 1 \({}^{\circ}\)C every two days to 40 \({}^{\circ}\)C during continuous fermentation. Therefore, the late-fermentation temperature variations of 30 \({}^{\circ}\)C\(\rightarrow\)39 \({}^{\circ}\)C, 30 \({}^{\circ}\)C\(\rightarrow\)40 \({}^{\circ}\)C, and 30 \({}^{\circ}\)C\(\rightarrow\)41 \({}^{\circ}\)C were selected for the response surface analysis to determine the best late fermentation variation in temperature. The response surface method was used to optimize the experimental results, as shown in Tables S1 and S2. According to Table S2, the \(p\)-value of the regression model was less than 0.01, which is a highly significant level, indicating that the model was significantly regressed, and the regression equation well represented the relationship between the amino acid nitrogen content and the four factors.