# Optimization of Vacuum Freeze-Drying Process and Quality Evaluation of _Stropharia rugosanmulata_
## 3 Results and Discussion
### Orthogonal Experimental Results  
As shown in Table 8, the optimal processing technique for each processing indicator can be determined. The three factors set in the experiment have varying impacts on the quality of _Stropharia rugosaannulata_, with the order of influence being pre-freezing temperature \(>\) freeze-drying time \(>\) pre-freezing time. Therefore, the optimal process for vacuum freeze-drying _Stropharia rugosaannulata_ is A\({}_{3}\)B\({}_{1}\)C\({}_{2}\), which corresponds to a pre-freezing temperature of \(-80\)\({}^{\circ}\)C, a pre-freezing time of 48 h, and a freeze-drying time of 72 h.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Ample Name** & **Colony Count/log CFU/g** \\ \hline Fresh _Stropharia rugosaannulata_ & 4.23 \(\pm\) 0.02 \({}^{\circ}\) \\ Blanched after nisin treatment & 2.26 \(\pm\) 0.24 \({}^{\circ}\) \\ Direct blanching & 3.32 \(\pm\) 0.05 \({}^{\circ}\) \\ Freeze-dried _Stropharia rugosaannulata_ & 3.52 \(\pm\) 0.03 \({}^{\circ}\) \\ Freeze-dried _Stropharia rugosaannulata_ with nisin treatment & 2.46 \(\pm\) 0.15 \({}^{\circ}\) \\ \hline \hline \end{tabular} Note: Different lowercase letters indicate significant difference at 0.05 level among the groups.  
\end{table}
Table 7: Colony counts of _Stropharia rugosaannulata_ in different treatments; unit: log CFU/g.  
The experimental results and range analysis are shown in Table 8. From Table 8, the order of the range values is R\({}_{\text{A}}\) \(>\) R\({}_{\text{B}}\) \(>\) R\({}_{\text{C}}\). The larger the range, the greater the impact of the factor on the comprehensive score. Therefore, the order of the three factors' impact on the overall effect of freeze-drying _Stropharia rugososanmulata_ is A \(>\) B \(>\) C, i.e., pre-freezing temperature \(>\) pre-freezing time \(>\) freeze-drying time. The optimal scheme is A\({}_{3}\)B\({}_{2}\)C\({}_{2}\), corresponding to a pre-freezing temperature of \(-80\)\({}^{\circ}\)C, a pre-freezing time of 48 h, and a freeze-drying time of 72 h.  
As seen in the data, the highest comprehensive score (263.54) was achieved with a pre-freezing temperature of \(-80\)\({}^{\circ}\)C, indicating a better freeze-drying effect of _Stropharia rugososanmulata_ at lower pre-freezing temperatures. This may be because, at lower temperatures, the water inside the cells freezes to form ice crystals more quickly, reducing cell structure damage and preserving higher levels of chemical substances and bioactivity in _Stropharia rugososanmulata_, thereby maintaining better quality. A pre-freezing time that is too short may lead to insufficient pre-freezing or browning of _Stropharia rugososanmulata_, affecting subsequent sensory scores. The highest comprehensive score (255.12) was achieved with a pre-freezing time of 48 h, indicating that good freeze-drying results can be achieved within a relatively short pre-freezing time. A pre-freezing time that is too long can cause low-temperature damage to the cells of _Stropharia rugososanmulata_, damaging cell tissue structure and affecting sensory scores. Prolonged pre-freezing time can also lead to degradation of the phenolic and saponin compounds [33] in _Stropharia rugososanmulata_, thereby affecting its health benefits. The highest comprehensive score (254.66) was achieved with a freeze-drying time of 72 h, but its difference from the other two levels was not significant, indicating that, within a certain range, the freeze-drying time has little impact on the final quality.