# Experimental Study of the Effect of Ultrasound on the Freezing Process of Bo Chinh Ginseng
## 3 Results and Discussions
### Effect of Ultrasound Initiation Temperature on Nucleation Temperature during Freezing of Materials  
Previous studies have also shown that ultrasound irradiation is instrumental in controlling the nucleation temperature. [PERSON] et al. [12] studied the effect of the broadcast initiation temperature on the nucleation temperature of radish cylinders. The temperature at the start of ultrasound irradiation in this study was located in the temperature range lower than 0 \({}^{\circ}\)C and higher than the nucleation temperature of the material when undergoing unsupported ultrasound freezing. The experimental results show that the higher the temperature during the application of the ultrasound, the sooner the nucleation takes place, i.e., the higher the nucleation temperature. In addition, some studies have shown that ultrasound-assisted frozen samples have higher nucleation temperatures than those frozen without ultrasound assistance. According to the studies of [PERSON] et al. [21] that used agar gel and [PERSON] et al. [20] that used mannitol and mannitol samples of bovine serum albumin (BSA), the lower the nucleation temperature of the ultrasound-assisted frozen samples, the smaller the ice crystal size.  
Figure 8 shows the effect of different irradiation initiation temperatures on the nucleation temperature of the materials. Corresponding to different transmitting initiation temperatures, the nucleation temperatures of the materials during freezing are also different. The lowest nucleation temperature (\(-2.8\)\({}^{\circ}\)C) corresponds to the freezing process without ultrasound support (control). The nucleation temperature further decreases as  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Treatment** & **Control** & **UF-0 W** & **UF-100 W** & **UF-150 W** & **UF-200 W** \\ \hline Freezing time (s) & \(15.1\) & \(11.6\) & \(10.7\) & \(11.5\) & \(12.3\) \\ Nucleation & \(-2.8\) & \(-2.6\) & \(-1.3\) & \(-1\) & \(-0.7\) \\ Temperature (\({}^{\circ}\)C) & & & & & \\ \hline \hline \end{tabular}  
* UF—ultrasound-assisted freezing; control—freezing without ultrasound support.  
\end{table}
Table 1: Parameters for ultrasound-assisted freezing of ginseng material.  
Figure 7: Effect of ultrasound power on nucleation temperature and freezing time.  
the irradiation initiation temperature decreases. The highest nucleation temperature of \(-1.3\)\({}^{\circ}\)C corresponds to the transmitting initiation temperature of \(-0.5\)\({}^{\circ}\)C, and the lowest nucleation temperature of \(-2.7\)\({}^{\circ}\)C corresponds to the lowest transmitting temperature of \(-2.5\)\({}^{\circ}\)C.  
Figure 9 shows a linear relationship between the irradiation temperature and nucleation temperature (\(y=-0.35x\)\(-\) 0.93, R\({}^{2}\) = 0.9976). The results show that ultrasound irradiation can control the nucleation of materials. This is very important for the research and application of ultrasound irradiation to support the freezing process of ginseng, as it helps to ensure product quality and freezing time, especially in the sublimation drying of materials that require freezing before drying.  
Figure 8: Effect of ultrasound irradiation initiation temperature at 100 W (ultrasound power) on the nucleation temperature: control—frozen sample obtained without ultrasound-assisted freezing. Arrows indicate the ultrasound-application-triggered temperature points.  
Figure 9: Relationship between irradiation and nucleation temperatures.