# Effect of Ultrasonic Treatment on the Quality of Pumpkin Juice Fermented by Yeast
## 3 Results
### Influence of Ultrasonic-Assisted Yeast Fermentation on the Antioxidant Activity of Pumpkin Juice  
The antioxidant effects of ultrasonic waves with different powers on the fermented pumpkin juice are shown in Figure 2N. In this experiment, the ability of pumpkin juice to scavenge free radicals was used as a measurement index to reflect the changing trend of its antioxidant activity after ultrasonic treatment. The experimental results clearly show that the antioxidant activity of pumpkin juice exhibits an upward trend with the increase in ultrasonic power, with only a slight decrease of 2.99% observed at 400 W. However, compared with the untreated pumpkin juice, this value does not show a significant difference. This phenomenon fully demonstrates that ultrasonic treatment can effectively retain the antioxidant activity of pumpkin juice to a large extent. This research result is consistent with the findings of [PERSON] et al. [32]. In their study, it was found that some enzymes, such as glucose oxidase, peroxidase (POD), and polyphenol oxidase (PPO), can be effectively inactivated via ultrasound. Meanwhile, the research conclusion obtained by [PERSON] et al. [29] that the antioxidant activity of pumpkin juice increases with the increase in power is also highly consistent with the results of this experiment. It is likely that the cavitation effect generated during the ultrasonic process plays a crucial role [33]. The cavitation effect can significantly enhance the extraction efficiency and utilization rate of phenolic compounds, thereby promoting improvements in the antioxidant properties of pumpkin juice. In addition, the factor of temperature also plays an important role in this process. An appropriate increase in temperature is beneficial in improving the solubility and diffusion rate of solutes, thus creating favorable conditions for the extraction of phenolic compounds. However, if the temperature is too high (exceeding 60 \({}^{\circ}\)C), it may cause the denaturation of phenolic compounds [11]; on the contrary, it will have a negative impact on its antioxidant performance. At the same time, some enzymes closely related to the oxidation process, such as PPO and POD involved in the enzymatic browning reaction, will be inactivated under the influence of ultrasonic cavitation, which also contributes to a certain extent to improvements in the antioxidant performance of pumpkin juice. In conclusion, through a comprehensive analysis of various factors, this study has deeply revealed the influence mechanism of ultrasonic waves on the antioxidant effect of fermented pumpkin juice, providing a valuable theoretical basis and data support for the optimization of pumpkin juice processing technology and research in the related fields. Influence of Ultrasonic-Assisted Yeast Fermentation on the Microbial Flora and Microstructure of Pumpkin Juice  
During the process of the ultrasonic treatment of pumpkin juice, the total number of colonies shows a significant regular change. That is, with the gradual increase in ultrasonic power, the total number of colonies in the pumpkin juice shows a continuous and obvious decreasing trend. This is consistent with the conclusion of [PERSON] et al, [34], who found during the experiment that using ultrasonic (US) treatment alone on juice samples could significantly reduce the total number of colonies, as well as the number of yeasts and molds. After a detailed comparison of the sterilization effects at different power levels, it was found that when the ultrasonic power reached 400 W, the sterilization effect on pumpkin juice reached the optimal level, and the sterilization rate was as high as 32% at this time. By further comprehensively considering all the experimental results, a clear trend can be observed: the greater the ultrasonic power, the more significant the sterilization effect in pumpkin juice. The reduction in the number of microorganisms in pumpkin juice may be due to the disruption of microbial cell membranes during the ultrasonic treatment process [35].