# Effect of Ultrasonic Treatment on the Quality of Pumpkin Juice Fermented by Yeast
## 3 Results
### Influence of Ultrasonic-Assisted Yeast Fermentation on the Color of Pumpkin Juice  
Color is a key indicator that affects the consumer acceptability of food [19]. As can be seen from Figure 2B-J, for the pumpkin juice treated with ultrasonic waves, the L* value hardly changed. It only increased slightly after being treated at a power of 400 W, but the change was still not significant. When [PERSON] [20] et al. studied the color changes in blueberries, they found that regardless of the amplitude, ultrasonic treatment did not affect the L* value results of blueberry juice. The a* and b* values of the pumpkin juice after ultrasonic treatment also showed little difference from those of the control group, with little color change. The color difference the value \(\Delta\)E between the two was less than 1.5, indicating that there was no significant color difference between the two samples. This result fully demonstrates that the pumpkin juice fermented by yeast after ultrasonic treatment can maintain its color extremely effectively, keeping it in a state similar  
Figure 2: The influence of different ultrasonic powers on the physicochemical properties of fermented pumpkin juice. **(A)**: The influence of ultrasonic treatment on the total acid content of pumpkin juice. **(B–J)**: The influence of ultrasonic treatment on the color of pumpkin juice. **(K)**: The influence of ultrasonic treatment on the carotenoids in pumpkin juice. **(L)**: The influence of ultrasonic treatment on the ascorbic acid (VC) in pumpkin juice. **(M)**: The influence of ultrasonic treatment on the flavonoid content in pumpkin juice. **(N)**: The influence of ultrasonic treatment on the antioxidant activity of pumpkin juice.  
to the color of natural pumpkin juice. [PERSON] et al. (2018) found in their research that the total color difference between kiwifruit juice after thermo-ultrasonic treatment and before treatment was small, which is consistent with this conclusion. When the pumpkin juice is treated with ultrasonic waves, the water content inside the cells is reduced through the cavitation effect ([PERSON] et al., 2018); in this process, the dissolved oxygen content in the pumpkin juice decreases, and the reduction in the dissolved oxygen content plays an important inhibitory role in the enzymatic browning process of the pumpkin juice ([PERSON] et al., 2018). Enzymatic browning is one of the key factors leading to color changes in fruit and vegetable products. When the oxygen content decreases, it is difficult for the relevant enzymatic reactions to proceed fully, thus keeping the color of the pumpkin juice basically stable. This color stability is of great significance for the pumpkin juice fermented by yeast. It can ensure that the fermented pumpkin juice is more attractive in terms of color, and more in line with consumers' expectations of the color of pumpkin juice. Furthermore, it can play a positive role in market promotion and product quality improvement. This is consistent with the research findings of [PERSON] et al. (2018), who discovered that the cavitation effect of ultrasonic waves leads to a decrease in the activity of polyphenol oxidase (PPO), thus better maintaining the color of orange juice.