## 3 Results and Discussion
### Physical Properties of Bell Pepper Samples
In the case of fresh peppers, the dry matter content was recorded at 14.82%, which decreased to 12.67% following fermentation. The factors influencing consumer acceptance of food are crucial, encompassing aspects such as color, taste, texture, and nutritional value. pH levels significantly impact pigments like carotenoids, chlorophyll, and anthocyanins, which contribute to the coloration of vegetables. Moreover, pH affects texture and overall shelf life. During food processing, pH plays a vital role in protein denaturation, enzymatic activity, and the growth and survival of microorganisms. Therefore, a thorough understanding of pH is essential for ensuring the safety and quality of food products [41]. Fresh red bell peppers typically have a pH of around 5.2. However, this pH level tends to increase over time, often accompanied by visible signs of spoilage [42]. Lactic fermentation has been demonstrated to gradually lower fermented vegetables' pH [43]. The pH levels indicate the optimal endpoint of fermentation (pH \(\leq\) 3.9) and reflect the effectiveness of the fermentation process. After seven days of lactic fermentation, the pH levels in the bell pepper samples ranged from 3.01 (S_5) to 3.06 (S_1 and S_3), signifying adequate fermentation and the completion of the process (Table 2). No significant differences in pH were observed between samples subjected to varying levels of ultrasound and those that received no treatment. Furthermore, no correlation was found between the nature of the pre-treatment, the parameters used, and pH, as the variations in pH were negligible. Color  
The color of vegetables, especially peppers, is a key quality characteristic for consumers, determined by bioactive compounds such as chlorophyll, anthocyanins, and carotenoids. The skin of the pepper, particularly its cuticle, differs in color from the flesh; therefore, color was measured separately for the top and bottom of each sample [44; 45]. Following ultrasound treatments, the majority of samples exhibited enhanced brightness (L*) and a more pronounced red hue (a*), accompanied by a decrease in yellow coloration (b*). This phenomenon was noted in the top and bottom measurements of a* and b* (Figure 2). The peak brightness was observed after 15 min of ultrasound immersion. The effects on skin color vary based on the methods and parameters employed. Notably, a 30 min ultrasound treatment resulted in an approximate 25.6% increase in red coloration, while the contact ultrasound method led to an elevation in yellow color. Extending the sonication duration from 15 to 30 min resulted in a 30.3% rise in yellow color. In contrast, the contact method, with a duration extension from 1 to 5 min, caused a reduction of about 13.1% in yellow coloration. Lactic acid fermentation resulted in a modest increase in brightness but led to a significant reduction in red and yellow color compared to fresh samples (Figure 2). After fermentation, skin brightness showed a slight improvement in most samples, while the proportions of red and yellow decreased notably compared to unfermented peppers without pre-treatment. An exception was noted for the pepper subjected to a 5 min contact ultrasound treatment, which exhibited a significant increase in red and yellow color post-fermentation, achieving the highest yellow color proportion among all samples. All pre-treated and fermented samples exhibited higher levels of red and yellow coloration in the skin than untreated, fermented peppers. Notably, increasing the duration of immersion sonication from 15 to 30 min led to a significant reduction in the proportions of red and yellow colors, decreasing by approximately 27.6% and 25.8%, respectively. Incontrast, extending contact sonication from 1 to 5 min increased the proportions of red and yellow colors by about 54.8% and 101.6%, respectively (Figure 2). An analysis of the color in the lower layer revealed that ultrasound treatment slightly decreased brightness (L*) across most samples.