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Application of three physical treatments on fresh-cut bitter gourd (Momordica charantia L.) to reduce microbial risks
Thesis Abstract:
Fresh-cut produce are ready-to-eat, convenient, and retain maximum nutrients. However, even minimal processing accelerates product deterioration and reduces food safety due to microbial infection. In this study, we evaluated the impacts of UV-C irradiation, low temperature, ultrasound, and UV-C followed by low temperature treatments on microbial risk of fresh-cut bitter gourd. Firstly, the next-generation sequencing (NGS) technology through full length 16S rRNA analysis was utilized to identify microorganisms on the surface of fresh-cut bitter gourd after 12 h of exposure to room temperature. The findings revealed that a total of 34 bacterial species were identified, with Buttiauxella izardii, Enterobacter mori, and Atlantibacter hermannii emerging as dominant with 26%, 24%, and 9% species richness and abundance, respectively. Subsequently, fresh-cut bitter gourd treated with UV-C, low temperature, ultrasound, and UV-C followed by low temperature and then kept at room temperature for 6 h was assessed for determining bacterial numbers using standard aerobic plate count method with 3M Petri films. The results showed that both 0.5 and 1.5 kJ.m-2 UV-C irradiation significantly inhibited microbial growth with 6.75 x 103 and 6.21 x 103 CFU.mL-1, respectively, compared to low temperature and ultrasound with 1.08 x 104 and 1.59 x 104 CFU.mL-1, respectively. Particularly, lower doses of UV-C treated fresh-cut bitter gourd displayed a substantial 10-folds decrease in bacterial population compared to low temperature and ultrasound treatments. Meanwhile, no significant differences were observed between UV-C alone and the combined treatments of UV-C followed by low temperature. In addition, lower doses of UV-C irradiation decreased hydrogen peroxide (H2O2) production, increased proline level, reduced MDA content and improved superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities. Moreover, the phenylpropanoid pathway was activated by UV-C treatment by inducing phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) activity in fresh-cut bitter gourd. Collectively, these findings suggest that applying UV-C irradiation alone can decrease the level of bacterial contamination in fresh-cut bitter gourd to an acceptable level of 103 CFU.mL-1 in accordance with the EU Food Safety Regulation.