Microbiological Shelf-Life Extension and Quality Retention of a Novel Vegetable Product Through an Optimized Preservation Treatment Combining Citric Acid, Oregano Essential Oil, and UV-C Radiation

A treatment combining citric acid disinfection, oregano essential oil application, and UV-C radiation was developed to enhance quality and extend the microbiological shelf-life of a novel ready-to-eat salad (50% Creole purple lettuce, 25% arugula, and 25% beet leaves). For that, response surface methodology was applied to find the level of each treatment that simultaneously optimize the responses (counts of mesophilic aerobic bacteria and Enterobacteriaceae, antioxidant potential, total polyphenol content, and PPO/POD enzymatic activity). The treatments, evaluated according to a Box-Behnken design, showed varying effectiveness in reducing the microbiological load and enzymatic activity, as well as in increasing the antioxidant potential within the evaluated treatment ranges. All responses presented a good fit to quadratic models, revealing significant linear and quadratic dependencies, as well as significant interactions among factors in some of the studied responses. Optimal conditions (0.3325% citric acid, 240 ppm oregano essential oil, and 6.4 kJ/m² UV-C) yielded significant improvements compared to control samples: 1.56 and 1.94 log cycles significant reductions in mesophilic aerobic bacteria and Enterobacteriaceae, 40.92% increase in polyphenol content, 15.75% and 16.16% increase in FRAP and DPPH antioxidant potential, and 58.07% and 32.69% decrease in PPO and POD enzyme activity, respectively. Finally, the optimized treatment extended the microbiological shelf-life by at least 7 days, also showing superior quality retention, with significant differences with control counts on that day. In conclusion, the study provides insights into the multifaceted responses of a novel ready-to-eat salad combining these non-thermal treatments, highlighting the potential synergies for microbiological and antioxidant improvements.