Electrolyzed water and gaseous ozone application for the control of microbiological and insect contamination in dried lemon balm: Hygienic and quality aspects

In this study, the sanitization efficacy of decontamination techniques was evaluated on lemon balm (Melissa officinalis). Dried aromatic herbs are minor food components with widespread use and, despite their low water activity, they are often contaminated with microorganisms, including toxigenic and pathogenic ones. Gaseous ozone (GO) and electrolyzed water (EW) treatments were applied on lemon balm after and before drying (traditional at 40 °C and cold at 20 °C), respectively. Microbiological and entomological decontamination aspects were assessed as well as the sensory quality and compositional properties of the product in terms of essential oil, total polyphenol and ascorbic acid contents, and antioxidant capacity. The most interesting results concerned EW treatment (400 ppm × 1 min dipping) reducing aerobic mesophilic bacteria, Enterobacteriaceae, moulds and yeasts of about 4.0, 2.5, 2.0 and 1.0 Log cfu/g, respectively, thus below law limits. Moreover, 200 ppm EW x 1 min dipping was enough for limiting Bacillus cereus growth. However, sanitization against the beetle species Tribolium castaneum and Lasioderma serricorne was less efficient with EW (less than 40% mortality) compared with GO (200,000 ppm × min) (more than 95% mortality). Noteworthy, sensory analysis highlighted that lemon balm exposed to EW treatment did not lose organoleptic quality, in particular the color even seemed to improve in brightness when the herbs were subsequently cold dried. Furthermore, the loss in essential oils was not significant in terms of the overall content as well as total polyphenol, ascorbic acid and antioxidant capacity in EW treated lemon balm then submitted to cold drying. Differently, the combination of EW treatment and traditional drying led to a significant detriment of compositional properties. The results obtained in this study are encouraging and deserve to be discussed with producers. •EW treatment reduced microbial contamination below law limits in dried lemon balm.•EW treatment did not negatively affect sensorial quality of dried lemon balm.•EW treatment did not negatively affect chemical properties of cold dried lemon balm.•GO was more efficient than EW in insect control in lemon balm.•EW and GO were used to reduce microbial and insect contamination in lemon balm.