Disinfection of selected vegetables under nonthermal treatments: Chlorine, acid citric, ultraviolet light and ozone

Lettuce, tomatoes and carrots were evaluated under four disinfection methods. Chlorine (50, 100 and 200 ppm) was compared for effectiveness with citric acid (0.5, 1 and 1.5%), ultraviolet light (UV-C) (0.65 and 1.6 mW/cm2) and ozone (5 ppm) to inactivate Escherichia coli ATCC 11775. Processing times were from 3 min up to 60 min. Hunter color parameters, color functions (ΔE, hue, chroma), tomato color index (TCI) and whiteness index (WI) were evaluated after disinfection. Results showed that citric acid was not effective for inactivation of E. coli at the tested conditions. UV-C was effective in the inactivation of the microorganism when fluence was higher, being more effective in the smooth surface of tomato (2.7 log). Meanwhile, ozone was also able to inactivate bacteria in tomatoes (2.2 log) after only 3 min. Carrots and lettuce showed lower inactivation for all treatments because of their porous and roughened surfaces. UV-C was the treatment that most affected the color of the produce; it generated browning of lettuce, and increase of TCI and WI of carrots. Ozone also affected the greenness of lettuce. Concentration, dose and processing times of novel disinfection methods need to be evaluated not only for microbial counts, but also sensory properties.