UV-C light-activated gallic acid and ultrasound: A novel approach for reducing enteropathogens inoculated in lettuce (Lactuca sativa L.)

The effect of UV-C light-activated gallic acid (AGA) alone or combined with ultrasound (US) on the inactivation of E. coli and S. Typhimurium inoculated in aqueous solution and lettuce was studied. The contact time (0–30 min) and AGA concentration (0.05–0.25 M) were evaluated against microorganisms inoculated in aqueous solutions. At selected conditions, the combined effect of AGA and US process was evaluated against microorganisms inoculated in lettuce leaves; samples were taken from washing peptone water and the surface of lettuce using a cotton swab. The microbial inactivation of AGA in lettuce was described using the Monod model, which adequately reproduces the inactivation kinetics (R > 0.96). In aqueous solutions, 10 min of contact time and 0.15 M and 0.25 M of AGA were required to reduce more than 5 log reduction of S. Typhimurium and E. coli, respectively. In lettuce, the E. coli showed higher resistance than S. Typhimurium to the AGA treatment, obtaining a maximum microbial reduction (4.33 ± 0.17 log reduction) using washing peptone water as a sampling method and AGA plus US process. Moreover, the AGA treatment combined with the US process presented a higher microbial inactivation compared to a common disinfectant (colloidal silver). Therefore, it is possible to indicate that AGA combined with the US may be an adequate alternative to reduce enteropathogens in lettuce.