Titanium dioxide/UV photocatalytic disinfection in fresh carrots

Increased occurrences of fresh produce-related outbreaks of foodborne illness have focused attention on effective washing processes for fruits and vegetables. A titanium dioxide (TiO₂) photocatalytic reaction under UV radiation provides a high rate of disinfection. The photo-killing effects of TiO₂ on bacteria in liquid cultures under experimental conditions have been widely studied. However, the disinfection effects of the TiO ₂ photocatalytic reaction on fresh vegetables during a washing process have not been evaluated. Our objectives were to design a pilot-scale TiO₂/UV photocatalytic reactor for fresh carrots and to compare the bactericidal effects of the TiO₂/UV reaction against bacteria in liquid media and on carrots. TiO₂/UV photocatalytic reactions for 40, 60, and 30 s were required for the complete killing of Escherichia coli, Salmonella Typhimurium, and Bacillus cereus (initial counts of approximately 6.7 log CFU/ml), respectively. The counts of total aerobic bacteria in fresh carrots and foodborne pathogenic bacteria in inoculated carrots were also measured. Counts of total aerobic bacteria were reduced by 1.8 log CFU/g after TiO₂/UV photocatalytic disinfection for 20 min compared with a 1.1-log CFU/g reduction by UV alone. E. coli, Salmonella Typhimurium, and B. cereus (8 log CFU/ml) were inoculated onto carrots, and the number of surviving bacteria in carrots was determined after treatment. The TiO₂/UV treatment exhibited 2.1-, 2.3-, and 1.8-log CFU/g reductions in the counts of E. coli, Salmonella Typhimurium, and B. cereus, respectively, compared with 1.3-, 1.2-, and 1.2-log CFU/g reductions by UV alone. The TiO₂/UV photocatalyst reaction showed significant bactericidal effects, indicating that this process is applicable to nonthermal disinfection of fresh vegetables.