Efficacy of Slightly Acidic Electrolyzed Water and UV-Ozonated Water Combination for Inactivating Escherichia Coli O157:H7 on Romaine and Iceberg Lettuce during Spray Washing Process.

Spray washing is a common sanitizing method for the fresh produce industry. The purpose of this research was to investigate the antimicrobial effect of spraying slightly acidic electrolyzed water (SAEW) and a combination of ozonated water with ultraviolet (UV) in reducing Escherichia coli O157:H7 on romaine and iceberg lettuces. Both romaine and iceberg lettuces were spot inoculated with 100 μL of a 3 strain mixture of E. coli O157:H7 to achieve an inoculum of 6 log CFU/g on lettuce. A strong antimicrobial effect was observed for the UV-ozonated water combination, which reduced the population of E. coli by 5 log CFU/g of E. coli O157:H7 on both lettuces. SAEW achieved about 5 log CFU/g reductions in the bacterial counts on romaine lettuce. However, less than 2.5 log CFU/g in the population of E. coli O157:H7 was reduced on iceberg lettuce. The difference may be due to bacteria aggregation near and within stomata for iceberg lettuce but not for romaine lettuce. The UV light treatment may stimulate the opening of the stomata for the UV-ozonated water treatment and hence achieve better bacterial inactivation than the SAEW treatment for iceberg lettuce. Our results demonstrated that the combined treatment of SAEW and UV-ozonated water in the spray washing process could more effectively reduce E. coli O157:H7 on lettuce, which in turn may help reduce incidences of E. coli O157:H7 outbreaks.