Chlorine dioxide as water disinfectant during fresh-cut iceberg lettuce washing: Disinfectant demand, disinfection efficiency, and chlorite formation

Abstract

The use of chlorine dioxide (ClO2) as water disinfectant during fresh-cut iceberg lettuce washing was studied concerning three key issues: i) disinfectant demand, ii) disinfection efficiency, and iii) production of chlorite (ClO2−). Standardized process water (SPW), a watery suspension of iceberg lettuce, was used as model water system. In SPW (chemical oxygen demand (COD) 1130 mg O2/L, 4 °C, pH 7) the chlorine demand was more than 10 times higher than the ClO2 demand. Dosing 5 mg/L ClO2 (0.40 mg/L residual after 2 min contact time) inactivated the total psychrotrophic plate count (TPC), including molds, to undetectable levels (>3 log reduction) after 2 min, and reduced Escherichia coli (E. coli) to undetectable levels (>5 log reduction) within 3 min. A dose of 70 mg/L chlorine (free chlorine residual of 1.7 mg/L after 2 min) was unsuccessful to inactivate molds to undetectable levels. About 77% of the consumed ClO2 was reduced to ClO2− due to reaction with the SPW. Concerning disinfectant dose, ClO2 is more efficient than free chlorine for disinfecting fresh-cut lettuce wash water. However, data on the transfer of ClO2− and chlorate (ClO3−) to the lettuce is needed before ClO2 can be recommended as wash water disinfectant.