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