Efficacy of chlorine for inactivation of Escherichia coli on vegetables

The effectiveness of calcium hypochlorite on inactivation of Escherichia co li inoculated on fresh produce was investigated. Different exposure times a nd concentrations of chlorine were studied. Dipping was not effective at el iminating E. coli populations although it significantly reduced the E. coli counts compared with inoculated, undipped lettuce. Dipping inoculated cos lettuce leaves into hypochlorite solutions containing 50 mg/l or greater fr ee chlorine for times of 30 s or greater reduced E. coli cells by approxima tely 1.9-2.8 log(10) CFU/g from an initial population of approximately 6.8 log(10) CFU/g. Dipping inoculated broccoli florets into hypochlorite soluti on reduced E. coli cells by approximately 1.7-2.5 log(10) CFU/g depending o n the time and concentration of the free chlorine. Dipping lettuce or brocc oli in water alone reduced cell numbers by 1.5-1.5 log(10) CFU/g. Dipping b roccoli florets for 2 min in a 100 mg/l free chlorine solution at temperatu res between 4 and 25 degrees C reduced E. coli cells by approximately 2.4 l og(10) CFU/g. No significant effect of temperature on the rate of cell redu ction was observed. (C) 2000 Elsevier Science B.V. All rights reserved.