Efficacy of chlorine for inactivation of Escherichia coli on vegetables

The effectiveness of calcium hypochlorite on inactivation of Escherichia coli inoculated on fresh produce was investigated. Different exposure times and concentrations of chlorine were studied. Dipping was not effective at eliminating 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 free chlorine for times of 30 s or greater reduced E. coli cells by approximately 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 solution reduced E. coli cells by approximately 1.7-2.5 log(10) CFU/g depending on the time and concentration of the free chlorine. Dipping lettuce or broccoli in water alone reduced cell numbers by 1.5-1.5 log(10) CFU/g. Dipping broccoli florets for 2 min in a 100 mg/l free chlorine solution at temperatures between 4 and 25 degrees C reduced E. coli cells by approximately 2.4 log(10) CFU/g. No significant effect of temperature on the rate of cell reduction was observed. (C) 2000 Elsevier Science B.V. All rights reserved.