Survival of Escherichia coli following hydrogen peroxide treatment at differ temperatures

RAFFELLINI, S; GUERRERO, S; ALZAMORA, STELLA MARIS

New Orleans

Congreso; 2005 IFT Annual Meeting; 2005

IFT

Various interventions to reduce contamination of fresh fruits have been proposed: decontamination with water, chlorine, chlorine dioxide, organic acids, peroxyacetic acid, hydrogen peroxide, ozone and others. However, there is an insufficiency in quantitative information concerning the efficacy of the sanitizers as affected by environmental conditions. The objective of this study was to evaluate and to model the survival of E. coli as affected by H2O2 treatment at various exposure times, concentrations and temperatures. E. coli ATCC 35218 was cultivated at 37° C to stationary-phase in TSB. The culture was centrifuged, washed twice and concentrated 10-fold with sterile 0.85% physiological saline solution. 1ml of this suspension was added to 99 ml of each assayed system (final concentration 7.5 log CFU/ml). Inactivation experiments were carried out at 12.5; 25.0; 37.5, or 50.0 °C in sterile citric acid – Na2HPO4 buffer solution (pH 5.8) containing different H2O2 concentrations (0.0 to 3.5%w/v). Aliquots were periodically collected, neutralized with 4% Na2S2O3.5H2O, serially diluted in 0.1% peptone water and pour plated using PCA. The plates were counted following incubation at 37° C for 48 h. The efficacy of H2O2 treatment was less as temperature and concentration decreased. 2%w/v H2O2 caused 6.0 log CFU/ml reduction after 1 min exposure at 50º C. But at 37.5 and 25.0º C, the 1 min treatment killed up to 2.5 and 2.0 log CFU/ml respectively. At 12.5º C, the effect was only bacteriostatic. Kinetics was modelled by using a Weibull type distribution of resistances. Although these results must be validated in fruits, they give useful information about of how different temperatures/concentrations affect H2O2 effectiveness.