Destruction of Escherichia coli O157:H7 on whole apples via single and sequential application of chemical sanitizers
This study was conducted to determine if single and sequential application of selected chemical sanitizers can achieve a 5-log reduction in Escherichia coli O157:H7 populations on apple surfaces. Sanitizers were utilized with and without mild heat to determine if increased temperatures would have an effect on sanitizer efficacy. Apples were spot-inoculated with a non-pathogenic strain of E. coli O157:H7, immersed in a sanitizer for 2 min and rinsed in distilled water for 5 sec. Chemical sanitizers used for single application were chlorine (200 ppm), hydrogen peroxide (5%), sodium bicarbonate buffer (pH 11.5), 1.5% H2O2 + 1.5% lactic acid, Tsunami100[superscript trademark symbol] (80 ppm) and ProSan[superscript trademark symbol] (1%). Among these chemical sanitizers, chlorine, 5% hydrogen peroxide, 1.5% hydrogen peroxide + 1.5% lactic acid, sodium bicarbonate buffer and Pro-San[superscript trademark symbol] were used sequentially on apple surfaces for 2 min per sanitizer. Bacterial populations were enumerated by duplicate plating on Tryptic Soy agar (TSA) and Sorbitol MacConkey agar (SMA) after 24 or 48 hr incubation at 35 or 370C. Populations of E. coli O157:H7 on apples immersed in (single) chemical sanitizers at 250C were reduced by 1.35 to 3.07 log10CFU/apple (TSA) and 1.82 to 3.77 log10CFU/apple (SMA). Log10 reductions for single treatments applied at 550C were 1.46 to 3.72 log10CFU/apple (TSA) and 2.31 to 3.90 log10CFU/apple (SMA). Sequential treatments at 250C eliminated E. coli O157:H7 by 2.10 to 3.17 log cycles based on TSA counts and 1.47 to 3.01 log cycles based on SMA counts. At 550C, E. coli O157:H7 populations were eliminated by 2.59 to 3.54 log cycles (TSA) and 1.96 to 3.27 log cycles (SMA). Single application of 1.5% hydrogen peroxide + 1.5% lactic acid and sequential application of chlorine (200 ppm) and 1.5% hydrogen peroxide + 1.5% lactic acid at 550C achieved the highest reductions of E. coli O157:H7 populations on apple surfaces at 3.90 and 3.27 log cycles (SMA), respectively. Results suggest that single and sequential application of chemical sanitizers were not effective in achieving a 5-log reduction of E. coli O157:H7 on whole apples based on conditions of the present study but can reduce the populations of the pathogen by approximately 4-log.