Efficacy of chlorine dioxide (ClO2) gas in reducing Escherichia coli O157:H7 and Listeria monocytogenes on strawberries was determined using batch and continuous flow ClO2 gas treatment systems. Effects of continuous ClO2 gas treatment on total aerobic plate count, color, and residual ClO2 and chlorite on strawberries were also evaluated. Strawberries were spot inoculated with 7 to 8 log CFU per strawberry of each pathogen (E. coli O157:H7 and L. monocytogenes), stored for 1 day at 4 degrees C, and treated at 22 degrees C and 90 to 95% relative humidity with 0.2 to 4.0 mg/liter ClO2 gas for 15 or 30 min using a batch treatment system or with 0.6, 1.8, and 3.0 mg/liter for 10 min using a continuous treatment system. Surviving microbial populations were determined using a membrane-transfer plating recovery method. Increased ClO2 gas concentrations resulted in increased log reductions of each pathogen for both the batch and continuous systems. A batch treatment of strawberries with 4 mg/liter ClO2 for 30 min and continuous treatment with 3 mg/liter ClO2 for 10 min achieved greater than a 5-log reduction for both E. coli O157:H7 and L. monocytogenes. After continuous exposure to 3.0 mg/liter ClO2 gas for 10 min followed by 1 week of storage at 4 degrees C, no aerobic microorganisms were detected and the color of the strawberry surface did not change significantly (P > 0.05). Residues of ClO2 and chlorite on strawberries after the treatment were 0.19 +/- 0.33 mg ClO2 per kg and 1.17 +/- 2.02 mg Cl2 per kg, respectively, whereas after 1 week of storage no ClO2 residues were detected and residual chlorite levels were down to 0.07 +/- 0.12 mg Cl2 per kg. These results suggest that ClO2 gas treatment is an effective decontamination technique for improving the safety of strawberries while extending shelf life.

No abstract

A modified Gompertz equation was used to model the effects of temperature (55, 60, and 65ЊC), sodium lactate (0, 2.4, and 4.8%), and sodium diacetate (0, 0.125, and 0.25%) on inactivation of Listeria monocytogenes strain MFS 102 (serotype 4b) in frankfurter slurry. The effects of these factors were determined on the shouldering region (parameter A), maximum death rate (parameter B), and tailing region (parameter C) of microbial inactivation curves. Increased temperature or sodium diacetate concentrations increased the death rate, whereas increased sodium lactate concentrations decreased heat resistance. Complex two-way interactive effects were also observed. As both temperature and sodium lactate increased, the death rate decreased; however, as temperature and sodium diacetate increased, the death rate increased. The effect of the interaction between sodium lactate and sodium diacetate on the maximum death rate varied with temperature. Increases in both acidulants at temperatures above 56.7ЊC decreased the death rate, whereas at temperatures below 56.7ЊC, increases in both acidulants increased the death rate. To test for significant differences between treatments, D-values were calculated and compared. This comparison revealed that, in general, sodium lactate increased heat resistance and sodium diacetate decreased heat resistance of L. monocytogenes. This information is important for reducing and minimizing contamination during postprocessing thermal treatments.Listeria monocytogenes (LM) is responsible for approximately 2,500 cases of listeriosis and 500 deaths in the United States each year (5, 13). LM is a foodborne pathogen of concern because of the high death rate (20%) associated with LM infection and the ability of LM to target particular subsets of the population and to grow under refrigerated food storage conditions (6). In 2003, an LM risk assessment for ready-to-eat (RTE) foods was published by the U.S. Food and Drug Administration (FDA), U.S. Department of Agriculture Food Safety and Inspection Service (USDA-FSIS), and the Centers for Disease Control and Prevention (CDC) (17). According to the assessment, consumption of deli meats and frankfurters (not reheated) is associated with the highest risk of contracting listeriosis on a per serving and per annum basis (17). The presence of LM in RTE foods often is associated with environmental contamination in the postlethality processing and/or packaging area. In RTE food products, postprocessing heat pasteurization can be used to reduce or eliminate LM from product surfaces and/or acidulants can be added to the product formulations to prevent growth of any LM survivors over the shelf life of the product (16).The addition of lactate and diacetate salts to product formulations has been successful in controlling the growth of LM during product shelf life (7, 11); however, the effects of these two food grade chemicals, which are generally recognized as safe and can be used together, on the heat resistance of LM have not been well studied, especially a...