Control of Foodborne Pathogens and Spoilage Microorganisms by Antimicrobial Compounds

NON-TECHNICAL SUMMARY: Traditionally and naturally occurring food preservatives will be evaluated for their effectiveness in preventing the growth of or killing food poisoning microorganisms. The overall goal of the project is to improve food safety.

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APPROACH: Selected foodborne pathogens and spoilage microorganisms will be evaluated for susceptibility to food grade antimicrobials and natural antimicrobials in microbiological medium, food model systems and in foods. Antimicrobials will be evaluated under a variety of environmental conditions. Various food processing procedures including heat and ultrasound will be utilized to evaluate their interactive effect with antimicrobials. Research will be done to improve the efficiency of antimicrobials by developing delivery systems that have better interaction with microorganisms. Factors involved in the development of resistance of microorganisms to food antimicrobials will be evaluated.

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PROGRESS: 2002/10 TO 2007/10<BR>
The overall goal of a study was to investigate the sporicidal capabilities of commercially available household disinfectants and other products against spores of Bacillus cereus used as surrogates for B. anthracis. Products were evaluated on fresh spinach and cantaloupe. The purpose of the study was to develop recommendations for consumers to decontaminate food and/or household areas in the event of a large scale terrorism event. For the cantaloupe melon rind the control population was 7.15 log CFU/ml. The log reduction was > 5.15 for undiluted sodium hypochlorite and inactivation took 120 min. For the 1.84%-2.40% NaOCl-containing compounds, log reductions were between 2.75 and 3.40 over 180 min. This may be due in part to the complex matrix and microstructure of the netting of the rind of the cantaloupe. For spinach, the control population mean was 7.37 log CFU/leaf. A greater than 5.84 log reduction in B. cereus spores was found for both sodium hypochlorite and an HCl-containing product. However, the former reduced the viable spore population to the lowest detectable level in 10-60 min while the latter took approximately 3 h. The objective of a second study was to determine if the shape of survivor curves for Escherichia coli O157:H7 was influenced by the physiological state of the microbial cells at the time of heat exposure. E. coli O157:H7 was grown aerobically in tryptic soy broth for 24 hr at 35 degree C without shaking (traditional method) for two consecutive transfers prior to use. This culture was also used to inoculate a chemostat vessel for constant harvesting of cells in the growth phase (chemostat method). D58C values were 5.30, 2.27 and 3.95 minutes for traditional cells and chemostat cells heated in peptone and traditional cells adjusted to pH 7, respectively. D59C values were 3.12 min, 1.41 min and 1.49 min for the same respective cells. Although the non-linear Weibull function resulted in a cleaner fit for traditional cells in peptone, there was no significant difference in correlation for log-linear versus the non-linear regression. Significant decreases in D and z-values for both growth types in pH 7 phosphate buffer represent increased heat sensitivity. Results suggest differences in the inactivation response of microbial cells depending on their growth state and pH at the time of inactivation. In a third study, E. coli K12 cells, grown statically or in chemostat, were exposed to HPH-processing pressures of 50-350 MPa in the absence or presence of nisin. Survivors were enumerated via plating on non-selective growth media. Significant HPH-induced inactivation of the gram-negative microorganism was observed in the range of 100-250 MPa. Above 300 MPa, heat was the main factor promoting microbial inactivation, regardless of whether cells were grown in chemostat or statically. Chemostat-grown cells were significantly more resistant to HPH processing then statically grown cells. Data indicated potential synergistic effects of nisin and HPH on the inactivation of bacterial contaminants.
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IMPACT: 2002/10 TO 2007/10BR>
Studies demonstrated that differences in heat inactivation of pathogenic foodborne microorganisms, such as E. coli O157:H7, depend on the physiological state and environment of the test microorganism. As many industrial food processes use heat to produce safe food, these processes could be inadequate if the model or models used are based upon inactivation of microorganisms that are not representative of the natural microflora. Therefore, the physiological state of test microorganisms needs to be determined when heat inactivation data is used in modeling inactivation kinetics. Chlorine-containing products are recommended for decontamination of fresh produce in the event of a large scale intentional bioterrorism incident in which product has been distributed to consumers. HCl-containing consumer products were useful if longer exposure periods could be utilized. A home emergency kit should contain commercial bleach and/or chlorine-containing sprays. Homogenization is used widely in the dairy industry to improve product stability and quality. High-pressure homogenization (HPH) of fluid foods up to pressures of 300 MPa was shown to have excellent potential for microbial inactivation without significant heat. Microbial inactivation can be enhanced during HPH with the inclusion of natural antimicrobial compounds.