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Validation of Acceptable Log Reduction of Pathogenic Bacteria using Thermal and Non-Thermal Processes

Griffis, Carl; Crandall, Philip
University of Arkansas
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  1. Survey manufacturers of Ready-to-Eat (RTE) and Ready-to-Heat (RTH) meat and poultry products to understand the limitations of the methods they currently use to validate an acceptable pathogen log reduction from a matrix of processing treatments, food ingredients and packaging systems. Do this for both naturally occurring pathogens and hazards that may be of potential concern for food defense.
  2. Develop a series of microbial, biological and physical surrogates to measure: the log reductions, the bacteriastatic effects during storage, the time and temperature integration (TTI's) during processing and storage.
  3. Study the effects of stress factors on the thermal resistance of food pathogens under processing conditions and look at the physiological inducible mechanisms that pathogenic microorganisms use to adapt to changes in their environment that can significantly increase their resistance to destruction and limits to their recovery after treatment by heat and chemicals.
  4. Measure the newly developed surrogates against known food pathogens, organisms that are potential food defense concerns, publish D and z values and model these log reductions, kinetic parameters, affect on quality and safety attributes for both RTE and RTH foods.
  5. Use laboratory and pilot plant processing systems to substantiate the log reductions demonstrated in objectives 2,3 & 4 before testing under simulated commercial conditions.
  6. In conjunction with industrial representatives, help them to develop improved guidelines and protocols that will more accurately verify the log reduction for RTE and RTH HACCP plans, pasteurization, cooking and non-thermal treatments. As a final end product we want to have RTE foods that have been given a known lethal treatment with a known safety margin, but have the maximum sensory quality by minimizing the over processing of the food.
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NON-TECHNICAL SUMMARY: Food processors have to be sure that the products they are producing are safe--that they contain no microorganisms that can grow in the product and harm consumers. We will work with food processors to understand their needs and cooperate in developing indicators that will fit their current manufacturing operations.

APPROACH: Manufacturers of Ready-to-Eat, (RTE) and Ready-to-Heat, (RTH) meat and poultry products will be surveyed to understand the limitations of the current methods they use to validate an acceptable pathogen log reduction from a matrix of processing treatments, food ingredients and packaging systems. The first steps in accomplishing this objective will be to survey the literature and grant project reports that are available. We will try to coordinate this survey to develop a questionnaire with a professional organization to 'open the door' to the persons receiving the survey. The method will be a telephone survey style with a standard questionnaire. A series of three potential microbial surrogates are already being screened for possible replacement of Listeria innocua (LI) and Listeria monocytogenes (LM). Previous research at the University of Arkansas has established that under the experimental conditions tested that Listeria innocua (LI) is significantly more heat tolerant than LM. For example at 62.5 degree C LM D value was 1.6 min while LI's was 3.24. Preliminary work on a enzyme/protein denaturation system that will undergo linear thermal inactivation. There are several reports in the literature of possible enzyme systems to validate 'end point heating' requirements. Preliminary work on alkaline phosphatase presented the initial problem of having excessive phosphate interference because most of the RTE products already containing high levels of sodium phosphate. We will develop additional devices for RTE processors concerned about introducing any microorganisms into their plants, Time and Temperature Integrators TTI's. These devices are designed for VERY small plants that have a minimal amount of laboratory support. After insulating small recorders can be placed inside a food, go through pasteurization process with the food and integrate a time-temperature profile. From a thermistor embedded at the thickest part of the product, lethality for pathogenic LM can be calculated. After the TTI's are developed and tested, then for each food product studied, D and z values will be determined both for pathogens of interest and for surrogate organisms. Then, the particular product under study will be inoculated with the surrogate and placed into a pilot-scale water pasteurizer, oven or retort along with the TTI. After the cooking process is complete, a determination will be made of the number of survivors in the food product using standard plate count methods and this number will be compared to lethality calculations based on the time-temperature data from the computer. Once the relationship between lethality calculations and actual numbers of survivors has been established, verification of thermal processes can be accomplished using only the computer and the laboratory data for D and z values. These values can then be added to the lethality models we are developing.

Funding Source
Nat'l. Inst. of Food and Agriculture
Project source
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Food Preparation and Handling
Food Defense and Integrity
Bacterial Pathogens