Intervention Strategies to Control Stressed and Non-Stressed Pathogens in Poultry Meat

NON-TECHNICAL SUMMARY: Trends in the food industry have been towards the convenient, refrigerated foods with extended shelf life and the consumer concerns about cholesterol, saturated fat, total calories, and sodium chloride have incited food processors to modify product formulations in order to satisfy the demands of health conscious consumers. Although such foods may be readily accepted and greatly appreciated by consumers, the recent resurgence of certain pathogens in such foods has been attributed to processing techniques and ingredient changes that may have contributed to its higher incidence and survival in meat products. Outbreaks have historically been linked but not limited to raw foods of animal origin together with cross-contamination to ready-to-eat foods through inadequate processing or personal hygiene as being significant contributory factors to the cause of outbreaks. Although, cross-contamination is inevitable there is a need to minimize this by implementing safety measures throughout the farm-to-table continuum. Organic and inorganic acids have been widely used in the food industry by deliberate addition to control foodborne pathogens and through controlled fermentations. Addition of organic acids and their salts during the manufacture of meat products is well documented. Although these applications in a variety of processes has been effective in controlling certain pathogenic bacteria, new hazards to the safety of the food supply are being posed due to the emergence of microorganisms resistant to the physical and chemical processes of traditional preservation. Acids have a lethal or inhibitory effect on microorganisms when they are used in high enough concentrations, but when used in moderate concentrations they often encourage the bacteria to have increased acid tolerance. This increased tolerance to acidic conditions can lead to long term survival in acidic foods and increased probability of survival in the gastric environment. The efficiency of thermal processing protocols to eliminate/ reduce the risk of foodborne pathogens in processed meats is generally targeted towards non-adapted strains whereas the increased thermal tolerance of acid tolerant/ adapted strains could be a reason for concern. Despite the widely published literature on the thermal tolerance of acid adapted pathogens such as Salmonella and E. coli O157:H7 there are some limitations to the existing research. These limitations range from research being done in laboratory media and liquid foods to foods being held under conditions that do not reflect the current practices of storage and distribution in the industry. Another weakness of this widely researched area is that the data obtained from conducting studies on laboratory media and liquids foods may or may not be extrapolated to actual food systems including meat matrices such as ground beef and conditions that are closely related to the processing, storage and distribution of these food systems.

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APPROACH: Cultures (Salmonella spp.and Listeria monocytogenes)will be grown in laboratory media supplemented with glucose to a stationary phase and held for 12-18 hours. Thermal tolerance of acid adapted cells will be determined by D-values and compared to those of non-adapted cells. D-values will be determined in a poultry meat matrix. Heat tolerant cultures will be developed by growing multiple strains in laboratory medium maintained at sub-lethal temperatures for 18-24 hours in the stationary phase. Heat tolerant cells will then be enumerated by growing on laboratory media supplemented with glucose and compared to those grown in regular media. These pathogens will be inoculated into poultry meat products to determine if adaptations help in survival against stressors in a food system. Ground turkey will be separately inoculated with tolerant bacteria, while homologous non-adapted bacteria will be inoculated to serve as controls. Inoculated meat will be stored at refrigerated and frozen temperatures up to 28 and 180 days respectively. Populations of specific bacteria will be enumerated and thermal tolerance of the surviving bacteria will be determined. Poultry carcasses will be separately inoculated with acid adapted bacteria which exhibit increased thermal tolerance, while non-adapted strains will be inoculated to serve as controls. Samples will then be treated by spraying organic acids (acetic or lactic acids) in varying concentrations, held at 4C for up to 24 hours to allow maximum attachment of bacteria and the greatest opportunity to demonstrate any additional acid resistance. Populations of specific bacteria will be enumerated and organic acid treatments will be applied to the carcasses as illustrated previously. Thermal tolerance of the bacteria will be determined in laboratory media and in meat by comparing D-values at different temperatures. Briefly, 5g of inoculated poultry meat will be placed in a vacuum bags, immersed in water baths set at appropriate temperatures, and the timing will start as soon as the set point is reached. Control bags with thermocouples will serve as temperature monitors. D-values of the bacteria will be measured in the inoculated laboratory media and the D-values will be compared to that of the bacteria inoculated into poultry meat. Due to high probability of injured bacteria, the bacterial populations will be enumerated on selective and non-selective media. Initial experiments will be conducted to determine optimal incubation conditions for maximum recovery of the injured bacteria. Control (non-inoculated) samples will also be stored for the same time under identical conditions and evaluated for quality parameters including aerobic plate counts (APCs), coliform counts, yeasts and molds, color (measured as L, a, and b values), and texture. APCs, coliform counts, and yeast and mold counts will serve as an indicator of microbial shelf life stability of these products. A Texture Profile Analyzer will be used to determine the firmness of the product. Evaluation of color of the products will be done while in the package.