USING OXYGEN AND BIOPRESERVATION AS HURDLES TO IMPROVE SAFETY OF COOKED FOOD DURING STORAGE AT REFRIGERATION TEMPERATURES
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Cook-chill food products are of concern because they can support the microbial growth of pathogens when subjecting to time/temperature abuses during processing and distribution. The maximum recommended storage temperatures for such products is 5 to 8 °C. In retail and domestic storage, product temperature violations are often 2 to 4 °C higher than those recommended. During consumer transport, temperature violations may rise to 13 °C higher than those recommended. Since temperature alone cannot be regarded as an adequate barrier to control the growth of pathogens in cook-chill food products, additional barriers should be considered to ensure food safety. This study examined two strategies for protecting low-acid cook-chill food products in terms of temperature violations. These strategies include the incorporation of oxygen or a protective culture as a secondary barrier, along with low temperature storage. The first strategy investigated the use of headspace oxygen in different model foods to prevent the growth of anaerobic pathogenic bacteria in in-pack pasteurized chilled food at various storage temperatures. Results showed that the structure and properties of the food significantly affected the mobility of the oxygen within it. Oxygen diffusion from the pouch headspace was limited to the food surface. Oxygen did not reach the center and bottom portions of the food during storage time so that oxygen levels which favor C. botulinum growth were maintained. Findings suggest that the air/oxygen present in the package headspace may not be considered as a food safety hurdle in the production of pasteurized packaged food. In the second strategy, the antagonistic activity of Lactobacillus rhamnosus GG on five pathogens and its heat sensitivity in soup products were observed. Then Lactobacillus rhamnosus GG effectiveness as a protective culture on Listeria and Salmonella growth at conditions simulating the application of cook-chill processing was determined. Overall, Lactobacillus rhamnosus GG showed an inhibitory effect against all pathogens tested. Heat resistance of Lactobacillus rhamnosus GG depends on temperature and soup properties. Lactobacillus rhamnosus GG had a bactericidal effect on Listeria and Salmonella at 15 °C and a bacteriostatic effect on Listeria at 10 °C during storage for 21 days.