Purpose: This trend has prompted the Army to investigate the potential long-term survival of Salmonella in LMF, since they are frequently included in military rations and are required to have a minimum three year shelf-life at 25°C.
Methods: Simulated commercial products with low aw, such as peanut butter (0.21), mocha dessert bars (0.43), boil-in-bag eggs (0.091), and chocolate protein drinks (0.34), were prepared with a dry inoculum of Salmonella. A five strain inoculum of Salmonella Agona, Salmonella Enteritidis, Salmonella Montevideo, Salmonella Tennessee and Salmonella Typhimurium was prepared and added to one ingredient in each product. The carrier ingredient was then added to a Robot Coupe to combine all product ingredients into the final ration item. Products were weighed into 40 g samples and vacuum sealed in tri-laminate pouches. Products were stored at 4°C, 25°C, or 40°C for up to three years. Salmonella was enumerated by dilution and plating on TSA and selective Hektoen Enteric Agar (HE) for each product at two weeks, one month, six months, one year, two years and three years.
Results: Results indicated no loss in Salmonella viability for peanut butter, chocolate protein drink, and boil-in-bag eggs when stored at 4°C and 25°C and an approximately three log loss when stored at 40°C for six months. Mocha desert bars, which had the highest aw of the stored products, had a loss of approximately 0.5 log at 4°C, 1.5 log at 25°C, and a loss of seven log at 40°C after six months of storage.
Significance: The data from this study suggested that Salmonella can survive in low moisture military ration products at elevated temperatures for extended periods of time. This indicates the need for additional safety protocols.