The thermal characteristics of the spores and vegetative cells of three strains of Bacillus coagulans (ATCC 8038, ATCC 7050, and 185A) in tomato juice were evaluated. B. coagulans ATCC 8038 was chosen as the target microorganism for thermal processing of tomato products due to its spores having the highest thermal resistance among the three strains. The thermal inactivation kinetics of B. coagulans ATCC 8038 spores in tomato juice between 95 and 115°C were determined independently in two different laboratories using two different heating setups. The results obtained from both laboratories were in general agreement, with z-values (z-value is defined as the change in temperature required for a 10-fold reduction of the D-value, which is defined as the time required at a certain temperature for a 1-log reduction of the target microorganisms) of 8.3 and 8.7°C, respectively. The z-value of B. coagulans 185A spores in tomato juice (pH 4.3) was found to be 10.2°C. The influence of environmental factors, including cold storage time, pH, and preconditioning, upon the thermal resistance of these bacterial spores is discussed. The results obtained showed that a storage temperature of 4°C was appropriate for maintaining the viability and thermal resistance of B. coagulans ATCC 8038 spores. Acidifying the pH of tomato juice decreased the thermal resistance of these spores. A 1-h exposure at room temperature was considered optimal for preconditioning B. coagulans ATCC 8038 spores in tomato juice.
Long-duration space missions require a high-quality, shelf-stable food supply but must also contend with packaging waste after use. We have developed a package, adapted from a military pouch, that enables heating of foods to serving temperature. After the food is consumed, the package may be reused for containment and sterilization of waste, and, potentially, for packaging and sterilizing foods grown on a Mars base. Packages are equipped with electrodes to permit ohmic heating of internal constituents. Heat transfer within the package was modeled using the energy transport equation, coupled with the Laplace equation for electric field strength distribution. The model was verified by temperature measurements during a sample experimental run, and it was used to optimize the package design. Waste sterilization within the package was also studied and confirmed. Mass transfer (electrode component migration) was studied by inductively coupled plasma mass spectrometry; the findings have shown concentrations within products to be well below current daily dietary exposure levels. Microbiological studies for sterilization indicated the need for package redesign to ensure parallel electrode configuration, as well as the use of supplemental external heaters along the nonelectrode walls of the package. Temperature profiles during heating of these packages have been determined.
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