MODELING PATHOGEN REDUCTION USING VACUUM ASSISTED STEAM ON LOW WATER ACTIVITY FOODS AS IMPACTED BY PHYSICAL PROPERTIES AND HEAT TRANSFER

Objective 1: Develop validated processes to reduce Salmonella, E. coli O157:H7 and L. monocytogenes and the potential surrogate bacteria E. faecium and P. acidilactici using vacuum-assisted steam pasteurization on LWAF (macadamia nuts, mint leaves, raisins, pumpkin seeds, mustard seeds) that differ in their inherent chemical, physical and thermal properties.Hypothesis: Reduction of foodborne pathogens in LWAF will be dependent on the product density, and the relationship between the particle size and shape that, together, will determine the porosity and heat transfer within the package. We hypothesize that LWAF with increased porosity and food chemical compositions that promote increased heat transfer will require decreased heat or contact times in standardized packaging compared to LWAF with decreased porosity. Less dense products such as mint leaves will require shorter contact times or lower temperatures to achieve comparable reductions. There may be an interaction between low water activity and product density.Hypothesis: Heat resistance of E. faecium and P. acidilactici will be greater than Salmonella, E. coli O157, L. monocytogenes on each of the tested LWA commodities. We will also determine the stability of the surrogates over time to simulate conditions where the commodity would be inoculated, shipped, processed and returned for enumeration in a period that may be 7-14 d.Objective 2: Develop mathematical models to describe the dynamic heat transfer rate (heat flux) of the product as a function of steam penetration, density and porosity of packaged product. These models can be used to create a 3D visualization that will allow the prediction of the temperature of the product at any point in the package. Compare the heat transfer rate for several LWAF that have been considered for grouping based on similarities in water activity and density, and porosity.Hypothesis: Intrinsic properties of the LWAF including density and porosity will alter the heat transfer. Commodities with similar compositions may have different heat flux if the products differ in density and porosity. The heat flux can be directly measured with a sensor in both laboratory and commercial scale systems. The predicted heat transfer from the mathematical model will be comparable to the measured heat flux using the miniatured sensorsObjective 3: Determine the suitability of dynamic models for heat inactivation kinetics to predict the inactivation of the three pathogens and potential surrogates. Compare the predicted vs. observed log reductions of Salmonella, E. coli O157, L. monocytogenes and the identified surrogates on different spices, seeds and a mixed LWAF (e.g. trail mix) to determine the effectiveness of the model to predict treatment times.Hypothesis: We anticipate that inactivation times predicted for LWAF of similar properties will be effective for decontamination on other LWAF provided the heat flux and spatial temperature profiles are comparable. This will include successfully scaling to commercial facilities from small laboratory test facilities.Objective 4: Determine if vacuum-assisted saturated steam-pasteurized LWAF are different in overall sensory quality compared to control (no treatment) LWAF based on similarity testing (triangle tests). For significantly different products, characterize quality changes: color, and water activity as a function of process.Hypothesis: We anticipate that vacuum steam pasteurization of the macadamia nuts, pumpkin seeds, mustard seeds, and raisins will not result in visible or aroma differences detected by human subjects using a similarity sensory test.