VALIDATION OF BAKING TO INACTIVATE SALMONELLA IN HIGH-PROTEIN AND HIGH-FAT MODEL FOODS
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Baked food products, such as dry pet foods, undergo changes of temperature and water activity (aw) during forced hot air processes. As one of the most thermal resistant microorganisms in low-moisture/intermediate moisture foods, Salmonella’s thermal inactivation kinetics during these processes is not well understood and difficult to predict. The objective of this study was to evaluate thermal inactivation kinetics of Salmonella enterica serovar Agona 447967 in model high-protein (HP) and high-fat (HF) multiple-component foods baked in a laboratory-scale oven, as influenced by oven temperature and relative humidity (RH). Model high-protein and high-fat foods, formulated with wheat flour, soy protein and soy oil, were inoculated with Salmonella Agona to a level of ~9 log CFU/g, and mixed to form a homogenous dough. Dough samples (57 mm diameter x 6 mm thick) were baked (3 samples per dwell time, 6 dwell times per condition) in a lab-scale oven at 120°C (10% RH) and 85°C (20%, 35% RH, 50% RH), respectively. Temperature and aw were measured at the surface and geometric center of the product during baking. Processed samples were collected in sterile bags and immediately cooled in an ice-water bath. Salmonella was enumerated on trypticase soy agar supplemented with yeast extract and incubated at 37°C for 24 h. Similar reductions (p>0.05) of 5.12-, 5.11-, 4.55-, and 4.78-log CFU/g were achieved after 40 min at 120°C/10% RH, 90 min at 85°C/20% RH, 50 min at 85°C/35% RH, 8 min at 85°C/50% RH, respectively, in the high-protein model food. Similar results were achieved in the high-fat matrix. The aw at the geometric center of the product (initially at aw =0.98) did not change appreciably during baking, while the aw at the product surface, the location of least lethality, decreased significantly (p<0.05) during baking; the decreases were more pronounced at lower oven RH. The results indicate that thermal inactivation of Salmonella Agona was driven by temperature and relative humidity in the oven. Higher temperature and higher relative humidity level led to greater Salmonella inactivation.