Inactivation and modeling of food-borne pathogens in low-moisture foods using the thermal treatment and non-thermal cold plasma

In recent years, numerous multistate foodborne outbreaks have been reported that are often associated with low moisture foods (LMFs). The survival of microorganisms in low moisture conditions has become one of the major concerns in the food industry. With the increasing number of recalls, it is necessary to ensure food safety by developing and validating the process parameters. Establishing a thermal process requires a detailed understanding of the inactivation kinetics of the target pathogen with respect to both the process (temperature, time, equipment) and the product conditions (water activity, composition). Along with the most widely used conventional thermal processing, there has been an increase in the demand for natural or minimally processed foods. As a result, many alternative non-thermal processing approaches that provide antimicrobial benefits while retaining the quality attributes of the food product are under investigation. This research focused on studying the inactivation kinetics of foodborne pathogens Salmonella enteritidis PT30 and Cronobacter sakazakii in powdered LMFs using both the thermal and non-thermal (cold plasma) processing technologies. The efficacy of a dielectric barrier discharge cold plasma equipment was tested against pathogens Salmonella enteritidis PT30 and Cronobacter sakazakii in LMFs at 70 kV, resulting in 3.8 log reduction in Cronobacter, and 4.41 log reduction in Salmonella after 5 min of cold plasma treatment in pea protein. The cellular damage to the pathogens was examined by transmission electron microscopy (TEM), and the reactive oxygen (ROS: OH, O) and nitrogen (RNS: N₂, N₂⁺) species were identified using optical emission spectroscopy. The RMSE for the model was found to be between 0.11 and 0.36 with the low standard error of the parameters (δ, n, and log N₀), which illustrated that the Weibull model was a good fit for the experimental inactivation data. 

In the thermal processing study, the inactivation kinetic parameters of these pathogens were estimated at 70, 80, and 90 °C at 0.11, 0.22, and 0.33 water activity in pea protein powder. The non-isothermal temperature profiles were simulated by building a two dimensional, axisymmetric heat transfer model of the test cell. The inactivation parameters D_ref, z_T, and z_aw were estimated in MATLAB by using a one-step non-linear regression analysis, which was a combination of the primary log-linear model with the secondary modified-Bigelow model. The model was found to be a good fit, showing lower root mean square error (RMSE) and residuals. Further, Enterococcus faecium was observed to have higher D-values at all the processing temperatures and water activity levels as compared to Salmonella enteritidis PT30 and Cronobacter sakazakii, which provides valuable evidence that Enterococcus faecium can be used as a surrogate microorganism for validating the thermal process for pea protein powder.