Development and validation of engineering charts: Heating time and optimal salt content prediction for microwave assisted thermal sterilization

Through decades of research and development efforts, Microwave Assisted Thermal Sterilization (MATS) systems started commercial operation for production of shelf-stable meals in 2019. It is now highly desirable to develop user-friendly tools to facilitate the development of commercial MATS processes. The aim of this research was to develop engineering charts by applying Maxwell's and heat transfer equations to illustrate the relationships among dielectric properties, temperature, salt content, product thickness and heating rate for microwave heating in a MATS system. Three G -T (Gezahegn-Tang) charts were developed for mashed potato, peas, and rice products with MATLAB software. The charts can be used to determine the heating temperature, time and optimum salt content for a maximum heating rate at the center of a product. Experimental validation tests using mashed potato samples confirmed that the temperature profiles measured at the cold spots of the samples in the microwave heating section of the MATS system were positively correlated with predicted temperatures from the chart (R2 = 0.94-0.99). Furthermore, the predicted optimal salt contents for 23 mm thick mashed potato (0.1%), 18 mm thick pea (0.5%) and 25 mm thick rice (1%) samples agreed with the experimental heating pattern test results. The optimal salt content is inversely proportional with a product temperature and thickness, which increases the microwave power decay before reaching the center. With the help of these charts, the food industry practitioners can save significant time and resources during the development of food products and schedules for the MATS processes.