A procedure to achieve fine control in MW processing of foods

A two-dimensional analytical model for predicting the unsteady temperature field in a cylindrical shaped body affected by spatiallyvarying heat generation is presented. The dimensionless problem is solved analytically by using both partial solutions and the variation ofparameters techniques. Having in mind industrial microwave heating for food pasteurization, the easy-to-handle solution is used to confirmthe intrinsic lack of spatial uniformity of such a treatment in comparison to the traditional one. From an experimental point of view,a batch pasteurization treatment was realized to compare the effect of two different control techniques both based on IR thermographyreadout: the former assured a classical PID control, while the latter was based on a ‘‘shadowing’’ technique, consisting in covering portionsof the sample which are hot enough with a mobile metallic screen. A measure of the effectiveness of the two control techniques wasobtained by evaluating the thermal death curves of a strain Lactobacillus plantarum submitted to pasteurization temperatures. Preliminaryresults showed meaningful increases in the microwave thermal inactivation of the L. plantarum and similar significant decreases inthermal inactivation time with respect to the traditional pasteurization thermal treatment.