NEW SEMIEMPIRICAL APPROACH TO HANDLE TIME-VARIABLE BOUNDARY-CONDITIONS DURING STERILIZATION OF NONCONDUCTIVE HEATING FOODS

Semi-empirical methods for the prediction of time-temperature histories in conductive and non-conductive (convective and mixed mode) heating foods subjected to a time-variable processing temperature are proposed. Four alternatives are considered: (i) Hayakawa's method (Duhamel's theorem and Hayakawa's formulae); (ii) Duhamel's theorem with analytical solution; (iii) numerical solution with apparent time (time shift); (iv) numerical solution with apparent position. The incorporation of the empirical heating characteristics f and j in conductive models was accomplished by evaluating the existing analogies with thermophysical properties in the solutions of the Fourier equation. Approaches using Duhamel's theorem or finite difference solutions were used to handle variable boundary conditions. The application of the models in the calculation of processing values for thermal processes with different come up times and different boundary conditions during come up time and thermal processes with process deviations is discussed. The numerical solution with apparent position was preferred because it combines accuracy and flexibility.