73C-17 |
Uniqueness and reproducibility issues for modified complex method in the optimization of thermal processing |
F. ERDOGDU, Dept. of Biological & Agricultural Engineering, Univ. of California, Davis, 1308 Bainer Hall, Davis, CA 95616 and M. O. Balaban, Food Science & Human Nutrition Dept., Univ. of Florida, PO Box 110370, Gainesville, FL 32611. Thermal processing optimization studies and presentation of methods should address the uniqueness and reproducibility issues for the particular methods in terms of calculated decision variables (temperature profiles) and resulting objective functions (lethality and nutrient retention). The objective of this research was to explore the uniqueness and reproducibility of the modified complex method for thermal processing of conduction heated foods of different geometries. The objective function was chosen as the volume average/surface concentration of a nutrient; the implicit constraints were the target lethality at the cold point and a threshold below which the center temperature must reach at the end of the process. A process temperature range of 5-150 C was used as one explicit constraint, that the process temperature had to reach 5 C at the end of the process was another. The control variables for the optimization were process temperatures at equidistant time steps throughout the process. Numerical heat transfer simulation models for various shapes (slab, cylinder, and sphere) were used to develop the objective functions and constraints. All calculations were performed using a computer program written in Visual Basic V. 6.0. Process temperature profiles for different shapes, together with resulting objective function values are presented for 10 replicate runs. Standard deviations of the replications in terms of the resulting objective function values were found to be less than 1%, showing the methods’ reproducibility. However, the process temperature profiles resulting from these runs were found to be different, even though they show similar trends in heating and cooling sections. The results showed that the modified complex method is a reproducible technique in terms of the objective function in thermal processing problems, however, it resulted in non-unique decision variables. This should be investigated more, to see if existence of uniqueness can be mathematically proven.
Session 73C, Food Engineering: Transport Processes and Kinetics
|