NONLINEAR CONSTRAINED OPTIMIZATION OF THERMAL PROCESSING Ⅱ. VARIABLE PROCESS TEMPERATURE PROFILES TO REDUCE PROCESS TIME AND TO IMPROVE NUTRIENT RETENTION IN SPHERICAL AND FINITE CYLINDRICAL GEOMETRIES

摘要

Conventional methods for thermal processing of foods use constant processing temperature profiles (CPTPs) for a prescribed processing time, which is based on achieving a required microbial lethality to comply with public health standards. This also results in degradation of nutrients and quality factors. The variable process temperature profiles (VPTPs) obtained by using optimization methods can reduce quality losses and/or processing time compared to CPTPs. The objective of this research was to evaluate VPTPs using the Complex Method to reduce the processing time and/or improve quality retention for a specified level of lethality in thermal processing of conduction heated foods. The VPTPs were obtained for volume average retention of thiamine considering different sizes of spheres (small and large) and finite cylinders (small and large), and the thiamine retention andprocessing time results were compared with a conventional method (processing at 121.1C) for a specified lethality level. The use of VPTPs resulted in a 37 and 10% decrease in processing times in spherical and 40% and 67% for finite cylindrical shapes, for the same objective function value and specified lethality compared to the CPTP process. For the same processing time, the improvements in thiamine destruction were 3.7 and 2 % for spheres, and 3.9 and 2.2% for finite cylinders.