The aim of this research was to develop and validate a mathematical model coupled with an optimization technique for thermal processing of conduction-heated foods in retortable pouches in order to: (a) search for variable retort temperature profiles to minimize process time, and (b) search for variable retort temperature profiles to minimize quality gradient (thiamine) within the product. The model was validated utilizing Jack mackerel (Trachurus Murphyi) packed in retortable pouches. The conjugated gradient method was utilized as a search technique to find the best variable retort temperature profile to satisfy the specific objectives. The simulation results were in good agreement with the observed temperatures. The prediction errors obtained in the validation study were under 5%. Non-significant differences (P < 0.05) were found between the experimental and predicted values. Simulations showed that significant reduction in process time (20-30%) could be attained utilizing variable retort temperature profiles while maintaining product quality. (C) 2003 Elsevier Ltd. All rights reserved.