Modelling post-frying oil absorption, water loss, and cooling of potato cylinders

A simultaneous heat and mass transfer model based on global coefficients was proposed to describe the oil absorption, water loss, and temperature changes occurring during the post-frying period of potato cylinders. The model was solved in Matlab® and simultaneously fitted to post-frying kinetics from literature, describing the surface and penetrated surface oil contents, as well as the surface and centre temperatures of potato cylinders at six holding temperatures (25, 100, 120, 140, 160, and 180°C). Besides, simple algorithms were developed to evaluate the oil layer thickness and the minimum oil penetration distance, obtained by assuming the potato cylinder was split into a dry zone, where the oil was absorbed, and a moist zone free from oil. The model achieved a good reproduction of fitted responses with average deviations ranging from 1.9 to 11.7% for all post-frying holding temperatures. Estimated distribution coefficients evidenced higher oil absorption at low holding temperatures, increasing from 0.66 kg surface oil/kg absorbed oil at 25°C to 2.60 kg surface oil/kg absorbed oil at 180°C, while no temperature influence on mass transfer coefficient was found under the explored experimental conditions (p > 0.05). The estimated minimum oil penetration distance (thickness of the dry zone region) after the post-frying stage (229 to 506 µm) showed a good agreement with crust thickness values from literature.