Two-scale modeling of transport mechanisms and quality changes during frying of foods

Deep fat frying is a popular cooking technique, which involves immersion of foods in edible oil at high temperatures. An excessive fat consumption by humans has been linked to serious health diseases. Frying occurs at temperatures well above the boiling point of water and involves short time duration. Frying results in a rapid change in the quality of the food products. The transport mechanisms along with complex physico-chemical processes such starch gelatinization, protein denaturation, glass transition, phase change, food matrix deformation, etc. that occur during frying govern the final quality of the product. Due to fast paced and dynamic nature of the frying process, it is experimentally challenging to obtain information on transport mechanisms and account for microscale physical phenomena that affect the quality at macroscale. Limited information is available that explains the transport mechanisms during frying and their role in affecting the quality of the product.;Hybrid mixture theory (HMT) based multiscale modeling approach was employed to study transport mechanisms during frying of snack foods. Multiscale simulations studies on the frying of rice crackers and chicken nuggets provided useful information about the nature of transport in these two products of different nature. The heat and mass transfer equations were solved using the finite element method to obtain spatial and temporal profiles for moisture and oil content, rate of evaporation, temperature distribution, pore and gas pressures. Average absolute deviation (AAD) for the predicted and the experimental data was calculated for the model validation. Simulations were also used to predict the quality (texture and color) of products during frying. Rice crackers exhibited much higher values of coefficient of elasticity (in the order of 10 7 Pa) compared to the chicken nuggets (in the order of 105 Pa). Temperature inside a rice cracker reached higher than 100°C in 10 s after the start of the frying process. Whereas, chicken nuggets meat core stayed below 100°C during frying and starch coating experienced temperatures greater than 100°C. The rice crackers exhibited positive values of gage pore pressure for the most part of the frying process. By comparison, pore pressure in the chicken nuggets remained below atmospheric pressure. Existence of negative pore pressure at the start of the frying appeared to be the reason of oil uptake. Kinetics equation for color change obtained from colorimetry experiments was coupled with simulations during post-processing to predict the color (L, a, b) as a function of frying time for chicken nuggets. Lightness value was around 30 for frying at 175°C. Color was more yellow for lower frying temperatures, and redness increased with increasing frying temperature. HMT based model was suitable for simulating the heat and mass transfer mechanisms during frying.