Modeling of dehydration and color degradation kinetics of maize grain for mixed flow dryer

Effects of drying temperature (60, 70, and 80 °C) and air velocity (3.0, 6.0, and 9.0 m/s) on thin layer and color kinetics of maize grain during mixed flow dryer (MFD) were investigated for the present study. Five thin layer grain drying models (Henderson and Pabis, Page, Lewis, Midilli et al. and Wang and Singh) as well as Zero order reaction rate were applied with the experimental data to predict the drying and color kinetics of maize, respectively. Increased drying temperature had significant leverage on drying time whereas proliferation of air velocity (>6.0 m/s) is scarcely imperative. Model fitting analysis revealed that Lewis and Page model is aptly applied in evaluating drying kinetics for mixed flow drying of maize as coefficient of determination (R2) is higher. Effective moisture diffusivity (4.92 × 10−7 to 8.38 × 10−7 m2/s) was maximum both for higher temperature and air flow whereas specific energy consumption was lowest (2.75 MJ/kg) for lower temperature and air flow. Regression analysis of color attributes (L*, a*, and b*) designates that color kinetics of maize grain occurred according to the zero order reaction. L* and b* indices of color decreases while a* and color difference (ΔE) increases with drying temperature and time. Thin layer and kinetic constant (k) is proportionate with drying temperature while adverse results were noticed for color attributes. Drying and color degradation kinetics of maize can readily be described by Lewis and Page model and zero order reaction, respectively for mixed flow drying.