Ohmic Heating Soaking of Millets: Effects of Equilibrium Moisture Content, Soaking Time, Hydration Kinetics, Moisture Diffusivity, Activation Energy, and Surface Morphology

ABSTRACT The research focused on analyzing the hydration kinetics of Foxtail millet ( Setaria italica ), Proso millet ( Panicum miliaceum ), and Kodo millet ( Paspalum scrobiculatum ) at different soaking temperatures. Millets were studied at different ohmic heating (OH) temperatures (50°C, 60°C, and 70°C). Moisture data were recorded and fitted into hydration models like Page, logarithmic, modified Page, Henderson and Pébis, Lewis, Midilli, and Verma; and SEM microstructure of millets was observed. It was observed that the Foxtail millet soaked at 50°C and 60°C exhibited different moisture absorption patterns than soaked at 70°C. The equilibrium moisture contents (EMCs) of Foxtail millet soaked at 50°C, 60°C, and 70°C were 29.6%, 30%, and 34%, and the soaking times were 180, 120, and 60 min, respectively. The equilibrium EMC of millet soaked at 50°C, 60°C, and 70°C were 30%, 32%, and 35%, and the soaking times were 300, 210, and 180 min, respectively. Similarly, the EMCs of millet soaked at 50°C, 60°C, and 70°C were 27%, 29%, and 31%, and the soaking times were 360, 210, and 150 min, respectively. The hydration kinetics revealed that all seven models were well fitted for Foxtail and Proso millets; only six models were well fitted for Kodo millet, except for the logarithmic model. Among them, the Midilli model showed the coefficient of determination ( R 2 ), root‐mean‐square error (RMSE), and sum of square error (SSE) values for FM; for PM, the R 2 , RMSE, and SSE values from the Midilli model were 0.98817–0.99944, 0.013278–0.008543, and 0.034743–0.000510, and for KM, the Verma model values R 2 , RMSE, and SSE were 0.99519–0.99584, 0.02099–0.02133, and 0.00485–0.0036405 for 50°C, 60°C, and 70°C, which were more suitable. Moisture diffusion coefficients and activation energy ranged from 5.16 × 10 −10 to 3.77 × 10 −10 m 2 .s −1 and from 105.75 to 262.8 kJ/mol, respectively. The study implies that the OH assisting soaking enhances the hydration kinetics of millets.