Moisture diffusivity, hardness, gelatinization temperature, and thermodynamic properties of ultrasound assisted soaking process of cowpea

Abstract

AbstractThis study describes the combined effect of ultrasound and temperature on water absorption of cowpea kernel during soaking process. The process was made at 30, 40, 50, 60, 70, 80, and 90°C in water absorption conditions named control (without ultrasound) and ultrasound treatment (40 kHz, 200 W; 50% and 100% amplitude). Fick's second diffusion model for water absorption and asymptotic first order texture model for hardness together with Arrhenius and Eyring–Polanyi approaches were successfully used to evaluate effective moisture diffusivity coefficient (Deff), texture degradation coefficient (kF), gelatinization temperature, and thermodynamic properties of cowpea during soaking process. The models fitted the experimental data satisfactorily with R2 > 0.99, RMSE < 0.09 and X2 < 0.0137. Ultrasound treatment (50% and 100% amplitudes) and temperature increased significantly (p ≤ .05) the Deff and kF of cowpeas during soaking process. Average gelatinization temperature of cowpea from the Fick's and Asymptotic first order texture models together with Arrhenius equations was found as 68.5°C. Negative values of enthalpy, entropy, and increase of Gibbs free energy changes with increasing temperature and ultrasound treatment confirming the effect of temperature and ultrasound on effective moisture diffusivity of cowpea during soaking. Moisture content, harness, Deff, kF and thermodynamic properties of cowpea during soaking process were affected by both the temperature and ultrasound amplitude, which means shortening the soaking and cooking time of cowpea.Practical applicationsThe results of this study could be assisted to industrial producers of cowpea in understanding of heat and mass transfer phenomena during ultrasound‐assisted hydration process of cowpea kernel in soaking, cooking, wet milling, fermentation, formulation of meals, and storage processes.