Work

Desorption isotherms and thermodynamic analysis of water removal from couscous grains: Implications for drying behavior and storage stability

Year: 2026

Type: article

Abstract: This study aims to experimentally investigate the effect of grain diameter (size) and temperature on desorption isotherms of couscous grain and also to determine the thermodynamic properties associated with moisture desorption, including Gibbs Free Energy. Desorption isotherms were obtained using the static gravimetric technique at 30, 40, and 50 °C on couscous grains which had a fixed range diameter (2.5–3.15 mm), while at 40 degrees Celsius, different particle size ranges (1.6- 3.15 mm) were evaluated. The time taken for thermodynamic equilibrium to occur ranged from 1–11 days depending on moisture activity and temperature. Experimental data were fitted into five theoretical models (GAB, Harkins-Jura, Smith, Oswin, Henderson), and among the five sorption isotherm models evaluated in this study, the GAB equation provided the best fit over the investigated water activity and temperature ranges. The desorption isotherms exhibited a typical shape, with equilibrium moisture content decreasing with increasing temperature. Clausius-Clapeyron thermodynamic analysis revealed that both the net isosteric heat and entropy of desorption increase as moisture decreases. Moreover, Gibbs free energy, calculated using both the experimental water activity values and the GAB model, remained negative under all investigated conditions, confirming that the desorption process was thermodynamically spontaneous and entropy-driven. The findings of this study provide new insights into the combined effects of temperature and particle size on moisture desorption in couscous grains and offer a scientific basis for optimizing industrial drying processes and improving storage stability.

Source: Applied Food Research

DOI: 10.1016/j.afres.2026.102509

Authors: Hamza Bagar, Fouad AIT Hmazi, Taoufik Hachimi, Ibrahim Mrani

Institutions: Chouaib Doukkali University, Université Moulay Ismail de Meknes

Language: English

Topic: Food Drying and Modeling

Subfield: Food Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

SDG: Zero hunger

Open Access status: gold

Estimated APC paid: $2,050