Moisture Desorption Isotherms and Thermodynamic Properties of Sorghum-Based Complementary Foods

Moisture desorption and thermodynamic properties of sorghum-based complementary foods were investigated. Products were obtained from various ratios of Non-fermented sorghum (NFS), Fermented sorghum (FS), crayfish (C), Mango mesocarp (M) and fluted pumpkin leaf (P) powders. Four products, NFSMC, FSMC, NFSPC and FSPC were formulated based on 16% protein using material balance. Established procedures/methods were used for sample preparation and analyses. The equilibrium moisture contents (EMCs) generated through static gravimetric method was fitted with Guggenheim-Anderson-de Boer (GAB) model by polynomial regression analysis. The moisture desorption isotherms of the samples exhibited sigmoidal shape (Type II). The enthalpy of monolayer ranged from 48.12 - 61.78 kJ/mol, multilayer ranged from 44.53 - 47.98 kJ/mol and bulk water ranged from 42.98 - 44.20kJ/mol. The isosteric heat of sorption decreased with increase in moisture content while the entropy of desorption for all the products increased as their moisture contents increased. The isosteric heat and entropy of desorption exhibited asymptotic behaviour at 14% moisture content. The isokinetic temperature ranged from 376.50 - 814.14 K while the harmonic mean temperature was 297.78 K. The enthalpy-entropy compensation theory indicated that the desorption process was enthalpy controlled