Moisture Adsorption and Thermodynamic Properties of Sorghum-Based Complementary Foods

Abstract

The moisture adsorption and thermodynamic properties of sorghum-based complementary foods were investigated. Non-fermented and fermented sorghum, crayfish, Mango mesocarp and fluted pumpkin leaf powders were blended in the ratios of 91.06% non-fermented sorghum: 0.17% mango mesocarp: 8.77% fish (NFSMC), 91.06% fermented sorghum: 0.17% mango mesocarp: 8.77% fish (FSMC), 91.04% non-fermented sorghum: 0.19% fluted pumpkin: 8.77% fish (NFSPC) and 91.04% fermented sorghum: 0.19% fluted pumpkin: 8.77% fish (FSPC). The sample formulations were done based on 16% protein using material balance. Established procedures were used for sample preparation and analyses. The equilibrium moisture contents (EMCs) generated through static gravimetric method was fitted with Guggenheim-Anderson-deBoer (GAB) model by polynomial regression analysis. The moisture adsorption isotherms of the samples exhibited sigmoidal shape (Type II). The enthalpy of monolayer ranged from 50.34 to 60.75kJ/mol, multilayer ranged from 43.83 to 45.89kJ/mol and bulk water ranged from 42.98 to 44.20kJ/mol. The isosteric heat of sorption decreased with increase in moisture content, the entropy of adsorption of NFSMC, FSMC and FSPC decreased as the moisture content increased. The isokinetic temperature ranged from 326.51 to 603.33K while the harmonic mean temperature was 297.78K. The adsorption process was enthalpy driven. Therefore, NFSMC, FSMC and NFSPC are recommended for their relatively lower moisture content.