Thermodynamic Properties of Spray-Dried Ximenia americana Pulp Powders through Moisture Sorption Isotherms Study

Abstract

The objective of the present work was to investigate the sorption isotherms of moisture in spray dried microcapsules powder of X. americana at 25°C, 35°C and 45°C temperatures. A gravimetric storage study of spray dried microcapsules of Ximenia americana fruit extracts was conducted for 0.22 to 0.93 water activity (aw) at 25°C, 35°C, and 45°C. The net isosteric heat (qst) of water adsorption was calculated using the Clausius–Clapeyron equation. Experimental data were fitted to mathematical models developed by GAB, BET and Peleg, since R2 was close to 1 for the investigated conditions. It resulted that the moisture content of spray dried microcapsules of X. americana fruit extracts had an increasing trend by increasing of aw value, and these microcapsules adsorbed 55-65 g H2O/100 g solid. The adsorption isotherm of spray dried microcapsules of X. americana detected as Type II according to Branuer classification. The monolayer moisture contents (Xm) of microcapsules formulated were determined as 8.14-9.67 g H2O/100g solid according to GAB and BET equations. Lower moisture concentrations caused a more drop in isosteric heat, after which there was no further change. The results of this study therefore suggest that for a long and high-quality storage of whole spray dried microcapsules powders of X. americana fruits extracts, the relative humidity should be lowered to 35 g/100g.