Thermodynamic analysis for assessing the physical stability of core materials microencapsulated in taro starch spherical aggregates.

Taro starch has the ability of producing spherical aggregates under spray-drying without the addition of binding agents. This property makes taro starch suitable for microencapsulation of dietary compounds. This study addressed the physical stability of hydrophilic and hydrophobic core materials microencapsulated by spray-drying into taro starch spherical aggregates determined from a thermodynamic standpoint via vapor adsorption isotherms. Ascorbic acid and almond oil were used as compound models. Encapsulation efficiency, GAB sorption parameters, differential and integral thermodynamic properties, Gibb's free energy, entropy-enthalpy compensation, spreading pressure, effective diffusion rate, activation energy and critical water activity were determined. The encapsulation efficiency of ascorbic acid and almond oil was 99% and 56%, respectively. Monolayer moisture content was relatively low for ascorbic acid microcapsules. The adsorption process was driven by entropic mechanisms. The physical stability of taro starch spherical aggregates microcapsules with different core material was guaranteed for a range of water activities and temperatures.

Thermodynamic criteria analysis for the use of taro starch spherical aggregates as microencapsulant matrix.

Spherical aggregates can be obtained from taro starch by spray-drying without using bonding agents. Accurate information about thermal issues of spherical aggregates can provide valuable information for assessing the application as encapsulant. Spherical aggregates of taro starch were obtained by spray-drying and analyzed using dynamic vapour sorption. The use of the Guggenheim, Anderson and de Boer (GAB) model indicated a Type II isotherm pattern with weaker interactions in the multilayer region. Differential enthalpy and entropy estimates reflected a mesoporous microstructure, implying that energetic mechanisms dominate over transport mechanisms in the sorption process. The limitation by energetic mechanisms was corroborated with enthalpy-entropy compensation estimates. The diffusivity coefficient was of the order of 10-8 m2·s-1, which is in line with results obtained for common materials used for encapsulation purposes. The thermodynamic properties and the lack of a bonding agent indicated the viability of spherical aggregates of taro starch for encapsulation of biocompounds.