Thermal transitions and enthalpic relaxations as related to the stability of microencapsulated paprika powders

Present work investigates the effect of thermal transitions and enthalpy relaxation phenomenon on the physico-chemical stability of paprika microencapsulated powders. Wall materials were combinations of soy protein isolates, maltodextrin and gum arabic. Powders stability was evaluated through the solid-water interactions, determined by sorption kinetics, calorimetry and color changes. The water sorption isotherms were well described by the GAB model. Below the critical condition, a_w 0.6 and water content 11% (d. b.) the systems were in amorphous state at 25 °C, and enthalpy relaxations were detectable as endothermal events in the stored samples. The magnitude of the enthalpy relaxations increased with storage temperature below T_g and with time of storage. In the amorphous microencapsulates, luminosity changes measured as (L_o*-L*) values decreased as a function of time and a_w, indicating pigment decoloration. The kinetics of the enthalpy relaxations changes, instead of the punctual values of the variables under study, were related to the dynamics of deteriorative changes. It can be concluded that enthalpy relaxation phenomenon can be established as a criterion for defining storage conditions or predict changes in microencapsulated and other systems that have to be stored in the glassy state.