Studies on thermal stability of high-power short time microwave dried paprika (Capsicum annuum L.) considering the interaction of water molecules with sorption sites

Abstract

The moisture adsorption isotherms of high-power short time microwave dried paprika (Capsicum annuum L., a pulverized product of dried red pepper) were determined for thermodynamic analysis and assessment of its stability at elevated temperatures. The thermal stability of paprika was evaluated based on alterations in quality characteristics due to the interaction of water molecules with sorption sites during the adsorption process. The GAB model constants revealed the physical significance and the exothermic interaction of the water molecules with the sorption sites on the surfaces of the paprika. The differential enthalpy was found to decrease with increasing water activity due to the existence of highly active polar sites on the surface of paprika at low water activity. The differential entropy decreases due to a rise in water activity as molecular water movement was highly restricted at an elevated water activity. The safe water activity levels corresponding to monolayer moisture content (M o) of paprika at 30°, 40°, 50°, and 60 °C were found to be 0.58, 0.49, 0.43, and 0.30, respectively. Moreover, the acceleration in quality degradation of paprika was found to increase beyond M o at the respective adsorption temperature.