MODELING WATER ADSORPTION ISOTHERMS OF PINHÃO (ARAUCARIA ANGUSTIFOLIA SEEDS) FLOUR AND THERMODYNAMIC ANALYSIS OF THE ADSORPTION PROCESS

Abstract

ABSTRACT The seeds of Araucaria angustifolia, commonly known as pinhão, are widely consumed in both Southern and Southeastern Brazil because of their high nutritious value. The literature on the technological aspects of this seed is still very scarce. Moisture adsorption isotherms of pinhão flour were determined at 10, 20, 30 and 40C using the gravimetric method. Results show that temperature has little effect on the adsorption process and the Chirife model was found to best represent the experimental data. The isosteric heat of sorption (differential enthalpy) was calculated by using the moisture adsorption isotherm and decreased as moisture content increased, becoming almost constant at 0.3 kg water/kg dry solids. The enthalpy–entropy compensation theory was applied to adsorption isotherms and the isokinetic temperature for pinhão flour was calculated by plotting the differential enthalpy versus differential entropy. It was found that the adsorption process investigated was enthalpy controlled.PRACTICAL APPLICATIONSMoisture isotherms are important for several applications in food technology (they can be used to predict potential changes in food stability, for storing method determination, packaging and ingredients selection, design and optimization of drying equipment, among others). This work presents the isotherms of a new product (pinhão flour), that do not exist in the market yet and with very scarce literature. As pinhão is a seasonal product, the study of new products using pinhão as raw material is also important.