Isosteric heat, entropy, and Gibbs free energy of pumpkin seeds (Cucurbita moschata)

Abstract

To maintain seed and soil quality of pumpkin, energy knowledge associated with processing and storage stages is strategic for the optimization of the thermodynamic processes needed for product stabilization. Thus, the objective of this study was to determine isosteric heat, differential entropy, and Gibbs free energy within a temperature range from 20 to 70° C, and relative air humidity levels between 10.75 and 85.11%. The study was based on empirical data for water activity determination. As a result, we verified that as moisture content decreased, the integral isosteric heat of the product increased from 2502.35 to 6231.17 kJ kg-1, differential entropy raised from 1.18 to 12.43 kJ kg-1 K-1, and Gibbs free energy ranged from -243.84 to -432.59 kJ kg-1. Thus, we concluded that the lower the water availability in seeds, the greater the energetic requirement for its removal, as there is a major interaction between water and the product (seeds), indicating an increasingly less spontaneous desorption process.