Abstract
ABSTRACT Studies about the thermodynamic properties of ryegrass seeds are necessary to improve post-harvest processes, relating the factors that affect product quality with the interaction between water and its chemical components. Given the importance of recognizing and understanding the intrinsic behavior of water in ryegrass seeds and providing data for the improvement of industrial drying equipment, this work aimed to calculate and evaluate the thermodynamic properties of moisture desorption of ryegrass seeds as a function of the equilibrium moisture content. Ryegrass seeds with initial moisture content of 10.4 (% d.b.) was used. The equilibrium moisture content of seeds was determined by static-gravimetric method at different temperatures (10, 20, 30, 40, and 50 °C) and water activity values (between 0.10 and 0.90), in three repetitions. The Chung Pfost model presented the best fit to the experimental data. It was observed that the integral isosteric desorption heat increased as the equilibrium moisture content decreased, ranged from 2499.95 to 4241.96 kJ kg-1 in the moisture content range 2.80 to 22.10 (% d.b.). Differential entropy also increased with decreasing equilibrium moisture content, as did Gibbs free energy, being positive for all temperature studied, indicating that ryegrass seeds desorption is a non-spontaneous process. The enthalpy-entropy compensation theory was satisfactorily applied to the sorption phenomenon, being controlled by enthalpy.
Highlights
The ryegrass (Lolium multiflorum L.) is a species of the Poacea family, widespread in southern Brazil
Water activity reports the amount of water molecules available for different reactions in the product, as well as the development of microorganisms; by increasing the equilibrium moisture content, a greater amount of moisture is available for these reactions, resulting in an increase in water activity
The results demonstrate that differential entropy behaves to integral isosteric desorption heat with equilibrium moisture content
Summary
The ryegrass (Lolium multiflorum L.) is a species of the Poacea family, widespread in southern Brazil The spread of this crop is primarily due to its ability to adapt to different soil and climate conditions, as well as its ease of management (Pellegrini et al, 2010). Thermodynamic properties can be calculated by sorption isotherms (Noshad et al, 2012; Hassini et al, 2015), allowing a greater understanding of the properties of water molecules and assisting in the calculation of energy in relation to heat transfer and heat transfer mass of biological systems (Goneli et al, 2016) Determining these properties is critical to predicting the drying threshold in order to obtain a product that can be stored for long periods, consuming a minimum amount of energy to reduce moisture content at safe storage levels (Resende et al, 2017)
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