Determinação das isotermas de equilíbrio higroscópico de frutos de crambe pelo método dinâmico

Abstract

The objective of this work was to determine the sorption isotherms of crambe fruits by dynamic method for several conditions of temperature and water activity and adjust different mathematical models to experimental data, and obtain the values of isosteric heat of desorption versus the equilibrium moisture content of the product. The equilibrium moisture content of crambe fruits was determined by dynamic-gravimetric method to temperatures of 25, 30, 35, 40 and 45 °C and water activity for each temperature, from 0.270 to 0.825. From the results obtained it was calculated for each isosteric heat of moisture content equilibrium. The experimental data were adjusted several models available in the literature (Chung-pfost, Copace, GAB, Modified Halsey, Sabbah, Sigma Copace, Cavalcanti Mata, Modified Henderson, Henderson, BET, Oswin e Modified GAB). It was observed that the equilibrium moisture content decreases with increasing temperature for a given water activity like the hygroscopic products. The model Sigma Copace was best described what the hygroscopicity of the crambe fruits. It was observed that the isosteric heat increases with decreasing moisture content of the product, indicating an increase in energy required for water removal. The values of isosteric heat of crambe fruits in the range of moisture content from 3.85 to 11.86 (d.b.%) varied from 4731.73 to 2698.35 kJ kg-1.