Moisture sorption isotherms of castor beans. Part 1: Mathematical modeling and hysteresis

Abstract

A B S T R A C TSorption isotherms are of great importance in post-harvest procedures, especially for predicting drying and storage, which help to establish the final moisture content of the product under certain environmental condition. Hysteresis is a phenomenon that occurs due to the difference between adsorption and desorption curves, which aids the evaluation of chemical and microbiological deteriorations, indicating the stability of stored products. Moisture sorption isotherms of castor beans were determined and hysteresis was analyzed. Static gravimetric technique at different temperatures (25, 35, 45 and 55 ± 1 °C) was used. Saturated salt solutions in the range of 37-87% ± 2% were utilized to create the required controlled relative humidity environment. Equilibrium moisture content data were correlated by different mathematical models and the Modified Halsey model presented good adjustment for the data, according to statistical procedures. Hysteresis between adsorption and desorption isotherms is present over the range of 0.2-0.9 of water activity, regardless of the temperature. This phenomenon decreases with temperature increase.Isotermas de sorção de grãos de mamona. Parte 1: Modelagem matemática e histerese R E S U M O As isotermas de sorção são de grande importância em procedimentos pós-colheita de produtos agrícolas, em especial para predizer os processos de secagem e armazenamento os quais auxiliam a estabelecer o teor de água final no produto em determinada condição ambiental. A histerese é um fenômeno que ocorre em virtude da diferença entre as curvas de adsorção e dessorção que auxilia a avaliação de deteriorações químicas e microbiológicas indicando a estabilidade de produtos armazenados. Isotermas de sorção de grãos de mamona foram determinadas e a histerese analisada. Utilizou-se a técnica de gravimetria estática em diferentes temperaturas (25, 35, 45 e 55 ± 1 °C). Soluções salinas saturadas na faixa de 37-87% ± 2% foram utilizadas para criar o requerido ambiente controlado de umidade relativa. Os dados de teor de água de equilíbrio foram correlacionados com diferentes modelos matemáticos e o modelo de Halsey Modificado apresentou bom ajuste aos dados, de acordo com procedimentos estatísticos. Histerese entre as isotermas de adsorção e dessorção está presente na faixa de 0,2-0,9 de atividade de água independentemente da temperatura; este fenômeno decresce com o aumento da temperatura.

Moisture Sorption Isotherms of Quinoa Seeds: Thermodynamic Analysis

“…Parameters Tables 2 and 3, it is observed that among the eight models tested, the Modified Halsey model was the most suitable to describe the desorption and adsorption phenomenon of the quinoa seeds, since the statistical parameters are in agreement with which is advocated by several researchers (Resende et al, 2014;Chaves et al, 2015;Sousa et al, 2015), such as, high coefficient of determination (R 2 ), mean relative error (MRE) until 10%, standard deviation of the estimate (SDE) reduced and aleatory residual distribution. These results are similar to those found by Goneli et al (2016), who also recommended the Modified Halsey model for the representation of the equilibrium moisture content, by desorption and adsorption, of castor beans.…”

“…Analyzing Figure 2, it can be seen that the hysteresis (desorption equilibrium moisture content less moisture content of the adsorption) was more pronounced at lower temperatures, besides being observed throughout the water activity range, as verified by several authors (Bejar et al, 2012;Corrêa et al, 2014;Koua et al, 2014;Souza et al, 2015;Goneli et al, 2016) in orange peel, coffee fruits, cassava, turnip seeds and castor beans.…”

Thermodynamic properties for different equilibrium moisture content in sunn hemp seeds

“…However, when T B >T hm , the process is governed by enthalpy. These results are in agreement with the previous investigations that the values of isokinetic theory lie with in the general range for biologics materials, and similar to jatropha grains (Santos and Martins, 2016) and castor beans (Goneli et al, 2016).…”

Isotherms and Isosteric Heat Desorption of Hymenaea stigonocarpa Mart. Seeds

“…The desorption isotherms obtained for the Hymenaea stigonocarpa Mart. seeds by the Modified Oswin model (9) were presented in the sigmoidal format, as observed for most vegetable products such as castor beans (Ricinus communis L.) (Goneli, Corrêa, Oliveira, Resende, & Mauad, 2016), beet seeds (Beta vulgaris) (Corrêa, G. H. H. Oliveira, A. P. L. R. Oliveira, Goneli, & Botelho, 2016).…”