The Hygroscopic Properties and Sorption Isosteric Heats of Different Chinese Wheat Types

Abstract

The moisture sorption isotherm data of fourteen Chinese wheat varieties were determined using the static gravimetric method at five different temperatures (10, 20, 25, 30 and 35 °C ) and relative humidity ranging from 11.3 to 96%. Eight models, namely Brunauer-Emmett-Teller, CAE, Chen-Clayton, Modified-Chung-Pfost (MCPE), Modified-Henderson, Modified-Guggenheim-Anderson-deBoer, and Modified-Oswin and Strohman-Yoerger, were used to fit the sorption data. MCPE shows the best fitting results. A significant hysteresis effect was found between wheat desorption and adsorption isotherm at lower ERH, but the similar hygroscopic properties remained for different wheat types like hard vs. soft, red vs. white, and winter vs. spring, respectively. The experimental results show that the isosteric heats for both wheat adsorption and desorption, and all the sorption heats for different wheat types decrease rapidly with increasing seed moisture initially, however, after the moisture is more than 15% w.b. they decrease tardily with increasing moisture content. The isosteric heats of wheat desorption were considerably higher than those of adsorption below 17.5% m.c., but the similar sorption isosteric heats were found for wheat types like hard vs. soft, red vs. white, or winter vs. spring, respectively. It is concluded that the wheat grains from different types have similar hygroscopic properties and sorption isosteric heats and can be synchronously dealt with during physical control in storage.

Mathematical Modeling and Hysteresis of Sorption Isotherms for Paddy Rice Grains

“…According to Ullmann et al (2016), the Chung Pfost model has been used for starchy products, being the model chosen to represent the hygroscopicity of sweet sorghum seeds. This model also fitted satisfactorily to hygroscopic equilibrium of okra (Goneli et al, 2010), wheat (Li, 2012), cotton (Oliveira et al, 2013), sugar beet (Corrêa et al, 2016), kalibu chickpea, black sesame and white sesame (Armstrong et al, 2017) and red kidney beans (Jian & Jayas, 2018) seeds.…”

Isotermas De Dessorção De Sementes De Beterraba

“…Nota-se que na distribuição dos resíduos do modelo Chung-Pfost não é possível perceber nenhuma tendência em seus resíduos, sendo distribuído aleatoriamente na faixa de teor de água de equilíbrio, com resíduos de valores positivos e negativos (Figura 1). O modelo de Chung-Pfost também representou, de forma satisfatória, a higroscopicidade de sementes de quiabo (Goneli et al, 2010) sementes de caju-de-árvore-de-cerrado (Caetano et al, 2012), para sementes de trigo (Li, 2012) e para sementes de algodão (Oliveira et al, 2013). Verifica-se a influência da temperatura sobre a higroscopicidade das sementes de beterraba em que, para se atingir um mesmo teor de água de equilíbrio, o aumento da temperatura requer o aumento da umidade relativa.…”

Modelling the effect of temperature on the water sorption isotherms of chitosan films

“…This might result in a reduction in the total number of active sites in which the water molecules interact as a consequence of the physical changes in the polymeric material. Therefore, an increase in temperature results in a reduction in the amount of moisture adsorbed at a given water activity value (Li, 2012;Mrad et al, 2013;Muzaffar & Kumar, 2016;Souza et al, 2015). Water molecules also have the capability to increase the free volume in the polymer matrix, thus increasing the mobility of the polymer chains and the permeability of the material (Schmid et al, 2015).…”