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The sorption isotherms of Aloe vera were determined at 8, 30 and 45 _C, for a range of water activity (0.10-0.95). Modeling of the isotherms was done using the GAB, BET, Oswin, Halsey, Henderson, Smith, Caurie and Iglesias-Chirife equations. The fit quality of the models on experimental data was evaluated using the determination coefficient, sum squared errors and chi-square statisticals. The statistical results showed that the best fit quality was obtained by the Iglesias-Chirife model, followed by the GAB and Halsey. Monolayer moisture contents were obtained between 0.05-0.19 g water/g d.m. In addition, these parameters were temperature ependent according to an Arrhenius-type equation. The sorption heat was calculated using the Clausius-Clapeyron equation giving 133.40 kJ mol 1 (desorption) and 49.60 kJ mol 1 (adsorption) at a moisture content of 0.01 g water/g d.m. The experimental heat data showed a good fit quality when these were evaluated by the Tsami equation. [ABSTRACT FROM AUTHOR]

Moisture sorption isotherms of Granny Smith apples hot-air dried and texturized by Controlled Sudden Decompression (D´ etente Instantann´ee Contr¿ol´ ´ee DIC) were determined and compared using a gravimetric method. The DIC has been developed to confer a porous structure to partially dehydrated foods by expanding them and facilitating the drying process at lower water content. The samples were stored in a chamber; the relative humidity is controlled by an atomizing humidifier at 20, 30 and 40_C, and relative humidities ranging from 10% to 90%. The sorption capacity decreased with increasing temperature at a given water activity. The hysteresis effect was not significant for both of the dried and texturized apples. The experimental sorption data were fitted to 8 various isotherm models including two parameter relationships (BET, Halsey, Smith, Henderson, Oswin), three parameter equations (Ferro-Fontan, GAB) and four parameter equations (Peleg). A non-linear least square regression software was used to evaluate the model's constants. The goodness of fit of each isotherm was quantified through the mean relative percentage deviation modulus E. The Ferro-Fontan, Peleg, GAB and Oswin equations were best for characterizing the sorption behaviour of Granny Smith apples for a whole range of temperatures and water activities studied. The surface area corresponding to the monolayer was determined for the texturized apples and compared to the dried samples. The results showed that the treatment by DIC increases the surface area of apples. For understanding the water properties and calculating the energy requirements phenomena, net isosteric heat was evaluated by the applying Clausius-Clapeyron equation. [ABSTRACT FROM AUTHOR]

Moisture sorption isotherms of osmotically dehydrated sweet peppers were determined at 15oC, 30oC and 40oC using static desiccator techniques. In the study, seven levels of water activity in range of 0.08 to 0.91 were used by the use of saturated salt solutions. The isotherms were found to be sigmoid type and of BET classification II. Out of seven sorption models i.e. BET, modified BET, Hasley, Caurie, GAB, Oswin and Smith, fitted to the experimental data, Oswin model was found to be the best for accurate prediction of moisture sorption isotherm with highest value of coefficient of determination (R2) and lowest values of standard error (SE) and relative deviation parentage (Rd). The value of monolayer moisture content of the osmotically dehydrated sweet pepper was found to be 3.037%, 3.934% and 4.432% (db) at 15oC, 30oC and 40oC respectively. The values of net isosteric heat of sorption as calculated by Clausius-Clapeyron equation showed a regular fall with increase in moisture content. [ABSTRACT FROM AUTHOR]

AbstractThe equilibrium moisture content in wood depends not only on the current relative humidity in ambient air, but also on the history of relative humidity variations. This hysteresis dependence of sorption in wood implies that in the worst case the moisture content for a given relative humidity may deviate by 30–35%. While researchers seem to have reached a general agreement on the hypothesis for the sorption hysteresis phenomenon, only a few models describing the phenomenon are available. Current models such as the independent domain model have numerical deficiencies and drawbacks. This paper presents a new hysteresis model, which mathematically resolves in closed-form expressions, with the current relative humidity and moisture content as the only input parameters. Furthermore, the model has the advantage of being applicable to different sorption isotherms, i.e., different species and different temperatures. These features make the model relatively easy to implement into a numerical method such as the finite element method. [ABSTRACT FROM AUTHOR]

Presents a study on the equilibrium moisture content (EMC) of semi-defatted pumpkin seed flour. Temperature used to determine the EMC of the flour; Equations used to verify the description of the sorption isotherms; Experimental data obtained for adsorption and desorption.