Net Isosteric Heat Of Desorption Research Articles

Desorption properties of taioba (Xanthosoma taioba E.G. Gonç.) leaves: A non-conventional edible plant

This study aimed to determine the desorption isotherms and the thermodynamic properties of taioba leaves. For this, gravimetric-static method was used to determine the equilibrium moisture content (EMC) and water activity of taioba leaves at nine storage and drying temperatures (5–80 °C). The proximate composition was also determined. The Clausius-Clapeyron and Gibb's-Helmholtz equations were used to determine the net isosteric heat of desorption and differential entropy, respectively. The enthalpy-entropy compensation theory was also investigated. The relationship between water activity and equilibrium moisture content was best described by GAB model (Radj2 ≥0.987; χ2.105≤3.126; RMSE≤0.006) for the whole range of relative moistures and temperatures. The sigmoid-shaped type II was predominant at all temperatures. The net isosteric heat of desorption decreased from 8907.62 to 1120.15 J/mol as the moisture content increased. The linear relationship between enthalpy and entropy endorsed the enthalpy-entropy compensation mechanism in which TB > Thm, thus, an enthalpy-driven process. The free Gibbs energy was less than zero spontaneous (ΔGBstorage = −728.79 J/mol and ΔGBdrying = −1217.20 J/mol), indicating that water desorption is spontaneous. The spreading pressure varied from 0.001 to 0.05 J/m2 for all temperatures studied. The water surface area tended to decrease with increasing temperature, ranging from 185.71 to 251.97 m2/g. Therefore, this study provided an understanding of the water desorption properties of taioba leaves, contributing to the development of storage and drying practices.

Relation between hydrophilic/hydrophobic characteristics of sludge extracellular polymeric substances and sludge moisture-holding capacity in hot-pressing drying

Sludge poses a serious threat to the environmental health. Hot-pressing drying has been proven efficient in sludge treatment because of the reduced thermal contact resistance, rapid increase in sludge temperature, and high drying rate. Sludge extracellular polymeric substances (EPS) significantly influence moisture transfer. However, whether in hot-pressing or traditional thermal drying, the effect of EPS on sludge moisture-holding capacity is rarely reported. Thereby, this study investigated the relationship between hydrophilic/hydrophobic characteristics of EPS and sludge moisture-holding capacity at various drying time and mechanical compression using XAD resin fractionation. Thermodynamic analysis indicated that sludge moisture desorption isotherms, net isosteric heat of desorption, and differential entropy presented a downward trend with the increase in drying time and mechanical compression, suggesting reduced sludge moisture-holding capacity. EPS analysis showed that at the same drying time, applying 25 kPa mechanical compression increased sludge temperature by 16 % and protein content by 13.8 %. At the same sludge temperature, protein content rose by 7.3 % compared to the drying without mechanical compression. It was concluded that the fast rise in sludge temperature and the mechanical extrusion facilitated the destruction of sludge microbial flocs, accelerating the release of intracellular and EPS-bound moisture and contributing to the decrease in moisture-holding capacity. Besides, tryptophan protein-like substances were the major source of hydrophilic/hydrophobic organic matter, compared to polysaccharide and humic acid-like substances. The gradually reduced sludge moisture-holding capacity was divided into three stages. Below 67 °C, the moisture desorption was dominated by the release of intracellular moisture. Below 85 °C, the increase in protein and the enhanced exposure of hydrophobic functional groups in protein improved the hydrophobicity of EPS. Above 85 °C, protein consumption due to thermal decomposition and browning reaction facilitated the desorption of EPS-bound moisture. Hence, this study provided novel insights into the mechanism of sludge drying.

Water desorption isotherms and thermodynamic properties of Ora-pro-nóbis (Pereskia aculeata Miller)

Desorption isotherms of ora-pro-nóbis leaves were determined at storage (5 °C, 10 °C, 20 °C, 30 °C, and 40 °C) and drying (40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) temperatures by the gravimetric static method using saturated saline solutions to obtain relative humidities ranging from 5.20% to 98.48%. The net isosteric heat of desorption and thermodynamic properties such as differential enthalpy, differential entropy, and Gibbs free energy were also estimated. The GAB model presented the best parameters of fitting and the lowest Akaike and Bayesian information criteria values. The desorption isotherm patterns presented a sigmoid shape and were categorized as BET Type II sigmoid shape. The monolayer moisture content was estimated in 0.06 kg of water/kg of dry matter using the GAB model, and it remained constant at all temperatures. The leaves presented an optimal water activity equal to 0.35 at storage temperatures. The net isosteric heat of desorption decreased with increasing Xeq, and differential entropy increased with rising equilibrium moisture content (Xeq > 0.07). The enthalpy-entropy compensation was evaluated, and the desorption process is revealed to be entropy-driven and non-spontaneous.

Determining the heat of desorption for cassava products based on data measured by an automated gravimetric moisture sorption system.

The isosteric heat of desorption is vital in evaluating the energy performance of food dryers. The isosteric heat of desorption was investigated for different cassava (Manihot esculenta Crantz) products prepared as flour or starch, with and without fermentation. An automated moisture sorption gravimetric analyser was used to measure the desorption isotherms over 10-90% relative humidity of the drying air at temperatures ranging from 25 to 65 °C. Analysis of variance showed an imperceptible contribution of the preparation method in the measured desorption data. This finding also agreed with microscopical images, which revealed the lack of compelling structural differences among different products. A set of empirical sorption equations suggested by the ASAE standard was examined over the measured desorption isotherms. The standard error of estimation was found to be in the acceptable range of 2.36-3.71%. Furthermore, the fulfilment of the enthalpy-entropy compensation theory was considered as an additional criterion in the thermodynamic results of different sorption equations, besides their fitting adequacy. The modified Chung-Pfost equation has proved to be the most suitable equation for cassava products, as it is capable of reflecting the temperature dependency of the isosteric heat of desorption. The net isosteric heat of desorption obtained was in the range of 540-1110 kJ kg-1 for 0.10kg kg-1 dry-basis moisture content and 52-108 kJ kg-1 for 0.25 kg kg-1 dry-basis moisture content. These findings are technologically relevant for optimising common drying technologies such as flash and flatbed dryers. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evaluation of desorption isotherms, drying characteristics and rehydration properties of crab stick by-product

Crab stick by-product is the underspecification product from crab stick production. The by-product contains high moisture content inducing a short shelf life. Therefore, drying is considered as a food preservation technique to extend its shelf life. This study is focused on an investigation of desorption isotherms, drying characteristics and rehydration properties of crab stick by-product. Desorption isotherms were determined at three different temperatures (20, 35 and 50 °C). The experimental data obtained were modeled by fourteen sorption isotherm models for water activity ranging from 0.36 to 0.99 and Double Log Polynomial model was found to be the best-describing model. The net isosteric heat of desorption increased continuously with decreasing of equilibrium moisture content. The crab stick by-products were dried at 50, 60 and 70 °C with a constant air velocity of 1 m/s. The drying data were fitted with five thin layer drying models and Approximation of diffusion model was the best-describing model. Drying curves showed only falling rate period. Moisture diffusivities (Deff) of the by-product drying were ranging from 8.87 × 10−10 to 1.47 × 10−9 m2/s and increasing drying air temperature led to an increment of Deff. Rehydration properties including weight gain (%), rehydration ratio and co-efficient of reconstitution of dried sample at 60 and 70 °C were higher than the drying at 50 °C. Peleg model was the best fit with rehydration data. The Deff of moisture absorption was in the range from 6.49 × 10−9 to 7.31 × 10−9 m2/s.

Drying Kinetics, Desorption Isotherms and Apparent Diffusivity of Sage Leaves

The use of fresh herb is limited in the food and pharmaceutical industry thats why the dry form of the herb is the one commonly used. To save the quality of medicinal and aromatic plants it is very important to provide optimum drying and storage conditions. The aim of this study is to determine and model the drying kinetics of sage leaves. Initially the desorption isotherms are determined for different temperatures (30, 45 and 60°C). The drying experiments were carried out in a convection oven at the same temperature range. For the desorption isotherms and the drying kinetics various models reported in the literature were used and from the statistical view, the Yanniotis and Blahovec and the Fick models fit well the results of desorption isotherms and the oven drying, respectively. The net isosteric heat of desorption of the sage leaves ranged from 6.86 to 63.45 kJ/mol. The total time of oven drying reduced substantially with an increase of the drying temperature. Effective moisture diffusivity values ranged from 1.1x10-12 to 3.7x10-12 m2/s and significantly affected by temperature. An Arrhenius relation with an activation energy value of 66.87 kJ/mol expressed effect of temperature on the diffusivity. Keywords: Desorption isotherms, Drying kinetics, Modelling, Effective diffusivity, Sage leaves

THERMODYNAMIC PROPERTIES OF TAMARIND SEEDS (Tamarindus indica L.)

Tamarind is used in the food and pharmaceutical industry, and its seed is the main means for the reproduction of this species, thus justifying studies that ensure its post-harvest viability. This research aimed to study the thermodynamic properties of tamarind seeds as a function of the equilibrium moisture content. The experimental data of the water activities were obtained by the indirect static method. The Cavalcanti Mata model was used to determine the thermodynamic properties of tamarind seeds, as it was the model that best fitted the experimental data of the desorption isotherms. The results showed that the thermodynamic properties are influenced by the moisture content and temperature, with an increase in the energy required to remove water from the product with a decrease in moisture content. The net isosteric heat of desorption increases with a reduction of moisture content ranging from 2,618.85 to 2,510.25 kJ kg−1 for the moisture content range of 10.52 to 21.10% db. The latent heat of vaporization, the differential enthalpy, and the Gibbs free energy increase with a reduction of the moisture content of tamarind seeds.

Moisture sorption isotherm characteristics and Taguchi analysis of rice bran extraction parameters

AbstractThis work determined the moisture sorption isotherm of rice bran and investigated the effects of the pre‐treatment method, solvent type, solid–liquid ratio and soaping temperature on extract yield, total phenolic content, 2,2‐diphenyl‐1‐picrylhydrazyl radical‐scavenging activity assay and 2,2′‐azino‐bis antioxidant capacity assay of rice bran extract. The Taguchi method and L9 (34) orthogonal array were employed in this study. The sorption isotherms of rice bran showed a sigmoidal pattern and displayed type II of van der Waals adsorption. Adsorption and desorption data on rice bran were best fitted using the Henderson model among the six models tested at three temperatures. The net isosteric heat of desorption was higher than the net isosteric heat of adsorption. Based on the analysis of the signal‐to‐noise ratio, solvent selection effected the largest contribution to the overall performance. Confirmation experiments showed that the optimal combination that contained the four quality attributes was appropriate (error margin <5%) and reproducible. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Effect of Sodium and Its Substitution with Potassium on Desorption and Thermodynamic Properties of Cheddar Cheese

Desorption isotherm of full sodium Cheddar cheese (FSCC) and low sodium Cheddar cheese (LSCC) was obtained at 5C and 10C using a static gravimetric method. Both cheeses desorption isotherms show Type II of the five general types of sorption isotherms due to the presence of casein as a major constituent and also due to the presence of salts. Desorption curves in both cases indicate that increase in temperature results in decrease in equilibrium moisture content. Several models were tested of which BET and GAB model were best fitted to the experimental data in the water activity range of 0.11–0.98. The porosity of FSCC and LSCC showed general increasing trend with increase in temperature and moisture content. Net isosteric heat of desorption was evaluated by Clausius–Clapeyron equations to provide an understanding of the properties of water and energy requirements associated with the desorption behavior. Practical Applications The results may be utilized for predicting water activity values of low sodium Cheddar cheese (LSCC) at different temperature and moisture content. Properties calculated viz., equilibrium moisture content, monolayer moisture content, and many others may find application in representing the state of water present in LSCC at different temperatures for revealing physico-chemical and microbiological changes.

Moisture sorption isotherm characteristics of Hemerocallis Fulva and Cymbopogon

AbstractThe moisture sorption isotherms of Hemerocallis Fulva and Cymbopogon are measured by the static gravimetric method at 25, 35, and 45 °C over a water activity range of 0.09 to 0.95 using standard saturated salt solutions. The sorption isotherms of H. fulva and Cymbopogon display type III (J‐shaped) and type II (nearly sigmoid shapes) isotherms. In addition, the adsorption and desorption data of H. fulva and Cymbopogon fit well with the White & Eiring model and the Oswin model, respectively. The Brunauer–Emmett–Teller equation is applied to determine the monolayer moisture content, and the surface area of a monolayer was calculated. The values of the net isosteric heat of sorption are found to increase with decreases in the equilibrium moisture content. Moreover, the net isosteric heat of desorption is higher than that of the adsorption heat. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Analysis of adsorption–desorption moisture isotherms of rosemary leaves

The moisture sorption isotherms data of rosemary leaves were investigated via the gravimetric static method at three different temperatures (30, 40 and 50°C). The sorption isotherms obtained were of sigmoid shape and of type II of Brunauer classification. From various mathematical models used for our experimental data, The GAB model best described the experimental data.The sorption data were analyzed for determination of monolayer moisture content (3.4–9.7%), and properties of sorbed water. Analysis of sorption isotherm by the model of the Yanniotis and Blahovec shows that the contribution of surface adsorption in relation to solution water at each water activity was higher in desorption than in adsorption The net isosteric heat of desorption and adsorption of the rosemary leaves ranged respectively from 1.77 to 47.37kJ/mol and from 0.85 to 26.86kJ/mol. The enthalpy–entropy compensation suggested that the sorption mechanism involved was enthalpy driven. The net integral enthalpy of adsorption and desorption decreased with increasing equilibrium moisture content.The integral entropy increased with moisture content, but was of negative value.

Water desorption isotherms and net isosteric heat of desorption on lignite

Water vapor desorption isotherm studies were performed on lignite at the temperature 30, 40 and 50°C to investigate the behavior of water on coal. For a description of desorption process, a Guggenheim–Anderson–de-Boer (GAB) model provided a good fit. At the monolayer region, the overlapping isotherms at different temperatures could not provide valid data to calculate the isosteric heat by applying the Clausius–Clapeyron equation, and hence the isosteric heat was only determined at the moisture content from 0.125 to 0.280mg/mg dry coal. Then, the Brunner–Emmet–Teller (BET) theory was applied to calculate the isosteric heat at the moisture content below 0.125mg/mg dry coal. Net isosteric heat of desorption determined from the isotherms increases from 1.88kJ/mol in the capillary water to 8.17kJ/mol at the monolayer region. This increase is most likely that the forces from coal surface act on all types of water in raw lignite, and as the moisture content decreases, the forces are becoming stronger. Besides, with the effect of the interaction among adsorbed water molecules and the bonding force between water molecules and active sites, at the monolayer region, a maximum energy peak appears on the curve of isosteric heat.

Moisture desorption isotherms of cucumber seeds: modeling and thermodynamic properties

Hygroscopic equilibrium curves or sorption isotherms are important in order to define dehydration limits of the product, estimate moisture content alterations under environment conditions and to acquire moisture content values for safe storage. This work aimed to determine desorption isotherms of cucumber seeds stored at different temperature (10, 20, 30, 40 and 50 ºC) and relative humidity (0.11 to 0.96) and the thermodynamic properties of this process. Mathematical models were fitted to experimental data in order to represent the agricultural products hygroscopicity. Net isosteric heat of desorption was performed based on the Clausius-Clapeyron thermodynamic relation and Gibbs free energy through the Van't Hoff equation. Based on statistical parameters, Modified Henderson model was the one that best represented hygroscopicity of cucumber seeds. Equilibrium moisture content of cucumber seeds decreased with temperature increment at a constant value of relative humidity. Differential enthalpy values, representing the energy required to remove moisture from the cucumber seeds, ranged from 2923 to 2469 kJ. kg-1. Values of differential entropy and Gibbs free energy decreased with moisture content increase. Enthalpy-entropy compensation theory is valid for the sorption of cucumber seeds, in which the water sorption mechanism in cucumber seeds can be considered to be enthalpy controlled.

Thermodynamic Properties of Water Desorption of Papaya

Thermodynamic properties were obtained from desorption isotherm data for papaya at 40, 50, 60 and 70C. The specific objectives were to model desorption isotherms by GAB and BET models and to apply the enthalpy-entropy compensation theory to desorption isotherm. The GAB model fitted well the data with monolayer moisture content varying from 0.086 to 0.103 g water/g solids. Equilibrium moisture content decreased with increasing temperature. The net isosteric heat of desorption was determined using Clausius–Clapeyron equation and decreased with increasing moisture content varying from 2.52 to 14.26 kJ/mol. The differential entropy values decreased with moisture content from 0.037 to 0.007 J/mol K. The enthalpy-entropy theory proved to be valid since the relationship between enthalpy and entropy was linear and the harmonic temperature (327.6 K) differed from the sample isokinetic temperature (383.4 K). Through the entropy-enthalpy theory, it could be concluded that the water desorption isotherm of papaya is a nonspontaneous process and enthalpy controlled. Practical Applications This work presents information about the moisture sorption properties of papaya fruit. Moisture sorption isotherms are important to estimate drying time, predict ingredients behavior upon mixing, select packaging, model moisture changes that occur during storage and estimate shelf life stability. In addition, moisture isotherm supplies thermodynamic properties that permit estimation of energy requirement of drying process. Because papaya is extremely perishable, dehydration could be a necessary step in the processing. Therefore, this work intends to contribute in providing useful information for designing drying process of papaya.

Desorption Isotherms and Isosteric Heats of Fermented Cocoa Beans (Theobroma cocoa)

<p>Water desorption isotherms of fermented cocoa beans from Ivory Coast were determined using the gravimetric static method of saturated salts solutions at 30 °C, 40 °C and 60 °C, and isosteric heats of desorption were calculated from Clausius-Clapeyron equation. The experimental data were fitted to several isotherm equations. The best fittings were obtained for the BET equation for aw<0.50 (with an average mean relative deviation (MRD) value of 1.56%) and for the Harkins-Jura equation for aw?0.50 (with an average value MRD equation of 4.17%). The isotherms obtained at 30 °C and 40 °C are practically coincident and overlapped for aw below 0.40. Fermented cocoa beans presented a monolayer moisture content of 0.083 dry basis (d.b.) at 30 °C and this value decreases with increasing temperature. The net isostheric heats of desorption for fermented cocoa beans for the temperature range studied (30-60 °C) were estimated as a function of moisture content. The maximum net isosteric heat of desorption for fermented cocoa beans was estimated at around 13.51 kJ/mol corresponding to a moisture content value of 2.85%. The energy requirement for maintaining the moisture content low of 8.7% (d.b.) or 8% wet basis (w.b.) for safe storage of this product or for reducing the moisture content during drying was estimated at around 9.58 kJ/mol.</p>

Determination of the Moisture-Sorption Isotherms and Isosteric Heat of Henna Leaves

Equilibrium moisture desorption and adsorption isotherms of Lawsonia inermis L. (commonly known as henna) leaves at temperatures of 30, 40 and 50°C with a water activity ranging from 0.057 to 0.898 were obtained by the gravimetric-static method. It was established that when the temperature of these leaves increases, their moisture content increases too with a hysteresis effect. The experimental data on the sorption of the indicated leaves were compared with the corresponding calculation data obtained with the use of the GAB, modified BET, Henderson–Thompson, modified Halsey, modified Oswin, and Peleg models. Evaluation of these models on the basis of statistical processing of the data obtained with them, including the calculus of the standard error and the correlation coefficient, has shown that the GAB and Peleg models represent sorption curves more adequately. The net isosteric heats of desorption and adsorption of henna leaves were determined by the sorption isotherms constructed using the Clausius–Clapeyron equation. An expression for predicting these thermodynamic properties of plants is proposed.

Mathematical Modeling of Moisture Sorption Isotherms and Determination of Isosteric Heats of Sorption ofZiziphusLeaves

Desorption and adsorption equilibrium moisture isotherms ofZiziphus spina-christileaves were determined using the gravimetric-static method at 30, 40, and 50°C for water activity(aw)ranging from 0.057 to 0.898. At a givenaw, the results show that the moisture content decreases with increasing temperature. A hysteresis effect was observed. The experimental data of sorption were fitted by eight models (GAB, BET, Henderson-Thompson, modified-Chung Pfost, Halsey, Oswin, Peleg, and Adam and Shove). After evaluating the models according to several criteria, the Peleg and Oswin models were found to be the most suitable for describing the sorption curves. The net isosteric heats of desorption and adsorption ofZiziphus spina-christileaves were calculated by applying the Clausius-Clapeyron equation to the sorption isotherms and an expression for predicting these thermodynamic properties was given.

Moisture sorption isotherms – Experimental and mathematical investigations of orange (Citrus sinensis) peel and leaves

The aims of this work were to determine chemical composition and sorption isotherms of Tunisian orange peel and leaves of the “Maltaise” variety. These by-products were found to be rich in fibre, soluble sugars, protein, minerals and phenols. The equilibrium moisture contents of “Maltaise” peel and leaves were measured using the static gravimetric method at three temperatures (40, 50 and 60°C) and in wide range of water activity (0.109–0.891). Desorption and adsorption data of peel and leaves were best fitted by the Peleg model at 40, 50 and 60°C. The net isosteric heats of desorption and adsorption were determined from sorption isotherms. For both peel and leaves, the net isosteric heat of desorption was higher than the net isosteric heat of adsorption and both decreased continuously with increasing of the equilibrium moisture content.

Modelling the Water Sorption Isotherms of Quinoa Seeds (Chenopodium quinoa Willd.) and Determination of Sorption Heats

Adsorption and desorption isotherms of quinoa seeds (Chenopodium quinoa Willd.) were measured using the static gravimetric method at three temperatures (20, 40 and 60 °C). Water activity ranged from 0.118 to 0.937. The moisture sorption behaviour of quinoa was temperature dependent, as indicated by a decrease in equilibrium moisture content, at all levels of aw, with increasing temperature. Eight mathematical equations available in the literature were used to model the experimental data, namely, GAB, BET, Caurie, Henderson, Oswin, Halsey, Smith and Iglesias–Chirife. All the equations showed generally a good fit; however, the Iglesias–Chirife and Oswin equations were considered the best to predict the experimental data for both isotherms. Effect of temperature on model parameters was analysed and studied through an Arrhenius-type equation. The net isosteric heats of desorption and adsorption were determined by applying the Clausius–Clapeyron equation resulting in 69.24 kJ mol−1 for desorption and 61.26 kJ mol−1 for adsorption. The experimental heat data were satisfactorily modelled by Tsami’s equation.

Mechanism of lowering water activity of konjac glucomannan and its derivatives

Moisture retaining materials are widely used in the food, cosmetic and tobacco industries. Conventional materials, for example, glycerin and propylene glycol have reasonable moisture absorption abilities, but poor moisture retention. Konjac glucomannan (KGM) is a heteropolysaccharide made up of glucose and mannose, linked with β-1,4 glycosidic bonds. Konjac superabsorbent polymer (KSAP) is a derivative containing hydrophilic groups and a network structure prepared by grafting sodium acrylate on to KGM. Previous work has shown that KGM and KSAP have properties which can lower water activity (a w). The objective of this paper is to consider the mechanism of this process. Filter-paper is used as a model fiber instead of tobacco, where this effect is practically important. Moisture absorption and retention of KGM and KSAP are compared with glycerin and propylene glycol. Moisture desorption isotherms have been determined and fitted to the GAB model. The results show that the moisture retention of KGM and KSAP are better than propylene glycol and glycerol. At a given moisture content, a w of filter-paper containing KSAP was the lowest. The monolayer moisture content and net isosteric heat of desorption of filter-paper containing KGM and KSAP were greater than that of the control groups. This study demonstrated that KGM and KSAP have the potential to be used as moisture retaining ingredients.