Equilibrium Moisture Content Data Research Articles

Yerba Maté (Ilex paraguariensis St. Hil.): Chemical and Physical Changes under Different Aging Conditions

AbstractThe variation of different physicochemical parameters related to yerba maté quality (caffeine, water extract, total polyphenol content, color parameters and antioxidant activity) was studied in yerba maté samples obtained by three different aging methods: (1) natural aging (NA); (2) temperature‐controlled aging (TCA); and (3) humidity‐ and temperature‐controlled aging (HTCA). Adsorption isotherms at low temperatures (20, 30, 40 and 50C) were also determined. Water extract and color parameters (L and a) increased significantly during aging in the three methods studied (P < 0.05). The results also showed that during NA the polyphenol content of yerba maté diminished (P < 0.05), while caffeine remained constant (P > 0.05). The antioxidant activities of yerba maté obtained by NA and HTCA were significantly higher (P < 0.05) than the antioxidant activity of yerba maté without aging and the yerba maté obtained by TCA. These variations were explained by 0, 1 and 2 kinetic order equations. Kinetic rate constants were higher in the HTCA than in the TCA, and these values were higher than in the NA according to temperature decrease. Experimental data of equilibrium moisture content at different temperatures showed good fitting (P < 0.05) with the three models tested (GAB, Halsey and Henderson). No significant differences were found either with temperature or with the materials obtained using different aging methods. Although the results obtained demonstrate that different aging methods originate similar products, HTCA method is better because it provides a yerba maté with higher total polyphenol content.Practical ApplicationsAging is one stage in yerba maté (Ilex paraguariensis) processing. There are three methods commonly used to age yerba maté in industry, in which different air conditions (temperature and humidity) are employed. Sensorial analysis, usually carried out by expert tasters, is commonly used to control the aging method and the degree of aging of yerba maté. These tests are subjective and suffer from inconsistency and inaccuracy, so it is necessary to develop objective methods to identify the yerba maté quality, chemically or physically. This work evaluates the variation of different physicochemical parameters during the aging stage of yerba maté in order to differentiate the products obtained using the three aging methods. Data were fitted to different kinetic equations in order to predict the degree of aging and the time necessary to reach the end point.

Sorption Isotherm of Southern Yellow Pine-High Density Polyethylene Composites.

Temperature and relative humidity (RH) are two major external factors, which affect equilibrium moisture content (EMC) of wood-plastic composites (WPCs). In this study, the effect of different durability treatments on sorption and desorption isotherms of southern yellow pine (SYP)-high density polyethylene (HDPE) composites was investigated. All samples were equilibriumed at 20 °C and various RHs including 16%, 33%, 45%, 66%, 75%, 85%, 93%, and100%. EMCs obtained from desorption and absorption for different WPC samples were compared with Nelson’s sorption isotherm model predictions using the same temperature and humidity conditions. The results indicated that the amount of moisture absorbed increased with the increases in RH at 20 °C. All samples showed sorption hysteresis at a fixed RH. Small difference between EMC data of WPC samples containing different amount of ultraviolet (UV) stabilizers were observed. Similar results were observed among the samples containing different amount of zinc borate (ZB). The experimental data of EMCs at various RHs fit to the Nelson’s sorption isotherm model well. The Nelson’s model can be used to predicate EMCs of WPCs under different RH environmental conditions.

Equilibrium relative humidity method used to determine the sorption isotherm of autoclaved aerated concrete

The sorption isotherm of porous building material is basic information needed for the design and maintenance of materials. The equilibrium moisture content (EMC) method is used to determine this physical property. In this study, the equilibrium relative humidity (ERH) method was used to determine the adsorption data for autoclaved aerated concrete at seven temperatures and found that the ERH method could be used to determine the sorption data within a short time. Comparing with previous published data, no significant difference could be found at humidity >20%. Two different sizes of samples (small and large) revealed the same EMC data throughout the whole relative humidity (RH) range. The Oswin equation was the best ERH model for adsorption isotherm data. A temperature term could be incorporated into model for the adsorption data. Sorption isotherm data for other building materials could be determined with the ERH method.

Effect of Hemicellulose as a Coating Material on Water Sorption Thermodynamics of the Microencapsulated Fish Oil and Artificial Neural Network (ANN) Modeling of Isotherms

In this study, effect of hemicellulose as a coating material on sorption behavior of the microencapsulated fish oil is presented. For this purpose, water sorption isotherms of the fish oil microcapsules prepared using gum arabic (GA) and gum arabic-hemicellulose (GA-HC) were determined at 10, 25, and 35 °C using the gravimetric technique. The equilibrium moisture content (EMC) data were fitted to several empirical mathematical models, namely Oswin, BET, GAB, and Freundlich equations and the novel artificial neural network (ANN) model. The GA-HC microcapsules had higher EMC values than GA, due to the sugar content of hemicellulose. The EMC of the samples were more accurately predicted by the ANN model than by the empirical models at the entire range of a w. Heat of sorption of fish oil microcapsules was then predicted using the data obtained from the ANN model and fitted to the power model (R 2 = 0.985–0.978). A linear relation existed between the differential enthalpy and the differential entropy for microcapsules, thus satisfying the enthalpy-entropy compensation theory.

Moisture Sorption Characteristics of Pineapple Processing Waste: Shell and Central Cylinder

The moisture adsorption isotherms of pineapple processing waste – shell and central cylinder – were determined at 40, 50, 60 and 70C using a gravimetric method. The sorption data were fitted to six well-known sorption isotherm models. The Guggenheim–Anderson–de Boer model was found to be the most satisfactory to represent the equilibrium moisture content data for the pineapple shells and central cylinders. The thermodynamic properties – differential enthalpy and entropy – were estimated by the Clausius–Clapeyron method. The differential enthalpy of the pineapple shells and central cylinders ranged between 11.486 to 1.671 kJ/mol and 23.655 to −0.945 kJ/mol, respectively. The differential entropy had minimum values at 0.04 and 0.005 kgwater/kgdry solids for the pineapple shells and central cylinders, respectively. The pineapple shells presented two lines of compensation, one controlled by entropy and the other controlled by enthalpy and the pineapple central cylinders showed only one zone controlled by enthalpy mechanisms. Practical Applications This work presents information about the moisture sorption characteristics of pineapple processing waste. This kind of information is important for designing the unit operations necessary in the waste process use. In addition, knowledge of the moisture sorption characteristics is useful with respect to selection of packaging materials and storage stability. In general, this work gives relationship between water activity, entropy, enthalpy and moisture content of pineapple processing waste.

Modeling of the Equilibrium Moisture Content (EMC) of Switchgrass

<abstract><title><italic>Abstract.</italic></title> Moisture sorption isotherms of milled switchgrass (Panicum virgatum) were developed to provide guidelines for proper storage and drying of biomass. Samples were stored for a minimum of 8 days inside incubators set at 15°C, 25°C, or 35°C at different relative humidities, ranging from 16% to 88%. Equilibrium moisture content (EMC) data were fitted with the Henderson model and modified versions of the Chung-Pfost, Guggenheim-Anderson-deBoer (GAB), Halsey, Henderson, and Oswin models. The modified GAB model (R² = 0.99; SE = 0.58% d.b.) followed by the modified Henderson model (R² = 0.99; SE = 0.68% d.b.) produced randomized residuals and the best fit for milled switchgrass. The results have practical applications in the handling, drying, storage, and transportation of switchgrass to ensure that quality deterioration and spoilage by microorganisms are minimized.

Equilibrium moisture content of dead fine fuels of selected central European tree species

Fine fuel moisture content is a key parameter in fire danger and behaviour applications. For modelling purposes, equilibrium moisture content (EMC) curves are an important input parameter. This paper provides EMC data for central European fuels and adds methodological considerations that can be used to improve existing test procedures. Litter samples of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) were subjected to three different experiments using conditioning in a climate chamber and above saturated salt solutions. Climate chamber conditioning yielded the best results and can generally be recommended, however saturated salt solutions are able to produce lower relative humidities, which are relevant to forest fire applications as they represent the highest fire danger. Results were within the range of published sorption isotherms for forest fine fuels. A fairly clear gradation was present with higher EMC values in leaf litters than in needle litters. These differences are in accord with values from the literature and suggest general differences in the sorption properties of leaves and needles, which may be caused by differing chemical and physical properties. The influence of temperature on EMC described in the literature could be confirmed.

Thin Layer Drying and Equilibrium Moisture Content Equations for Canola (Brassica napus L.)

A fully instrumented air conditioning laboratory unit capable of controlling drying air temperature and humidity integrated with an instantaneous weighing thin layer drying system was used to investigate the thin layer drying behavior and desorption equilibrium moisture content of canola (Brassica napus L.). To this aim, freshly harvested canola samples with moisture content of about 12±0.5% (d.b.) were dried at temperature levels of 40, 45, 50, 55 °C and absolute air humidity levels of 0.005, 0.01, 0.015, and 0.02 kg/kg. The instantaneous grain moisture content was measured by weighing the sample periodically. Drying was continued until canola kernels reached a constant weight to obtain the hygroscopic equilibrium moisture for different combinations of drying air temperature and absolute humidity. To select a suitable model for describing the thin layer drying of canola, experimental drying data were fitted with three thin layer drying models, namely, Page, Modified Page and Two-Term Exponential models. Furthermore, four widely used desorption isotherm models including Chung-Pfost, Modified Chung–Pfost, Modified Oswin, and Modified Smith were used to fit the experimental data of equilibrium moisture content. Finally, non-linear regression analyses were run and based on the highest value for R2 and the lowest value for, mean bias error (MBE) and root mean square error (RMSE), the most suitable models for thin layer drying and equilibrium moisture content were determined to be Two-Term Exponential and Modified Smith, respectively.

Water sorption properties of coffee fruits, pulped and green coffee

Thermodynamic properties of coffee in three different forms (green, pulped and coffee fruit) were obtained during the desorption process. Desorption was accomplished by static method using saturated salt solutions, providing relative humidity range of 11–95%. Five different temperatures were utilized (10, 20, 30, 40 and 50 °C). Equilibrium moisture content data were correlated by the Guggenheim–Anderson–de Boer model, which presented good fit to the data, according to statistical procedures. Equilibrium moisture content ranged from 4.34 to 10.75 g/100 g dry solids. Enthalpy values for each model coefficient were estimated, ranging from −8.09 to 82.64 kJ kg−1. Differential enthalpy and differential entropy increased with decreased equilibrium moisture content, which was also found for Gibbs free energy. Coffee fruits presented higher values of these thermodynamic parameters.

Equilibrium moisture content of radiata pine at elevated temperature and pressure reveals measurement challenges

Relatively few studies have been performed on the equilibrium moisture content (EMC) of wood under conditions of elevated temperature and pressure. Eight studies indicated that EMC near saturation decreased between 100 and 150 °C, whilst five studies indicated that EMC increased. The aim of this study was to identify the likely source of the disagreement using radiata pine (Pinus radiata D. Don) sapwood which was conditioned to a moisture content of around 3 % and then exposed for 1 h at 150 °C and relative humidities of either 50, 70 or 90 %. Mean values of EMC, obtained through in situ gravimetric analyses, were 5.7, 7.6 and 12.6 % with 95 % confidence intervals of the order of 1 %. In two further experiments, the humidity was allowed to rise briefly above 90 % and the moisture content after 1 h was found to be >30 % as in the five studies that indicated EMC increased above 100 °C. The high moisture contents were attributed to condensation of liquid water on the specimen with subsequent evaporation at a rate that was too slow for the moisture content to reach equilibrium before it was measured. Reliable EMC data at elevated temperatures require (1) tight process control of experimental conditions with minimal standard error, (2) specimens with low initial moisture content to avoid unwanted wood mass loss over time, (3) a relative humidity upper limit that avoids drift above 95 %, and (4) extrapolation of data to humidity approaching 100 %.

Sorption and capillary condensation in wood and the moisture content of red pine

The major purpose of this study is to improve hygrothermal simulation of wood responses to environmental vapor and moisture conditions under high relative humidity conditions. The article first reviews moisture property–related wood microstructures, sorption behavior, the concept of fiber saturation point, the potential for vapor to condense in wood under high relative humidity conditions, the measurement of equilibrium moisture content using traditional sorption methods, and the use of pressure plate test method at relative humidities above 95%. It then summarizes the results of equilibrium moisture content measurements for red pine sapwood at high relative humidity conditions using both sorption and pressure plate methods, with capillary saturation as maximum moisture content. It also discusses a number of wood microstructure and end-use-related factors that could influence the moisture content in service and the measurement of equilibrium moisture content in laboratory. Inconsistencies were found with other equilibrium moisture content data using the pressure plate test method.

Moisture Adsorption Characteristics of Solar-Dehydrated Mango and Jackfruit

The moisture adsorption isotherms of solar dehydrated mango and jackfruit were determined at temperatures ranging from 30 °C to 50 °C. The equilibrium moisture content (EMC) of mango and jackfruit increased sharply as the temperature increased at water activity (aw) above 0.6 and 0.8, respectively. However, there were no clear isothermal intersection points observed at higher aw and temperatures. The EMC of solar dehydrated jackfruit showed the isothermal characteristics between types II and III. In contrast, dehydrated mango followed the characteristic type III adsorption isotherms due to high total soluble solids content of 67.8 °Brix and total sugars of 14.21 g/100 g fresh mango. Estimated parameters and fitting ability of three isotherm models were also evaluated. The Guggenheim-Anderson-Boer (GAB) model gave the best fit to the experimental EMC data. The GAB monolayer moisture contents (mo) of mango and jackfruit ranged from 11.1–10.0 % and 4.7–3.4 %, respectively. Specific surface area of active binding sites (S) was calculated based on the mo values. The S value of dehydrated mango was 2.5 to 2.8 times larger than jackfruit. The maximum net isosteric heat (qs) of sorption of solar dehydrated mango and jackfruit were determined as 19.5 and 33 kJ mol−1, respectively, and qs decreased significantly at high moisture.

Evaluation of thermodynamic properties using GAB model to describe the desorption process of cocoa beans

SummaryThe desorption isotherms and thermodynamic properties of cocoa beans were obtained during the drying process of this product. The isotherms were determined by dynamic method for various temperature (25, 35, 45 and 55 °C) and relative humidity (RH) conditions (30, 40, 50, 60, 70 and 80%). Equilibrium moisture content data were correlated by the Guggenheim–Anderson–de Boer (GAB) model, which presented good fit to the data, according to statistical procedures. Equilibrium moisture content ranged from 5.90 to 16.67 d.b.; it increased with an increment in the RH and decreased with increased temperature at a constant RH. Enthalpy values for each model coefficient were encountered, ranging from −90.05 to 545.96 kJ kg−1. The integral isosteric heat of desorption and differential entropy increased with decreased equilibrium moisture content, a tendency also found for Gibbs free energy.

Nano Zinc Oxide-Loaded Calcium Alginate Films with Potential Antibacterial Properties

In this work, zinc oxide nanoparticles-loaded calcium alginate films were investigated for their moisture uptake behavior at different temperatures. The equilibrium uptake data was interpreted quantitatively by GAB isotherm models. The monolayer moisture contents were 0.301 ± 0.003, 0.0214 ± 0.092, and 0.171 ± 0.102 at 20, 30, and 37°C, respectively. The water vapor transmission rate was found to be 0.816 ± 0.143, 1.42 ± 0.045, and 1.632 ± 0.064 g s−1 m−2 respectively. For the moisture content range of 0.2 to 0.6, the net ∆H and ∆S values were found to be 22.73 to 11.14 KJ/mol and 0.064 to 0.034 KJ/mol/K, respectively. The moisture uptake of films increased with water activity but showed negative temperature dependence. The enthalpy of sorption (∆H) and differential entropy (∆S) were determined at different moisture content values, ranging from 0.2 to 0.6 g/g db. The two parameters showed a higher degree of correlation. The equilibrium moisture content data was used to evaluate harmonic mean temperature Thm. Finally, the biocidal action of films was tested against model bacteria Escherichia coli.

ISOSTERIC HEAT AND ENTROPY MODELING OF PISTACHIO CULTIVARS USING NEURAL NETWORK APPROACH

Artificial neural network (ANN) method was used to predict the equilibrium moisture content (EMC) of Pistachio cultivars (Ohadi, Kalleghoochi and Fandoghi). ANN model was trained by two training algorithms. After well training of the ANN models, proved that the ANN model was better than the Oswin and Guggenheim–Anderson–de Boer models. The isosteric heat of sorption of pistachio cultivars were predicted by power models applied in this study with about R2 = 0.99. Also a regression model was developed for entropy of sorption. All cultivars had the identical pattern of variation in heat of sorption with identical moisture content levels, which might be because of the identical physical and biological structure and dimensions of these cultivars. At moisture content above 8% dry basis (d.b.), the isosteric heat and entropy of sorption of all cultivars were lower and they were highest at moisture content about 4% (d.b.). PRACTICAL APPLICATIONS The net isosteric heat equations are suggested for use in the computation of heat of sorption of pistachio cultivars whereas both the isosteric heat and entropy equations are essential to compute the humidity during simulation of stored dried pistachio cultivars. If artificial neural network models are developed using experimental equilibrium moisture content data of pistachio, the models developed can be used to predict more accurately the equilibrium moisture contents using computer and also can be used to predict the isosteric heat and entropy more accurately for modeling and simulation of drying and storage of pistachio.

Analysis of Moisture Desorption Isotherms of Eggplant (Solanum melongena)

Sorption isotherms of eggplant were determined employing, as experimental technique, a static gravimetric method, using saturated salt solutions to achieve the equilibrium. The experiments were carried out at different temperatures (20, 35, 50 and 65 °C). The sorption isotherms can be classified, according to Brunauer's classification, as type II or III depending on temperature. Equilibrium moisture content data were correlated by two models usually applied to foodstuffs (Brunauer--Emmet--Teller (BET) and Halsey). BET model was employed to determine monolayer moisture content (0.121 kg/kg d.b.). Halsey model was selected by the goodness of fitting. Experimental data were analyzed by a thermodynamic approach to obtain some properties as net isosteric heat, equilibrium heat and differential and net integral entropy. The differential enthalpy and entropy decreased with increasing moisture content and satisfied the compensation theory. The net integral enthalpy and entropy showed maximum values (≈31 kJ/mol and ≈88 J/mol.K) at 0.093 (kg/kg d.b.) of moisture content.

Moisture adsorption isotherms of guar ( Cyamposis tetragonoloba) grain and guar gum splits

Moisture adsorption isotherms of guar grain and guar gum splits were determined at 10, 20, 30 and 40 °C and 23–96% relative humidities using gravimetric method. The sorption data were fitted to six well-known sorption isotherm models (modified Chung–Pfost, modified Halsey, modified Henderson, modified Oswin, Chen–Clayton, and GAB models) using non-linear least square method. The GAB model was found the most satisfactory for representation of the equilibrium moisture content data for guar grain and guar gum splits. The equilibrium moisture content of guar gum splits was found to be significantly higher ( p < 0.05) than that of guar grain. The isosteric heat of sorption was determined from the equilibrium moisture adsorption data using Clausius–Clapeyron type equation. Exponential relationship described well the dependence of isosteric heat of sorption on the equilibrium moisture content. The enthalpy–entropy compensation theory applied to sorption isotherms indicated enthalpy controlled sorption process.

The sorption isosteric heats of rice grains in China

Equilibrium moisture content (EMC) data for the grains of thirteen rice cultivars were obtained by gravimetric method at 11% to 96% equilibrium relative humidity (ERH) and 10, 20, 25, 30, and 35°C above nine saturated salt solutions. Six commonly used mathematic models, namely, BET, Modified-Guggenheim–Anderson-deBoer (MGAB), Modified-Chung-Pfost (MCPE), Modified-Henderson (MHE), Modified-Oswin (MOE), and Strohman-Yoerger (STYE), were fitted to the data with evaluating the coefficient of determination, residue sum-of-squares, standard error of estimate, mean relative percent error, and residual plots. The best fitted equations to the EMC/ERH data were MCPE and STYE, but MCPE is three-parameter, readily transformed equation and adopted in this study. The isosteric heats for both rice desorption and adsorption, and for both the sorption of Japonica and Indica rice, decreased rapidly with an increase in seed moisture content until the moisture content of 20% d.b. (dry basis) was reached, and thereafter they decreased smoothly with increasing moisture content. The isosteric heats of rice desorption were higher than those of adsorption below 22.5% d.b. EMC, but thereafter there was no difference found between desorption and adsorption. The sorption isosteric heats of Indica rice were slightly higher than those of Japonica rice under all moisture contents at a constant temperature. Keywords : Equilibrium moisture content, Rice, Adsorption, Desorption, Mathematic model, Ventilation,Drying

Moisture sorption isotherms and isosteric heat of sorption of coffee in different processing levels

SummaryThe desorption isotherms and thermodynamic properties of coffee from different processing stages were obtained during the drying process of this product. The isotherms were determined by a static gravimetric method for various temperature and humidity conditions. Equilibrium moisture content (Me) data were correlated by several mathematical models and an artificial neural network (ANN) model. The Me for coffee fruits, pulped coffee and green coffee increased with an increase in the water activity (aw) at any particular temperature. At a constant aw, coffee fruits samples had higher Me than the remaining coffee samples. Based on statistical parameters, the ANN model, modified Henderson and GAB models were adequate to describe the sorption characteristics of the samples. Isosteric heat of sorption was evaluated by means of the Clausius–Clapeyron equation. It decreased with increasing moisture content. The coffee fruits had higher isosteric heat of sorption than that pulped coffee and green coffee.

Modeling of heat and entropy sorption of maize (cv. Sc704): neural network method

Equilibrium moisture content of maize affects its values of dehydration heat and entropy. Precise prediction of heat and entropy with regard to its equilibrium moisture content is a simple and fast method for proper estimation of energy required for dehydration of maize and simulation of dried maize storage. Artificial neural network and thermodynamic equations for computation of maize heat and entropy of sorption were used, as a new method. The artificial neural network method for prediction of the equilibrium moisture content of maize was utilized. The heat of sorption of maize is predicted by a power model. After well training of equilibrium moisture content data sets using the artificial neural network models, predictive power of the model was found to be high (R&lt;sup&gt;2&lt;/sup&gt; = 0.99). A power regression model was also developed for entropy of sorption. At moisture content above 11% (d.b.) the heat and entropy of sorption of maize decreased smoothly and they were highest at moisture content about 8% (d.b.).