Equilibrium Moisture Content Values Research Articles

Determination and modeling of the isotherms of adsorption/desorption and thermodynamic properties of obeche and lotofa using nelson’s sorption model

Equilibrium moisture content (EMC), net isosteric heat of sorption (NIHS), net entropy of sorption (NES) and standard free energy of Gibbs (SFEG) of Triplochiton scleroxylon (obeche) and Sterculia rhinopetala (lotofa) are modeled using Nelson’s sorption isotherm model. Experimental data are determined using a dynamic vapor sorption apparatus. Air relative humidity is ranged from 0 to 90% and two air temperatures (20 °C and 40 °C) are used. Experimental data of EMCs obtained from adsorption and desorption for the mentioned woods were compared with the predicted results using Nelson’s sorption model by the application of the same operating conditions (i.e. temperatures and relative humidity conditions). The results showed that the predicted ones were in good agreement with the experimental data, when the relative humidity varied from 1.2 to 90%. Both adsorption and desorption phase presented a mean relative errors value inferior to 6.3%. The parameters that define the sorption isotherm varied with the wood type and the sorption mode. Thus, Nelson’s sorption isotherm model is a useful tool that can be used for prediction of the moisture change in wood under different environmental conditions and for predicting indirectly the thermodynamic parameters such as NIHS, NES and SFEG. In adsorption and desorption mode, the NIHS are estimated using Clausius-Clapeyron’s equation. The desorption values were higher than the adsorption ones. NIHS versus EMC varied exponentially and the parameters of the function were presented variable with the sorption mode and the wood type. The total energy that we needed to extract and evaporate all bounded water is 12,398.6 J/mol for obeche and 11,627.7J/mol for lotofa. The total energy that we needed to condense and fix all bounded water taken from the state vapour is 11,829.34 J/mol for obeche and 11,379.39 J/mol for lotofa. Water molecules are more mobile during desorption than adsorption in the case of obeche. In the case of lotofa, these molecules are more mobile during adsorption. SFEG is higher in desorption than adsorption and it is influenced by species and less by the temperature. When the temperature increased, the SFEG increased as well. At low values of EMC, NIHS and SFEG are higher and decreased with the increase of EMC until reaching the fibre saturation point.

Moisture Sorption Isotherms and Prediction Models of Carboxymethyl Chitosan Films from Different Sources with Various Plasticizers

Carboxymethyl chitosan (CMCH) from different chitosan sources (shrimp, crab, and squid) and molecular sizes (polymer and oligomer) were synthesized via carboxymethylation reaction. The CMCH films were prepared by solution casting. All the CMCH films had high water solubility, higher than 85% of the dry matter of the films. The sorption isotherm of the CMCH films was evaluated at several values of relative humidity (0% RH, 23% RH, 34% RH, 43% RH, 65% RH, 77% RH, and 86% RH) at 25 ± 1°C. The equilibrium moisture content values of all the CMCH films were low at lower aw but increased considerably above aw = 0.65. The sigmoidal moisture sorption isotherms of this product can be classified as type II. Understanding of sorption isotherms is an important prerequisite for the prediction of moisture sorption properties of films via moisture sorption empirical models. The experimental data were analyzed and fitted by the nine sorption models. The various constants determined by linear fitting of the sorption equation with r2 values were in the range of 0.7647 to 0.999. The GAB model was found to be the best-fitted model for CMCH films (aw = 0.23–0.86, 25 ± 1°C), and the model presented the optimal root-mean-square percentage error (%RMS) values when compared with other models. In conclusion, it can be stated that the GAB model was found to be better estimated for predicting the CMCH films than other models. Therefore, the constant derived from different sorption models were applied for use in terms of information and for the determination of the stability of CMCH packaging films for specific end uses.

Equilibrium Moisture Content of Hazelnut Husks, Shells, and Kernels

Abstract. Hybrid hazelnuts that are predominately a cross between the American hazelnut () and the European hazelnut () are being grown and evaluated as part of an effort to develop a thriving hazelnut industry for the Upper Midwest of the U.S. Along with this plant development effort, researchers are investigating and assessing various harvesting and processing methods and equipment in an effort to create a robust and food-safe production industry. One harvesting alternative is to pick hazelnut clusters off plants before the nuts fully ripen and fall to the ground, an approach that requires greater attention to drying. Whether entire clusters are dried or the nuts are separated from the husks prior to drying is a decision that will be influenced by the drying requirements and potential uses for these hazelnut fractions. To this end, a study was undertaken to establish desorption isotherms for the husks, shells, and kernels of hybrid hazelnuts grown in the Upper Midwest. Clusters were hand-picked from shrubs in Wisconsin and immediately placed in 18 different controlled environments (six different relative humidity levels at three different temperatures). Actual moisture conditioning took place over saturated salt solutions in specially fabricated biomaterial moisture conditioning units. After a six-week period during which the clusters reached equilibrium with their environment via desorption, they were separated into husk, shell, and kernel fractions and returned to their respective conditioning units. After another six weeks in the conditioning units, the moisture content (MC) of each fraction was determined by oven-drying at 103°C for 48 h. Under equilibrium conditions, the kernel MC was found to be only 37% of that for shells, whereas the equilibrium moisture content (EMC) values for husks were on average 14% greater than those for shells. On a dry basis, the average cluster mass was 32.9% husk, 43.9% shell, and 23.2% kernel. Likewise, on a dry basis, the average whole nut mass was 65.5% shell and 34.5% kernel. The desorption data were fit to the Modified Henderson, Modified Chung-Pfost, Modified Halsey, Modified Oswin, and Modified GAB equations. Overall, the best fit to the experimental data was provided by the Modified Chung-Pfost equation with parameters determined using equilibrium relative humidity (ERH) as the dependent variable in regression analyses. For ERH values above 0.70, the temperature-modified form of the GAB equation is recommended for predicting desorption EMC values for hazelnut fractions. Keywords: Desorption, Equilibrium moisture content, Equilibrium relative humidity, Hazelnuts, Kernels, Nuts, Shells, Water activity.

Quantifying and reducing errors in equilibrium moisture content measurements with dynamic vapor sorption (DVS) experiments

Dynamic vapor sorption (DVS) measurements are widely used to collect water vapor sorption isotherms for wood and other cellulosic materials. Equilibrium moisture content (EMC) is typically assumed to have been reached when the rate of change in moisture content with time ( $${\text{d}}M/{\text{d}}t$$ ) drops below a certain value. However, the errors associated with determining EMC in this manner have never been characterized. Here, an operational definition of equilibrium for DVS measurements is provided, and twenty test cases over four cellulosic materials are presented where the relative humidity was stepped up or down and then held constant until equilibrium was reached. Then, both the time to reach various $${\text{d}}M/{\text{d}}t$$ “stop criteria” and the errors in EMC associated with those stop criteria are quantified. The errors in the EMC from the widely used 0.002% min−1 stop criterion are found to be as large as 1.2% MC, and the average error for 20 test cases is 0.5% MC, which are much larger than the 0.1% MC error claimed in the literature. Longer data collection times are recommended, and a more stringent $${\text{d}}M/{\text{d}}t$$ criterion (0.0003% min−1, using a 2-h window) for cellulosic materials is proposed. The errors with this criterion are less than 0.75% MC, and the average error is 0.3% MC. Furthermore, it is shown that the errors for a given stop criterion are systematic and can be fairly well characterized with a simple linear regression. Finally, a correction for systematic error is proposed that results in more accurate EMC values with shorter hold times.

Improving Impregnation and Penetration Properties of Refractory Woods Through Cryogenic Treatment

Cryogenic treatment via liquid nitrogen (LN) was evaluated as a means to improve the capability of impregnation and penetration in fir and spruce wood. There are a few vital problems that occur during the impregnation process of wood protection. One problem is that refractory woods have different anatomical features that make the impregnation process difficult. For the specimens that were conditioned with the air and oven, the retention changes were determined with an image analysis, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). In addition, the density and equilibrium moisture content (EMC) values were measured. The LN treatment resulted in degradation in the bordered pits. Then, the margo and torus bonds were torn, the bordered pits were opened, and the liquid transportation of wood was facilitated. It was determined that the LN treatment and impregnation increased the depth and dispersion capability of the penetration. The LN treatment helped facilitate the flows from pores to pores by hindering the aspirations of the bordered pits, and thus the flow of chemicals was facilitated. Obtaining deeper penetration in refractory wood species will result in an improved impregnation process.

Effect of anti-caking agents on moisture sorption isotherms of palmyra-palm jaggery granules

Jaggery granules, prepared from palmyra-palm syrup, were mixed with five levels (0.5 to 2 %w/w) of anti-caking agents [tri calcium phosphate, (TCP) or corn starch (CS)] and their moisture sorption isotherms were determined without or with addition of anticaking agents by the static equilibrium method using saturated salt solutions at four temperatures of 25, 35 and 45°C. The moisture sorption isotherms for this granular jaggery samples are Type-III isotherms and the effect of temperature on equilibrium moisture content (EMC) values upto a water activity values of 0.3 to 0.5 show no significant effect. Among two moisture sorption isotherms (MSI) models tested with the experimental data for this high sugar food, GAB model was found to be the best fit followed by Iglesias and Chirife model. The monolayer moisture content (M 0 ) of the granular jaggery samples varied from a minimum of 4.195% (d.b.) for the granulated jaggery without anticaking agent at 45°C to a maximum of 7.303% (d.b.) for granulated jaggery with TCP and 9.178% (d.b.) for granulated jaggery with corn starch @ 2.0% at a temperature of 25°C. A decreasing trend for both Mo and C values but increasing trend for K was obtained with the increase in temperature. The monolayer moisture content of jaggery granules with addition of TCP or CS has been found to posses good correlation with temperature. The net isosteric heat of sorption (q st ) of jaggery granules without addition of anti-caking agents, decreased exponentially from 29.132 to 4.833 kJ mol -1 with the increase in moisture content from 2.5 to 15% (d.b.). It was also observed that, net isosteric heat of sorption was found to be higher for the jaggery granules without addition of anti-caking agents as compared to samples with addition of anti-caking agents.

Decay resistance of rubberwood (Hevea brasiliensis) impregnated with ZnO and CuO nanoparticles dispersed in propylene glycol

Efficacy of nanoparticle is essentially influenced by the medium in which it is dispersed, the size of the particles in dispersion and the stability of dispersion. The major constrain in dealing with nanoparticle dispersion can be resolved by identifying a proper dispersive medium. In the present study, dispersions of zinc oxide and copper oxide nanoparticles was prepared in propylene glycol (PG). Dynamic light scattering analysis showed that particles remained in nano size without formation of aggregates. UV-vis. absorption spectroscopy showed that the nano-dispersion in propylene glycol is stable without adding any additional surfactants or dispersive agents. Fungal decay and moisture adsorption of rubberwood (Hevea brasiliensis Muell Arg.) specimens impregnated with nano-ZnO and nano-CuO dispersion in PG was evaluated. Dispersion of ZnO and CuO nanoparticles in PG inhibited white-rot (Trametes hirsuta) and brown-rot (Polyporus meliae) decay effectively. The changes observed in FTIR spectra and SEM further support the results. Nano-dispersions treated specimens showed some reduction in moisture adsorption with lower equilibrium moisture content values as compared to untreated wood.

Modeling Equilibrium Moisture Content of Brown Rice as Affected by High-Pressure Processing

Moisture sorption isotherms (MSI) of presoaked brown rice after high-pressure (HP) treatment (100 to 500 MPa for 10 min at ~20°C) were evaluated at 20°C to 40°C, and five existing models were tested for prediction performance. Equilibrium moisture content (EMC) of HP-treated samples at various relative humidities showed a concave upward trend, with the 300 MPa treated samples yielding the lowest EMC value. Hysteresis was observed with all treated samples. All MSI models performed well, and the modified Guggenheim-Anderson-de Boer (GAB) model gave the best fit. The mobility and distribution of water in equilibrated brown rice were studied by nuclear magnetic resonance (NMR) analysis. The proton distributions of the samples revealed three or four distinct water populations, which varied with equilibrium relative humidity (water activity). HP treatment resulted in a change in the water distribution and caused the water to be less mobile. Scanning electron microscopy (SEM) confirmed that HP treatment resulted in alteration of the surface structure of the starch granules. This study helped to develop a modified MSI model and better understanding of the water distribution in brown rice treated with HP.

Enhancing dimensional stability of oriented strand composites within biorefinery

The objective of this study was to investigate the effects of hot water extraction process on the dimensional stability of oriented strand composites. Aspen wood strands were extracted using various severity factor levels. Phenol formaldehyde and polymethylene diphenyl diisocyanate resins were used for production of the oriented strandboard panels. Six panel groups were produced from the extracted or unextracted aspen wood strands. The dimensional stability of the material was evaluated by measures of equilibrium moisture content and thickness swell and water absorption after soaking in water for 2 hours and 24 hours. Results obtained in this study showed that thickness swell and water absorption values significantly decreased with the hot water extraction process, with the thickness swell of phenol formaldehyde bonded panels decreasing 70% after 2 hours soaking. The panels with polymethylene diphenyl diisocyanate resin exhibited lower thickness swell and water absorption relative to the panels prepared with phenol formaldehyde resin. Equilibrium moisture content values of the panels bonded with both phenol formaldehyde and polymethylene diphenyl diisocyanate resin decreased with the extraction process. The findings of this work indicate that hot water extraction process could be effectively used to produce oriented strand composites having an enhanced dimensional stability property.

Pengaruh Suhu pada Pengeringan Tepung Kimpul (Xanthosoma sagittifolium)

Taro flour can be used as an alternative for wheat. This study aims to determine the optimal conditions on the operation of the drying resulting in minimal water content, but did not damage the properties of the desired material. This research will be obtained the parameters that can be used to design a dryer with a larger scale. After the taro peeled, washed, chopped and soaked with a solution of salt. Samples inserted into a dryer equipped with a balance, so that it can be read sample weight at a certain time. The drying process is stopped until the weight remains. The process of making flour baked, steamed after soaking the taro, and then do the drying process as the raw flour. The variables studied were temperature drying. The result showed that higher drying temperatures will accelerate the achievement of equilibrium moisture content, which means the drying operation requires a shorter period of time. Lower values of equilibrium moisture content on 0,02 (g water / g dry matter) can be achieved at a temperature of 90 0 C, with a time of 80 minutes.

Moisture sorption isotherms of castor beans. Part 2: Thermodynamic properties

ABSTRACT Knowledge on the water sorption within agricultural products is extremely important for decision making during post-harvest procedures. In order to improve this knowledge, thermodynamic properties regarding water sorption provide useful data. Thermodynamic properties of castor beans, related to sorption, were determined. Static gravimetric technique under different conditions of temperature (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 humidity environment. After the sorption procedure, differential enthalpy, differential entropy and Gibbs free energy of this process were calculated and decreased with increased values of equilibrium moisture content.

Effects of heating humidity on the physical properties of hydrothermally treated spruce wood

To clarify the effects of humidity during heating on the physical properties of hydrothermally treated wood, Sitka spruce wood was heated in an autoclave at 120 °C and different heating humidity (HRH), and their equilibrium moisture content (EMC), specific dynamic Young’s modulus (E′/ρ), and mechanical loss tangent (tanδ) were measured at 25 °C and 60 % RH prior to and after the hydrothermal treatment. Higher values of HRH resulted in greater loss in weight (WL) because of the acceleration of thermal degradation in the presence of moisture. The time–humidity superposition was applicable to the changes in WL. The EMC was minimized by heating at intermediate HRH (60 %), but it recovered significantly after the wood was moistened at 100 % RH. This fact suggested that the reduction in hygroscopicity due to hydrothermal treatment included both reversible and irreversible effects. The reversible effect was not observed when the wood was heated at 92 % HRH or above. After the moistening, the EMC value of hydrothermally treated wood decreased monotonically with increasing HRH and WL. An irreversible chemical change such as decomposition of hemicelluloses was responsible for the irreversible effect, whereas the reversible effect may have resulted from the annealing of amorphous wood polymers. After hydrothermal treatment at 80 % HRH or lower, E′/ρ increased and tanδ decreased mainly because of the reduction in EMC. On the other hand, high-humidity heating (92 % HRH) resulted in significant decrease in E′/ρ and remarkable increase in tanδ probably because of the depolymerization of hemicelluloses. The color of wood was darkened by the hydrothermal treatment, and the CIELAB color parameters of hydrothermally treated wood were closely connected to the WL.

UMIDADE DE EQUILÍBRIO DE PAINÉIS OSB EM FUNÇÃO DA UMIDADE RELATIVA E DA TEMPERATURA AMBIENTE

http://dx.doi.org/10.5902/1980509820661O trabalho teve como objetivo obter modelos estatísticos para a estimativa da umidade de equilíbrio de painéis OSB em função da temperatura e da umidade relativa do ar, assim como também avaliar o efeito de algumas variáveis de produção sobre a umidade de equilíbrio dos painéis. O delineamento experimental se constituiu de seis condições de processamento, três temperaturas do ar e seis umidades relativas do ar. Nas condições de processamento, foram avaliadas três diferentes espessuras das partículas strand (0,4; 0,7 e 1,0 mm), duas densidades aparentes do painel (0,65 e 0,90 g/cm³) e também três níveis de pressão na prensagem dos painéis (40, 60 e 80 kgf/cm²). Para cada tratamento foram produzidos quatro painéis com a madeira de Pinus taeda e 6% de adesivo fenol-formaldeído. Na avaliação do experimento foi considerado um delineamento inteiramente casualizado disposto em esquema fatorial triplo 6 x 3 x 6, ou seja, 6 variáveis de produção (condições de processamento), 3 temperaturas do ar (30, 40 e 50°C) e 6 umidades relativas (40, 50, 60, 70, 80, 90%). As médias foram comparadas estatisticamente pelo Teste Scott-Knott em nível de 5% de significância. A modelagem da umidade de equilíbrio dos painéis OSB foi realizada mediante o ajuste de modelos polinomiais múltiplos para cada tratamento. Com base nas medidas de precisão e nos resultados obtidos pode-se concluir que: 1) recomenda-se a utilização do modelo UEQ = β0 + β1UR + β2UR² + β3UR³ + β4Temp + ε para a estimativa indireta da umidade de equilíbrio dos painéis OSB; 2) A temperatura apresenta influência linear na umidade de equilíbrio dos painéis, enquanto que a umidade relativa do ar apresenta comportamento polinomial de terceira ordem, sendo que a umidade relativa do ar influência de forma mais pronunciada a umidade de equilíbrio dos painéis OSB do que a temperatura ambiente; 3) Quanto ao efeito das variáveis de produção, a pressão de prensagem de 80 kgf/ cm² e o aumento da espessura das partículas strand para 1,0 mm de espessura promoveu tendência de reduções nos valores médios de umidade de equilíbrio dos painéis OSB. Já o aumento da densidade do painel promoveu uma tendência de aumento da umidade de equilíbrio dos painéis OSB; e 4) O uso de modelos polinomiais múltiplos permite que sejam produzidas curvas de nível para a obtenção dos valores de umidade de equilíbrio dos painéis OSB em função da umidade relativa e da temperatura do local onde o painel esta exposto, se destacando pela sua praticidade de utilização.

Hygroscopic properties of PEG treated archaeological wood from the rampart of the 10th century stronghold as exposed in the Archaeological Reserve Genius loci in Poznań (Poland)

Abstract The archaeological wood from the rampart of the Poznan stronghold built in the 10th century was subjected to the investigations. The material was obtained during the excavations and conservation works of the earthen and wooden relicts. The archaeological wood, both untreated and treated with polyethylene glycol (PEG), was characterized by determining adsorption and desorption isotherms, which were formed by GAB and GDW models. The anomalous increase of the equilibrium moisture content for air relative humidity values above 80% was found for the PEG treated wood. It was clearly presented that the safety of wood exposition strongly depends on the proper maintaining of air parameters. The mechanisms of the reduction of equilibrium moisture content and sorption hysteresis for the PEG treated wood were explained. It was not recommended to predict equilibrium moisture content values with the Hailwood-Horrobin model fitted to the sorption data collected by the US Forest Products Laboratory as it was not accounting for sorption hysteresis, decay of archaeological wood and the influence of the PEG treatment.

The Effects of Heat Treatment with the ThermoWood® Method on the Equilibrium Moisture Content and Dimensional Stability of Wild Cherry Wood

Low hygroscopicity is an important factor favoring the use of heat-treated wood materials. Hence, wild cherry (Cerasus avium (L.) Moench) wood was subjected to heat treatment with the ThermoWood® method for about 1 and 2 hours at temperatures of 190 and 212 °C in an industrial business. Then, trial samples were prepared and divided into two groups. By being conditioned in the environments of 20 °C and 65% relative humidity (WC1), 20 °C and 85% relative humidity (WC2), 20 °C and 30% relative humidity (WC3), and 23 °C and 50% relative humidity (WC4), equilibrium moisture content (EMC) and dimensional stability (DS) values of the samples in the first group were determined. The water thickness swelling (WTS) and water retention (WR) features of the samples of the second group were examined by keeping them in water both 24 and 72 h. The results show that EMC and WTS decreased with increasing treatment temperature and durations. Also, DS was improved. On the other hand, the WR values of all the samples stayed approximately the same.

English

The objective of this work was done to investigate the effect of temperature and relative humidity on the equilibrium moisture content (EMC) of local cardamom (Amomum cardamomum Wild) and to get the appropriate mathematical models. The EMC of local cardamom were determined by dynamic method using laboratory air dryer at the temperature of 40, 50 and 60 0 C and at the relative humidity of 20, 40 and 60%. Four widely used three parameters sorption isotherms equations such as modified Henderson, modified Chung-Pfost, modified Oswin and modified Halsey were used to fit the experimental data. The accuracy of the model was evaluated by comparing the value of the coefficient of determination (R 2 ) and the value of the root mean square error (RMSE) between the experimental and the predicted value of EMC by using nonlinear regression analysis. The effects of relative humidity were found to significantly influence the EMC. Based on statistical analysis the modified Chung-Pfost equation have the highest value of R 2 = 0.979 and the lowest value of RMSE = 0.758, it can be

Moisture adsorption of sprouted bambara groundnut flour (Vigna subterranean)

This study investigated the moisture adsorption characteristics of sprouted Bambara groundnut (Vigna subterranean). The adsorption isotherm for sprouted Bambara groundnut was determined and studied at room temperature (27±2 °C) using the static gravimetric method. Samples were equilibrated in desiccators containing tetraoxosulphate (VI) acid solution of known relative humidity varied from 20%, 30%, 40% and 50%. The moisture content was then calculated using the data of initial moisture content and the amount of moisture gained or lost at equilibrium. The desiccators were made into each relative humidity and were studied at room temperature (27±2 °C). The plot of equilibrium moisture content against water activity at 20%, 30%, 40% and 50% for adsorption process gave a sigmoidal shaped isotherm curve. The equilibrium moisture content value increased with water activity. The Henderson and Oswin models gave the best fit and could be used to present the moisture adsorption isotherm of sprouted bambara groundnut flour for water activity content range of 0.2 to 0.5.

Kinetics of the Vacuum Drying of Cheeses

Cheeses are analyzed as vacuum drying objects. An experimental vacuum drier and its elements are schematized. The operating principle of the experimental setup is described. Moisture is demonstrated to be among the most important components of cheese. The physicochemical composition of cheeses is considered. The forms and energy of moisture binding in cheese are discussed. The hygroscopic and thermophysical properties of cheeses are reported. The kinetics of the vacuum drying of cheeses has been investigated. The vacuum drying of cheeses includes two stages: the drying rate is constant at the first stage and decreases at the second stage. The temperature curves of cheeses have been plotted in the temperature-moisture weight fraction coordinates. Drying curves in the heat load- time, temperature-time, and moisture weight fraction-time coordinates have been obtained and analyzed for various cheeses. Cheese drying rate curves have been constructed by graphical differentiation. The maximum cheese drying rates have been determined. Equilibrium moisture content values for cheese drying have been found. The cheese shrinkage ratio has been correlated with the thickness of the cheese bed being dried and with the shape and size of cheese pieces. Cheese shrinkage at both stages of vacuum drying proceeds uniformly. Raising the drying temperature above the prescribed temperature reduces the shrinkage ratio.

MODELING ISOSTERIC HEAT OF BANANA FOAM MAT USING NEURAL NETWORK APPROACH

Information on the adsorption isotherm and the thermodynamic properties can assist in optimizing food processing operations such as drying, packaging and storage in the assessment of the quality of food. In this study, an Artificial Neural Network (ANN) was used for modelling the water activity/Equilibrium Relative Humidity (ERH) of banana foam mat under a range of values of the Experimental Equilibrium Moisture Content (EMC) to calculate the isosteric heat of sorption (qst) by applying the Clausius-Clapeyron equation. The EMC of three dry banana foam samples at different densities of 0.21, 0.26 and 0.30 g/cm3 was determined by a standard gravimetric method over a temperature range of 35-45°C and a relative humidity range of 32-83%. The modified-GAB model best fitted the EMC data. However, the modified-GAB model was not acceptable for predicting the heat sorption behaviour. A negative value of qst estimated using the modified-GAB equation was found at a moisture content above 0.24 kg/kg d.b., showing the poor fit of the model. A multilayer feed-forward ANN trained by back-propagation algorithms was developed to correlate the output ERH to three exogenous inputs (foam density, EMC and temperature). The developed ANN models could predict the ERH more accurately than the modified-GAB model. The predictions from the ANN models produced R2 values higher than 0.97. No negative qst values were found using the ANN method."

Water sorption properties of Dutch type semi-hard cheese edge in the range of common storing temperatures

Moisture sorption isotherms of Dutch type semi-hard cheese edge in the temperature range of 10–25 ºC and water activity (Aw) from 0.11 to 0.98 were determined using manometric method. The sorption curves had a sigmoid shape. The equilibrium moisture content (EMC) of cheese samples increased with an increase in Aw at a constant temperature both for water adsorption and desorption. An increase in temperature caused an increase in Aw for the same moisture content (MC) and, if Aw was kept constant, an increase in temperature caused a decrease in the amount of absorbed water. Critical values of equilibrium moisture content, corresponding to the Aw = 0.6, were between 11 % MC (w.b.) and 17 % MC (w.b.) both for moisture adsorption and desorption. Values of sorption heat were calculated from moisture sorption isotherms by applying the Clausius-Clapeyron equation. Values of the heat of desorption are higher than those of adsorption and the difference increases with the MC decrease. Heat of sorption decreased from 48.5 kJ/mol (~5.5 % MC w.b.) to the values approaching the heat of vaporization of pure water, free MC. The critical value for free water evaporation is about w = 27 % (w.b.) for the range of temperature 10–25 ºC.