Equilibrium Moisture Content Values Research Articles

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.

Changes in dimensional stability of Pinus roxburghii sarg. and Mangifera indica L. woods after retification

The present study was conducted to investigate the influence of heat treatment temperature and duration on the dimensional stability of chir pine (Pinus roxburghii Sarg.) and mango (Mangifera indica L.) wood. For this purpose, wood was heated at different temperatures for periods of 4, 8 and 12 h in an inert atmosphere. Differential responses of both wood species to different parameters, namely, volumetric swelling and shrinkage, water absorption and equilibrium moisture content (EMC) at different relative humidities, were observed. Results revealed that increase of heat treatment temperature in conjunction with time leads to a significant drop in the shrinkage of mango wood, whereas a reverse trend prevailed in chir pine until 210°C for 12 h treatment. Least values of EMC were recorded for chir pine and mango wood treated at 190 and 210°C for 4 h respectively. Further, increase in temperature and/or time of treatment significantly decreased the water absorption capacity of mango wood.

Modeling and Simulation of the Drying of Beech Timber (Fagus sylvatica)Using Oscillating Regimes

This paper represents a numerical study of the massive (60mm) and thin (38mm) wood drying using oscillating drying regimes applied on beech timber (Fagus sylvatica). All thermo-physical properties relative of studied wood are taken from the literature on appropriate experiments. We showed that Luikov’s model can be used to predict temperature and moisture content evolutions using oscillating regimes. First numerically tests on 60mm timber wood consists in increasing and decreasing alternation of the drying parameters (temperature), at the rising 12-15°C and at the descent 10- 12°C, every alternation being higher than the precedent with 2-4°C. Second numerical test consists to oscillate the values of equilibrium moisture content with the oscillation amplitudes of ±10% and ±20% at the frequencies of 6hours. These practical experiments are detailed in the literature. Luikov’s model gives satisfactory results, according to the experiments obtained in the literature. But, convective transfer coefficients are function of each experiment and we observed a short difference between oscillation amplitudes of ±10% and ±20% on moisture content evolution. Thus, Luikov’s model can be a tool to study oscillation drying timber in order to reduce consumption of energy during the drying process.

Moisture sorption isotherms of whole milk powder in the temperature range of 5–35 °C and critical values of water activity prediction

The study presents results of water sorption tests of whole milk powder in the temperature range of 5–35 °C and water activity (aw) from 0.11 to 0.97. The experimental procedure used was the manometric static method. Four sorption models recommended in literature sources (Chung-Pfost, Halsey, Henderson, Oswin) were analysed and evaluated with the aim of aw prediction. The modified Oswin’s equation was the best model for moisture adsorption and desorption of the whole milk powder. Critical values of the equilibrium moisture content (EMC) from the viewpoint of microorganism growth corresponding to the aw = 0.6 were calculated for the temperature range tested. The critical EMC was 7.82% and 8.51% wet basis (w.b.), for water adsorption and desorption, respectively, at the temperature of 20 ºC. Sorption capacity of samples tested decreased as temperature increased, and vice versa. The differences between the EMC values at a constant aw were small in the temperature range measured, and rehydration of the dried material resulted in hysteresis but this effect was non-significant.

Effects of veneer drying at high temperature and chemical treatments on equilibrium moisture content of plywood

Moisture content (MC) is one of the most important factors that can affect many physical and mechanical properties of wood and veneers. MC strongly affects the final strength and durability of joints, development of surface checks in the wood and dimensional stability of the bonded assembly. In this study, plywood panels made from Alnus glutinosa (Alder), Fagus orientalis (Beech) and Picea orientalis (Spruce) wood veneers were treated with ammonium acetate, borax and boric acid by using dipping method to test for their equilibrium moisture content (EMC). Borax and boric acid solutions were used for fire-retardancy, and ammonium acetate for reducing formaldehyde emission. Two different veneer drying temperatures (20°C and 180°C) were used to reveal the effects of veneer drying at high temperature on the hygroscopicity of plywood panels. EMC values of alder, beech and spruce panels decreased significantly with veneer drying at high temperature. Picea orientalis (Spruce) plywood panels had the highest EMC values and followed by Alnus glutinosa (Alder) and Fagus orientalis (Beech) panels. EMC values of plywood panels increased significantly for both drying temperatures after ammonium acetate, borax and boric acid treatments.

Modelling the moisture sorption isotherms of Roselle (Hibiscus sabdariffa L.) in the temperature range of 5-35 °C

Water sorption tests of Roselle (Hibiscus sabdariffa L.) carried out under laboratory conditions are presented together with mathematical analyses of the moisture sorption isotherms (MSI’s). Moisture equilibrium data for adsorption and desorption of water from Roselle powder were investigated at near ambient air temperatures in the range of 5 and 35 °C and water activity (Aw) ranging from 0.11 to 0.97. The manometric method has been used for water sorption tests. Models for MSI’s are exponential equations. Coefficients of determination are 0.998 and 0.996 (for adsorption and desorption at 5 °C, respectively), 0.998 and 0.999 (for adsorption and desorption at 20 °C, respectively), and 0.998 and 0.999 (for adsorption and desorption at 35 °C, respectively). The equilibrium moisture content (EMC) of Roselle samples increased with an increase of Aw at a constant temperature both for adsorption and desorption. Adsorption curve equates to desorption curve at higher temperatures of tests carried out. Critical values of EMC of samples tested corresponding to the Aw equal to 0.6 were between 13.401% moisture content wet basis (MC w.b.) and 15.934% MC (w.b.) for moisture adsorption and desorption, respectively. These values are useful for storing conditions optimisation from point of view microorganisms grow and structural changes analyses. Crystal structure changes were observed during adsorption and desorption in the microscope, too. It was found out glass transition in dependence on the water content of samples tested.

Effect of thermomechanical treatment on physical properties of wood veneers

Thermomechanical modification is a technique that allows wood densification, improving mechanical properties and reducing hygroscopicity. In veneers, this technique is commonly used to improve bonding quality in wood based panels. This study aimed to evaluate the effect of thermomechanical modification on some physical properties of rotary peeled veneers of amescla (Trattinnickia burseraefolia). Veneers were treated in a hydraulic press at 140 and 180°C, for 1 and 2 min at 2·7 N mm−2 pressure. The apparent density was evaluated as well compression ratio, weight loss, equilibrium moisture content, thickness swelling and water absorption. The results showed that apparent density and compression ratio increased after treatment. Equilibrium moisture content values were lower in samples treated at 180°C. Dimensional stability was not improved due to release of compressive stresses. The surface of veneers was modified and its roughness and wettability were reduced significantly.

Comparison of Freeze-Drying and Freeze-Drying Combined with Microwave Vacuum Drying Methods on Drying Kinetics and Rehydration Characteristics of Button Mushroom (Agaricus bisporus) Slices

Button mushroom slices were dried using freeze-drying (FD) and freeze-drying combined with microwave vacuum drying (FD + MVD) methods. Drying parameters including drying temperatures (20, 30, and 40 °C), chamber pressures (70, 100, and 130 Pa) and material layer thicknesses (single, double, and triple) during FD process, and microwave power densities (20, 40, and 60 W/g) and material layer thicknesses (single, double and triple) during MVD period of FD + MVD process, were investigated for their drying characteristics. The FD and FD + MVD products were then rehydrated at two temperatures (20 and 70 °C). Different mathematical models were tested with the drying and rehydration behaviors of button mushroom slices, and the effective diffusivities (D eff) in the FD and FD + MVD processes were also calculated. The results indicated that based on the statistical tests, the Page model and logarithmic model provided the best fit for FD (in both FD and FD + MVD processes) and MVD (in FD + MVD process) curves, respectively. The regression equations obtained from selected models can accurately predict the relationships between moisture ratio (MR) and time (t). Furthermore, the D eff values of the MVD period in FD + MVD process (2.318–5.565 × 10−5 m2/s) were about ten times greater than those in FD process (1.291–3.389 × 10−6 m2/s). In addition, the Peleg model gave a better fit for rehydration conditions applied in both FD and FD + MVD products. The values of equilibrium moisture content (W e) of FD + MVD products were almost similar to those of FD products, which indicated that the rehydration capacities of the two dehydrated products were comparable.

Response of colour and hygroscopic properties of Scots pine wood to thermal treatment

The effect of heat treatment on the surface colour and hygro- scopic properties of pine wood were investigated in this study. Boards of Scots pine wood (Pinus sylvestris L.) were subjected to thermal treatment at 200oC, for 4, 6, and 8 h. The change of equilibrium moisture content and density values of the specimens in order to facilitate the understand- ing of the treated material behavior. The colour parameters L*, a* and b*, used to depict the total colour change (ΔE) of wood surface, were shown to change proportionally to the treatment intensity. Moreover, swelling in the tangential and radial directions and absorption of the specimens ap- peared to be enhanced in great extent by the thermal treatment process. The mean value of swelling percentage in the tangential direction de- creased 10.26%, 17.22%, and 19.60% for specimens treated for 4, 6, and 8 h, respectively, referring to the final measurement after 72 h of immer- sion. In radial direction, mean value of swelling percentage decreased 19.56%, 32.75%, and 34.65% for treated for 4, 6 and 8 h, respectively, after 72 h immersion, which attests the decrease in swelling and im- provement in the hygroscopic behavior of Scots pine wood.

Water sorption isotherms of skimmed milk powder within the temperature range of 5-20 °C

Moisture sorption isotherms (MSI’s) of skimmed milk powder in the temperature range of 5–20 °C were determined using manometric method. MSI’s, which show the water content versus water activity (Aw) at a constant temperature, are used to describe relationships between water content and equilibrium state relative vapour pressure (RVP). The equilibrium moisture content (EMC) of skimmed milk powder samples is growing with an increase of Aw at a constant temperature both for water adsorption and desorption. Isotherms were found to be type II of Brunauer-Emmett-Teller classification. It is the type most common for foods. The shape of created isotherms was sigmoid. Structural modifications of crystals were observed during adsorption in the microscope, too. Critical value of EMC of tested samples corresponding to the Aw equal to 0.6 for adsorption was 6.50% MC (w.b.) at temperature 5 °C, 9.15% MC (w.b.) at temperature 10 °C, and 7.71% MC (w.b.) at temperature 20 °C. These values determine optimal conditions for storage from the point of view microorganisms grow, Aw<0.6.

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.

Effects of glycerol, sorbitol, xylitol and fructose plasticisers on mechanical and moisture barrier properties of pullulan–alginate–carboxymethylcellulose blend films

SummaryThe effects of glycerol, sorbitol, xylitol and fructose plasticisers on water sorption, mechanical properties, water vapour permeability (WVP) and microstructure of pullulan–alginate–carboxymethycellulose (PAC) blend films were investigated. At low plasticiser concentrations (below 7% w/w dry basis), antiplasticisation effect was observed, causing an increase in tensile strength (TS) but a decrease in the equilibrium moisture content. As glycerol concentration increased from 0% to 7%, TS increased from 68.1 to 69.6 MPa, whereas equilibrium moisture contents at 0.84 aw decreased from 0.37 to 0.3 g H2O g−1 dry basis. At higher plasticiser concentrations (14–25% w/w), an opposite trend was observed on the PAC films, resulting in the reduction of TS and elevation of moisture content. Among the four plasticisers tested, the fructose‐plasticised films were the most brittle, showing the highest TS, but had the lowest elongation at break (EAB), WVP and equilibrium moisture content values than films plasticised with other polyols. On the other hand, glycerol resulted in the most flexible film structure, exhibiting opposite materials' properties as compared with the fructose‐plasticised films. For instance, at 25% (w/w) plasticiser concentration, EAB and WVP values of fructose‐plasticised films were 33.5% and 3.48 × 10−6 g m Pa−1 h−1 m−2, which were significantly lower than that of glycerol‐plasticised films (58.6% and 4.86 × 10−6 g m Pa−1 h−1 m−2, respectively). Scanning electron microscopy showed that the plasticised PCA films were less homogeneous and more porous than the unplasticised counterparts, indicating that plasticisers had an effect on the microstructural morphology of the film matrix.

Effect of freezing on physical properties of whey protein emulsion films

The objective of this work was to study the effect of the freezing process on physical properties of whey protein emulsion films with different beeswax content dried at 5 °C. Thickness, microstructure, water vapour permeability, solubility in water, sorption isotherms and mechanical properties were measured in Control and Frozen films. The freezing process did not cause fractures or perforations in films, but films with beeswax showed a change in the appearance of the lipids after freezing. Only films with 40% of beeswax showed a significant increase in the water vapour permeability after freezing. The freezing process did not affect film solubility in water but produced small differences in the equilibrium moisture content values. In the puncture test, the freezing process increased puncture strength and deformation of films without beeswax but those parameters were not affected in films with beeswax. In tensile test, tensile strength and elastic modulus decreased, but elongation was not affected by freezing process. Principal component analysis accomplished an adequate condensation of the date grouping samples according to film formulation and treatment (Control and Frozen films). Indeed, the relationships of sample grouping and measured parameters were enlightened by principal component analysis. In conclusion, whey protein emulsion films were resistant to the freezing process (freezing, frozen storage and thawing) and could be a good alternative as a treatment to preserve the quality of frozen foods.

Applying Peleg's equation to modelling the kinetics of solid hydration and migration during soybean soaking

Legume soaking is an important practice in food processing; the characteristics of beverages and tofu mainly depend on this operation regarding soybeans. Peleg's equation has been used in this work to describe the kinetics of water absorption and solid loss during soaking at 20°C, 40°C and 80°C. The moisture content of grain and solids in the remaining water was measured for 10 hours. Variance analysis and principal components analysis showed high fitting of kinetics to Peleg's equation for predicting both transference phenomena. This work found that the value of k1 (rate) depended on temperature according to a polynomial function while k2 (capacity) did not, meaning that the value of equilibrium moisture content was independent of soaking temperature. k1 had the minimum value for the migration of solids to soaking water at 40°C; this was related to lost solids' high speed and the microbial degradation of carbohydrates; the values obtained for k2, showed that it was possible to lose total soluble solids at 20°C, while further migration of insoluble compounds occurred at 80°C.

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 %.

Moisture Sorption Isotherms of Lentil Extrudates

Abstract The equilibrium moisture contents (EMC) were determined for lentil extrudates produced under different processing conditions at 25°C and eight relative humidity (RH) in the range of 0.113 – 0.902. It was established that for the ten extruded samples the EMC values at the same RH were not statistically equal. Four models – Chung-Pfost, Halsey, Oswin, and Henderson equations were applied for analyzing the experimental data. The Oswin model was most suitable for describing the relationship between the EMC and RH.

Moisture sorption characteristics of switchgrass and prairie cord grass

Moisture content plays an important role both in the biochemical and thermochemical conversions of various feedstocks into energy. Knowledge of the relationship between relative humidity of air and moisture content of the feedstock is essential for drying and storage. The aim of this work was to determine the sorption isotherms of switchgrass and prairie cord grass and to compare the experimental data with isotherm models found in the literature. The equilibrium moisture content (EMC) of switchgrass and prairie cord grass was determined using the static gravimetric method at equilibrium relative humidities (ERH) and temperatures ranging from 12 to 89% and 20°C to 40°C. Depending upon the ERH values, the EMC values ranged from 9.2 to 20.8%, and 7.0 to 21.0% db for switchgrass and prairie cord grass, respectively and they followed typical the type II isotherm found in food materials. Non-linear regression was used to fit five commonly used three-parameter isotherm models to the experimental data: modified Oswin model, modified Halsey model, modified Chung–Pfost model, modified Henderson model, and the modified Guggenheim–Anderson–de Boer (GAB) model. Modified Halsey emerged as the best model followed by modified Oswin for both feedstocks with high F-statistic and R2 values with low Em and Es and fairly random scattered residual plots. Because of the range of the environmental temperature and RH values, these models can be used to predict the equilibrium moisture content of these feedstocks starting from harvesting, drying, and preprocessing, through transportation, storage, and conversion/processing.

Dynamic vapor sorption isotherms of medium grain rice varieties

It is known that the two popular medium rice varieties, namely M202 and M206, in California have different fissuring resistances. Therefore, the main goal of this study was to investigate the sorption behavior of these two varieties by a new approach using dynamic vapor sorption (DVS) method for elucidating the differences in fissuring resistance. The moisture sorption isotherms of rough, brown and white rice and husk were determined at 25 °C over a water activity range of 0–0.98. Although it was found that the sorption isotherms of different forms of M202 and M206 were similar, M202 absorbed and desorbed moisture faster than M206 which might make it more susceptible to fissuring. All obtained moisture sorption isotherms exhibited the sigmoid (Type II) shape and hysteresis was observed for all forms of rice. Absorption curves obtained using DVS method were compared with the traditional saturated salt solution (SSS) method. For all forms of rice, the maximum difference for equilibrium moisture content value between two methods was observed at 0 and 98% relative humidities, which was approximately 8–11% and 7–9%. Although at a single relative humidity point equilibrium with DVS was attained much faster than SSS method, obtaining a full isotherm with more than 10 data points might make SSS method more feasible for low diffusion materials. Among the select equations to describe sorption behavior of different forms of rice, Peleg equation gave the best fit for all forms of rice.

Thermo-Physical Properties And Mathematical Modeling Of Thin-Layer Drying Kinetics Of Medium And Long Grain Parboiled Rice

This research was to investigate some thermo-physical properties and to determine a mathematical model for describing drying kinetics for medium and long grain parboiled rice varieties. The thermo-physical properties in terms of equilibrium moisture content (EMC), apparent density, void fraction, specific heat capacity at moisture content ranging from 30 to 58% dry-basis (d.b.) for both Leb Nok Pattani (LNP) and Suphanburi 1 (SP 1) rice varieties were determined by conventional standard techniques.The evaluated results showed that EMC values for both rice varieties predicted by the GAB’s model yielded the best fitting with experimental data. To determine thermo-physical properties, the results stated that apparent density and specific heat capacity of parboiled LNP and SP1 rice varieties were linearly dependent on moisture content. In contrast, percentage of void fraction of medium grain LNP and long grain SP1 rice variety was inversely proportional to moisture content. For employing empirical thin-layer drying models, the Two terms model was the best fitting model to describe the experimental data for both rice varieties.

Comparative study of the 35 ºC sorption isotherms of cork stripped from the tree in 1968 and 2006

A study was made of the hygroscopicity of two samples of cork with the same characteristics, taken from trees of the same age but with a 38-year gap between debarking. This was achieved by plotting the 35ºC sorption-desorption isotherms and fitting them using the GAB model. Infrared spectra were used to determine any chemical changes in the cell wall. Extended exposure to controlled relative humidity and temperature did not cause hygroscopic changes to the cork. The equilibrium moisture content values were not significantly different in the two samples, but the monolayer saturation moisture content values were significantly lower in the older cork. This may be due to partial saturation of the moisture sorptive sites in the cell wall over time.