Desorption Equilibrium Moisture Content Research Articles

Whole wheat flour enriched with nectarine powder - antioxidant activity, microbiological and moisture sorption characteristics

The aims of the current scientific study are to present the initial data research on the flour mixture of whole wheat flour enriched with nectarine powder of Bulgarian origin – intended for sponge cake production - was created. The natural content of the antioxidants was evaluated through the in vitro methods DPPH, ABTS, FRAP, and CUPRAC. The equilibrium moisture content (EMC) and monolayer moisture content (MMC) were investigated at 10°C, 25°C, and 40°C, resembling the diapason of temperature conditions in the storage house. The water activity (from 0.1 to 0.9) is provided through saturated salt solutions of LiCl, CH3COOK, MgCl2, K2CO3, MgNO3, NaBr, NaCl, and KCl. The obtained adsorption and desorption EMC declare the tendency – with its increase, the temperature decrease at the constant value of aw. According to Brunauer’s classification, sorption isotherms are of the second class, showing their characteristic S-shape profile. The modeling of the obtained sorption data includes their mathematical description using one of the three-parametrical models of modified Halsey, Oswin, Chung-Pfost, and Henderson. The Brunauer-Emmett-Teller linearization was presented to the values of the monolayer moisture content – for the adsorption process they are between 5.78% and 8.94%; and for the desorption - between 7.25% and 8.89%.

Experimental Analysis of Drying Conditions’ Effect on the Drying Kinetics and Moisture Desorption Isotherms at Several Temperatures on Food Materials: Corn Case Study

This work studied the effect of external conditions on the drying kinetics of a thin layer of corn during convective drying. The density and the specific volume of the corn grain were reported and the desorption isotherms of the corn were determined at three temperatures and for a water activity from 0.1 to 0.9 using the static gravimetric method. Initially, a thin layer of corn about 7 mm thick with an initial moisture content of 45% (d.b) was investigated, and the external conditions were tested. Afterwards, a comparison between the experimental convective drying of a packed bed and a thin layer was performed under the same conditions. Finally, the values of equilibrium moisture contents, water activities and temperatures obtained were fitted using seven sorption models. It was found that the experimental desorption data exhibited type II behavior, according to Brunauer’s classification. The GAB model was found as the most suitable semi-empirical model which was well suited to represent the desorption equilibrium moisture content of corn kernels in the suggested ranges of temperature and water activity. It can be concluded from the entropy–enthalpy compensation theory that the desorption process of the corn kernels is controlled by the enthalpy mechanism.

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.

보리의 평형함수율/평형상대습도에 관한 연구

Desorption equilibrium moisture content (EMC)/equilibrium relative humidity (ERH) experiments were performed on two cultivars (Sae naked and Hin-chal naked) of barley (Hordeum vulgare L.) at 5, 15, 25, 35, and 45℃ for moisture contents between 9.51 and 29.13%,db. The method employed involved measuring the ERH of air in contact with the grain under static conditions, using an electronic hygrometer. The effects of temperature and moisture contents were investigated, and the measured values were fitted to the modified Henderson model, the modified Chung-Pfost model, the modified Halsey model, the modified Oswin model, and the modified GAB model. The ERHs of barleys decreased with decreasing moisture content and temperature, and the EMCs increased with decreasing temperature and increasing relative humidity. The increase in moisture content with increasing relative humidity at a given temperature is not linear: the moisture content increased rapidly at high relative humidities, and the differences between ERH values at different temperature (5-45℃) were insignificant at high relative humidity (>80%). The effect of the cultivars on EMC/ERH was insignificant at the same temperature. The modified Halsey model was found to be the best in describing the EMC/ERH of barleys.

Application of response surface methodology for optimization study of equilibrium moisture sorption content for efficient drying and storage of pearl millet flour

Pearl millet due to its high nutritional quality and adaptability to adverse cultivation is highly consumed in Asia and Africa. Prevalent flour form of pearl millet is susceptible to oxidation and microbial growth, demanding proper drying and storage conditions. Moisture sorption isotherm plays an essential role for proper storage and drying operation optimization. This study used response surface methodology to optimize equilibrium moisture content (EMC) of adsorption and desorption (closely related to moisture sorption isotherm) as response and the independent variables affecting the response were sorption temperature, water activity of sorption of flour and time of pre-treatment of grains before grinding them to flour. Linear relationship was found for water activity and time of pre-treatment with the response but an inverse relation was noted between the sorption temperature and the response. The optimized conditions obtained for minimized response of adsorption EMC were 19.85 °C temperature, 1.34 h of pre-treatment time and 0.41 sorption water activity which gave optimized EMC of 9.0554 g/100 g dry basis. Optimization condition for minimized desorption EMC were 24.47 °C temperature of sorption for 0.13 h pre-treated pearl millet grain flour and 0.360 sorption water activity providing an optimized EMC of 11.07 g/100 g dry basis. Isosteric sorption heat was also calculated and was found to be in range 22.03–0.736 kJ/mol for adsorption and 33.03–1.067 kJ/mol for desorption. Present work was an effort to evaluate optimized conditions to develop effective storage and drying processes to preserve pearl millet flour thereby increasing its shelf life.

Effects of preservative pretreatments on moisture adsorption and desorption properties of corn stalk fiber/high-density polyethylene composites

The impact of alkaline copper quat (ACQ) and zinc borate (ZB) on the moisture adsorption and desorption properties and leaching resistance of corn stalk fiber (CSF) reinforced high-density polyethylene (HDPE) composites was investigated. The equilibrium moisture content (EMC) was fitted by the Nelson model, and the interaction between the CSF component and the preservatives was characterized by Fourier transform infrared spectroscopy (FTIR). The effective components of the preservative were successfully immobilized on the CSF, which was observed by FTIR analysis. The leaching resistant analysis showed that the leaching amount of copper and boron elements reached a plateau, and that the leaching resistant performance in the ACQ treatment was better than in ZB. The moisture adsorption of CSF/HDPE composites was significantly reduced with ACQ treatment at low CSF content, but clearly increased in ZB treatment at high CSF content. The moisture adsorption and desorption EMC increased with the increased preservative (ACQ or ZB) embedding at a given CSF/HDPE component ratio. The experimental values were fitted well with the Nelson model; thereby this model could be used to predict the moisture adsorption and desorption EMC of CSF/HDPE composites at various relative humidity.

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.

Effect of Blanching on Sorption Isotherms of Spinach

A study was conducted to determine the effect of blanching on moisture adsorption and desorption characteristics of spinach. Moisture sorption was determined by gravimetric method. Different saturated salt solutions were prepared to provide constant relative humidity environments. Four spinach samples (unblanched, unblanched dried, blanched and blanched dried) were kept at 3 temperatures (300C, 400C and 60ºC) with corresponding 5 relative humidity levels (10.95 to 92.31%). It was observed that for all samples, equilibrium moisture content (EMC) of spinach increased with increase in relative humidity at constant temperature. At constant relative humidity levels, EMC decreased with increase in temperature. The adsorption EMC of the spinach was lower than the desorption EMC for blanched as well as unblanched spinach for all temperature and relative humidity ranges. The blanched dried spinach exhibited lowest EMC at all temperature and relative humidity ranges.

Moisture desorption isotherms of rough rice at high temperatures

Moisture desorption isotherms of medium-grain rough rice ( Lido cultivar) at temperatures from 40 to 80 °C and water activity from 0.14 to 0.90 were determined using the static gravimetric method. The moisture isotherms were sigmoid shaped and showed a clear effect of temperature. The most commonly used models, modified Henderson, modified Halsey, modified Chung–Pfost, modified Oswin and modified GAB, were used to fit experimental values using a non-linear regression analysis. The models were compared using the standard error of estimate, relative percent error, coefficient of correlation and residuals plot. Results probed that the modified GAB model was more appropriated to predict desorption equilibrium moisture content of rough rice for the range of temperatures and water activities studied. Modified Chung–Pfost model and modified Henderson model gave an acceptable fitting, while modified Halsey model and modified Oswin model did not seem appropriate for the description of the desorption moisture isotherms of rough rice at drying temperatures. Monolayer moisture content of rough rice for the range of temperatures and moisture contents studied ranged from 2.905% to 4.870% (d.b.). Isosteric heat of desorption ranged from 2.510 to 18.387 kJ/mol for moisture contents ranging from 0.04% to 24% (d.b.), and an expression for predicting this thermal property was developed.

Water sorption and dehydration kinetics of Tunisian rosemary leaves

Water sorption isotherms of rosemary were investigated at three temperatures: 30, 40 and 50°C, corresponding to drying temperatures, by the static method consisting of the use of different sulphuric acid solutions, over a range of relative humidity from 0.05 to 0.9. Experimental data are used to determine the best models for predicting the desorption equilibrium moisture content of rosemary for known values of temperature and relative humidity. The second part of this study deals with the drying kinetics of rosemary in an infrared dryer. The experimental results are used to determine the characteristic curve of drying.

Moisture sorption isotherms of sorghum malt at 40 and 50 °C

The desorption and adsorption equilibrium moisture isotherms of sorghum malt at the temperatures of 40 and 50 °C, over the water activity range of 0.1–0.9, were determined using the static gravimetric method. A non-linear regression programme was used to fit five moisture sorption isotherm models [Modified Henderson, Modified Chung-Pfost, Modified Guggenheim–Anderson–de Boer (GAB), Modified Halsey and Modified Oswin] to the experimental data. The models were compared using the standard error of estimate, mean relative percentage deviation, fraction explained variation and residual plots. The Modified Chung-Pfost model was found to be the best for predicting the desorption equilibrium moisture content, while the adsorption equilibrium moisture content was best predicted by the Modified Oswin model. The desorption and adsorption water activities were found to be best fitted by the Modified Oswin model. The moisture sorption isotherms were sigmoidal in shape and showed a marked effect of temperature. The span of the moisture sorption hysteresis loop formed, decreased with increase in temperature, while the size increased with increase in temperature.

벼 및 현미의 평형함수율/평형상대습도

Adsorption and desorption experiments were carried out on rough rice and brown rice (Nampyung) at 5, 15, 25, 35, <TEX>$45^{\circ}C$</TEX> for moisture contents between 8.7 and <TEX>$25\%$</TEX> (db). The method employed was to measure the equilibrium relative humidity (ERH) of air in contact with the grain under static conditions, using an electronic hygrometer The effects of temperature and moisture contents were investigated, and the measured values were fitted to the modified Henderson, the modified Chung-Pfost, the modified Halsey and the modified Oswin model. The ERHs of rough rice and brown rice decreased with an decrease in moisture content and temperature, and the effects of temperature was no significant at moisture content of <TEX>$25\%$</TEX> (db). Equilibrium moisture content (EMC) of brown rice was higher than rough rice at same temperature and relative humidity. Desorption EMC is higher than the adsorption, but there is no significant difference between desorption and adsorption EMC in moisture content near <TEX>$25\%$</TEX> (db) at rough rice and near 9, 21 and <TEX>$25\%$</TEX> (db) at brown rice. The modified Oswin model was the best in describing the adsorption EMC and the modified Chung-Pfost model was the best in describing the adsorption ERH of rough rice. The modified Oswin model was the best in describing the adsorption EMC/ERH of brown rice. The modified Chung-Pfost model was the best in describing the desorption EMC/ERH of rough rice and brown rice.

Sorption Equilibrium and Thermodynamic Characteristics of Soya Bean

Desorption equilibrium moisture content and water activity data for soya bean ( Glycine max) TGX 1440-1E were determined using the static gravimetric method. Measurements were taken in the water activity range of 0·07–0·98 at four temperatures (40, 50, 60 and 70 °C). A non-linear regression programme was used to fit five moisture sorption isotherm models [modified Henderson, modified Chung–Pfost, modified Halsey, modified Oswin and modified Guggenheim–Anderson–de Boer (GAB)] to the experimental data. The models were compared using the standard error of estimate, mean relative percent deviation and residual plots. The modified Oswin model, which gave the least standard error of 1·91% and least mean relative percent deviation of 10·15 among the five models, when equilibrium moisture content was taken as the dependent variable, was considered to be the best for predicting the equilibrium moisture content of soya bean. The moisture sorption isotherms of soya bean were sigmoidal in shape, of the type II and were markedly affected by temperature. The modified Halsey model, which gave the least standard error of 0·07 and least means relative percent deviation of 16·67, when water activity was taken as the dependent variable, was considered the best for predicting the water activity of soya bean. The desorption equilibrium moisture content and water activity relationships as expressed by the moisture sorption isotherm models that best predicted the experimental data, were used to determine the thermodynamic characteristics of soya bean. The heat of vaporisation of moisture in soya bean decreased with increase in moisture content and approached the latent heat of pure water at a free water point of between 20 and 22% moisture content (d.b.). The surface potential of moisture in the seed increased with increase in water activity, but was not significantly affected by temperature. Net integral enthalpy decreased from a value of 550 J g −1 as the moisture content increased from 5·20% (d.b.). The trend became asymptotic at a value of 80 J g −1 as the moisture content of 13% (d.b.) was approached. Net integral entropy decreased with increase in moisture content to a minimum value of –0·38 J g −1 K −1 at the moisture content of 11% (d.b.), and thereafter, increased with further increase in moisture content.

Water vapour sorption and transmission by onion ( Allium cepa L.) scale under different temperature and humidity conditions

The sorption behaviour of isolated outer dry scales of onion bulbs showed a higher equilibrium moisture content (EMC) at 25°C than at 40°C, when the relative humidity (RH) was < 80%, while at higher RH a tendency to an increase in EMC at 40°C was seen. Large differences between the adsorption and desorption EMC were noted during holding at room temperature (25–32°C) in the 35 and 80% RH range, and the least at 40°C. At 80% RH, the EMC was ∼ 12%, with the differences between adsorption and desorption EMC being lower than at other RH. In comparison to isolated dry scales, the EMC of intact scales was higher at 50% RH and below, both at 25 and 40°C, but tended to decrease with an increase in RH from 50 to 80%. Under all RH combinations tested, the water vapour transmitted through the scales was lower at a constant temperature of 25°C than either at a constant temperature of 35°C or at ambient conditions, as the vapour pressure deficit at 25°C was lower. Further, storage of onion bulbs in ventilated low-density polyethylene (LDPE) bags, at 21 ± 1°C and 60–65% RH showed a highly significant reduction in microbial spoilage along with marginal differences in physiological loss in weight (PLW) and sprouting compared with those stored at ambient conditions (22–32°C and 50–80% RH).

Evaluation of Models to Describe Sorption and Desorption Equilibrium Moisture Content Isotherms of Virginia-Type Peanuts

ABSTRACT AKNOWLEDGE of the equilibrium moisture content of a biological material is essential for the efficient design and operation of systems for drying, wetting or storing the material. The equilibrium mois-ture content of a material in a given environment may be defined as the moisture content which the material would reach if exposed to the environment for an infinite period of time. Since several investigators in-cluding Babbitt (1945), Hubbard et al. (1957), Breese (1955), and Young and Nelson (1967), found a hysteresis between the equilibrium moisture curves for wetting and drying proc-esses, it is necessary to define both sorption and desorption equilibrium moisture content isotherms. The objective of this study was to experimentally determine sorption and desorption equilibrium moisture content isotherms for Virginia-type peanut kernels and hulls at various temperatures, to use the experi-mentally determined curves to eval-uate the parameters of several pub-lished equations for equilibrium moisture content, and to investigate the implications of parameter values on such physical and thermal proper-ties as surface area per unit mass of dry matter and heat of sorption or desorption of water by peanut components.