Modified Chung-Pfost Equation Research Articles

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

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

Modeling Heat and Mass Transfer of Long-Grain Hybrid Rice in a Chilled Environment

HighlightsThis study determined adsorption and desorption isotherms of long-grain hybrid rough rice in chilled environments.Parameters of the sorption models were evaluated by fitting experimental data in a thin layer drying equation.The moisture diffusivity and activation energy values of rough rice subjected to chilled environments were determined.The finite element method was used to simulate the heat and mass transfer of long-grain hybrid rice at low temperatures. Abstract. While chilling aeration technology for grains has found use in other countries, application in the U.S. for rice has not yet been widely adapted by the industry. The aim of this study was to determine the moisture sorption behavior of rough rice in chilled environments. Such data is vital for automated grain conditioning monitoring and control of aeration systems at cool ambient conditions. Adsorption and desorption isotherms of hybrid long-grain rough rice (XL745) subjected to temperature environments which are typical in U.S. storage conditions (5°C to 15°C) were measured. A dynamic vapor sorption analyzer, the IGAsorp, which consists of an ultrasensitive microbalance within a controlled environment was used to accurately measure water sorption in rice. Changes in sample weight were continuously monitored across a range of equilibrium relative humidity (10% to 70%) until a steady-state mass was attained. Nonlinear regression analysis was used to estimate empirical constants of five models used for describing grain sorption isotherms. The appropriateness of each model in describing the equilibrium data was evaluated to minimize the root mean square error (RMSE). The modified Chung-Pfost equation best described the experimental data with RMSEs of 0.557 and 0.912 for adsorption and desorption data, respectively. The equilibrium moisture content (EMC) of rice measured at 5°C with 10% relative humidity (RH) was 12.5% (dry basis), which was higher than the EMC value predicted from other studies by extrapolation at 30°C (9.1% d.b.). All five prediction models (modified Chung-Pfost, modified Henderson, modified Oswin, modified Halsey, and GAB) were in good agreement for experimental data at moderate temperature conditions (e.g., at 30°C). The results indicated that it is more accurate to use newly developed constants for EMC models of rice in chilled environments. A three-dimensional ellipsoid shape was used to describe rough rice geometry. Mathematical models were developed to predict the moisture and temperature distribution during the drying processes at 5°C and 15°C. Models were solved by the finite element method using Comsol Multiphysics® simulation program. Increasing the drying temperature from 5°C to 15°C increased the effective moisture diffusivity from 9.0×10-13 to 1.1×10-12 m2/s. The drying activation energy value was 25.1 kJ/mol in the chilled environments investigated. Keywords: Activation energy, Chilled environment, Equilibrium moisture content, Mathematical modeling, Moisture diffusivity, Rough rice.

Effect of Drying Systems on the Parameters and Quality of Dried Basil

The main aim of this study is to investigate the possibility of drying the basil plants under different conditions. Fresh basil was dried using different systems: sun-drying, shadow-drying, room-drying, solar-drying and oven-drying systems. Weight losses, moisture content and oil content were recorded. Drying parameters were studied to determine the equilibrium moisture contents (EMC) using different models. The obtained results indicated that the accumulated weight loss of basil plants increased from 3.57 to 83.76, 2.12 to 70.48, 0.72 to 82.07, 0.44 to 84.34 and 1.29 to 84.90 %, for sun-drying system, shadow-drying system, room-drying system, solar-drying system and oven-drying system, respectively. The moisture content of basil plants decreased from 515.95 to 6.91, 490.18 to 6.59, 479.97 to 4.66, 538.02 to 0.93 and 565.40 to 5.40 % d.b. for sun-drying system, shadow-drying system, room-drying system, solar-drying system and oven-drying system, respectively. The highest value of equilibrium moisture contents were 13.25 and 35.16 % at 10 and 90 % equilibrium relative humidity was found from Modified Chung-Pfost equation under room system. The lowest value of equilibrium moisture contents were 0.91 and 16.58 % at 10 and 90 % equilibrium relative humidity was found for modified Oswin equation for oven system. The basil oil content values were 2.3, 2.5, 2.9, 2.7 and 2.0 % for the sun-drying, shadow-drying, room-drying, solar-drying and oven-drying, respectively.

Sorption equilibrium moisture and isosteric heat of cold plasma treated milled rice

Abstract To promote industrial adoption of cold plasma as a sustainable and safe processing technology for rice, data on equilibrium moisture content (EMC) for cold plasma treated milled rice of five Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and a temperature range of 15–35 °C. Nine models were fitted well to the sorption data, with the modified Guggenheim–Anderson–deBoer equation (3-MGAB), modified Henderson equation (MHE), and a polynomial equation being the best fits. At a constant ERH, the EMC was negatively correlated with temperature, whereas there was a strong effect of temperature on the sorption isotherms of the milled rice. Initially, the isosteric heats of sorption for the cold plasma treated rice decreased rapidly with increasing sample moisture content (MC); however, when MC was higher than 15% of the wet basis (w.b.), further increases in MC caused a slight decrease in heat sorption values. The heat of vaporization of the milled rice approached the latent heat of pure water at a moisture content of ~17.5% w.b., which was ~2500 kJ/kg. The isosteric heat of sorption values of the milled rice predicted by the modified Chung-Pfost equation (MCPE) and MHE models negatively correlated with temperature. At 70% ERH, the safe-storage MC of the cold plasma treated rice were ≤14.5% w.b. at 25 °C. In comparison to the untreated milled rice, the cold plasma treated rice with 120 W for 20 s and 60 s significantly decreased the water contact angle and increased kernel broken index, without significantly changing the appearance quality of milled rice. The cold plasma treated rice with 120 W-20 s had insignificantly higher EMC than that of 120 W-60 s at the studied temperature range. This study demonstrates that helium cold plasma treatment insignificantly changed hygroscopic property of milled rice whilst maintaining the appearance quality.

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.

Basil Drying Performance and Quality under Different Drying Systems

The main aim of this study is to investigate the possibility of drying the basil plants under five different drying systems. The obtained results indicated that the accumulated weight losses of basil plants were 77.43, 74.00, 70.48, 74.92 and 77.99 %, for sun-drying system, shadow-d rying system, room-drying system, solar-drying system and oven-drying system, respectively at the end of experimental period. The highest values of equilibrium moisture contents were 13.94 and 37.01 % at 10 and 90 % equilibrium relative humidity was found from Modified Chung-Pfost equation under room system. The lowest values of equilibrium moisture contents were 0.83 and 15.07 % at 10 and 90 % equilibrium relative humidity was found for modified Oswin equation for oven system. The basil oil content values were 5.918, 7.911, 8.472, 6.547 and 5.230 % for the sun-drying, shadow-drying, room-drying, solar-drying and oven-drying, respectively.

Sorption equilibrium moisture and isosteric heat of adsorption of Chinese dried wheat noodles

Equilibrium moisture content (EMC) data for dried wheat noodles of ten Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C. Five models were fitted to the sorption data, namely the modified Chung Pfost equation (MCPE), modified Henderson equation (MHE), modified Guggenheim Anderson deBoer equation (MGAB), modified Oswin equation (MOE), and a polynomial equation. The best fitting equations were MGAB and the polynomial equation. At a constant ERH, the EMC decreased with increasing temperature, despite the minor effect of temperature on the sorption isotherms of dried noodles. Initially, the isosteric heats of adsorption for dried wheat noodles decrease rapidly with increasing sample moisture content (m.c.); however, after the moisture content is more than 15% of the dry basis (d.b.), they decrease slowly with increasing m.c. The heat of vaporization of Chinese dried wheat noodles approaches the latent heat of pure water at a moisture content of ∼20% d.b., which is ∼2500 kJ/kg. The isosteric heats of sorption of Chinese dried noodles predicted by MCPE and MHE models at lower temperatures were higher than those at higher temperatures. When the equilibrium relative humidity (ERH) is 60%, the safe-storage moisture content of Chinese dried wheat noodles are 11.74% and 11.57% d.b. at 25 °C and 35 °C, respectively. Among ten varieties of dried wheat noodles, the egg-flavoured noodle had the highest onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of gelatinization, but the golden-silk egg noodles had the highest peak enthalpy of gelatinization. The gelatinization To, Tp, and Tc of golden-silk egg noodles were the lowest. Most of the ten varieties of dried wheat noodles demonstrated similar thermal properties and hygroscopic behaviour.

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

Sorption Isotherms for Triticale Seed

<abstract> <bold><sc>Abstract.</sc></bold> Triticale is being evaluated as a substitute for corn in animal feed and as a forage crop for Florida. Storage of triticale seed is difficult in Florida’s hot and humid climate, and more information about the relationships between equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) at constant temperature (sorption isotherms) of triticale is needed to develop improved storage methods. Therefore, the primary research objective was to measure the EMC for triticale seed at different ERH values at three different constant temperatures (5°C, 23°C, and 35°C) using six desiccation jars containing different saturated salt concentrations. The secondary objective was to determine the best fit equation describing these relationships. The six saturated salt solutions provided relative humidity (RH) values of 11%, 23%, 33%, 58%, 75%, and 84% at 25°C. An average of ten weeks was required to reach equilibrium when the initial moisture content (MC) of the seed was 13.35% (wet basis). The results of this experiment were used to develop three prediction equations, (modified Henderson, modified Chung-Pfost, and modified Oswin equations) representing the relationship between ERH and EMC. The results show that the modified Chung-Pfost equation represented this relationship most accurately, with a standard error of 2.4% and a coefficient of determination obtained from the scatter plot for the predicted vs. measured RH (R²) equal to 0.99. Overall, this result will aid the development and improvement of drying and storage methods for triticale seed.

Equilibrium Moisture Contents of Pureline, Hybrid, and Parboiled Rice

Equilibrium moisture contents of long- and medium-grain rough rice of both pureline and hybrid cultivars, and a parboiled rough rice of unknown cultivar, were measured in a near-static air environment at five temperatures (10C, 20C, 30C, 45C, and 60C) and relative humidities in the range of 10% to 70% using a gravimetric method. Results showed that there were no consistent significant differences between the equilibrium moisture contents of pureline and hybrid or medium- and long-grain rice cultivars. However, the equilibrium moisture content of parboiled rice was significantly less than that of non-parboiled rice for almost all air conditions. Nonlinear regression analysis was used to estimate empirical constants of five models used for describing grain sorption isotherms. The appropriateness of each model in describing the equilibrium data was evaluated using root mean square errors and residual patterns. The modified Chung-Pfost equation best described equilibrium data of non-parboiled samples, followed by the modified GAB, modified Oswin, modified Halsey, and modified Henderson equations. The modified Chung-Pfost and modified GAB equations were equally effective when describing equilibrium data of individual cultivars.

Technical Note: Equilibrium Moisture Contents of Rough Rice Dried Using High-Temperature, Fluidized-Bed Conditions

Desorption isotherms of long-grain rough rice with initial moisture content of 20.6% (wet basis) and dried in a fluidized-bed system at temperatures ranging from 60C to 90C and relative humidities from 7% to 75% were measured. Rice sample mass and drying air conditions were recorded throughout the drying duration for each test until a steady-state mass was attained. The Page equation, with experimentally determined drying parameters, was used to describe the drying data. Equilibrium moisture contents were used to estimate empirical constants of the modified Chung-Pfost equation. The resulting modified Chung-Pfost equation described the experimental data with a root mean square error (RMSE) of 0.73 and a coefficient of determination (R2) of 0.94.

Effect of γ‐Ray Irradiation on Modeling Equilibrium Moisture Content of Wheat

The experimental research found that gamma irradiation dose affected the equilibrium moisture content of wheat at the same relative humidity and temperature of ambient. Values of the equilibrium moisture content decreased with an increasing dose of gamma-ray irradiation during both adsorption and desorption. These were due to the changes of wheat starch granules and their water bound ability caused by different irradiation doses. Factor of irradiation dose was added in 3 widely used models for modeling the equilibrium moisture content of irradiated wheat, and the parameters in models were estimated based on the experimental data. Based on the study of correlation coefficient, mean relative error, and standard error the modified Chung-Pfost equation and the modified Henderson equation were found to fit the desorption and adsorption isotherms for wheat, respectively, in the range of experiment at conditions studied.

Study of Adsorption and Desorption Equilibrium Relationships for Yellow Dent, White, and Waxy Corn Types Using the Modified Chung-Pfost Equation

Three different corn types (yellow dent, waxy, and white) harvested in the fall of 2003 were used to run a set of desorption and adsorption EMC/ERH experiments. The range of temperature and moisture content (MC) were designed to cover the typical operating conditions for natural air / low-temperature in-bin drying systems in the Midwest during the fall (0°C to 25°C and 12% to 20% for temperature and MC, respectively). Standard deviations of the experimental data ranged from 0.00°C to 0.58°C, 0.00% to 0.52% for EMC values, and 0.01% to 4.36% for ERH values. Non-linear regression analysis was used to determine the best adsorption and desorption parameters for the modified Chung-Pfost equation for each corn type. A second adsorption and desorption EMC/ERH experiment was carried out with samples of yellow dent and white corn harvested during the 2004 drying season. The modified Chung-Pfost equation using the 2003 set of parameters was validated with the 2004 EMC/ERH data. The MRD and SE for the three corn types ranged from 1.9 to 2.6 and 1.6 to 1.9 compared to 4.3 and 5.0, respectively, reported for the ASAE Standard data. The main conclusions of this study were that the different corn types investigated had different EMC/ERH relationships, the adsorption and desorption relationships were different for each corn type, and the prediction of EMC/ERH values during desorption using the current ASAE Standard set of parameters available only for yellow corn was substantially different compared to the yellow dent, white, and waxy corn EMC/ERH data reported in this research.

Modeling Equilibrium Moisture Content of γ-Ray Irradiated Rough Rice

Experimental studies show that gamma irradiation dose affects the values of equilibrium moisture content of grain at the same relative humidity and temperature of ambient. Values of the equilibrium moisture content decreased with increasing dose of γ-ray irradiation during both adsorption and desorption. Factor of irradiation dose was included in three widely used models for equilibrium moisture content; the parameters in the models were estimations from experimental data. Based on the correlation coefficient, mean relative error, and standard error of moisture, the modified Chung-Pfost equation and the modified Henderson equation were found to fit the desorption and adsorption isotherms for rough rice in the range of experimental conditions studied.

Moisture sorption isotherms for mungbean ( Vigna radiata L)

Adsorption equilibrium moisture contents of mungbean were determined by standard gravimetric method at the temperature of 20, 30, 40 and 50 °C and the relative humidity range of 11–97%. The effects of temperature were found to be significant and all the isotherms were found sigmoid in shape. Five widely used three parameters sorption isotherms equations such as modified Henderson, modified Chung–Pfost, modified Oswin, modified Halsey and GAB were used to fit the experimental data. The modified Chung–Pfost and modified Oswin equations have the ability to describe well the EMC/ERH relationship selected range of the relative humidity and temperature. The modified Chung–Pfost equation is the most suitable in M = f(rh, T) form while the modified Oswin equation is the most suitable in rh = f( M, T) form.

Sorption isotherms for amaranth grains

Compiling of EMC–ERH data for amaranth grains ( Amaranthus cruentus L.) in the range of water activity from 0.029 to 0.979 and temperature from 25 to 90 °C was performed. Included data sets comprised experimental values of EMC–ERH that summarize 78 identified points for desorption, 53 for adsorption and 16 not discerned points that were considered for mean sorption. Five isotherm equations for grains included in the ASAE Standards (Modified Henderson, Modified Chung–Pfost, Modified Halsey, Modified Oswin and GAB) were evaluated for their ability to fit sorption data from the literature ( M e vs. a w for adsorption, desorption and mean sorption). The goodness of fit for each isotherm was quantified through the correlation coefficient ( R 2), the sum of squares (RSS), the standard error of the estimate ( S y ), the mean relative deviation (MRD) and the plots of residuals. The three-parameter GAB isotherm was the best and gave a good correlation ( R 2 > 0.9817, RSS < 0.0293, MRD < 0.1380, S y < 0.0141, and random residuals-plots) for the general data-fit in the range of a w from 0.1 to 0.9, of interest in seed storage and processing. The Modified Halsey equation was rejected because it gave poor statistic parameters of agreement and patterned residual plots. For desorption, the Modified Chung–Pfost model gave the lowest mean relative deviation; the Modified Henderson equation was the second best in describing the EMC–ERH data, followed by the Modified Oswin and GAB models. For adsorption, the GAB equation presented the lesser MRD, followed by the Modified Chung–Pfost, Henderson and Oswin models. When mean sorption data were analyzed, the Modified Chung–Pfost equation was the best. However, when the GAB isotherm was adjusted at each temperature, a higher quality of agreement was obtained compared with the other isotherms, demonstrating the adequacy of GAB model to describe the experimental data of EMC–ERH for amaranth.

Adsorption isotherms of barley at low and high temperatures

Thirty-three measurements of adsorption equilibrium moisture content (EMC) for barley were experimentally determined using a constant environment chamber for various combinations of air relative humidity (48.2–88.6%) and temperature (5.7–46.3 °C). A thin-layer technique was used to obtain uniform re-wetting. Each test required from 4–6 days to attain dynamic equilibrium moisture contain. Four commonly used: three-parameter EMC/ERH (equilibrium relative humidity) equations, modified Henderson, modified Chung–Pfost, modified Oswin and modified Halsey, were evaluated for their ability to fit the experimental EMC/ERH data using non-linear regression techniques. Comparisons were made on the basis of standard error of estimate (SEE), residual sum of squares (RSS) and residual plots. The comparison showed that the modified Chung–Pfost equation was the most appropriate equation for modeling the EMC/ERH adsorption isotherms of barley. The coefficients both for EMC as a function of ERH and temperature, and ERH as function of EMC and temperature are given. The adsorption EMC data obtained in this work agree with previous published data. The equations were fitted to EMC/ERH data obtained at a wide range of temperatures and therefore will be helpful for future work on drying, re-wetting and storage of barley.

Modelling the water sorption isotherms of yoghurt powder spray

Moisture sorption isotherms of yoghurt powder spray were determined using a gravimetric dynamic method with continuous recording of changes in sample weight. Equilibrium data for adsorption and desorption of water from yoghurt powder spray were investigated at ambient temperatures in the range of 20-40 °C and water activity ranging from 0.40 to 0.99. Sorption capacity decreased as temperature increased. Four models available in the literature (Chung-Pfost, Halsey, Henderson and Oswin) were evaluated by determining the best fit to the experimental data. The modified Chung-Pfost equation was found to be a good model for moisture adsorption and desorption of yoghurt powder spray. The critical value of equilibrium moisture content (EMC) of samples tested, corresponding to the water activity equal 0.6, was 8.1-8.9% (wet basis, w.b.) at the temperature of 20 °C.

MODELLING ADSORPTION EQUILIBRIUM MOISTURE CHARACTERISTICS OF ROUGH RICE

Equilibrium Moisture Content (EMC) data for medium rough rice grain, Lido variety were obtained by equilibrating rice samples at different Equilibrium Relative Humidities (ERH) and Temperatures. The employed models to fit the data were GAB, modified Chung-Pfost, modified Halsey, Modified Henderson, and modified Oswin. The data were evaluated using the standard error of moisture content, mean relative standard error (%P) of the model and the correlation coefficient r2. The GAB model by indirect regression described the EMC the best, however its parameters lacked of physical meaning. The modified Chung-Pfost and modified Henderson equations presented a similar fit of the EMCERH relationships. The modified Chung-Pfost equation had lower residual values than the modified Henderson equation and was considered the best model to explain the EMC-ERH relationships.

Moisture desorption isotherms of medium-grain rough rice

Moisture desorption isotherms (EMC/ERH) of medium-grain rough rice (Japonica variety) were determined using a constant environment chamber for various combinations of air temperature (11.8–51.0°C) and relative humidity (37.1–89.7%). The initial moisture contents were in the range of 24.7–41.6% dry basis. A thin-layer technique was used to achieve uniform drying. Each test was continued until the moisture content change in 24 h was less than 0.1% dry basis. The final moisture content was considered as the dynamic equilibrium moisture content. Four three-parameter EMC/ERH equations, the modified Henderson, modified Chung–Pfost, modified Oswin and modified Halsey equations, were compared for their ability to fit the experimental EMC/ERH data. The residual sum of squares (RSS) and standard error of estimate (SEE) were adopted as the criteria to evaluate the fitting performance of the models. The modified Chung–Pfost equation was identified as the most appropriate equation for representing the EMC/ERH desorption isotherms of rough rice. Coefficients for equilibrium moisture content as a function of equilibrium relative humidity and temperature are given. The EMC/ERH data obtained in this study agreed well with previously published data. However the average isotherm, combining desorption and adsorption data, of ASAE does not predict the desorption EMC of rough rice accurately.