The moisture content/equilibrium relative humidity relationship of macaroni

The moisture content/equilibrium relative humidity relationship obtained at three temperatures is reported. The safe storage moisture content was found to be between 12 and 12·8 per cent, depending on the treatment of the macaroni. There is no hysteresis between the adsorption and desorption isotherms. In the normal storage range of moisture content, the effect of temperature on the equilibrium relative humidity (e.r.h.) was 3–4% r.h., or 0·7 per cent moisture content for every 10°C change in temperature. Samples of macaroni exposed to high controlled r.h.'s took 7 days to reach constant weight. A heavy duty polythene container with a tight fitting lid investigated as to its efficiency in providing an adequate water vapour barrier proved satisfactory. Virtually no change in moisture content of the packed macaroni took place after exposure to 92% r.h. and 30°C for 100 days.     

A mean moisture content-equilibrium relative humidity relationship for nine varieties of wheat

A mean moisture content-equilibrium relative humidity relationship for nine varieties of wheat at 25°C is presented, for which the curves were fitted by eye. The mean safe storage moisture content in equilibrium with 70% relative humidity (r.h.) for all the wheat varieties adsorbing moisture was 14.7% (wet weight basis) but if varietal differences and errors in measurement are taken into account, the moisture content of stored wheat may need to be as low as 13% to be safe from attack by mites. The hysteresis between adsorption and desorption reached a maximum of 0.7% moisture content at 40–50% r.h. Hysteresis was found to be statistically significant up to 75% r.h. Equilibrium moisture contents were calculated from data transformed using the Chung and Pfost equation and compared with the measured moisture contents.     

The relationship between moisture content and equilibrium relative humidity of pig feed

The moisture content-equilibrium relative humidity relationships at 5, 15 and 25°C of 3 pig meals and pellets made mostly from barley meal and wheatings, with various proportions of soya meals, were very similar to each other. The moisture content in equilibrium with 70% r.h. at 25°C was about 14%, similar to that for cereal grains but these pig feeds should be stored at or below 12% mositure content at this temperature, to avoid the risk of the development of mites.     

The influence of the method used for moisture adjustment on the equilibrium relative humidity of stored products

This paper examines some possible causes of differences in the magnitude of the hysteresis effect reported by different workers when studying the moisture content/equilibrium relative humidity relationship of stored products.Three techniques of changing the moisture content during sample preparation were used on Cappelle wheat and the results compared. It was found that the position of the adsorption isotherm was not affected by these techniques, but the position of the desorption isotherm was. At 35% r.h. the moisture content was 0·8 per cent higher on the desorption isotherm by one technique than by the other two. This is equivalent to a difference of 6% r.h.The effect of a fungistat, propylene oxide, on the equilibrium relative humidity, was also included. This caused a ‘reverse’ hysteresis, in that the moisture content at a given relative humidity was lower on the desorption isotherm than on the adsorption isotherm instead of higher, as with previous techniques.     

Equilibrium moisture content of groundnut and chillies

Hygroscopic material, when it comes into contact with atmospheric air, desorps or absorps the moisture from the surroundings until it reaches equilibrium. In the present study, groundnut and chillies were dried in a controlled air supply (at a particular temperature and relative humidity). The equilibrium moisture content (e.m.c.) and relative humidity (r.h.) relationships were studied at different temperatures. Values of constants c and n of Henderson's equation were computed and desorption isotherms were drawn for groundnut components and chillies. It was observed that e.m.c. depends upon type of material, the temperature and r.h. of the air.     

Effect of sodium chloride, sodium nitrite and temperature on desorption isotherms of previously frozen beef

Moisture desorption isotherms of beef were determined in the relative humidity range of 23 to 90% at 5, 15 and 25 °C and at 2.5% NaCl and 2.5% NaCl + 150 ppm NaNO₂ content. Desorption isotherms were found to be typical type II sigmoid. The water content at equilibrium was higher in beef with NaCl and NaCl + NaNO₂ than control samples. Experimental data were fitted to various mathematical models and it was found that the Peleg model was best in describing the equilibrium moisture content relationship for beef samples over the entire range of temperatures. The net isosteric heat of sorption was estimated from equilibrium desorption data, using the Clausius-Clapeyron equation. Isosteric heats of desorption were found to increase with decreasing moisture content.     

Technical note: Sorption isotherms and monolayer moisture content of raw peas, and peas dehydrated after pressure cooking

The moisture sorption isotherms of raw and pre-cooked Century, MP 888 and MP 889 peas at 10, 25 and 40°C were determined by the standard salt solution technique. Pea cultivars, although different in composition, did not differ in equilibrium moisture content. At 40°C and in the water activity range 0.50 a _w 0.90, the sorption capacity of raw peas was higher than that of pre-cooked peas. All adsorption-desorption isotherms were of sigmoid shape and the quantity of sorbed water, at a given relative humidity, increased as the temperature was decreased. The monolayer moisture content of pre-cooked dehydrated peas stored at 40°C was 6.2%, with corresponding equilibrium relative humidity value of about 27%.     

Moisture sorption isotherms of some Nigerian food grains

A fluidized bed apparatus that can be used to determine moisture sorption isotherms of granular food products is described. This apparatus was used to obtain moisture sorption isotherms for maize, cowpeas, groundnuts and soyabeans at temperatures of 30, 40 and 50°C. Hysteresis was observed in the isotherms for the four products and the equilibrium moisture content was lower for the oily grains (soyabeans and groundnuts) at the same value of relative humidity. The Hailwood and Horrobin equation was used to correlate the experimental data and the values of the correlating constants are tabulated. The Brunauer, Emmett and Teller equation was also used to obtain estimates of the monolayer water content for the four grains.     

基于不同数学模型的魔芋水分吸湿等温线模拟

根据吸附原理,采用静态调整环境湿度法,测定了魔芋在20、30、40℃3个温度下,0%~98%水活度范围内的平衡含水率,绘出魔芋的吸湿等温线。结果显示,魔芋的吸湿等温线属于II型等温线;在一定的水活度下随着温度的升高魔芋的吸附能力下降。并以平均相对误差和决定系数为评价指标,用八种数学模型对实验数据进行拟合,结果表明Peleg模型对魔芋的吸湿等温线拟合效果最好。      

Moisture content/relative humidity equilibrium of some cereal grains at different temperatures

The concept of the equilibrium relative humidity (e.r.h.) of a product as a measure of storage potential is discussed. It is stressed that whilst moisture content gives an estimate of the amount of water in a product it does not, by itself, indicate the biological activity, or potential activity, of the product. Graphs are presented giving the e.r.h., at a given moisture content, for different temperatures of a soft wheat, barley, American yellow dent maize, flint maize grown in England, and tick beans (Vicia faba L.).     

Einfluß der Temperatur auf die Gleichgewichtsfeuchte bei konstanter relativer Luftfeuchte

Temperature influence on the equilibrium moisture content in case of constant relative air humidity. The possibility of determining the equilibrium moisture content of materials at different hygrothermal conditions by a smaller number of experiments is investigated. It has been established for a large number of foodstuffs that the equilibrium moisture content in case of constant relative air humidity depends linearly on the temperature. Two equilibrium isotherms are sufficient to determine the equilibrium moisture content of these foodstuffs at different temperatures and relative air humidities.     

Moisture Sorption Isotherms of Canola Meals, and Applications to Packaging

Moisture sorption isotherms were determined for defatted canola meal at 16, 22, and 34°C. The isotherms were fitted to the Guggenheim-Anderson-deBoer (GAB) sorption equation. This equation was then used to develop a packaging model that predicted the changes of moisture con-tent of canola meal under stated environmental and packaging conditions. The model was tested using Melinex 813 (12 μm) and Propafilm C (28 μm) packaging films at 86% relative humidity and 23°C. The GAB equation provided a good fit to experimental data (<3% RMS). The monolayer moisture content of the meal was 9.5%. The enthalpy of sorption of the monolayer at 22°C was 84.61 KJ/mol. The model predicted the time required by packaged canola to attain a selected moisture content ± 0.5 days.     

MOISTURE ADSORPTION BEHAVIOR OF BISCUITS FORMULATED USING WHEAT, OATMEAL AND PASSION FRUIT FLOUR

Moisture adsorption isotherms from a new biscuit considered as functional food were determined using a gravimetric static method at 25 and 40C and over a range of relative humidity from 0.112 to 0.903. The biscuit had 2.5, 3.3, 10.0 and 31.0% of ash, fiber, protein and fat, respectively, and 4.7% moisture content. The equilibrium moisture content of the biscuit (kg/kg) increased when the storage temperature at any given water activity ( A _w) was reduced. The experimental data were analyzed using different models, namely Guggenheim–Anderson–de Boer (GAB) (three-parameter relationships), Henderson and Oswin (both models with two parameters), which exhibited a sigmoid shape at the studied temperatures. The maximum isosteric heat of sorption was 21.6 kJ/mol, which exponentially decreased when the moisture content was increased. The GAB model was found to be the most suitable for describing the adsorption characteristics at the temperature and A _w range studied, according to the relative error and the coefficient determination.

PRACTICAL APPLICATIONS

This article describes the characterization of moisture adsorption behavior of a new biscuit considered as functional food. In general, the sorption behaviors of several foods have been studied extensively; nevertheless, a reduced number of published articles about biscuit sorption isotherms are found in the literature. The experimental data reported in this article may be important for the scientific community of the food science and technology. Isosteric heat of sorption is important for the determination of the binding strength of water to the food, as well as the amount of water present in the food.     

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 degrees 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 24h 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.     

A simple technique for the determination of humidity equilibria in particulate foods

An apparatus is described which incorporates a pump, a hygrometer and a sample of food. It can be used to determine the equilibrium relative humidity of the air between the food particles in three minutes. It has been used to determine the moisture sorption isotherms for maize, tea, cocoa, parchment coffee and green coffee at 28°C.     

Moisture relations of dried peas,shelled almonds and lupins

The relationship between moisture content and equilibrium relative humidity (e.r.h.) measured by a dew-point method, was determined over the range 30–90% r.h. for dried peas, shelled almonds and lupins at 15, 25 and 35°C. For dried peas the e.r.h. relationship was conventional, and at 70% r.h. and 25°C the equilibrium moisture contents were 14.8% when desorbing and 14.3% when adsorbing moisture. The relationship for three varieties of almonds was unusual in that there was little hysteresis between adsorption and desorption. The mean moisture content of the two, in equilibrium with 70% r.h. at 25°C was 5.9% for Moroccan sweet, 6.4% for Moroccan bitter and 6.8% for Californian sweet almonds. With dried peas and almonds the e.r.h. increased with temperature, and the moisture contents determined before and after e.r.h. determination were similar, which has been usual with stored products previously studied. However when the moisture of lupins was raised above 11% by adding water as a liquid, the moisture content after e.r.h. determination at 35°C was apparently lower than it had been just previously following e.r.h. determination at the lower temperatures. This implied loss of moisture was not detected when water was added in the vapour phase. At 70% r.h. and 25°C the equilibrium moisture contents were 12.3% when adding liquid water and 13.0% when water was added in the vapour phase.     

Effect of gamma-ray irradiation on modeling equilibrium moisture content of wheat

ABSTRACT:  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 γ-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.     

Equilibrium moisture content and sorption isosteric heats of five wheat varieties in China

The moisture sorption isotherm data of five Chinese wheat varieties were investigated via the gravimetric static method at five different temperatures (10, 20, 25, 30, and 35 °C) and relative humidity ranging from 11.3 to 96.0%. The sorption data of wheat decreased with an increase in temperature at a constant relative humidity (r.h.). The hysteresis effect was observed between adsorption and desorption isotherms. The width and span of the hysteresis loop decreased with increased temperature, but was not influenced by the hardness of wheat varieties. Six models, namely the Chen-Clayton (CCE), Modified BET (BET), Modified-Chung-Pfost (MCPE), Modified-Henderson (MHE), Modified-Oswin (MOE) and Strohman-Yoerger (SYE), were employed to describe the experimental data. The BET, MCPE and MOE models were selected to best describe the sorption isotherms of wheat in the ranges of 11.3-49.9, 11.3-96.0 and 11.3-96.0% r.h., respectively. The hygroscopic property difference between hard wheat (cv. ‘Longyuan’ and ‘Nanduan’) and soft wheat (cv. ‘Zhaozhuang’ and ‘Lumai’) was very small. The sorption isosteric heat of wheat decreased with an increase in moisture content until the dry bulb moisture content (m.c.) of 20% was reached, and then decreased smoothly with increasing moisture content. A big difference was found between adsorption and desorption isosteric heats of wheat below 20% m.c., but the sorption isosteric heat difference between hard and soft wheat isotherms was small.     

Moisture sorption isotherms and isosteric heat of sorption of leaves and stems of lemon balm (Melissa officinalis L.) established by dynamic vapor sorption

The equilibrium moisture contents (MC) of leaves and stems of lemon balm (Melissa officinalis L.) were determined separately at temperatures of 25, 35 and 45 °C over a stepwise increase of relative humidity (RH) ranging from 3 to 90% by an automatic, gravimetric analyzer (DVS system). Equilibrium was achieved within 6 h for most of the target values of relative humidity. The equilibrium moisture content of leaves was significantly higher than that of stems (p < 0.05). Differences in moisture sorption capacity between the leaves and stems can be attributed to chemical composition and structure of the tissues. Five three-parameter moisture sorption models (modifications of Chung–Pfost, GAB, Halsey, Henderson and Oswin) were tested for their effectiveness to fit the experimental sorption data. The modified Oswin equation was found to be the best model to describe the adsorption isotherms of both leaves and stems of lemon balm. The recommended MC values of leaves and stems for microbial safe storage at 25 °C were 0.124 and 0.113 kg water per kg dry solids, respectively. The net isosteric heat of sorption was computed from the predicted sorption data by applying the integrated form of the Clausius–Clapeyron equation.     

Equilibrium moisture content and heat of desorption of saffron

The equilibrium moisture contents of saffron (Crocus sativus L.) stigmas were determined experimentally using the standard gravimetric method at temperatures 30, 45 and 60 °C and water activity ranging from 11% to 83%. The sorption isotherm curves of saffron were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models GAB, modified Henderson, modified Chung‐Pfost, modified Halsaey and modified Oswin were tested to fit the experimental isotherm data. Modified Oswin and modified Henderson models were found acceptable for predicting desorption moisture isotherms and fitting to the experimental data, respectively. The isosteric heats of desorption, determined from equilibrium data using the Clausius‐Clapeyron equation, were found to be a function of moisture content. The net isosteric heat of desorption of saffron varied between 1.38 and 5.38 kJ mol^?1 at moisture content varying between 2% and 20% (d.b).