Moisture sorption isotherms of sorghum malt at 40 and 50º C (original) (raw)
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Moisture sorption isotherms of sorghum malt at 40 and 50°C
Journal of Stored Products Research, 2006
The desorption and adsorption equilibrium moisture isotherms of sorghum malt at the temperatures of 40 and 50 1C, 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.
Moisture sorption isotherms of Nigerian millet at varying temperatures
Journal of Food Engineering, 1990
Moisture sorption characteristics of millet at 2o"C, 25°C and 40°C were studied over a range of water activity 0. &I-0*98. A static gravimetric method was employed and five sorption models were used in the analysis. At the same water activity, moisture adsorbed or desorbed reduced with temperature. The Chung-Pfost model gave the best fit to the experimental data with or without coupling the temperature effect. 283 Journal of Food Engineering 0260-8774/90/$03.50 -0 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
Sorption in 2020s
Moisture sorption characteristics of agricultural and food products play important roles in such technological processes as drying, handling, packaging, storage, mixing, freeze-drying and other processes that require the prediction of food stability, shelf life, glass transition and estimation of drying time and texture and prevention of deteriorative reactions. They are useful in the computation of thermodynamic energies of moisture in the products. An understanding of moisture sorption phenomena in products, moisture sorption isotherm (MSI) determination techniques and moisture sorption isotherm model evaluation procedures would be useful in the development or selection, modeling and controlling as well as optimization of appropriate processes to make for enhanced efficiency. The phenomena addressed in this chapter are equilibrium moisture content (EMC)-water activity (a w) relationships and MSI types, temperature influence on isotherms and occurrence of moisture sorption hysteresis. MSI measurement techniques highlighted are the gravimetric, vapor pressure manometric (VPM), hygrometric and inverse gas chromatographic and the use of AquaLab equipment. Commonly used moisture sorption isotherm models (BET, GAB, modified GAB, Hailwood-Horrobin, modified Hailwood-Horrobin, modified Halsey, modified Henderson, modified Chung-Pfost and modified Oswin) were selected, and their evaluation procedures using moisture sorption data were outlined. Static gravimetric technique involving the use of saturated salt solution appears to be the most widely used and recommended method of determining the EMC of agricultural and food products. Most of the MSI models can be fitted to moisture sorption data thorough linearization by logarithmic transformation, while others can be solved using such expression as second-order polynomial. Model goodness of fit can be determined using standard (SE) error of estimate, coefficient of determination (R 2), mean relative percentage deviation (P) and fraction explained variation (FEV). The acceptance of a model depends on the nature of its residual plots. A model is considered acceptable if the residual plots show uniform scatter around the horizontal value of zero showing no systemic tendency towards a clear pattern. A model is better than another model if it has lower SE, lower P, higher R 2 and higher FEV. Although it appears as if a generalized MSI model is yet to exist, it is recommended that the Ngoddy-Bakker-Arkema (NBA) model should be given thorough going and extensive testing on the MSI of different categories of food as it could prove true to its generalized model posture due to the fundamental nature of its derivation.
Mathematical Models for Moisture Sorption Isotherms of Barley and Wheat
Moisture sorption isotherms play an essential role in preservation and storage of dehydrated foods. To study the behavior of different cereals (wheat, barley), in a certain equilibrium static environment, gravimetric methods were applied for temperatures ranging between 16 and 25°C and water activities from 0.533 to 0.909. The moisture isotherms were sigmoid shaped and showed a clear temperature dependence of water activity (aw). GAB and a second order polynomial equation were used to model the experimental data.
Moisture Sorption Isotherms of Sesame Flour at Several Temperatures
Moisture equilibrium data (adsorption and desorption) of sesame flour were determined using the static gravimetric method of saturated salt solutions at three temperatures, 10, 25 and 40°C. The range of water activities for each temperature was between 0.11 and 0.85. Equilibrium moisture content decreased with the increase in storage temperature at any given water activity. The experimental data were fitted by five mathematical models (modified Oswin, modified Halsey, modified Chung-Pfost, modified Henderson and Guggenheim-Anderson-de Boer (GAB)). The GAB model was found to be the most suitable for describing the sorption data. The monolayer moisture content was estimated using the Brunauer-Emmett-Teller equation.
Moisture sorption characteristics and modeling of energy sorghum (Sorghum bicolor (L.) Moench)
Journal of Stored Products Research, 2013
Long-term low cost storage of whole-stalk lignocellulosic energy sorghum biomass (specialized forage varieties of Sorghum bicolor (L.) Moench) is essential for the feedstock's successful role as a dedicated energy crop for ethanol production. As an alternative to expensive ensiling methods, aerobic storage of S. bicolor (L.) Moench biomass in traditional rectangular bale formats could alleviate feedstock supply costs if material deterioration in storage could be minimized. Moisture desorption and adsorption isotherms for S. bicolor (L.) Moench were created at 15 C, 20 C, 30 C, and 40 C with water activities from 0.1 to 0.9 using the dynamic dew-point method. Sorption isotherms were modeled using four temperature dependent and three temperature independent equations. The relationship between equilibrium moisture content and water activity was found to decrease with increasing temperatures. GAB (GuggenheimeAndersonede Boer) monolayer moisture content and the moisture content at which microbial activity becomes limited were found to range from 5.6% db to 10.4% dry basis (db) and 12.0% db to 18.4% db, respectively. The net isosteric heat of sorption was calculated using the ClausiuseClapeyron equation and determined to be higher for desorption than adsorption with both trends decreasing exponentially at increasing levels of moisture content. The differential entropy of S. bicolor (L.) Moench was shown to exhibit a log normal relationship with moisture; peaking near the monolayer moisture content. The results of the study indicate that aerobic storage of energy sorghum biomass may be similar to other herbaceous feedstocks should extensive drying occur before entering storage.
Sorption Isotherms of Barnyard Millet Grain and Kernel
Food and Bioprocess Technology, 2009
The moisture sorption isotherms of grain and kernel of barnyard millet (Echinochloa frumentacea) were determined at 20, 30, 40, and 50°C. A gravimetric static method was used under 0.112-0.964 water activity (a w) range for the determination of sorption isotherms. The models were compared using the coefficient of determination (r 2), reduced chi-square (χ 2) values, and on the basis of residual plots. In grain, modified Chung-Pfost (r 2 >0.99; χ 2 <0.7) and modified Oswin (r 2 >0.99; χ 2 <0.55) models were found suitable for predicting the M e-a w relationship for adsorption and desorption, respectively. Modified Henderson model was found to give the best fit (r 2 >0.99 and χ 2 <0.55) for describing the adsorption and desorption of the kernel. The isosteric heat, calculated using Clausius-Clapeyron equation, was varied between 46.76 and 61.71 kJ g −1 mol −1 at moisture levels 7-21% (d.b.) for grain and 47.11-63.52 kJ g −1 mol −1 at moisture level between 4% and 20% (d.b.) for kernel. The monolayer moisture content values ranged from 4.3% to 6% d.b. in the case of adsorption of barnyard millet grain and 5.2-6.6% d. b. in the case of desorption at the temperature ranges of 50-20°C. The monolayer moisture values of barnyard millet kernel ranged from 4.4% to 6.67% d.b. in adsorption and 4.6% to 7.3% d.b. in desorption in the temperature ranges of 50-20°C. Keywords Sorption isotherm. Barnyard millet. Equilibrium moisture content. Water activity. Isosteric heat. Monolayer moisture Nomenclature A, B, C constants used in sorption models P, q, r constants used in monolayer moisture content models a w water activity, decimal ΔH latent heat of vaporization of pure water, kJ mol −1 (43.53 kJ mol −1 at 35°C) M moisture content, % (d.b.) M e equilibrium moisture content, % (d.b.) M ex experimental equilibrium moisture content, decimal M pr predicted equilibrium moisture content, decimal n number of constants N number of observation Q st isosteric heat sorption, kJ g −1 mol −1 q st net isosteric heat of sorption, kJ g −1 mol −1 R universal gas constant, kJ mol −1 K −1 (0.008314 kJ mol −1 K −1) r 2 coefficient of determination T temperature, K χ 2 reduced chi-square m o monolayer moisture content, % (d.b.) t temperature,°C
Journal de Physique IV (Proceedings), 2004
This work is focused on some properties of dried apple (Red Chief) and carrot (Misky). Water sorption isotherms of carrot and apple were investigated at three temperatures: 30, 40 and 60°C, corresponding to drying temperatures, by the static method consisting of the use of different sulphuric acid solutions. Guggenheim-Anderson-de Boer (G.A.B) model is found to describe the experimental curves better than Henderson, Hasley and Oswin models with a correlation coefficient superior to 0.97 for both products. The hysteresis phenomenon was clearly observed in the case of apple isotherms. The experimental data were also used to determine the isosteric enthalpy of desorption of apple and carrot. The isosteric enthalpy of desorption decreased with increase in moisture content and the trend became asymptotic.
Water sorption isotherms and thermodynamic properties of pearl millet grain
International Journal of Food Science & Technology, 2010
The water sorption isotherms of pearl millet grain and the thermodynamic properties obtaining during the process of drying pearl millet were examined. Equilibrium moisture content (X eq) was determined under several temperature (T) and relative humidity (RH) conditions. The X eq data were correlated by six mathematical models. The modified Henderson was the model that best fitted the experimental data. The X eq decreased with an increase in T at constant RH. Hysteresis was also studied; increasing T led to a decrease in this phenomenon. Integral isosteric heat of sorption (Q st), differential entropy (DS) and the enthalpy-entropy compensation theory were studied. Q st values decreased when X eq increased because the Q st values of adsorption were lower than Q st desorption values. The values of DS decreased with increases in X eq , because DS values were higher for desorption than for adsorption. The enthalpy-entropy compensation theory is valid for describing the water sorption processes of pearl millet grain.