Moisture-Sorption Study of Dried Date Fruits (original) (raw)
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Sorption Isotherms Behaviour of Some Egyptian Date Fruit Varieties
World Journal of Dairy & Food Sciences, 2013
Moisture content of the date fruits is the limiting factor influencing their storage stability and shelf life. Therefore, the aim of this work was to determine the equilibrium moisture contents of Egyptian Sewi and Amry date fruits at different water activity values and to establish sorption isotherms curves for these fruits. Fresh date fruits were dried in a solar drier and subjected to different relative humidity atmospheres to establish their equilibrium moisture contents values. The static method, with standard saturated salt solutions, was applied to obtain equilibrium moisture contents at constant temperature (25°C±3) in the range of a = 0.11 to w 0.85. The obtained sorption isotherms curves were subjected to modeling by several isotherms equations such as Henderson, Halsey, Iglesias & Chirife and GAB equations. The results showed that Amry variety contained higher sugar content (69.42%) compared with Sewi variety (56.4%). The initial moisture contents for the dry Sewi and Amry date varieties were 15.78% and 22.04% respectively. At all water activity levels, equilibrium moisture contents of Amry date variety were higher than those of Sewi date variety. The optimum water activity level for their safe storage was 0.54 and 0.65, respectively. Sorption isotherms curves of the two date varieties took the sigmoid, "j" type typical for sugar foods. Evaluation of the different sorption isotherms models was carried out statistically according to their values for correlation coefficient (R-value), residual sum of squares 2 (SSR), error sum of squares (SSE) and mean relative percentage deviation modulus (E%). The GAB model was found to be the most suitable equation to represent the sorption data of the date fruits, due to its high R-values (0.892 to 0.967) and to the lowest E%-values (6.77% and 5.01%), respectively. The monolayer 2 moisture content (M) was in the range of 0.05 to 0.059g H O/g DM with Amry variety being have higher M o 2 o value than Sewi variety.
ANN modeling of water sorption isotherm of date fruits acquired by dynamic vapor sorption
2015
Water sorption isotherms of four Date cultivars at temperatures range of 10 to 80°C with increments of 10°C were determined separately over ranging relative humidity from 10 to 90% using an automatic, gravimetric analyzer. The significant differences in equilibrium moisture contents (EMC) of cultivars can be attributed to chemical composition and structure of each cultivar. The adsorption / desorption experimental data for each cultivar were fitted by modified GAB, modified Halsey, modified Smith and modified Oswin models. The modified Oswin was found as best model to describe adsorption isotherm behavior while modified Halsey was the best model to describe desorption isotherm. In addition, many configurations of artificial neural networks (ANN) were examined to obtain the best one to predict either EMC adsorption isotherm or EMC desorption isotherm for each cultivar. Correlation coefficient (R), c2, root mean square error (RMSE) and relative percent errors (PE) were used to measure...
Moisture sorption isotherms of mango slices
Moisture sorption isotherms (desorption and adsorption) of mango fruit, var. Kent, were investigated using the standard static gravimetric method. The sorption isotherms were obtained at the temperatures of 20, 30 and 40 °C and in the water activity (a w ) range from 0.111 to 0.813. The sorption isotherms of mango fruit followed type III (J-shaped) isotherms, characteristic of high sugar products. The reverse temperature effect occurred at a w >0.75, resulting in a crossing over of the sorption curves for the adsorption isotherms only. The application of the GAB model to the experimental data, using direct nonlinear regression analysis, provided agreement between the experimental and predicted values. The GAB model parameters monolayer moisture content (Mo) and heat of sorption for monolayer (C) were found to decrease with increasing temperature, whereas the heat of sorption for multilayer (K) was found to increase with increasing temperature. A hysteresis effect was observed at all three temperatures studied.
Sorption isotherms and moisture sorption hysteresis of intermediate moisture content banana
Journal of Food Engineering, 2008
Sorption isotherms of dried or intermediate moisture content (IMC) products are most important to model moisture uptake during storage and distribution. Working isotherms of IMC bananas were determined at five different temperatures (10, 15, 20, 30 and 40°C). Desorption and adsorption isotherms were determined at 10 and 40°C. All the sorption curves were found to be Type II, with non-zero moisture content (approximately 3-9% db for different temperatures) when the water activity was zero. Different models were fitted to the data and it was found that the best results were obtained with a modified Freundlich equation (valid from 0.06 to 0.76 water activity). The dependence of the models constants on temperature was investigated and the secondary models were built accounting for the effect of a w and temperature on the samples moisture content (R 2 = 99%). Hysteresis was observed at 10°C and 40°C, but the effect was greater at 10°C. The net isosteric heat of sorption (working isotherms) varied from 0.85 kJ g À1 mol À1 to 7.67 kJ g À1 mol À1 , decreasing with increasing moisture content. This effect was well described by an exponential function (R 2 > 99%). These results provide reliable experimental data on sorption isotherms which is important for designing an optimized packaging system.
Estimation of Moisture Sorption Isotherms of Mango Pulp Freeze-dried
system
The static gravimetric method, along with different saturated salt solutions, was used in a range of water activity (a w) of 0.11-0.88, and at 288.15, 298.15 y 308.15 K, to obtain sorption isotherms of freeze-dried pulp of mango. At a given a w the results show that the moisture content decreases with increasing temperature. BET, G.A.B, Halsey, Henderson, Oswin and Smith were evaluated to determine the best fit for the experimental data. A nonlinear regression-analysis method was used to evaluate the constants of equations. The BET and GAB models were the most suitable to described the sorption curves; the monolayer-content values for the sorption at different temperatures are calculated. The isosteric sorption heat was determines for adsorption of freeze-dried pulp of mango using the relevant thermodynamic relations (i.e., Clausius Clapeyron equation).
Desorption Isotherms and Isosteric Heat of Three Tunisian Date Cultivars
Food and Bioprocess Technology, 2007
The sorption isotherm of three Tunisian cultivars, Allig, Kentichi, and Deglet Nour, were obtained at 40, 60 and 80°C. The static gravimetric method was used, according to the COST 90 recommendations. The overall shape of the curves describing the water content as a function of water activity was typical of sugar-rich materials. A difference between varieties exists for the sorption isotherm, thus for the drying behavior. Data were compared with respect to several isotherm models. It was found that the GAB and the BET equations could satisfactorily represent the sorption data up to about 0.9 relative humidity. Through the BET equation, monolayer moisture content was calculated for the isotherm zone corresponding to monomolecular adsorption. In addition, isosteric heat of sorption was determined from sorption data using the Clausius-Clapeyron equation.
ETP International Journal of Food Engineering
The drying characteristics and moisture sorption isotherm (MSI) of batuan, an underutilized and commonly neglected fruit that is often found in tropical climate countries like the Philippines, were investigated. Whole and sliced fruits were dried using a convection dryer set at 50°C. The constant-rate period is absent from the drying curve, and the bulk of drying happened in the falling rate period. Drying data was fitted in four drying models, namely: Newton (Lewis), Handerson and Pabis, Page, and Logarithmic. The goodness of the fit of the model was evaluated by comparing the values of coefficient of determination (R 2) and Root Mean Square Error (RMSE) between the observed and predicted moisture ratios. Page model provided the best fit in describing the drying behavior of both whole and sliced fruits, with highest R 2 of 0.9867 and 0.9994 and lowest RMSE of 0.0360 and 0.0078, respectively. MSI of the dried fruits was meanwhile determined at 25°C using the static gravimetric method, and was fitted in seven different isotherm models, namely: Brunauer-Emmet-Teller (BET), Guggenheim-Anderson-DeBoer (GAB), Adam and Shove, Halsey, Oswin, Henderson-Thompson, and Peleg. Fitness of models was evaluated using the values of R 2 standard error (SE) and mean relative percentage deviation modulus (P). Among the models, Halsey showed the best fit for MSI with highest R 2 of 0.9946, SE of 0.0185 and P of 7.0207%. Using the same model, the monolayer value of the dried batuan fruits was determined as 0.1542 g H2O/g solid, with corresponding water activity (a w) of 0.3478.