Prediction of the effect of temperature on water sorption isotherms of food material (original) (raw)
A New Model for Predicting Sorption Isotherm of Water in Foods
A new model for predicting sorption isotherms of type II and III based on the Polanyi theory is proposed. This model allows the prediction of the sorption isotherms at different temperatures from one experimental isotherm. The theoretical predictions of isotherms and isosteric heat were validated successfully using data from literature for twenty one foods. This method allows total experimental time and operation costs to be reduced.
Physica A: Statistical Mechanics and its Applications, 2015
Water sorption isotherms of foodstuffs are very important in different areas of food science engineering such as for design, modeling and optimization of many processes. The equilibrium moisture content is an important parameter in models used to predict changes in the moisture content of a product during storage. A formulation of multilayer model with two energy levels was based on statistical physics and theoretical considerations. Thanks to the grand canonical ensemble in statistical physics. Some physicochemical parameters related to the adsorption process were introduced in the analytical model expression. The data tabulated in literature of water adsorption at different temperatures on: chickpea seeds, lentil seeds, potato and on green peppers were described applying the most popular models applied in food science. We also extend the study to the newest proposed model. It is concluded that among studied models the proposed model seems to be the best for description of data in the whole range of relative humidity. By using our model, we were able to determine the thermodynamic functions. The measurement of desorption isotherms, in particular a gas over a solid porous, allows access to the distribution of pore size PSD.
Analysis of a Model for Water Sorption Phenomena in Foods
Journal of Food Science, 1982
The validity of the physical model on which the Hailwood and Horrobin (Trans. Far. Sot. 42B: 84; 1946) isotherm equation was developed was investigated. The results indicate that although the equation may tit sorption data for almost any type of food, it satisfies thermodynamic requirements (i.e. prediction of the temperature dependence) only for proteins and starchy foods. The results also show that plotting enthalpic changes against entropic changes for water sorption satisfies the enthalpy/entropy compensation phenomenon.
Adsorption isotherms of pear at several temperatures
Thermal Science, 2014
The moisture adsorption isotherms of pear were determined at 15 °C, 30 °C, and 45i°C using the standard static gravimetric method over a range of water activity from 0.112 to 0.920. The experimental data were fitted with isotherm equations recommended in ASAE Standard D245.5. In order to find which equation gives the best results, large number of numerical experiments were performed. After that, several statistical criteria proposed in scientific literature for estimation and selection of the best sorption isotherm equations were used. For each equation and experimental data set, the average performance index was calculated and models were ranked afterwards. After that, some statistical rejection criteria were checked (D'Agostino-Pearson test of normality, single-sample run test and significance and precision of the model parameters). The performed statistical analysis shows that the Guggenheim-Anderson-de Boer equation has the highest value of average performance index, but higher correlation between pair of parameters leads to lower precision of estimated parameters.
ADSORPTION ISOTHERMS OF PEAR AT SEVERAL TEMPERATURES by
2016
The moisture adsorption isotherms of pear were determined at 15 °C, 30 °C, and 45i°C using the standard static gravimetric method over a range of water activity from 0.112 to 0.920. The experimental data were fitted with isotherm equations recommended in ASAE Standard D245.5. In order to find which equation gives the best results, large number of numerical experiments were performed. After that, several statistical criteria proposed in scientific literature for estimation and selec-tion of the best sorption isotherm equations were used. For each equation and ex-perimental data set, the average performance index was calculated and models were ranked afterwards. After that, some statistical rejection criteria were checked (D'Agostino-Pearson test of normality, single-sample run test and significance and precision of the model parameters). The performed statistical analysis shows that the Guggenheim-Anderson-de Boer equation has the highest value of average per-formance index, but...
2012
Moisture adsorption isotherms of amorphous cassava starch were determined at temperatures of 5, 30 and 45°C using a dynamic vapour sorption technique (DVS). Thirteen relative humidity values were set in a range from 0 to 94.5% for each temperature. Type-II isotherms were obtained in all cases. The effect of increasing temperature on the whole water activity range of the adsorption isotherms showed a decrease in the equilibrium moisture content. The data did not display any isotherm cross-over with temperature at elevated water activities as previously reported for this product using thymol as an antimicrobial agent. Different isotherm models were used to describe the sorption behaviour of amorphous cassava starch. The modified GAB model exhibited the best statistical results. For the temperature range studied, the A, B, C and D parameters in this model ranged from 0.127-0.255, 6.93-53.0, 0.493-0.0181 and 0.137-0.503, respectively. Monolayer water content ranged from 0.0547 to 0.0727 g.g -1 of dry solids using the BET equation and 0.0433 to 0.0637 g.g -1 of dry solids, when the GAB model was used. The net isosteric heat of sorption obtained ranged from 0.8 to 6.9 kJ.mol -1 in a moisture content range of 10-27 g.100 g -1 of dry solids. Contrary to previous research works no antimicrobial agents that could alter isotherms were used in isotherm determinations. Therefore, moisture adsorption data
Journal of Food Engineering, 2007
This paper points out the importance of the multitemperature fitting procedure in description of water sorption on foodstuffs. The data tabulated in literature (water sorption at different temperatures on: chickpea seeds, lentil seeds, potato and on green peppers) were described applying the BET, GAB and recently proposed GDW models. Our results explain total failure of the first model in description of multitemperature data and the similarities between the GAB and GDW are shown. Finally the general mechanism of water sorption on foodstuffs is proposed. This mechanism can be of the GAB or GDW type, depending on the arrangement and features of the primary water sorption sites. If the geometrical constraints for creation of the BET -like type clusters do not occur on surface, and if each from primarily sorbed water molecules convert only into one secondary surface site, one can say that the mechanism follows the GAB scenario (as for example in the case of lentil seeds). Contrary, in the case of rough or porous surfaces, where there are the geometric constraints for creation of secondary sites (for example sorption on chickpea seeds), and/or where one primary site produces more than one secondary site (potato and green peppers), the mechanism of water sorption is of the GDW type.
An equation for correlating equilibrium moisture content in foods
International Journal of Food Science & Technology, 2007
The object of this study was to show that a multilayer adsorption equation, originally developed for physical adsorption on nonuniform surfaces, can be used to describe reasonably well the water sorption isotherms of a great variety of foods and food components. Apparently, the proposed equation has not been applied to the food area before. Characteristics parameters of the adsorption equation for each of the foods tested were computed and a statistical analysis of its applicability was made.
Journal of Food Science, 2006
The water activity (aw) of eight salt solutions was determined at three temperatures (25, 30, 45°C) using a pressure transducer-vapor pressure manometer. The aws of the salts showed a decrease with increasing temperature, which was explained with the help of a thermodynamic equation. This is opposite to the increase in aw with increase in temperature for foods. Moisture sorption data for fish flour and cornmeal were obtained at 25–65°C. The Guggenheim-Anderson-deBoer model was evaluated and shown to be comparable to the Brunauer-Emmett-Teller model for prediction of the monolayer. Product was equilibrated at different aws at 25°C then subsequently shifted to 30°C and 45°C in a sealed chamber. The resultant a, change, measured on the Kaymont-Rotronics, was predictable from the isotherm at each temperature using the Clausius Clapeyron relationship.
Equations for fitting water sorption isotherms of foods: Part 1 - a review
International Journal of Food Science & Technology, 2007
The purpose of the present work is to present a review of literature on equations for fitting water sorption isotherms of foods and food products. Twenty-three equations, which have been proposed in the literature for correlating equilibrium moisture content in food systems, have been compiled and analysed. Their origin, range of applicability (both to type of food and water activity) and use are discussed. It is hoped that this critical compilation may be a useful guide for those researchers interested in the mathematical description of the water sorption isotherms of foods.