A Model for Describing the Water Sorption Behavior of Foods (original) (raw)
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New BET Type Multilayer Sorption Isotherms. Part II: Modelling Water Sorption in Foods
Two equations derived from a modification of BET theory were evaluated for goodness of fit over 74 experimental food isotherms representing spices, fruits, vegetables, meats, proteins, starchy foods and mi/k products. About 77% ofthe isotherms represented principally by starchy foods, proteins meatsand spices obeyed to Eqn [1}. Such isotherms when compared to BET equation showed lower sorption capacity than BET at high water activity. On the contrary, 23% of the products formed principally by high-sugar foods, i.e. fruits and some vegetables, whose sorption capacity resulted much higher than BET isotherm for water activities above 0.45 were adequately correlated by Eqn [2j.
Prediction of the effect of temperature on water sorption isotherms of food material
International Journal of Food Science & Technology, 1976
An empirically modified two-parameter multilayer adsorption equation is shown to take into account the effect of temperature on the water sorption isotherms of some food materials. Characteristic parameters of the sorption equation for each food tested are presented. The equation should be of value in predicting the shelf life behaviour of food products at different storage temperatures.
Water sorption isotherms of foods and foodstuffs: BET or GAB parameters
Journal of Food Engineering, 2001
The aim of the present work is to solve the dilemma about the dierences between the values of the monolayer and the energy parameters obtained by the regression of water sorption data by foods and foodstus using the Brunauer, Emmett and Teller (BET) two-parameter isotherm or the Guggenheim, Anderson and de Boer (GAB) three-parameter isotherm. It is shown that the GAB values are more general and have more physical meaning, and that the two BET parameters can be calculated in terms of the three GAB-parameters. Furthermore, the marked dependency of the BET constants on the regression range as well as the typical upswing at higher water activities observed in the so-called BET plots are explained. It is also shown that the rough agreement early reported by L. Pauling, J. Am. Chem. Soc. 67 (1945) 555±557 between monolayer values and number of polar groups in the aminoacid side chain in several proteins is enhanced if the former are evaluated by means of the GAB sorption equation. Ó
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.
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 of water on cereal-bread type dietary fibers
Journal of Food Engineering, 1993
A study involving the water sorption characteristics of cereal-bread type food fibers was conducted, using a gravimetrical adsorption apparatus. Water adsorption data for four dietary fibers, corn bran, wheat bran, oat fiber and rice fiber, were measured at 278,288,298 and 310 K. The results showed that the adsorption of water vapor on these fibers are primarily due to physical forces, and all fibers investigated exhibited energetically heterogeneous surfaces. It was found that the distribution of the major components of the dietary fiber has an impact on the fibers water sorption capacity. The isotherm data were correlated by using the BET and GAB multilayer adsorption models. The BET equation gave accurate correlations for up to 35 to 40% of the saturation pressure, while the GAB equation provided much better correlation of the data for the higher relative pressures. NOTATION '4 Solid surface area (m'/Kg) C Constant defined by eqn (4) k Constant defined by eqn (6) m Molecular weight (Kg/Kg mol) M Equilibrium uptake (mg H,O/lOO mg solid) 1+,&n Monolayer adsorption capacity (mg H,O/l 00 mg solid) I;, Number of multilayers Equilibrium pressure (mm Hg)
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.
Journal of Food Engineering, 2007
In this paper we adapt (developed by us recently) the Generalised D'Arcy and Watt (GDW) model to the description of water vapour sorption on foodstuffs. We show that this simple formula can successfully describe the set of sorption isotherms measured on pineapple (in the range of temperatures 20-50°C) and reported in this journal by Hossain et al. [Hossain, M. D., Bala, B. K., Hossain, M. A., & Mondol, M. R. A. (2001). Sorption isotherms and heat of sorption of pineapple. Journal of Food Engineering, 48, 103-107].
Model analysis of sorption isotherms
LWT - Food Science and Technology, 2009
The equation developed by Blahovec and Yanniotis, which is based on surface adsorption and solution water, was applied for fitting experimental sorption data for starchy and high protein foods, fruits and vegetables, nuts, legumes, and seeds. Analysis of sorption isotherms shows that surface adsorption is more important than solution water in the isotherms for cereals, potatoes, legumes and seeds, while in vegetables, fruits, meat, milk products and some nuts solution water is more important. The ratio of solution water to surface adsorption increases as water activity increases, it is higher for the adsorption isotherm than the desorption isotherm at any water activity value and decreases as temperature increases.
Food Research International, 2009
Water sorption on foodstuffs is very important in different areas of food science engineering. However, usually measured range of relative humidity covers only two of three stages of water sorption mechanism i.e. polymolecular sorption and capillary condensation. Since in this range different water sorption models can fit the experimental data well it is hard to decide which model is the most correct. In this study the results of water sorption isotherms measured from low humidity levels on marjoram, dill, granulated garlic, semolina, skim milk powder and ground coffee are reported. They are fitted by the most popular models applied in food science (i.e. proposed by: Halsey, Lewicki, Henderson, Chung and Pfost, Ferro Fontan et al. and Guggenheim, Anderson and de Boer (GAB)). We also extend the study to the newest models successfully applied in food engineering, i.e. the generalized D'Arcy and Watt model (GDW) and the approach of the cooperative multimolecular sorption (CMMS). Finally, we discuss the limits of the models at low humidity levels, the possibility of reduction to Henry's law and we show the advantages and disadvantages of all approaches. It is concluded that among studied models the GDW equation seems to be the best for description of data in the whole range of relative humidity.