ISOTERMAS DE ADSORCION PDF

Sorption isotherms for oat flakes Avena sativa L. Medellin Colombia. These curves were modeled using six equations commonly applied in food. The quality of the fit was assessed with the regression coefficient r 2 and the mean relative percentage error MRPE.

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Sorption isotherms for oat flakes Avena sativa L. Medellin Colombia. These curves were modeled using six equations commonly applied in food. The quality of the fit was assessed with the regression coefficient r 2 and the mean relative percentage error MRPE. The best fit were obtained with the Caurie model with r 2 of 0. The equilibrium moisture presented a dependence on temperature in the studied a w range, as did the security moisture X S. Oat Avena sativa L.

Compared with other cereals, oat is considered a source of proteins, carbohydrates, fiber, vitamins and minerals Gates, It has components of minor proportion, such as unsaturated fat and b -glucans, which contribute to the health and well-being of human beings Peterson, Oat flakes are an important raw material in the food industry Gates, One of the most important aspects concerning oat quality is its moisture content, since many of its physical properties depend on this property Prieto et al.

But its water activity a w is much more important, which indicates the water quantity in a food that may be used for developmental biochemical reactions i. Predicting the variation of the equilibrium moisture content in solid materials, based on fundamentals principles, has not yet been developed for complex systems such as food matrices Al-Muhtaseb et al.

A common practice is to correlate the experimental data through mathematical models, which render satisfactory results in certain a w ranges and certain food types Zhang et al. This adjustment is obtained by graphing the experimental moisture data in the product equilibrium at a pressure and temperature Corzo and Fuentes, with the thermodynamic activity of water. The water activity in equilibrium equals the relative moisture of the air that surrounds it Zhang et al.

The most used strategy for studies on sorption desorption phenomena is sorption isotherms, which are important in the analysis and design of several food processes and can be used to predict changes in food stability and to select appropriate packaging materials and ingredients Zhang et al.

The sorption-desorption behavior, as well as the isosteric heat of food products and the influence of temperature over the moisture content in equilibrium, provides very useful information for the processes of drying, preservation and conditioning of the food materials Badui, Besides, it defines the storing conditions that guarantee food stability Correa et al. Models that are available in the literature for describing moisture sorption isotherms can be divided into several categories: kinetic models based on a mono-layer Mod-BET model , kinetic models based on a multi-layer and condensed film Guggenheim, Anderson and de Boer - GAB, model , semi-empirical Ferro-Fontan, Henderson and Halsey models and empirical models Smith and Oswin models Al-Muhtaseb et al.

The GAB model is considered to be the most versatile sorption model available in the literature Al-Muhtaseb et al. The Smith model Smith, is useful in describing the sorption isotherm of biological materials such as starch and cellulose.

Henderson proposed a semi-empirical model for the equilibrium moisture content of cereal grains. In more recent years, the GAB isotherm equation has been widely used to describe the sorption behavior of foods Bizot, ; Weisser, ; Iglesias et al.

Having a reasonably small number of parameters three , the GAB equation has been found to adequately represent the experimental data in the range of water activity of the most practical interest in foods, i. This model has been used with protein, rice, turkey, chicken, tomato, potato starch, and wheat starch Timmermann, On the other hand, the Oswin model has been used with meat and fruits Boquet et al. The purpose of this study was to experimentally determine the equilibrium moisture curves of oat flakes Avena sativa L.

Furthermore, the present study aimed to establish the best storage and packaging conditions for oat flakes. The oat product Avena sativa or A. From then on, the weight of the sample was controlled every 10 d until it achieved a constant weight equilibrium condition. Before doing the equilibrium moisture trials, the initial moisture of the oat flakes was determined by triplicate, following the methods of the AOAC No.

The equilibrium moisture content on a dry basis was plotted against the a w , to obtain the equilibrium moisture curves. The quality of the fit of the proposed models was assessed with a linear correlation coefficient r 2 and the percentage of the mean relative error MRPE Eq.

The r 2 must be higher than 0. The oat flake sample initial moisture was 0. According to Fig. This behavior can be explained by the endothermic dissolution of sugars at raised values of a w Brett et al. This fact was attributed to the higher energy levels and lower stability of water molecules as temperature increases, promoting their separation from the binding sites within the food matrix Breett et al.

Under such conditions, the molecules in the glass stage may approximate to the glass transition region and become plasticized, thereby increasing their mobility and availability for sorption Brett et al.

The role of the glass transition in starch-rich products and how it affects their sorption mechanism has been studied by Al-Muhtaseb et al. The results obtained in this study confirm the premise of Van den Berg in relation to the modification of the sorption capacity around the transition region where the amorphous region of starch begins to be plasticized, increasing their availability of hydroxyl groups for the sorption of water molecules Brett et al.

On the other hand, starch, quantitatively the main component of cereals such as oat, contains two polymers that contribute to its molecular structure: amylose, mainly a linear molecule, and amylopectin, a nonlinear and highly branched molecule Damodaran et al.

Both molecules form semicrystalline superstructures with crystalline and amorphous layers arranged in an onion-like structure where most of the crystalline regions are formed by amylopectin although part of the amylose molecules are also present in them Zobel, ; Brett et al. Within such a system, amorphous zones are more water-accessible than crystalline regions in which the intermolecular interactions between the chains are too strong to allow solvent penetration.

Consequently, water influences the structure by acting as a plasticizer of the amorphous regions Al-Muhtaseb et al. This effect causes a depression of the glass transition temperature Tg. The plasticizing effect is very small at low a w values; therefore, the Tg associated with the amorphous regions in samples will be typically high and the material will be glassy at room temperature.

Increasing water activity causes an increase in the availability of the polar sites to the water molecules Al-Muhtaseb et al. Table 4 presents a summary of the results obtained for the proposed models with their respective constants and r 2 and MRPE values. The Henderson model also presented a good behavior in respect to the r 2 but produced a high MRPE superior to This result does not agree with Brett et al. In this study, X S values equal to 0.

Here, one can see that the curve predicted by the Caurie model is the best fit to the experimental data, consistent with those predicted by the r 2 and MRPE.

Additionally, based on the results from Fig. The oat flake moisture sorption isotherms showed a clear dependence on temperature for the working values in this study. Aaman, P. Analysis of starch and other main constituents of cereal grains. Al-Muhtaseb, A. McMinn, and T. Water sorption isotherms of starch powders.

Part 1: mathematical description of experimental data. Food Eng. Official methods of analysis. Arlington, VA. Ayala, A. Sector Agropec. Barreiro, J. Water sorption characteristics of six rowbarley malt Hordeum vulgare. Bizot, H. Using the GAB model to construct sorption isotherms. In: Jowit, R. Escher, B. Hallstrom, H. Meffert, W. Spiess, and G. Vos eds. Physical properties for foods.

Applied Science Publishers, London. Boquet, R. Chirife, and H. Equations for fitting water sorption isotherms of foods: II. Evaluation of various two-parameter models. Food Sci. Brett, B.

Figueroa, A. Sandoval, J. Barreiro, and A. Moisture sorption characteristics of starchy products: oat flour and rice flour. Food Biophys. Cassini, A. Marczak, and C. Water adsorption isotherms of texturized soy protein. Chirife, J. Equations for fitting water sorption isotherms of foods: A review. Correa, P. Da Silva, and L. Corzo, O. Moisture sorption isotherms and modeling for precooked flours of pigeon pea Cajanus cajans L.

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Por lo general, para alimentos en polvo el contenido de humedad a una cierta actividad de agua, decrece a medida que aumenta la temperatura [8]. El modelo de GAB ha sido ampliamente utilizado en muchos alimentos y cereales en polvo. TSAMI et al. Official Method of Analysis. Water sorption isotherm of starch powders Part 1: mathematical description of experimental data. Journal of Food Engineering , v. Water sorption isotherm of starch powders Part 2: Thermodinamic characteristics.

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Langmuir adsorption isotherms for different organic solutions of cholesterol. Medina-Meza 3 and J. Tejero-Andrade 1. E-mail: carlo. Recibido 7 de Noviembre de Aceptado 22 de Marzo de In this work, the surfactant properties of cholesterol in organic solvents are studied.

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