29E-13 |
Effect of pH on effective diffusivity of biopolymer electrolytes solutions using regular regime method |
J. G. BÁEZ-GONZÁLEZ1, C. Pérez-Alonso1, C. I. Beristain2, E. J. Vernon-Carter1, and M. G. Vizcarra-Mendoza3. (1) IPH, Universidad Autonoma Metropolitana-Iztapalapa, San Rafael Atlixco # 186, Mexico City, 09340, Mexico, (2) Instituto de Ciencias Básicas, Universidad Veracruzana, Luis Castelazo S/N, Col. Industrial-Animas, Xalapa, Ver., 91000, Mexico, (3) IPH, Universidad Autonoma Metropolitana, San Rafael Atlixco # 186, Mexico City, 09340, Mexico An adequate wall material selection for microencapsulation guarantees protection to the core material against environmental factors. The effective diffusion of biopolymer aqueous solutions upon isothermal drying provides a quantitative way of selecting the most suitable wall materials for microencapsulation by spray-drying. The formation of a more or less dense membrane depends on the physicochemical nature of each material. For example mesquite gum (MG) and gum arabic (GA) are considered choice wall materials for encapsulation. However, these biopolymers are polyelectrolytes whose conformation greatly changes with pH and electrolytes, and little is known how conformational changes affect effective diffusivity. The objective of this work was to determine the effective diffusivity of MG and GA aqueous solutions at different pH´s, by analyzing the isothermal drying curves through regular regime method. The requisite amounts of MG and GA were dispersed different buffers with the same ionic strength in order to obtain 40% (w/w) aqueous biopolymers solutions with pH´s of 8, 6 and 4, respectively. Single drops of each biopolymer treatment were dried isothermally at 50, 60, 70 y 80 °C using a thermogravimetric analyzer. Effective diffusivity as a function of moisture content and drop shrinkage was was calculated using regular regime methodology coupled with image analysis. Results show that at pH 4 and 8 the effective diffusivity of MG and GA increased. At these pH´s both gums have a more coiled configuration than at pH 6, and the rate at which a dense and fine film formation occurs is lower than at pH 6. Also, at pH 6 drop shrinkage is more drastic than at pH´s 4 and 8, having a greater effect on effective diffusivity. This work shows that by altering the conformation of MG and GA the functionality of microcapsules such as rate of release of core material may be controlled.
Session 29E, Food Engineering: Transport processes and kinetics
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