30D-14 |
Modeling of adsorption behavior of ultrasonically treated bovine serum albumin |
D. GUZEY1, B. Bruce, and J. Weiss. (1) Colloidal and Interfacial Food Science Laboratory, University of Tennessee, 2605 River Drive, Knoxville, TN 37996 Food proteins are surface-active biopolymers that adsorb readily at interfaces. Their dynamic adsorption behavior has shown to directly influence functionality in food systems i.e. emulsification, gelation and foaming. Studies conducted in our laboratories suggested that interfacial activity and thus protein functionality may be modified using high-intensity ultrasound. However, no theoretical model has yet been developed to describe this altered behavior. The objective of this study was to determine the adsorptions characteristics of native and sonicated BSA and to calculate diffusion coefficients based on three different adsorption models. 3x10-4M bovine serum albumin (BSA) solution were sonicated at an ultrasonic intensity of 20Wm-2 for times ranging from 0-45min and diluted up to 10-9M. Dynamic surface tension measurements were conducted using a drop shape analyzer. Experimental results were fitted to theoretical models using the Origin® 5.0 software. Changes in secondary structure of BSA were determined using a circular dichroism (CD) spectrometer. Adsorption isotherms (equilibrium surface tension as a function of protein concentration) were shifted to lower protein concentrations as sonication time increased, i.e. the mid-point of the sigmoidal isotherm c50 shifted from 1.0 to 0.1mM after sonication for 45 minutes. Multilayer protein formation as indicated by the secondary plateau started at lower protein concentrations. Diffusion coefficients (Deff) calculated from three different models showed significant differences (Deff ranged from 10-7 to 10-11 m2/s). Nevertheless Deff of sonicated protein solutions decreased by a factor of approximately 5-10 as sonication time increased (i.e. 2.0x10-7 versus 7.7x10-7 m2/s for model 1) indicating that protein adsorption was accelerated. CD studies revealed that this behavior could be correlated to an altered stability of the overall protein structure. Interfacial coverage and adsorption kinetic of food proteins can be significantly altered by the application of ultrasound thus yielding proteins with an enhanced ability to stabilize emulsions and foams.
Session 30D, Food Engineering: Physical and chemical properties
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