Coacervate formation of α-lactalbumin-chitosan and β-lactoglobulin-chitosan complexes

alpha-Lactalbumin (alpha-La) and beta-lactoglobulin (beta-Lg) are important whey proteins with isoelectric points of pH 4.80 and 5.34, respectively, and evidence negative charge over a range of pHs. Chitosan exhibits a cationic property under pH 6.5. In an effort to determine the physicochemical properties of mixtures of 0.5% alpha-La and 0.1% chitosan, and 0.5% beta-Lg and 0.1% chitosan, optical structure, turbidity, electrophoresis, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were assessed in a pH range of 2.0-8.0. The results demonstrated that alpha-La, beta-Lg, and chitosan precipitated at pH Values of approximately 5.0, 5,0, and 7.0, respectively. The mixtures of alpha-La and chitosan as well as beta-Lg and chitosan coacervated at a pH range of 6.0-6.5. The turbidity of alpha-La and alpha-La-chitosan achieved a maximum at pH 5.0, whereas those of beta-Lg and beta-Lg-chitosan achieved maximum values at a pH of 6.5. The electrophoregram showed a large band with high molecular weight in increasing pH values from 5.0 to 6.0, which suggested that alpha-La and beta-Lg form polymers with chitosan. The denaturation temperature and enthalpy of alpha-La were shown to increase, whereas those of beta-Lg were reduced. The SEM images demonstrated that the alpha-La was characterized by uneven and associated cluster morphology, whereas that of beta-Lg was even, globular, and harbored dense particles, whereas the chitosan evidenced a flat morphology. Our assessment of the complex demonstrated that alpha-La and beta-Lg attached to the surface of the chitosan. The alpha-La-chitosan and beta-Lg-chitosan complexes evidenced opposite charges at a pH range of 5.0-6.0, and formed coacervates. It appears, therefore, that the alpha-La-chitosan and beta-Lg-chitosan coacervates might be applied as a delivery system for foods, nutraceuticals, cosmetics, and drugs. (c) 2009 Elsevier Ltd. All rights reserved.