Studies on the interaction of metals and their hydrous oxide sols with proteins: Interaction of aluminium, chromium, iron and their hydrous oxide sols with casein

Abstract

Metal ion binding to anionic casein has been measured by potentiometric titration of Al3+, Cr3+, Fe3+ and their hydrous oxide sols with the protein.CP (the amount of hydrogen ions bound in presence of metal ions) has been plotted against pH of the metal-protein mixtures. These curves deviate markedly from linearity and a characteristic hump has been realised in case of Al-casein and Cr-casein system between pH 4.5 to 6.5, indicating the binding of metal ions to the carboxyl groups of protein. If the extent of deviation from linearity inCP-pH curve is taken to be a measure of metal ion binding to protein, then casein exhibits greater binding capacity to Cr3+ than to Al3+. On the other hand, ferric ions appear to combine either withE-amino groups or phenolic groups of casein. Results on viscosity measurements further support the above viewpoint.