Effect of pH on Protein-Binding of Orange G and Amido Black Dyes

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Abstract
The effect of pH on the absorbance of aqueous solutions of Orange-G dye was negligible between pH 2.0 and 9.5. There was a marked decrease in absorbance caused by dissociation of the hydroxyl on the [beta]-naphthol ring between pH 9.5 and 11.3. Oxalic acid has several advantages over citric acid as an acidifying agent in the dye-binding protein test of milk. Oxalic acid used at approximately 1/3 the amount of citric acid gave a lower and more reproducible pH and increased dye-binding. The dye-binding capacity of both casein sols and milk from individual cows was inversely related to the pH between 1.1 and 6.2.