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

Abstract

The effect of pH on the absorbance of aqueous solutions of Orange G dye was negligible between pH 2.0 and 9.5. Between pH 9.5 and 11.3 there was a marked decrease in absorbance, caused by dissociation of the hydroxyl on the β-naphthol ring. 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 one-third the amount of citric acid, gave a lower and more reproducible pH, and increased dye-binding. It also gave complete mold inhibition. 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. © 1966, American Dairy Science Association. All rights reserved.