Quantitative evaluation of food additive dyes on the aggregation of randomly coiled casein

Artificial food additives, quinoline yellow (QY) and allura red (AR), are widely used in food processing to improve the color and appearance. This study demonstrates the interaction and aggregation of milk protein, casein, at increasing concentrations of QY and AR at pH 2. The formation of the casein-dye complex was validated by UV-absorbance and fluorescence measurements. The interaction resulted in the formation of a ground-state complex via a static quenching mechanism and spontaneous binding, with van der Waals forces and hydrogen bonding playing key roles. Synchronous fluorescence indicates alterations in the microenvironment around tryptophan residues. With increasing concentration of QY and AR (0-400 μM), aggregation also increases, as assessed by turbidity measurements and RLS fluorescence. The randomly coiled casein was transformed into cross-β structures, as evidenced by CD and Congo red. These results suggest the adverse effect of food additive dyes on the physicochemical properties of proteins in the food industry.