Food Colorants Acid Yellow 23, Azorubine, and Acid Red 18 Cause Aggregation and Fibrillation of Proteins

Acid Yellow 23 (AY23), Azorubine (AR), and Acid Red 18 (AR18) are three of a string of approved synthetic food colorants, each of whose maximal daily intake is set to about 100 mg kg–1 day–1. This study deploys spectroscopy, electron microscopy, and X-ray diffraction (XRD) to examine the effect of dye binding to lysozyme, cytochrome c, myoglobin, and bovine serum albumin (BSA) under acidic and neutral pH conditions. The c1/2 value for binding of food dyes to globular proteins in vitro is lowest for AR18 (∼50 μM) but increases with AY23 (∼140 μM) and AR (∼190 μM). Dye binding reversibly transforms native proteins to quasi-native states, which enter the aggregation pathway to yield an initial amorphous mesopaque that reconfigures at longer times to produce crystalline fibrillar forms. In vivo protein aggregation is, however, unlikely because of a substantial negative gradient from intestinal to systemic concentrations of the dyes.