Identification of molecuar interactions between synthetic dyes and food macromolecules by fluorescence spectroscopy

Abstract

Recent studies have demonstrated that in glycerol, glycerol-water, mono and disaccharide solutions, the fluorescence emission intensity of GRAS synthetic colors exhibits a strong sensitivity to the physical properties of the medium, for example, as the viscosity increases, the fluorescence intensity increases. Although molecular mass, structure and intrinsic rigidity of the macromolecule might play a role in probe sensitivity in physical properties of the system, other aspects such as molecular interactions between the probe and the macromolecule may explain these behaviors, such as hydrogen bonding, electrostatic interactions, hydrophobic interactions, etc. The nature of the effect of macromolecules on the dye molecules are to be identified by fluorescence spectroscopy. The fluorescence emission intensity was measured by titrating five carbohydrates (alginate, amylopectin, carboxymethyl cellulose, chitosan and methylcellulose) and five proteins (gelatin, gliadin, albumin, whey protein and zein) into three GRAS synthetic dyes (allura red, sunset yellow and fast green) using a Fluoromax-3 (Horiba Scientific Inc.). Temperature (20°C) and dye concentration were kept constant throughout the study. Anisotropy, ionic strength and temperature studies were also carried out to further explore the nature of the molecular interactions. Results indicate that the fluorescence intensity of fast green is increased by the addition of all water soluble proteins, which are BSA, whey protein and gelatin. It is found that fast green exhibits a very strong binding with the bovine serum albumin molecule, involving electrostatic interactions, hydrogen bonding and hydrophobic interactions. Allura red, as an azo dye, shows less sensitivity to water-soluble protein molecules, while it has hydrophobic interactions with methyl cellulose. Sunset yellow does not show obvious sensitivity to any of the carbohydrates and proteins studied. These results provide insights into the molecular interactions between synthetic dyes and food macromolecules. Therefore, these findings can be used to enhance the performance of these dyes as intrinsic luminescent probes for the physical state of foods and can also contribute to the enhanced detection of synthetic dyes in food products.