Generation, characterization, and potential food applications of a novel red colorant formed by oxidative coupling of chlorogenic acid and tryptophan

Abstract

Due to growing consumer skepticism regarding synthetic food colorants and their potential health effects and environmental impact, there is a rising interest in novel natural compounds derived from plants. A red-colored pigment was produced via the oxidative coupling of chlorogenic acid (CQA), using sodium periodate (NaIO4) as the oxidizing agent, with tryptophan (Trp).<br /> The first part of the thesis deals with the preparation and characterization of the new red dye. The colorant generated was precipitated, freeze-dried, and purified by size exclusion chromatography before undergoing characterization with UHPLC coupled with mass spectrometry and NMR spectroscopy. Additional mass spectrometric studies were conducted on the reaction product generated with 15N and 13C labeled Trp educts. Based on the data obtained, a complex compound with two Trp moieties and one caffeic acid moiety was identified and a possible formation pathway was proposed.<br /> In the second part, the investigation focused on the optimization of the process by examining the effect of temperature and concentration of Trp and NaIO4 on the reaction progress. Once the optimal variables were determined, three different pH values were tested. This way, the reaction time decreased from 72 to 24 hours yielding 46 ± 2% w/w based on the quantity of CQA. The solubility of the pigment was evaluated, and the stability of its hydrolyzed form was analyzed under various pH values, storage conditions (in light and darkness for over 28 days), presence of reducing agents, and heat resistance. Ultimately, it was found that the pigment effectively colored various food matrices in quantities ranging from 0.005-0.01% (w/w).<br /> In conclusion, this thesis improves the understanding of the production of a new red pigment resulting from the oxidative coupling of CQA and Trp. It also provides valuable insights into the production and characterization of this red dye. Additionally, the potential application of this pigment in different food matrices was tested.