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

Abstract

The interest in new dyes, especially those derived from plants, can be linked to the limitation of actual natural food colorants and the growing consumer concern about the potential health and environmental impact of synthetic dyes.

Therefore, the focus of this dissertation was on the generation of a red pigment obtained from the oxidative coupling of chlorogenic acid (CQA) and tryptophan (Trp) in the presence of sodium periodate (NaIO₄) as the oxidizing agent.

The pigment was prepared, purified and characterized using advanced techniques such as LC-MS and NMR spectroscopy. A compound consisting of two Trp moieties and a caffeic acid moiety was identified and a reaction mechanism was suggested.

In the subsequent phase of the investigation, the emphasis was directed towards the optimization of the process. This involved the examination of the impact of temperature and concentration of Trp and NaIO₄ on the progression of the reaction.

After determining the optimal parameters, three different pH values were tested to identify the best condition. This allowed the reaction time to be reduced from 72 to 24 hours, yielding 46 ± 2% (w/w) based on the amount of CQA. To evaluate potential applications, the solubility of the pigment was tested, and its hydrolyzed form was analyzed under various pH values, storage conditions, the presence of reducing agents, and heat resistance. Finally, the pigment was tested in different food matrices and showed promising results in amounts ranging from 0.005 to 0.01% (w/w).

In conclusion, this research deepens the understanding of the production of a novel red pigment resulting from the oxidative coupling of CQA and Trp, providing valuable information on its synthesis, characterization and potential application in different food matrices.