Citral Photodegradation in Solution: Highlighting of a Radical Pathway in Parallel to Cyclization Pathway

Abstract

Citral, a lemon flavor molecule often used in the beverage and fragrance industry, is known to be unstable under light irradiation. Its deterioration is considered to be an important issue for the stabilization of lemon-flavored drinks. The aim of this study is to understand the degradation mechanisms of citral under light irradiation with the variation of three parameters: the solvent (citrate buffer solution at pH 3 vs ethanol), the atmosphere (air vs N2), and the concentration of citral. The photodegradation has been studied using UV–visible spectroscopy after photolysis, nuclear magnetic resonance spectrometry, and electron spin resonance spectroscopy. To extend the investigation, molecular orbitals and bond dissociation energies have also been calculated. They give an insight into the light absorption properties and the possible cleavage of citral molecular bonds. In addition, UV-light absorption and radical scavenging activities of two additives, potassium sorbate and ascorbic acid, have been studied for the inhibition of the citral photodecomposition by UV-light irradiation. Both theoretical and experimental results highlight a new degradation pathway involving free-radical intermediates in parallel to the already reported cyclization one, which could be prevented by the addition of stabilizers such as ascorbic acid or sorbate.

Thermal and Photochemical Stability of Anthocyanins from Black Carrot, Grape Juice, and Purple Sweet Potato in Model Beverages in the Presence of Ascorbic Acid

“…The electron spin resonance–spin trap (ESR-ST) experiment , was used to prove the presence of radicals formed from anthocyanin molecules in solution under irradiation, using 2,2,6,6-tetramethylpiperidine 1-oxyl, (CH 2 ) 3 (CMe 2 ) 2 NO • , abbreviated TEMPO, as the spin trap …”

“…The electron spin resonance−spin trap (ESR-ST) experiment 50,51 was used to prove the presence of radicals formed from anthocyanin molecules in solution under irradiation, using 2,2,6,6-tetramethylpiperidine 1-oxyl, (CH 2 ) 3 (CMe 2 ) 2 NO • , abbreviated TEMPO, as the spin trap. 52 For this study, an aqueous solution of TEMPO at 10 −4 M was prepared at pH 3 (HCl in distilled water). A part of this solution was kept as a reference, and the rest was added to the BC, GJ, and SP extracts to obtain concentrations of 30 g L −1 .…”

Iodinated Polystyrene for Polymeric Charge Transfer Complexes: Toward High-Performance Near-UV and Visible Light Macrophotoinitiators

“…This can be explained by (i) PBN does not react with the radicals arising from PSI cleavage (long chain substituted aryl radical, see Table ), (ii) long irradiation time needed which led to the photolysis of the PBN spin adduct. Therefore, we decided to use TEMPO as a radical scavenger through the reaction r as we previously did . We focus on the free radicals generated in (i) the CTC made of PSI/Am1 and (ii) PSI alone.…”

A Mild Method for Encapsulation of Citral in Monodispersed Alginate Microcapsules

“…Citral is a typical hydrophobic chemical with a special aroma, which is usually used as an additive in the food industry and the daily chemical industry because of its antioxidant and antibacterial properties [ 6 , 7 , 8 , 9 , 10 ]. However, citral is susceptible to deterioration by a series of cyclization and oxidation reactions when stimulated by some environmental factors, such as acid, UV light, and high temperature [ 11 , 12 , 13 ]. Therefore, microencapsulation technology has been used to increase the chemical stability of citral and realize controlled release.…”

“…Liu et al have prepared alginate microcapsules with oil cores by using a photoacid generator to trigger the Ca 2+ ions released from the CaCO 3 nanoparticles with UV irritation [ 35 ]. However, the UV irritation will initiate the photoreaction of citral [ 11 ]. In our previous study, calcium ethylenediaminetetraacetic acid (EDTA-Ca) complex is used as a water-soluble calcium source and acetic acid as a trigger to prepare alginate microcapsules with oil cores [ 36 ].…”