Oregan Essential Oil: interaction with photogenerated singlet molecular oxygen

MUÑOZ, V.A; MISKOSKI S.; MONTAÑA M.P; POSADAZ, A.C; FERRARI G.V; DIMARCO PALENCIA, F.C.D; CIFUENTE D.A; GARCÍA N.A

Villa Carlos Paz, Córdoba

Congreso; XIII Encuentro Latinoamericano de Fotoquímica; 2017

Asociación de fotoquímica y fotobiología

Introduction: Essential oils are a mixture of volatile compounds, products of the secondary metabolism of plants. Once these oils are extracted, they can be deteriorated losing their organolpetic and therapeutic properties due to various environmental factors. Exposure to light in aerobic conditions is the main cause of these decomposition and leads to the generation of allergenic compounds responsible for dermatitis, eczemas, among others. These degradations can be caused by reactive oxygen species (ROS) photogenerated from endogenous sensitizers. In this work the photodegradation of the essential oil of oregano (OEO) in presence of vitamin B2 (Riboflavin, Rf) was studied.Experimental: OEO was extracted by hydrodistillation with Clevenger trap from plants grown in the experimental field of the FTU-UNSL, which were in flowering state. The main compounds of OEO, carvacrol (CR) and thymol (TM), were characterized by EIMS and NIST Mass Spectrometry Data Center. In addition, CR and TM were quantified, in the extracted oil, by gas chromatography. The mixture Rf + OEO was irradiated at λ ˃ 400 nm in solvent MeOH: H2O 60:40 v/v and the spectral evolution is shown in the figure, indicating OEO reacts with photogenerated ROS. In order to identify the participating ROS in the photodegradation mechanism of the OEO, experiments of oxygen consumption of solutions in the presence and absence of specific ROS inhibitors were carried out. Oxygen consumption profiles indicate degradation occurs involving singlet molecular oxygen. The total quenching rate constant of singlet oxygen, kt, and the reactive quenching constant, kr, of OEO and its two major components were determined. The kr/kt ratio was calculated since it indicates the fraction of overall quenching of singlet oxygen that effectively leads to a chemical transformation.Discusion: Degradation of OEO, CR and TM in the presence of Rf involves participation of singlet oxygen, mainly through a physical process. The observed values of kr/kt suggest that with OEO, the chemical reactivity component is higher compared to CR and TM. This indicates that other species could contribute to reactive photoprotection from OEO.