Kinetic study of the quenching of singlet oxygen by naringin isolated from peels of the fruit of bitter orange (Citrus aurantium I)

Introduction: antioxidant activity is the capacity of a substance to inhibit oxidative degradation, mainly through its ability to react with both radical and non-radical species (e.g. singlet oxygen). Interest by scientific communities in the study of the antioxidant capacity of natural compounds has increased in recent years, due to their possible applications in the pharmaceutical, cosmetic and food industries. Objective: estimate the antioxidant capacity of naringin against singlet oxygen using the rubrene method. Methods: naringin was isolated from peels of the fruit of bitter orange (Citrus aurantium) and characterized using several spectroscopic techniques (UV-Vis and FTIR). The global rate constant for the reaction of 1O2 with naringin was determined with the Stern-Volmer plot derived from a stationary kinetic state based on the competition reaction with rubrene. Results: results showed that naringin acted as singlet oxygen quenching agent with a global rate constant of 2.1 x 107 M-1s-1 (derived from the linear relationship of Stern-Volmer). Conclusion: the kinetic study conducted suggests that naringin could be used as a singlet oxygen quenching agent in biological systems to protect them from oxidative damage(AU)

Introducción: la actividad antioxidante es la capacidad de una sustancia para inhibir la degradación oxidativa y actúa principalmente a través de su capacidad para reaccionar con las especies de radicales y no radicales (por ejemplo, oxígeno singulete). En los últimos años, se han incrementado el interés de las comunidades científicas en el estudio de la capacidad antioxidante de los compuestos naturales debido a sus posibles aplicaciones en la industria farmacéutica, cosmética y alimentaria. Objetivo: estimar la capacidad antioxidante de la naringina contra el oxígeno singulete usando el método de rubreno. Métodos: la naringina se aisló de cáscaras del fruto de la naranja agria (Citrus aurantium) y se caracterizó por algunas técnicas espectroscópicas (UV-Vis y FT-IR). La constante de velocidad global para la reacción de 1O2 con la naringina se determinó por medio del gráfico de Stern-Volmer derivado de una cinética en estado estacionario basada en la reacción de competición con el rubreno. Resultados: los resultados mostraron que la naringina actuó como un quenching del oxígeno singulete con una constante de velocidad global de 2.1 x 10 7 M-1s-1 (derivado de la relación lineal de Stern-Volmer). Conclusión: el estudio cinético sugiere que la naringina se podría utilizar como un quenching del oxígeno singulete en sistemas biológicos y protegerlos del daño oxidativo(AU)

Riboflavin as a photosensitizer. Effects on human health and food quality.

Riboflavin, vitamin B2, and flavins (as riboflavin building blocks or degradation products) are efficient photosensitizers inducing oxidative damage to light-exposed tissue and food by substrate-dependent mechanisms, for which protection is offered by specific nutrients. Phenolic and N-heterocyclic amino acids and their peptides and proteins deactivate triplet-excited state riboflavin in diffusion controlled processes, efficiently competing with deactivation by oxygen, resulting in direct (so called Type I) protein degradation through electron transfer or proton-coupled electron transfer. In light-exposed tissue, such often long lived protein radicals may as primary photoproducts initiate lipid and vitamin oxidation. In contrast, for lipid systems, oxygen deactivation of triplet-excited state riboflavin, resulting in formation of singlet oxygen, is under aerobic conditions faster than direct deactivation by lipids, which otherwise under anaerobic conditions occurs as hydrogen atom transfer from polyunsaturated lipids to triplet riboflavin. Singlet oxygen adds to unsaturated lipids and forms lipid hydroperoxides as primary lipid oxidation products or oxidizes proteins (Type II mechanism). Carotenoids seem not to deactivate triplet riboflavin, while chromanols like vitamin E and plant polyphenols are efficient in such deactivation yielding protection of proteins and lipids by these phenols. Indirect protection against the triplet reactivity of riboflavin is further important for polyphenols as riboflavin singlet excited state quenchers in effectively preventing riboflavin intersystem crossing to yield the reactive triplet state. Riboflavin photosensitization becomes critical for degradation of proteins, unsaturated lipids, and folate, thiamine, ascorbate and other vitamins during light exposure of food during storage. For skin, eye and other tissue exposed to high intensity light, dietary polyphenols like flavonoids are important in direct protection against photosensitized oxidation, while dietary carotenoids may yield protection through inner-filter effects, through scavenging of radicals resulting from Type I photosensitization, and through quenching of singlet oxygen formed in Type II photosensitization. Both carotenoids and polyphenols accordingly counteract the degenerative effect induced by riboflavin exposed to light, although by different mechanisms.