Abstract
Olive leaf (OLL) extracts contain a high load of antioxidant polyphenols with significant pharmacological potency. In this study, the use of a novel natural deep eutectic solvent enabled the effective extraction of OLL polyphenols and their testing as radical scavengers, in the presence or absence of methyl β-cyclodextrin (m-β-CD), using descriptive kinetics. Testing was extended to include interactions with ascorbic acid—a natural powerful antioxidant—by implementing a response surface methodology. The kinetic study showed that m-β-CD may hinder the radical scavenging effect of OLL extracts, yielding lower stoichiometry upon reaction with the radical probe 2,2-diphenyl-1-picrylhydrazy (DPPH). The extension of the reaction time to determine the total stoichiometry confirmed this effect. As a further concurrence, the interactions of OLL extracts with ascorbic acid showed lower radical scavenging performance in the presence of m-β-CD. These results were discussed on the grounds of the role that m-β-CD may play in similar systems.
Highlights
In recent years, there has been a growing demand for natural antioxidants to both replace synthetic ones and to act as functional additives that could provide biological systems with protection against harmful free radicals
Antioxidant activity may be effectively estimated in plant extracts—with several tests developed for such a purpose [3]—a few studies have investigated in detail the rate of antiradical reactions, which might represent the rate at which antioxidants react with free radicals
The H-transfer reactions from polyphenols to diphenyl-1-picrylhydrazyl radical (DPPH) can be very effectively assessed by monitoring the decay of at 515 nm (A515), using as molar absorptivity ε = 11,240 M−1 cm−1 and considering the purity of the reagent
Summary
There has been a growing demand for natural antioxidants to both replace synthetic ones and to act as functional additives that could provide biological systems with protection against harmful free radicals. Plant-derived antioxidant polyphenols are becoming increasingly important in this respect, as numerous of these substances have been shown to possess a very high capacity for quenching free radicals [1]. This has stimulated a broad spectrum of studies regarding the use of plant extracts as rich sources of natural antioxidants. 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) is widely used for quickly assessing the ability of antioxidants to transfer labile H atoms to radicals, based on the theory that a hydrogen donor is an antioxidant This reaction is stoichiometric with respect to the number of hydrogen atoms absorbed. The investigations included a kinetic assay and interactions with ascorbic acid (AA), after implementing a response surface methodology
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