Małgorzata Olszowy

Does antioxidant properties of the main component of essential oil reflect its antioxidant properties? The comparison of antioxidant properties of essential oils and their main components

This study discusses the similarities and differences between the antioxidant activities of some essential oils: thyme (Thymus vulgaris), basil (Ocimum basilicum), peppermint (Mentha piperita), clove (Caryophyllus aromaticus), summer savory (Satureja hortensis), sage (Salvia hispanica) and lemon (Citrus limon (L.) Burm.) and of their main components (thymol or estragole or menthol or eugenol or carvacrol or camphor or limonene) estimated by using 2,2′-Diphenyl-1-picrylhydrazyl, 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and β-carotene bleaching assays. The obtained data show that the antioxidant properties of essential oil do not always depend on the antioxidant activity of its main component, and that they can be modulated by their other components. The conclusions concerning the interaction of essential oil components depend on the type of method applied for assessing the antioxidant activity. When comparing the antioxidant properties of essential oils and their main components, the concepts of synergism, antagonism and additivity are very relevant.

The importance of solvent type in estimating antioxidant properties of phenolic compounds by ABTS assay

ABTS assay belongs to the most popular methods employed for estimating antioxidant activity. However, researchers seldom pay attention to specific factors influencing the determination of antioxidant activity of the examined compounds and mixtures. The paper shows that the type of alcohol used significantly influences the estimation of antioxidant activity of phenolic compounds in ABTS assay, namely that their antioxidant activity increase with the lengthening of the aliphatic chain in alcohol. It results rather from the changes in ABTS•+ solvatation energy by the employed alcohols than from dissociation variations of phenolic compounds. The obtained results point to the difficulties in the correct estimation of the real antioxidant properties of plant and food extracts by ABTS assay. The presented results have also an ecological implication as they refer to the difference in estimation of antioxidant properties of compounds resulting from the replacement of toxic methanol by GRAS (Generally-Recognized-As Safe) solvents, ethanol and propanol.

Essential oils as antioxidants: their evaluation by DPPH, ABTS, FRAP, CUPRAC, and β-carotene bleaching methods

Essential oils prevent several chronic diseases owing to the presence of compounds, which have may an important role in the reduction of oxidative stress. Estimation of antioxidant properties of essential oils and evaluation of their antioxidant ability was the aim of this work. The antioxidant properties of essential oils were estimated by DPPH, ABTS, FRAP, CUPRAC, and β-carotene bleaching methods and related to antioxidant properties of butylated hydroxyanisole and gallic acid. As our results indicate, these essential oils exhibit varying antioxidant activity, however, all of them are able to consume free radicals, to reduce cupric or ferric ions, and to protect or retard the oxidation process of lipids. Most of the essential oils can be applied not only as edible additives to improve the sensory and health promoting properties of foods but also as natural components enhancing the antioxidant stability of foodstuffs to increase their shelf-life.Graphical abstract

Depletion/protection of β-carotene in estimating antioxidant activity by β-carotene bleaching assay

The β-carotene bleaching assay belongs to the oldest and commonly applied methods of estimating the antioxidant activity of different substances and mixtures. In this method, the antioxidant activity of the examined substance is evaluated by the spectrophotometric measurement of β-carotene concentration changes in β-carotene/peroxyl radicals (LOO•) systems with and without antioxidant. The presented results confirm the essential influence of hydrogen ion concentration on the estimation of antioxidant activity of phenolic compounds and prove that the formation of peroxyl radicals in measuring system is inhibited by the presence of hydrogen ions. Contrary to hydrogen ions, alkali metal ions accelerate the formation of peroxyl radicals quickening β-carotene depletion, thus indicating the seemingly weaker antioxidant properties of the antioxidant at the presence of metal ions. The LOO•/β–carotene reaction rate, and hence the estimated antioxidative potential of the examined compound, is also dependent on the type and concentration of the anion accompanying the cation. The presented results show the difficulty in the estimation of true antioxidant properties of food components, plant extracts and even antioxidant additives protecting products against oxidative changes.