Emma M. Marinova

Antioxidant activity and mechanism of action of thymol and carvacrol in two lipid systems

The autoxidation of purified triacylglycerols of lard and sunflower oil (TGL and TGSO) containing 0.02, 0.05, 0.10 and 0.20% thymol and carvacrol was studied at ambient temperature. The results obtained with the inhibited lipid systems (thymol - TGL; carvacrol - TGL; thymol - TGSO and carvacrol - TGSO) showed that thymol had the highest antioxidant effectiveness and activity during TGSO oxidation. Thymol and carvacrol participated in one side reaction during inhibited TGL oxidation, and thymol took part in two side reactions during TGSO oxidation. Carvacrol molecules did not participate in side reactions during TGSO oxidation. Thymol and carvacrol contributed to chain initiation to a higher degree during TGSO oxidation than during TGL oxidation. Thymol radicals did not participate in chain propagation during TGL and TGSO oxidation. Carvacrol radicals took part in one reaction of chain propagation in both lipid systems. In general, during autoxidation of lipids at ambient temperature, thymol is a more effective and more active antioxidant than carvacrol. Both antioxidants differ in the mechanism of their inhibiting action which depends on the character of the lipid medium. Thymol is a better antioxidant in TGSO than in TGL, whereas the activity of carvacrol in the two lipid systems does not differ significantly.

Antioxidative activity of extracts from selected species of the family Lamiaceae in sunflower oil

Abstract The kinetics of peroxide accumulation during oxidation of sunflower oil at 100 °C in the presence of different concentrations of hexane, ethyl acetate and ethanol extracts of Melissa officinalis L., Mentha piperita L., Mentha spicata L., Ocimum basilicum L., Origanum vulgare L. and Saturejae hortensis L. have been studied. It has been established that the extracts from Ocimum basilicum L. and Origanum vulgare L. do not improve the oxidation stability of sunflower oil. The ethanol extracts from the other four spices have proved to be the most active in retarding the autoxidation process. The strongest action has been exhibited by the ethanol extracts from Saturejae hortensis L., followed by the ethanol extracts from Mentha piperita L. and Melissa officinalis L. The stabilization factor F for the ethanol extracts (0.1–0.5%) from Saturejae hortensis L. is 1.8–2.3. It is higher than F for 0.02% butylated hydroxytoluene BHT (F = 1.2). From a practical point of view (yield and stabilization factor), the direct ethanol extract from Saturejae hortensis L. should be recommended as the most suitable antioxidant for the stabilization of sunflower oil.

Effect of lipid unsaturation on the antioxidative activity of some phenolic acids

Antioxidative properties ofp-hydroxybenzoic, vanillic, syringic, 3,4-dihydroxybenzoic,p-coumaric, ferulic, sinapic and caffeic acids were studied in the concentration range 0.02–0.20 wt% during autoxidation at 100°C of lard and sunflower oil methyl esters (MEL and MESO, respectively). In both lipid systems, the derivatives of benzoic acid had weaker inhibiting properties than did the corresponding analogues of cinnamic acid. The effectiveness and strength of the antioxidative action were considerably lower in the lipid system MESO, which was rich in linoleic acid and was more easily oxidized. Thep-hydroxybenzoic, vanillic, syringic andp-coumaric acids in this system exercised no inhibiting effect. We established that the molecules of the investigated phenolic acids initiated the chain radical process of autoxidation, and the formed antioxidant radicals propagated the chains as a result of the reaction with the lipid substrate. These reactions proceeded at a higher rate in MESO than in MEL.

Effects of antioxidants on the stability of triacylglycerols and methyl esters of fatty acids of sunflower oil

Abstract The autoxidation of kinetically pure triacylglycerols and methyl esters of sunflower oil (TGSO and MESO) in the presence of four different concentrations of 3,4-dihydroxybenzoic, ferulic, sinapic and caffeic acids, and in the absence of metal ions, at 100 °C was studied. It was established that the effectiveness and strength of the phenolic acids was greater in TGSO than in MESO. The interpretation of the results by kinetic and computational methods allowed the mechanism of action of the antioxidants to be elucidated. In both lipid substrates the molecules of the phenolic acids participate in one side reaction. The rate constants of this reaction in TGSO and MESO are practically the same, which shows that the binding of the fatty acids to the triacylglycerol structure of the sunflower oil does not change the mechanism of phenolic acid consumption in side reactions. The phenolic acids participate in reactions of chain initiation, which have a three to six times higher rate in MESO than in TGSO. The radicals of 3,4-dihydroxybenzoic, sinapic and caffeic acids in MESO, and of 3,4-dihydroxybenzoic and caffeic acids in TGSO, take part in one reaction of chain propagation (with the lipid substrate). The radicals of ferulic acid in MESO, and of ferulic and sinapic acids in TGSO, participate in more than one reaction of chain propagation. The effectiveness and strength of the phenolic acids are higher in TGSO than in MESO because, during the oxidation of TGSO, the contribution of the inhibitor radicals and molecules to chain initiation and propagation is smaller than in the case of MESO oxidation.

Antioxidative activity of phenolic acids on triacylglycerols and fatty acid methyl esters from olive oil

The autoxidation of kinetically pure triacylglycerols and methyl esters of olive oil (TGOO and MEOO) in the presence of four different concentrations of p-coumaric, ferulic and caffeic acids at 100 °C was studied. It was established that effectiveness and strength of the phenolic acids were greater in MEOO than in TGOO. In both lipid substates the molecules of phenolic acids participate in one side-reaction (with hydroperoxides). The rate constants of this reaction in TGOO and in MEOO are practically the same. The phenolic acids take part in chain initiation. The rate of this reaction for ferulic and caffeic acids has equal values in TGOO and in MEOO, whereas for p-coumaric acid it is twice as high in TGOO than in MEOO. The radicals of the phenolic acids participate in one reaction of chain propagation (with the lipid substrate) both in triacylglycerols and in methyl esters of olive oil. Comparison with the data published recently for sunflower oil triacylglycerols and methyl esters demonstrates the strong influence of the unsaturation type and degree of the lipid system on the kinetics and mechanism of the antioxidative action of the phenolic acids.

Antioxidative action of the ethanolic extract and some hydroxycoumarins of Fraxinus ornus bark

Abstract The antioxidative effectivity and strength of different concentrations of ethanolic extract from Fraxinus ornus bark, as well as of esculetin, esculin, fraxetin and fraxin during the autoxidation at 100°C of kinetically pure triacylglycerols of lard (TGL) and triacylglycerols of sunflower oil (TGSO) were determined. The extract exhibited a pronounced antioxidative activity. Esculetin and fraxetin considerably retarded the process in both lipid systems, this being more significant in the less oxidizable lipid substrate (TGL). Fraxetin proved to be a more efficient and stronger inhibitor than esculetin. During the oxidation of TGSO the fraxetin caused a stronger decrease in antioxidative activity. The participation of both hydroxycoumarins in the side reactions of inhibited oxidation, which explains their kinetic behaviour, is discussed. Fraxin and esculin displayed a very weak antioxidative action.

Effect of an Ethanol Extract from Summer Savory (Saturejae hortensisL) on the Stability of Sunflower Oil at Frying Temperature

The effect of the ethanol extract from Saturejae hortensis L on the oxidative and thermal processes occurring in sunflower oil during its high-temperature treatment (180°C) was investigated. The changes during simulated deep fat frying were monitored by determination of the oxidation stability at 100°C, as well as by determination of unchanged triacylglycerols. It was established that the addition of 1 and 5 g kg-1 ethanol extract from S hortensis L leads to a decrease in the oxidative and thermal changes in the oil. The ethanol extract from S hortensis L improved the oxidative stability of sunflower oil even after 50 h at 180°C and it inhibited the oxidative processes more than the thermal processes under these conditions.

Antioxidative effectiveness of some natural antioxidants in sunflower oil

Sunflower oil has been oxidized at 25 and 100°C in the presence and in the absence of 0.01,0.02 and 0.05% 3,4-dihydroxybenzoic acid, caffeic acid, esculetin and fraxetin. 3,4-Dihydroxybenzoic acid shows no antioxidative activity at either temperature. Esculezin possesses a relatively low effectiveness at 100°C (stabilization factorF=1.3 for 0.05% esculetin), and at 25°C it does not improve the oxidative stability. Sunflower oil is more easy to stabilize at 100°C:F=3.0 for 0.05% fraxetin, andF=1.9 for 0.05% caffeic acid. Native sunflower oil is much more difficult to stabilize than are its kinetically pure triacylglycerols.

Accumulation of lead, zinc and cadmium in plant seeds growing in metalliferous habitats in Bulgaria

Seeds from some plants were collected from metalliferous region in Bulgaria. In this area the concentrations of lead, cadmium and zinc in soil were 3500 mg kg−1, 280 mg kg−1 and 30 mg kg−1, respectively. Plants accumulate heavy metal ions in their seeds selectively. It appears that peanut and corn seeds accumulate mainly Pb (5.2–9.6 mg kg−1), pea seeds accumulate mainly Cd (1.0–1.2 mg kg−1 l), and wheat seeds accumulate mainly Zn (59.4–73.2 mg kg−1). This shows that the accumulation of heavy metals in the seeds of plants from some polluted regions may reach dangerous levels, especially if they are used as forage or food.

Anti-tyrosinase, antioxidant and antimicrobial activities of hydroxycinnamoylamides

Synthetic hydroxycinnamoylamides of amino acids (precursors of aromatic amines) were studied for their antioxidant activity in vitro by two antioxidant assay systems, including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and inhibition of lipid peroxidation (LPO). Furthermore, these compounds were tested and compared with their corresponding cinnamoylamides of aromatic amines for their inhibitory activity using mushroom tyrosinase. In addition, five hydroxycinnamoyl amino acid amides were investigated for their antimicrobial effect. Structure–activity relationships analysis disclosed that the presence of catechol rest at amino acid or at benzene moieties of substituted cinnamic acid amides significantly scavenged DPPH radical and inhibited LPO. The results obtained by LPO clearly expressed the positive influence of indole moiety on the activity. Moreover, the existence of p-hydroxy substituted cinnamic acid moiety leads to better tyrosinase inhibition. Amongst the tested compounds, amides of p-coumaroyldopamine or tyramine and their corresponding amino acid precursors are the most potent tyrosinase inhibitors.