Comparison of the antioxidative properties of caffeic and chlorogenic acids

The antioxidative properties of caffeic and chlorogenic acids during autoxidation of triacylglycerols of sunflower oil at 100 °C were compared. The effects of the two acids within the concentration range 2.8–56.5 × 10⁻⁴ M (50–2000 ppm) were investigated. The stabilization factor (F) as a measure of the effectiveness of the antioxidants and the oxidation rate ratio (ORR) as a measure of their strength were determined. It was found that at concentration 2.8 × 10⁻⁴ M, the effectiveness and the strength of the two acids were practically the same, while at higher concentrations caffeic acid appeared as a much more effective and stronger inhibitor. The analysis of the kinetic data obtained showed that chlorogenic acid and its radicals participated more readily in side reactions with the hydroperoxides and the lipid substrate than caffeic acid and its radicals did.     

One Question,Multiple Answers: Biochemical and Biophysical Screening Methods Retrieve Deviating Fragment Hit Lists

Fragment‐based lead discovery is gaining momentum in drug development. Typically, a hierarchical cascade of several screening techniques is consulted to identify fragment hits which are then analyzed by crystallography. Because crystal structures with bound fragments are essential for the subsequent hit‐to‐lead‐to‐drug optimization, the screening process should distinguish reliably between binders and non‐binders. We therefore investigated whether different screening methods would reveal similar collections of putative binders. First we used a biochemical assay to identify fragments that bind to endothiapepsin, a surrogate for disease‐relevant aspartic proteases. In a comprehensive screening approach, we then evaluated our 361‐entry library by using a reporter‐displacement assay, saturation‐transfer difference NMR, native mass spectrometry, thermophoresis, and a thermal shift assay. While the combined results of these screening methods retrieve 10 of the 11 crystal structures originally predicted by the biochemical assay, the mutual overlap of individual hit lists is surprisingly low, highlighting that each technique operates on different biophysical principles and conditions.     

Antioxidant activity screening of extracts from Sideritis species (Labiatae) grown in Bulgaria

Plant samples from several species and populations of the genus Sideritis (Labiatae) grown in Bulgaria (S scardica, S syriaca and S montana) were extracted with different solvents. Their antioxidant activities were determined by the β‐carotene bleaching test (BCBT), 2,2′‐diphenyl‐1‐picrylhydrazyl (DPPH^?) radical scavenging method and static headspace gas chromatography (HS‐GC) and compared with the antioxidant activity of two reference compounds of different polarity, viz butylated hydroxytoluene (BHT) and rosmarinic acid. The pure reference compounds were applied in a ten‐times lower concentration than the plant extracts. The highest antioxidant activity in the BCBT, close to that of BHT, was observed for the more apolar extracts. The inhibitory effect on β‐carotene bleaching of the polar extracts and rosmarinic acid was much lower than that of BHT. The inhibition of hexanal formation in bulk safflower oil by most of S syriaca and S scardica extracts was as effective as BHT but less so than rosmarinic acid. S montana extracts showed weak antioxidant or even pro‐oxidant properties. Extracts from butanol and from ethyl acetate and the total methanol extracts from all Sideritis plants studied showed a strong radical scavenging activity against DPPH^?, close to that of rosmarinic acid. S montana extracts were, as a whole, slightly weaker radical inhibitors than the extracts from the other two species. The antioxidant activity of Sideritis extracts was attributed to the presence of flavonoid and phenylpropanoid glycosides. Copyright © 2003 Society of Chemical Industry     

Natural antioxidants from herbs and spices

There is a growing interest in natural antioxidants found in plants because of the world‐wide trend toward the use of natural additives in food and cosmetics. Herbs and spices are one of the most important targets to search for natural antioxidants from the point of view of safety. This review presents the results on stabilization of lipids and lipid‐containing foods with different herbs and spices (ground materials or extracts) and reports the structure of the main antioxidatively acting compounds isolated from them. The review presents information about the antioxidative effects of rosemary, sage, oregano, thyme, ginger, summer savory, black pepper, red pepper, clove, marjoram, basil, peppermint, spearmint, common balm, fennel, parsley, cinnamon, cumin, nutmeg, garlic, coriander, etc. Among the herbs of the Labiatae family, rosemary has been more extensively studied and its extracts are the first marketed natural antioxidants. Sage and oregano, which belong to the same family, have gained the interest of many research groups as potential antioxidants.     

Effect of the phenol antioxidant type on the kinetics and mechanism of inhibited lipid oxidation in the presence of fatty alcohols

A kinetic analysis of inhibited lipid autoxidation in the presence of a phenol antioxidant and a hydroxy compound is proposed. It is based on studies of the dependence of the W^ROH/W_inh ratio (between the inhibited oxidation rates in presence and absence of a hydroxy compound) on the hydroxy compound concentration. This analysis permits establishing the mechanism of action of the hydroxy compound in the presence of different types of phenol antioxidants during inhibited lipid oxidation. The kinetic analysis has been applied to the oxidation at 80°C of triacylglycerols of sunflower oil (TGSO) inhibited by 0.1 mM hydroquinone, butylated hydroxytoluene (BHT) or α-tocopherol in the presence of different concentrations of 1-tetradecanol (1-TD) and 1-octadecanol (1-OD). A linear character of this dependence is established during hydroquinone-inhibited oxidation of triacylglycerols of sunflower oil in presence of 1-TD. In the case of α-tocopherol this dependence is linear for both 1-TD and 1-OD. The equilibrium constant of interaction between the phenol antioxidant and the fatty alcohols is determined by the angle coefficient of the linear dependence. The hydroquinone-inhibited autoxidation of TGSO in the presence of 1-OD has shown a non-linear character of the dependence under consideration. A kinetic model describing simultaneous participation of 1-OD in reaction with both the phenol antioxidant and the lipid hydroperoxides is deduced. Studying the kinetics of BHT-inhibited autoxidation of TGSO in the presence of 1-OD, it has been shown that due to steric reasons there is no interaction between 1-OD and BHT, 1-OD participating in the process only by accelerating the decomposition of the lipid hydroperoxides.     

UV spectroscopy studies of the oxidation changes in depot and structural lipids in high-fat feeding

The degree of incorporation of conjugated dienes, trienes and tetraenes into reserve (depot fats) and structural liver lipids of rats is studied depending on the type of high-fat feeding (50 energy%): lard, lard + sunflower oil (2:1), butter, hydrogenated sunflower oil. It is found that in adipose tissue there are only conjugated dienes whose concentration is lower than that of lipids of the respective diets and of the liver. Structural lipids are characterized by a high concentration of conjugated tri- and tetraenes. It is established that the fatty acid compositions of the diets and their oxidizability coefficients, respectively, do not correlate with the degree of accumulation of conjugated fatty acid structures in living organisms. The disequilibrated high-fat regimens based on butter and partially hydrogenated sunflower oil create conditions for more intensive incorporation of oxidized fatty acid products into the tissues.     

Kinetics of lipid oxidation in the presence of cinnamic acid derivatives

The effects of seven (prenyl‐ and methoxy‐) derivatives of cinnamic acid (0.1 mM) on the kinetics of lipid (sunflower oil triacylglycerols, TGSO) bulk phase oxidation at 80 °C have been compared. Synthesis of prenyl cinnamic acid derivatives: 3‐prenyl‐4‐hydroxy‐cinnamic acid (PHC), 3,5‐diprenyl‐4‐hydroxy‐cinnamic acid (DPHC), 2,2‐di‐methyl‐6‐carboxy‐ethenyl‐2H‐benzopyran (DMCB), 2,2‐dimethyl‐6‐carboxy‐ethenyl‐8‐prenyl‐2H‐benzopyran (DCEPB) present in Brazilian propolis has been performed. The monoprenyl derivative (PHC) has been found to exert a higher antioxidant activity as compared to the diprenyl derivative (DPHC). However, cinnamic acid derivatives DMCB and DCEPB have caused no change in the kinetics of TGSO oxidation. The results obtained have been compared with those on related compounds containing a cinnamic acid moiety as a structural feature, such as 4‐hydroxy‐cinnamic (p‐coumaric), 3‐methoxy‐4‐hydroxy‐cinnamic (ferulic) and 3,5‐dimethoxy‐4‐hydroxy‐cinnamic (sinapic) acids, as well as with data on butylated hydroxytoluene (BHT) and α‐tocopherol (αToc). PHC has shown a stronger antioxidant efficiency than BHT, p‐coumaric and ferulic acid, but a weaker antioxidant efficiency than α‐Toc and sinapic acid. The observed antioxidant effect of DPHC was stronger than that of p‐coumaric and ferulic acids and weaker than that of α‐Toc, BHT and sinapic acid.     

On the participation of fatty alcohols in the autoxidation of lipids

The influence of 1-tetradecanol, 1-hexadecanol, 1-octadecanol and 1-eicosanol in concentrations of 5 to 80 mmol kg^?1 on the autoxidation of various types of lipid systems (sunflower and olive oils, lard, tristearin and olive oil methyl esters) is investigated at 70–135°C. A pro-oxidative effect of the fatty alcohols introduced into the systems is established. The extent of this effect depends on the type and degree of unsaturation in the lipid system, its hydroperoxide content, and the chain length and concentration of the alcohols. A further factor is the valency of the alcohols with which the fatty acids are esterified; thus the pro-oxidative effect of the fatty alcohols is less pronounced with triacyl glycerols than with fatty acid methyl esters given the same oxidation rate. The results obtained are explained on the basis of the theory of a radical chain process of lipid oxidation.