Search

The present study examined the radical scavenging potential of the two benzene derivatives found in the bay laurel essential oil (EO), namely methyl eugenol (MEug) and eugenol (Eug), theoretically and experimentally to make suggestions on their contribution to the EO preservative activity through such a mechanism. Calculation of appropriate molecular indices widely used to characterize chain-breaking antioxidants was carried out in the gas and liquid phases (n-hexane, n-octanol, methanol, water). Experimental evidence was based on the DPPH• scavenging assay applied to pure compounds and a set of bay laurel EOs chemically characterized with GC-MS/FID. Theoretical calculations suggested that the preservative properties of both compounds could be exerted through a radical scavenging mechanism via hydrogen atom donation. Eug was predicted to be of superior efficiency in line with experimental findings. Pearson correlation and partial least square regression analyses of the EO antioxidant activity values vs. % composition of individual volatiles indicated the positive contribution of both compounds to the radical scavenging activity of bay laurel EOs. Eug, despite its low content in bay laurel EOs, was found to influence the most the radical scavenging activity of the latter.

DFT calculation of various molecular descriptors was carried out in order to examine the radical scavenging properties of sesame oil lignans and some selected metabolites of sesamin formed in vivo. The major sesame oil lignans, namely sesamin and sesamolin may present antioxidant activity through hydrogen atom transfer, though lacking a phenolic group. This can be achieved via the contribution of allylic hydrogen atoms according to C–H bond dissociation enthalpy (BDE) values. Even so, the predicted activity is not higher than that of some phenolic derivatives (e.g. pinoresinol) or metabolites bearing catechol moieties. The contribution of non-phenolic hydrogen atoms may result in the formation of planar or semi-planar conjugated compounds. Some of the tested lignans (e.g. sesaminol, sesamolinol) may be efficient electron donors comparable to active flavonoids according to ionization potential (IP) values. Neutral sesamol can be an efficient electron donor rather than hydrogen atom donor according to IP and net electrophilicity values. Only computation in water could partially justify literature experimental findings on the higher reactivity of sesamol over that of sesamin. The metabolites of sesamin, bearing one or two catechol groups were found as the most efficient hydrogen atom donors and most prone to ionization. Therefore, they could be capable to act efficiently via hydrogen atom transfer (HAT) or sequential proton loss electron transfer (SPLET) in real systems as shown by gas-phase and calculations in solvents (benzene, water). Thus, these metabolites may account for the high in vivo antioxidant activity of sesamin. Examination of the succeeding products of metabolism indicated the progressive loss of radical scavenging efficiency which was predicted to be negligible in the compounds excreted from the body of mammals.

The phenolic content/composition and antioxidant activity of hot/cold infusion and decoction from the leaves of Arbutus unedo were studied for the first time. 1,1-diphenyl-2-picrylhydrazyl (DPPH●), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS●+), crocin-bleaching, copper-reducing, and liposome accelerated oxidation assays were used for the evaluation of the activity in vitro. In vivo, the extracts were examined for their ability to protect S. cerevisiae cells from H2O2 induced oxidative stress. An on-line high-performance liquid chromatography-DPPH● assay was applied to identify potent radical scavengers and comment on their contribution to the total activity. The addition of leaves to boiling water (decoction) was the most appropriate practice to apply since the highest phenol intake (220.2 mg gallic acid/cup served) was obtained. Additionally, its antioxidant activity was equal or superior to that of the other extracts. Flavonols (~51–61 mg/g dry extract) were the main phenols in all the extracts, with quercitrin accounting for ~20% of the total phenol amount. The on-line DPPH● method verified the high potency of the decoction and indicated as the most active radical scavengers, two galloylquinic acid derivatives and myricitrin, accounting for ~28–45% and ~11–13% of the total scavenging, respectively. Present data may contribute to the future exploitation of A. unedo leaves by the food industry for health-promoting herbal tea preparations and dietary supplements.

In this study, a two-stage process, alcoholic and acetic acid fermentation was applied for the first time to fresh pomegranate juice to examine its effect on the phenolic content together with the antioxidant activity of the fermented product(s). The total phenol content of the juice was not greatly affected during the process. On the contrary, the total anthocyanin content fluctuated; the alcoholic product was 10-fold poorer while the end product was as rich as the fresh juice. Both fermented products had qualitatively similar HPLC-DAD-MS profile of phenolic constituents with that of the starting material but lower content (e.g. 49 and 32% of individual phenolic acid derivatives remained, respectively). The acetification product retained 44% and 37% of the fresh juice activity to scavenge the DPPH• and reduce cupric ions, respectively. These characteristics along with attractive red colour suggest that the end product is a potential source of functional constituents.

The impact of alkaline or acid digestion to phenolic content (TPP), antioxidant activity (radical scavenging, copper (II) reducing and liposome oxidation) and phenolic composition of rice hull extracts was evaluated systematically for the first time. Alkaline digestion yielded extracts superior in TPP (13206-25498 mg gallic acid/kg dry hulls) and antioxidant activity. Chromatographic analysis showed that these were rich in hydroxycinnamic acids, whereas hydroxybenzoic acid/aldehyde derivatives, obtained as hydroxycinnamate degradation products, were the main phenolics in the extracts after acid treatment. Optimized alkaline digestion (120 °C, 120 kPa, 2 h) applied to hulls from selected rice varieties cultivated in Greece, showed a high p-coumaric (4879–6367 mg/kg dry hulls) and ferulic acid (1510–2037 mg/kg dry hulls) content, probably related to their low silicon levels (44,916–59,981 mg SiO2/kg dry hulls). Our study provides useful data for exploitation of rice hulls by the food industry.

Crocin Bleaching Assay (CBA) was applied to serum samples randomly collected from 22 obese donors, in order to investigate whether it could detect patients suffering from metabolic syndrome (MS), which is associated with oxidative stress. The same samples were also tested using the ORAC method, having analytical similarities with CBA (pH value, radical initiator and temperature) and commonly applied to biological fluids. Statistical analysis indicated that CBA was more promising in predicting the MS in obese subjects. The current study contributes to the commercial exploitation of saffron in the field of analytical chemistry.

The choice of reference compounds is examined as a “critical control point” of antioxidant activity assessment. Gallic, caffeic, sinapic, uric, and ascorbic acids, isoeugenol, and Trolox were tested using different redox (FRAP, Folin−Ciocalteu) and radical scavenging (DPPH•, ABTS•+, CBA, ORAC) assays. The ability to chelate transition metals was assessed to support some of the findings. Analytes were also tested in liposomes. On the basis of the findings, we do not recommend uric acid (due to solubility constrains) and ascorbic acid (due to fast degradation kinetics) as references. The behavior of the rest of the compounds could not always be attributed to typical structural characteristics. Selection of suitable reference compounds for in vitro antioxidant activity assays is not an easy task to achieve. The choice of reference compounds has to remain at the convenience of the researchers, with regard to the aim of the study. Keywords: Antioxidants; antioxidant activity assessment; reference compound; rad...

Storage effect on antioxidant content and capacity of grape seeds under different a w conditions ( a w 0.33; 0.53; 0.75/50 days, 25 °C) was examined. Total phenol content (determined by the Folin–Ciocalteu method) decreased during storage though changes were trivial for samples stored at 33% or 53% RH. High level of humidity (75%) accelerated degradation and resulted in a ∼50% reduction of total phenol content. Minor loss of the DPPH radical scavenging activity (%RSA) of the extracts was observed. Catechin and epicatechin content monitored by RP-HPLC was reduced during storage, particularly at 75% RH. Epicatechin content proved to be less sensitive to water activity conditions than catechin content. Results of various in vitro assays (Folin–Ciocalteu, FRAP, DPPH, ABTS, CBA, ORAC and copper induced liposome oxidation) did not support difference in terms of resistance to oxidation. Based on the continuous release of gallic acid, our finding was related to hydrolytic reactions. Control of a w of grape seeds can be of practical importance for the wine industry.

Some commonly used antioxidants, namely BHA, BHT, TBHQ, α-tocopherol and caffeic acid were comparatively studied in phosphatidylcholine liposomes and in o/w emulsions. Trolox was included as reference. Oxidation was monitored at 37 °C by measuring peroxide formation. Low polarity and sometimes the molecular size seem to be the determining factors for an appreciable antioxidant performance. BHA and BHT were the most effective at the low levels of addition used. α-Tocopherol had an intermediate activity. The pro-/antioxidant behaviour of caffeic acid was concentration dependent. TBHQ activity was slightly better than that of caffeic acid and comparable with that of Trolox. The results add to knowledge for structure antioxidant activity relationships in various systems and may also have a practical outcome concerning the optimum levels of use.

The importance of a catechol moiety to the radical-scavenging activity of p-hydroxycinnamic derivatives is widely accepted, whereas the role of the carbon side chain remains controversial. Extension of the conjugation to this chain is a molecular feature that requires some attention. Differences in the activity of caffeic and dihydrocaffeic acids were examined using a series of experimental procedures: assays using free radicals [1,1-diphenyl-2-picrylhydrazyl (DPPH•) and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•+)]; assays based on redox reactions; and accelerated tests in bulk oils and dispersed systems. To reinforce observations on the role of the side chain, a group of related monophenols, differing in one double bond and/or its position in the chain, was also examined. Extended conjugation was essential for the rapid scavenging of free radicals and for effectiveness in dispersed systems (both liposomes and emulsions). In the case of bulk oils, the contribution of conjugation remained unclear. Information based on redox reactions was not useful for the aim of our study. The experimental conditions may mask or enhance the effect of the chain characteristics on the activity, so the size and the order of activity may be influenced. Thus, structure-activity relationships should be drawn with caution.

Structure-activity relationships in the antioxidants caffeic acid and dihydrocaffeic acid as well as in the monophenols isoeugenol, eugenol, and dihydroeugenol were investigated by using the density functional theory (DFT). The higher antioxidant activity of caffeic acid, among the rest, could be attributed to its lower difference in the heat of formation (ΔHOF) value. Dihydrocaffeic acid exhibits less antioxidant activity than caffeic acid, owing to both its higher ΔHOF value and its limited spin delocalization. These two latter findings could also account for the lower antioxidant activity of both eugenol and dihydroeugenol as compared to isoeugenol. DFT calculations afford a good molecular descriptor, ΔHOF, that correlates well with the antioxidant activity in molecules exhibiting similar structural characteristics. The presence of a simple double bond in the side chain makes a difference in the antioxidant activity only if it leads to an extended conjugation. Calculated dipole moment values for both the parent molecules and the respective phenoxyl radicals correlate well with their antioxidant efficiency in some instances.

Three natural oil body emulsions of a similar fat content (similar to 5%), but differing in their protein composition were obtained from an aqueous maize germ extract. The first was prepared by concentrating the aqueous oil body extract with ultrafiltration to a fat content of similar to 5%. The other two were prepared by initially recovering the oil bodies from the extract by centrifugation, either in the presence of sucrose or by applying isoelectric precipitation at pH 5.0 and then diluting the resulting oil body creams with deionized water. The oxidative and physical stability of the three emulsions, either as they were or after submission to thermal treatment (100 degrees C for 15 min), were studied following storage at 45 degrees C. The emulsions differed both in their oxidative and physical stability, depending on the recovery method that in turn influenced their continuous phase and/or interfacial membrane protein and/or polar antioxidant composition. Ultrafiltration resulted in the most stable emulsion. Mixtures of the natural oil body emulsions with green tea extracts, aiming to serve as a base for functional beverages, were then prepared and studied for their creaming behaviour. The green tea polyphenols seem to interact with the oil bodies leading to intensive dispersion destabilisation which, however, was halted following carrageenan addition at a relatively very low level. (C) 2013 Elsevier Ltd. rights reserved.

Edible and nonedible grades of virgin olive oil (VOO), differing in quality characteristics, were evaluated for potential genotoxicity in the Drosophila somatic mutation and recombination test (SMART) before and after heating at high temperatures. Drosophila larvae were fed on medium containing 6 and 12% v/v of each of the examined oils. Edible VOOs did not exhibit any mutagenic or recombination activity even after thermal treatment. Lower grade VOO gave negative results at the concentration of 6% and inconclusive ones at 12%. However, after its thermal treatment, a statistically significant increase of large single spots was observed, giving a positive result for this spot category at both concentrations. Evaluation of the possible contribution of olive phenolic compounds to the nongenotoxic effects observed was carried out using a polar olive leaf extract and pure oleuropein. No significant increase in the frequency of any category of mutant spots was recorded for leaf extract (0.8-12 mg of total polar phenols/dose) or pure oleuropein (0.8-8 mg/ dose). These results are expected to contribute to the ongoing interest in the inherent properties of VOO as part of the everyday diet.

Data for antiradical properties of saffron extract and its bioactive constituents (crocins, crocetin) are limited and poorly discussed in comparison with those of extracts containing potent scavengers. Further examination was sought using the Folin-Ciocalteu (F-C) reagent and various free radical species produced in cell-free or cell model systems. Oregano and turmeric methanol extracts, rich in well established scavengers, and also crocetin, rosmarinic acid, and curcumin, representing the major types of constituents in the three studied extracts, were used as "reference". On the same weight basis, saffron extract activity was found to be rather negligible in all cell-free systems with regard to that found for reference ones. On the contrary, in the human monocyte system, saffron extracts or free crocetin were found to reduce ROS production as effectively as the phenolic antioxidants. Our findings point out that saffron extracts exhibit a remarkable intracellular antioxidant activity that cannot be revealed using assays repeatedly applied to the evaluation of phenolic-type antioxidants.

Rapid 1,1-diphenyl-2-picrylhydrazyl (DPPH•) tests are often applied to classify the scavenging activity of phenolic compounds (AH). Published analytical protocols differ in more than one experimental condition, and results for the relative order or magnitude of activity are often contradictory. In this work, parameters such as duration of test, [AH]/[DPPH•] molar ratio, and solvent effects were examined and discussed. The test duration and the value of the [AH]/[DPPH•] ratio did not influence the order of activity among tested antioxidants. Ethanol, commonly used as solvent in such tests, was compared with acetonitrile and tert-butyl alcohol. Solvent properties such as the ability to form hydrogen bonds with the AH seem to influence the level of the relative activity (%RSA). Higher %RSA values were observed in ethanol. The activity of the most polar compounds was affected the most, and in some cases (caffeic, dihydrocaffeic, and rosmarinic acids) the order of activity was changed owing to different kinetics. Standardization of the analytical protocol should include a 20-min reaction period and a molar ratio that permits attainment of a 60–80% RSA value for the most potent antioxidant. Solvent choice is critical for classifying activity. Safe classification can be based only on results from kinetic studies.