Antioxidant phenolic compounds of Dracaena cambodiana

The antioxidant activities of the petroleum ether, ethyl acetate, n-BuOH and water extract fractions from Dracaena cambodiana Pierre ex Gagnep were evaluated in this study. The ethyl acetate fraction contained the highest amount of total phenolics and total flavonoids, and showed the greatest DPPH˙, ABTS+ and Superoxide anion radical-scavenging capacities. The DPPH˙, ABTS+ and Superoxide anion radical-scavenging capacities of nine compounds isolated from the ethyl acetate fraction were also evaluated. The results indicated that these compounds contributed to the antioxidant activity of D. cambodiana. Therefore, D. cambodiana and these compounds might be used as natural antioxidants.     

Antioxidant activity of phenolic and flavonoid compounds in some medicinal plants of India

In this study, total phenolics, flavonoids and vitamin C content vis-a-vis antioxidant activities were assayed in leaves and stem bark of Azadirachta indica, Butea monosperma, Cassia fistula, Mangifera indica, Syzygium cumini and Tamarindus indica using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radical scavenging method. The DPPH radical scavenging activity positively correlated with the total phenolic content in both stem bark and leaf. Superoxide radical scavenging activity increased with increasing flavonoid contents. However, the vitamin C content could not be correlated with DPPH and superoxide radical scavenging capacity.     

Antioxidant activity of lignin phenolic compounds extracted from kraft and sulphite black liquors

The antioxidant activity of the phenolic compounds present in industrial black liquors obtained from the two cooking processes (kraft and sulphite) used in Portugal to produce Eucalyptus globulus pulp was evaluated. The black liquors treated at several pH values were extracted with ethyl acetate. Phenolic fractions were further separated by liquid chromatography of the crude extracts of kraft liquor at pH = 6 and sulphite liquor at the original pH. Total phenolic content was determined in terms of gallic acid equivalents (Folin-Ciocalteu colorimetric method), and the antioxidant activity in the crude extracts at several pH values and in the separated fractions was measured using the DPPH test for radical scavenging capacity. The total phenolic content of crude extracts and separated fractions ranged from 92.7 to 181.6 and from 91.6 to 1,099.6 mg GAE/g, respectively, while the antioxidant activity index (AAI) ranged from 2.20 to 3.41 and from 2.21 to 11.47 respectively, showing very strong antioxidant activity in all studied cases. The fractions separated by column chromatography were submitted to mass spectrometry analysis and the results were compared to others in the literature of natural products, mainly from Eucalyptus, and the characteristic bands of functional groups were identified by 1H-NMR and FTIR. These methods allowed the identification of 17 phenolic compounds.     

Antioxidant phenolic compounds from the rhizomes of Astilbe rivularis

The rhizomes of Astilbe rivularis, commonly known as ‘Thulo Okhati’ are widely used in Nepal as tonic for uterine and menstrual disorders. In our preliminary study, the 70% MeOH extract of the rhizomes showed potent antioxidant activity. Hence, present study was aimed for the isolation of potent antioxidant constituents. Bergenin (1), 11-O-galloylbergenin (2), (+)-catechin (3), (?)-catechin (4), (?)-afzelechin (5), (?)-epiafzelechin (6) and 2-(β-D-glucopyranosyloxy)-4-hydroxylbenzenacetonitrile (7) were isolated from the rhizomes. Structures of these compounds were elucidated on the basis of spectroscopic methods. All these isolated compounds were evaluated for their in vitro antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. 11-O-Galloylbergenin (2), (+)-catechin (3), (?)-catechin (4), (?)-afzelechin (5) and (?)-epiafzelechin (6) showed potent antioxidant activity.     

Determination of phenolic compounds in medicinal herbs by reversed-phase HPLC

An HPLC procedure is proposed for the determination of 12 phenolic compounds in plant tissues by reversed-phase HPLC with gradient elution and UV detection. The influence of pH, composition of the mobile phase, concentration of the organic modifier, and temperature on the separation of gallic, protocatechuic, trans-ferulic, trans-caffeic acid, rutin, quercetin, dihydroquercetin, and (_)-epicatechin for 30 min is studied. The lower limit of quantification of phenolic compounds is 1–2.5 μg/L. The procedure was applied to the determination of phenolic compounds in aqueous extracts of Hypericum perforatum; its sample was found to contain protocatechuic acid, (_)-epicatechin, and also rutin.     

Antioxidant activities, total phenolics and HPLC analyses of the phenolic compounds of extracts from common Mediterranean plants

In this study, the total phenolic amounts and antioxidant activities of plant extracts obtained from some common Mediterranean plant species collected from different places in Jordan were determined. The phenolic constituents of these extracts were also determined using HPLC. The total phenolic amounts ranged from 52.8 to 876.9 mg GAE per 100 g dry material. The antioxidant activities were evaluated according to the 2,2-diphenyl-1-picrylhydrazyl radical scavenger method. Sage (Salvia officinalis) showed the highest antioxidant activity (91%), while the lowest (11.3%) was seen in parsley (Petroselinum crispum). A strong correlation (r = 0.85) between antioxidant activity and total phenolic content was found. The phenolic compounds identified by HPLC were gallic acid, protocatechuic acid, catechin, gentisic acid, chlorogenic acid, vanillic acid, syringic acid, caffeic acid, epicatechin and benzoic acid. All the investigated plants contain gallic acid, whose phenolic content ranged from 0.4 to 37.8 mg per 100 g, catechin (0.3-339.9 mg per 100 g), protocatechuic acid (0.3-41.9 mg per 100 g) and gentisic acid (0.3-35.8 mg per 100 g), while caffeic acid (0.3-2.6 mg per 100 g) was detected in six species only. These natural plant phenolics could thus be a good source of antioxidants for applications in food.     

Recent developments in the HPLC separation of phenolic compounds

Phenolic compounds represent a class of highly complex naturally occurring molecules that possess a range of beneficial health properties. As a result, considerable attention has been devoted to the analysis of phenolics in a variety of samples. HPLC is the workhorse method for phenolic separation. However, conventional HPLC methods provide insufficient resolving power when faced with the complexity of real-world phenolic fractions. This limitation has been traditionally circumvented by extensive sample fractionation, multiple analysis methods and/or selective detection strategies. On the other hand, there is an increasing demand for improved throughput and resolving power from the chromatographic methods used for phenolic analyses. Fortunately, during the last decade, a number of important technological advances in LC have demonstrated significant gains in terms of both speed and resolution. These include ultra high-pressure liquid chromatography (UHPLC), high-temperature liquid chromatography (HTLC), multi-dimensional separations as well as various new stationary phase chemistries and morphologies. In recent years, these technologies have also found increasing application for phenolic analysis. This review seeks to provide an updated overview of the application of recent advances in HPLC to phenolic separation, with the emphasis on how these methodologies can contribute to improve performance in HPLC analysis of phenolics.     

Group-type separation and determination of phenolic compounds in coal-derived products by HPLC

Summary A rapid method was developed for the direct extraction of phenolic compounds from coal-derived products and subsequent isocratic HPLC analysis in a reversed-phase system by using the backflush technique.     

HPLC study of the efficiency of extraction of phenolic compounds

Summary The rate of extraction of phenolic compounds in two different solvents has been studied by liquid chromatography (HPLC) under reverse phase, gradient elution conditions. The solvents were diethyl ether and ethyl acetate. The method has been applied to two natural samples, a white wine and apple pulp.     

Determination of the antioxidant activity of phenolic compounds by coulometric detection

The combination of reversed-phase high-performance liquid chromatography with coulometric detection allows the detection of phenolic antioxidants in complex matrices like plant extracts with a high degree of sensitivity and selectivity. According to their voltammetric behaviour, phenolic acids and tocopherols show maximal detector response at low potentials (100-450 mV) while flavonoids show optimal response at two different potential values (one at 0-300 mV and one at 600-900 mV). The potential corresponding to maximal detector response (MDRP) of phenolic acids was shown to be inversely proportional to their antioxidant efficiency as determined in a lipidic model system under strong oxidizing conditions (110 degrees C, intensive oxygenation) or by the DPPH() test. However, such a relationship was not observed for flavonoids.     

Effect of processing on the release of phenolic compounds and antioxidant activity during in vitro digestion of hulless barley

Hulless barley contains phenolic compounds and possesses various antioxidant activities. To clarify the effects of thermal processing and in vitro digestion on the release of phenolic compounds in hulless barley, we studied the phenolic components and antioxidant activities of hulless barley after steaming, roasting processes, and in vitro digestions. Both total phenolic content (TPC) and total flavonoid content (TFC) in raw hulless barley (HB, 4.14 mg/g DW and 1.53 mg/g DW, respectively) were higher than that of steamed hulless barley (SHB) and roasted hulless barley (RHB). In vitro digestion significantly released more ferulic acid from its bound form, but hydrolyzed some amount of flavonoid (luteolin). Chrysoeriol-7-O-glucouronide was significantly detected (412.13 µg/g DW in HB, 382.19 µg/g DW in SHB, and 396.91 µg/g DW in RHB) in all three hulless barley. The total released content of phenolic compounds obtained from each phase after digestion reached to 46% and 45% for SHB and RHB, which was higher than that in the HB (41%). The antioxidant assay (via DPPH and ABTS free radical scavenging assays) indicated that the capacity of HB was obviously higher than that of SHB and RHB in undigested group. For digested group, the ABTS⁺ assay order was following, undigested > oral > small intestine > gastric > large intestine. The DPPH assay results indicated the antioxidant capacity as the order of undigested > oral > gastric > large intestine. Correlation analysis showed that ferulic acid, chrysoeriol-7-O-glucouronide, luteolin, chrysoeriol, and luteolin-7-O-glucouronide contributed to the antioxidant activities. Hierarchical cluster analysis (HCA) grouped samples accordingly. Roasting process could be considered as a better daily thermal treatment for hulless barley than steaming in terms of phenolic compounds and their antioxidant activities.     

Development of a CE-ESI-microTOF-MS method for a rapid identification of phenolic compounds in buckwheat

A sensitive CE-ESI-MS analytical method for the identification of buckwheat antioxidants has been developed. CE and ESI-TOF parameters (e.g. buffer composition and pH, sheath liquid composition, sheath liquid and gas flow rates, electrospray voltage) were optimized to obtain an optimal analytical separation and identification. The results confirmed the presence of phenolic acids, procyanidins and galloylated propelargonidins. The identification of swertiamacroside and 2-hydroxy-3-O-β-D-glucopyranosil-benzoic acid, found for the first time in our previous work, has been confirmed. Furthermore, 5,7,4'-trimethoxyflavan and dihydroxy-trimethoxyisoflavan have also been tentatively identified for the first time in buckwheat.     

水中挥发酚的在线蒸馏-固相萃取分离富集及测定

在顺序注射系统中实现了挥发酚的快速自动在线蒸馏,并用AmberliteXAD-7树脂微填充柱对其与4-氨基安替比林的衍生物在线固相萃取,被富集的衍生物可用少量乙醇有效地洗脱回收,以分光光度法检测.方法可用于较高浓度挥发酚(mg/L)样品的测定,也可根据需要适当增大进样体积,经富集后实现更低浓度水平(μg/L)挥发酚的测定.当富集过程中进样体积为4mL时,方法测定挥发酚的线性范围为0.004~0.3mg/L,检出限为0.002mg/L,相对标准偏差为1.4%(0.1mg/L,n=9).对多种实际水样中的挥发酚进行了测定,加标回收实验的回收率在96%~102%之间.     

Antioxidant phenolic compounds of cassava (Manihot esculenta) from Hainan

An activity-directed fractionation and purification process was used to isolate antioxidant components from cassava stems produced in Hainan. The ethyl acetate and n-butanol fractions showed greater DPPH˙and ABTS?+ scavenging activities than other fractions. The ethyl acetate fraction was subjected to column chromatography, to yield ten phenolic compounds: Coniferaldehyde (1), isovanillin (2), 6-deoxyjacareubin (3), scopoletin (4), syringaldehyde (5), pinoresinol (6), p-coumaric acid (7), ficusol (8), balanophonin (9) and ethamivan (10), which possess significant antioxidant activities. The relative order of DPPH? scavenging capacity for these compounds was ascorbic acid (reference) > 6 > 1 > 8 > 10 > 9 > 3 > 4 > 7 > 5 > 2, and that of ABTS?+ scavenging capacity was 5 > 7 > 1 > 10 > 4 > 6 > 8 > 2 > Trolox (reference compound) > 3 > 9. The results showed that these phenolic compounds contributed to the antioxidant activity of cassava.     

Antioxidant activity and total phenolic content in shiitake mycelial exudates

Exudates (DE) secreted from two shiitake mushroom mycelia (strains 1358 and L5458) were evaluated for their antioxidative properties and phenolic content. 1358DE and L5458DE showed distinct antioxidant activity in different in vitro assays, including scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, hydroxyl radical, superoxide anions and hydrogen peroxide; the ability to chelate ferrous ions; reducing power; hemolysis inhibition activity in rat erythrocyte; and lipid peroxidation inhibition (IC50 values of 1358DE and L5458DE were 3.3 and 132.6; 44.5 and > 1000; 26.9 and 53.7; 153.6 and > 175.0; 176.0 and 521.0; 26.7 and 746.4; 47.8 and 736.9; and 3.1 and > 1000 microg/mL, respectively). Their total phenolic content was 237.33 and 24.08 mg gallic acid equivalent (GAE)/g of dry DE, respectively. Overall, these results show that 1358DE generally possesses better antioxidant properties than L5458DE, possibly due to its larger total phenolic content. Shiitake mushroom mycelial exudates, particularly of 1358DE, could be a good source of natural antioxidants.     

Free and bound phenolic compounds in barley (Hordeum vulgare L.) flours. evaluation of the extraction capability of different solvent mixtures and pressurized liquid methods by micellar electrokinetic chromatography and spectrophotometry

The solution speciation of metals is a critical parameter controlling the bioavailability, solution-solid phase distribution and transport of metals in soils. The natural metal-complexing ligands that exist in soil solution include inorganic anions, inorganic colloids, organic humic substances, amino acids (notably phytosiderophores and bacterial siderophores) and low-molecular mass organic acids. The latter two groups are of particular significance in the soil surrounding plant roots (the rhizosphere). A number of analytical methodologies, encompassing computational, spectroscopic, physico-chemical and separation techniques, have been applied to the measurement of the solution speciation of metals in the environment. However, perhaps with the exception of the determination of the free metal cation, the majority of these techniques rarely provide species specific information. High-performance liquid chromatography (HPLC) coupled to a sensitive detection system, such as inductively coupled plasma mass spectrometry (ICP-MS) or electrospray ionisation mass spectrometry (ESI-MS), offers the possibility of separating and detecting metal-organic acid complexes at the very low concentrations normally found in the soil environment. This review, therefore, critically examines the literature reporting the HPLC separation of metal-organic acid complexes with reference to thermodynamic equilibrium and kinetic considerations. The limitations of HPLC techniques (and the use of thermodynamic equilibrium calculations to validate analytical results) are discussed and the metal complex characteristics necessary for chromatographic separation are described.     

Dispersive liquid-liquid microextraction of phenolic compounds using solidified floating organic droplets, and their determination by HPLC

We have developed a simple and efficient method for dispersive liquid-liquid microextraction of 4-nitrophenol, 2-naphthol and bisphenol A in real water samples. It is making use of solidified floating organic droplets of 1-dodecanol which has low density and a proper melting point. The type and volume of extraction solvent and dispersive solvent, the effect of salts, pH value and extraction time were optimized and resulted in enrichment factors of 84 for 4-nitrophenol, 123 for 2-naphthol, and 97 for bisphenol A. The limits of detection by HPLC are 1.50, 0.10 and 1.02 ng · mL^?1, respectively. Excellent linearity is observed in the concentration range from 10 to 800 ng · mL^?1, with coefficients of correlation ranging from 0.9988 to 0.9999. The relative standard deviations (for n?=?5) are from 3.2 to 5.3 %, and relative recoveries for the three phenols in tap, river and spring water range from 85.0 to 105.0 %, 98.3 to 110.0 %, and 98.6 to 109.0 %, respectively.

Antioxidant activity of propofol and related monomeric and dimeric compounds

This study was carried out to investigate the antioxidant activity of propofol (2,6-diisopropylphenol) and its related compounds, butylated hydroxyanisole (BHA), 2,6-dimethylphenol, 2,6-di-t-butylphenol, and their dimeric compounds. The degree of antioxidant activity was evaluated based on the degree of peroxidation induced with Fe-ascorbic acid in egg phosphatidylcholine through the determination of thiobarbituric acid-reactive substances (TBARS) formed during peroxidation. Their antioxidant activities were in the order of dipropofol>di(2,6-di-t-butylphenol)>diBHA>di(2,6-dimethylphenol). Dipropofol, a dimeric compound of propofol, showed the highest antioxidant activities. Dimeric compounds had higher activities than monomeric compounds, and the 1,1-diphenyl-p-picryhydrazyl-trapping ability of dimeric compounds was also greater than those of monomeric compounds (4-10-fold). These results suggest that dimeric phenols may increase their antioxidant activities along with increments in the conjugation system and play a inhibitory role in the propagation of free radical chain reactions.