Experimental design for extraction and quantification of phenolic compounds and organic acids in white “Vinho Verde” grapes

An experimental design was applied for the optimization of extraction and clean-up processes of phenolic compounds and organic acids from white "Vinho Verde" grapes. The developed analytical method consisted in two steps: first a solid-liquid extraction of both phenolic compounds and organic acids and then a clean-up step using solid-phase extraction (SPE). Afterwards, phenolic compounds and organic acids were determined by high-performance liquid chromatography (HPLC) coupled to a diode array detector (DAD) and HPLC-UV, respectively. Plackett-Burman design was carried out to select the significant experimental parameters affecting both the extraction and the clean-up steps. The identified and quantified phenolic compounds were: quercetin-3-O-glucoside, quercetin-3-O-rutinoside, kaempferol-3-O-rutinoside, isorhamnetin-3-O-glucoside, quercetin, kaempferol and epicatechin. The determined organic acids were oxalic, citric, tartaric, malic, shikimic and fumaric acids. The obtained results showed that the most important variables were the temperature (40 degrees C) and the solvent (acid water at pH 2 with 5% methanol) for the extraction step and the type of sorbent (C18 non end-capped) for the clean-up step.

Hydroxyl radical and hypochlorous acid scavenging activity of small centaury (Centaurium erythraea) infusion. A comparative study with green tea (Camellia sinensis)

Small centaury (Centaurium erythraea Rafin.) is a herbal species with a long use in traditional medicine due to its digestive, stomachic, tonic, depurative, sedative and antipyretic properties. This species is reported to contain considerable amounts of polyphenolic compounds, namely xanthones and phenolic acids as the main constituents. Although the antiradicalar activity of some pure polyphenolic compounds is already known, it remains unclear how a complex mixture obtained from plant extracts functions against reactive oxygen species. Thus, the ability of small centaury infusion to act as a scavenger of the reactive oxygen species hydroxyl radical and hypochlorous acid was studied and compared with that of green tea (Camellia sinensis L.). Hydroxyl radical was generated in the presence of Fe3+-EDTA, ascorbate and H2O2 (Fenton system) and monitored by evaluating hydroxyl radical-induced deoxyribose degradation. The reactivity towards hypochlorous acid was determined by measuring the inhibition of hypochlorous acid-induced 5-thio-2-nitrobenzoic acid oxidation to 5,5'-dithiobis(2-nitrobenzoic acid). The obtained results demonstrate that small centaury infusion exhibits interesting antioxidant properties, expressed both by its capacity to effectively scavenge hydroxyl radical and hypochlorous acid, although with a lower activity against the second than that observed for green tea. Green tea exhibited a dual effect at the hydroxyl radical scavenging assay, stimulating deoxyribose degradation at lower dosages.

Antioxidant effect of flavonoids after ascorbate/Fe2+-induced oxidative stress in cultured retinal cells11Abbreviations: BME, basal medium of Eagle; DCFH2, 2′,7′-dichlorodihydrofluorescein; LDH, lactate dehydrogenase; PC, partition coefficient; Rf, retardation factor; ROS, reactive oxygen species; TBA, thiobarbituric acid; and TBARS, thiobarbituric acid-reactive substances

In this study, we investigated the structure-activity relationship of four flavonoids, i.e. eriodictyol, luteolin, quercetin, and taxifolin, in cultured retinal cells after ascorbate/Fe(2+)-induced oxidative stress. The relative order of antioxidant efficacy, determined by the thiobarbituric acid method, was the following: eriodictyol > quercetin > luteolin > taxifolin. Upon preincubation, the flavonoids were also effective in reducing the extent of lipid peroxidation. Oxidative stress, determined by the changes in fluorescence of 2',7'-dichlorodihydrofluorescein, was also decreased in the presence of the flavonoids, showing the following order of antioxidant efficacy: eriodictyol > taxifolin approximately quercetin > luteolin. Ascorbate/Fe(2+)-induced oxidative stress or incubation in the presence of the flavonoids did not significantly affect the viability of retinal cells. We also evaluated the degree of membrane partition of the flavonoids. In this system, the results strongly suggest that the higher antioxidant activity of the flavonoids is not correlated with the presence of a double bond at C(2)-C(3) and/or a hydroxyl group at C(3) on the C ring, but rather may depend on the capacity to inhibit the production of reactive oxygen species to interact hydrophobically with membranes. Eriodictyol was shown to be the most efficient antioxidant in protecting against oxidative stress induced by ascorbate/Fe(2+) in the retinal cells.

Antioxidant activity of Centaurium erythraea infusion evidenced by its superoxide radical scavenging and xanthine oxidase inhibitory activity

Centaurium erythraea Rafin. (Gentianaceae) has long been used in traditional medicine. This plant contains considerable amounts of polyphenolic compounds, namely, xanthones and phenolic acids as the main constituents. Because phenolic groups exhibit activity as radical scavengers and/or metal chelators, this study evaluated the superoxide radical scavenging properties of a lyophilized infusion obtained from C. erythraea flowering tops. Superoxide radical scavenging activity was assayed using enzymatic (xanthine/xanthine oxidase) and nonenzymatic (NADH/phenazine methosulfate) superoxide generating systems. This study provided evidence that C. erythraea exhibits interesting antioxidant properties, expressed either by the capacity to scavenge superoxide radical or to noncompetitively inhibit xanthine oxidase. The main phenolic compounds present in this extract were several esters of hydroxycinnamic acids, namely, p-coumaric, ferulic, and sinapic acids.

Analysis of phenolic compounds in Spanish Albrariño and Portuguese Alvarinho and Loureiro wines by capillary zone electrophoresis and high-performance liquid chromatography

The concentration of different phenolic compounds was measured in Spanish Albariño and Portuguese Alvarinho and Loureiro white wines by capillary zone electrophoresis (CZE), in order to characterize them. Although all samples presented the same qualitative pattern (characterized by tyrosol; (-)-epicatechin; syringic acid; ferulic acid; p-coumaric acid; caffeic acid, gallic acid; 3,4-dihydroxybenzoic acid; cis-coumaroyl tartaric acid (COUTA); trans-COUTA; trans-caffeoyl tartaric acid (CAFTA), and hydroxycinnamic esters), some quantitative differences were observed. When samples were analyzed by high-performance liquid chromatography (HPLC), in order to compare the results obtained by both techniques, no significant qualitative or quantitative differences were obtained. Nevertheless, CZE proved to be a more convenient technique for the routinary analyses of these wines, due to better separation of the different compounds, better peak shapes, and higher speed than HPLC.

Flavonoids and phenolic acids of sage: influence of some agricultural factors

A reversed-phase high-performance liquid chromatography/diode-array detector procedure is proposed for the determination of six phenolic compounds (caffeic acid, luteolin 7-O-glucoside, rosmarinic acid, apigenin, hispidulin, and cirsimaritin) in sage. The chromatographic separation was achieved using a reversed-phase Spherisorb ODS2 (5-microm particle size, 25.0 x 0.46 cm) column. Of the several extractive solvents assayed only ethyl ether, ethyl acetate, and acetone were able to extract all the compounds mentioned. Best resolution was obtained using a gradient of water/phosphoric acid (999:1) and acetonitrile. Ten samples cultivated in two experimental fields (1997-1999) were analyzed and the individual compounds quantified. Four commercially available samples were also analyzed and the results are discussed.

Analysis of phenolic compounds in the evaluation of commercial quince jam authenticity

The phenolic compounds present in 17 samples of Portuguese commercial and three homemade quince jams were analyzed by reversed-phase HPLC/DAD, to determine their authenticity. Two different extraction methods were needed for the complete definition of quince jams profiles, one of them including an Amberlite XAD-2 cleaning step. These analyses showed that all the samples presented a similar profile composed of at least eight identified phenolic compounds, several unidentified characteristic procyanidin polymers, and sodium benzoate as preservative of quince jams. Several samples also contained arbutin, suggesting that these quince jam samples were fraudulently adulterated with pear puree.

Analysis of vervain flavonoids by HPLC/Diode array detector method. Its application to quality control

A reversed-phase HPLC procedure is proposed for the determination of seven flavonoids (luteolin, nepetin, hispidulin, jaceosidin, cirsimaritin, cirsilineol, and eupatorin) in vervain samples. A simple extractive technique was developed, involving only extraction with ethyl ether, which allowed the elimination of phenolic acids, yielding a sufficiently purified flavonoid fraction. All of the analyzed vervain samples showed a common flavonoid pattern, in which hispidulin and jaceosidin were the major compounds and nepetin was the minor compound.