Antioxidant activity of grape skin aqueous extracts from pressurized hot water extraction combined with electron paramagnetic resonance spectroscopy

Pressurized hot water extraction (PHWE) was employed to prepare extracts from dried grape skin of two wine grape varieties (St. Laurent and Alibernet) at various temperatures (from 40 up to 120 °C) and amounts of sample (0.5, 1.0 and 1.5 g). To assess the antioxidant activity of the extracts, electron paramagnetic resonance (EPR) spectroscopy was applied involving DPPH and ABTS⁺ assays. Other extract characteristics including HPLC profile of anthocyanins and total phenolic compound content were obtained as well. PHWE has also been compared with earlier results of extractions of the same grape skin samples with compressed methanol and compressed ethanol under the conditions of pressurized fluid extraction (PFE). From this comparison, PHWE emerges as the more benign and efficient extraction method to recover valuable phenolic antioxidants from grape skins for the prospective use in functional food supplements.     

Supercritical fluid extraction and HPLC determination of relevant polyphenolic compounds in grape skin

The polyphenols determined are: (+)-catechin, (-)-epicatechin, rutin, quercetin and trans-resveratrol. Suitable conditions of supercritical fluid extraction were established using ethanol as a modifier of the polarity solvent (supercritical carbon dioxide). Final extraction conditions were: 20% v/v ethanol, 60degreesC, 250 bars and flow rate 2 mL/min. Static step time and dynamic step time were established using a selected grape skin sample. The extract was collected in water; the more polar polyphenols ((+)-catechin and (-)-epicatechin) remain in solution but rutin, quercetin and trans-resveratrol precipitate in this medium, thereby the solution of the extracted polyphenols was filtered. (+)-Catechin and (-)-epicatechin were determined in the liquid fraction, while the solid fraction, containing rutin, quercetin and trans-resveratrol, was solved with ethanol/H20 (40:60). HPLC determination was carried out at C18 stationary phase, with ethanol/water/acetic acid as mobile phases and UV-visible diode array detection. Due to the significant differences between the polarity of the polyphenols, two different mobile phases were used. An ethanol/water/acetic acid (5:93:2) mobile phase was used to determine (+)-catechin (280 nm) and (-)-epicatechin (280 nm). On the other hand, rutin (254 nm), quercetin (254 nm) and trans-resveratrol (306 nm) were resolved using ethanol/water/acetic acid (40:58:2) as mobile phase. Instrumental parameters were optimised and analytical parameters obtained. The analytical method was validated and applied to five different varieties of Vitis vinifera from the geographical area of Valencia.     

Ethanol-free extraction of curcumin and antioxidant activity of components from wet Curcuma longa L. by liquefied dimethyl ether

As a solvent, ethanol can extract a wide range of polar substances, but its consumption is sometimes avoided for religious and cultural reasons. In this study, liquefied dimethyl ether (DME) was used to extract curcumin and antioxidants from highly moist, untreated turmeric. Higher amounts of curcumin (7.94 mg/g dry weight (DW)) were extracted using liquified DME compared with ethanol (6.77 mg/g DW). Almost all the water and 5.10 mg/g DW of lipids were extracted from raw turmeric using liquefied DME, corresponding to 56 % the amount extracted using ethanol. In addition, microscopic and spectroscopic analyses revealed that liquefied DME neither destroyed cell walls nor extracted cellulose. However, liquefied DME had a slightly lower extraction capacity for total phenolic compounds than ethanol and slightly lower antioxidant effect. DME extracts an equivalent amount of curcumin as ethanol and only slightly fewer antioxidants while simultaneously avoiding sun-drying degradation and prolonged freeze-drying.     

Pressurized liquid extracts from Spirulina platensis microalga. Determination of their antioxidant activity and preliminary analysis by micellar electrokinetic chromatography

In this work, different extracts from the microalga Spirulina platensis are obtained using pressurized liquid extraction (PLE) and four different solvents (hexane, light petroleum, ethanol and water). Different extraction temperatures (115 and 170 degrees C) were tested using extraction times ranging from 9 to 15 min. The antioxidant activity of the different extracts is determined by means of an in vitro assay using a free radical method. Moreover, a new and fast method is developed using micellar electrokinetic chromatography with diode array detection (MEKC-DAD) to provide a preliminary analysis on the composition of the extracts. This combined application (i.e., in vitro assays plus MEKC-DAD) allowed the fast characterization of the extracts based on their antioxidant activity and the UV-vis spectra of the different compounds found in the extracts. To our knowledge, this work shows for the first time the great possibilities of the combined use of PLE-in vitro assay-MEKC-DAD to investigate natural sources of antioxidants.     

Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple

The polyphenols were extracted from the unripe apple assisted by a highly efficient and simple method of the ultrasound. Response surface methodology was used to investigate the effects of processing parameters, including ultrasound power, extraction time, temperature, and ethanol concentration on total polyphenols yield and polyphenols composition was analyzed by HPLC. Antioxidant activity of the polyphenols was evaluated as 2, 2-diphenyl-1-picrylhydracyl scavenging activity and inhibition activity of lipid peroxidation. The results showed that 10-100 times higher total polyphenols yield was obtained from the unripe apple than those from the reported apple pomace. The optimum extraction conditions were ultrasonic power of 519.39 W, extraction time of 30 min, extraction temperature 50°C, ethanol concentration of 50% gave the total polyphenols yield of 13.26 ± 0.56 mg GAE/g. HPLC analysis indicated that (-)-epicatechin, procyanidin B2, chlorogenic acid, and procyanidin B1 were the predominant polyphenols in unripe apple, which contributed to the higher antioxidant activity to 2, 2-diphenyl-1-picrylhydracyl of unripe apple polyphenols than other apple polyphenols. The extracted polyphenols had higher ability to inhibit lipid peroxidation than butylated hydroxy toluene, which demonstrated that the unripe apple polyphenols have the potential to be used as a substitute of some synthetic antioxidants.     

The direct combination of HPLC solute focusing with supercritical fluid chromatography and mass spectrometry to enhance sensitivity and improve identification of trace components in polar solvent extracts

A system for combining normal and reversed phase high-performance liquid chromatography solute focusing with packed column supercritical fluid chromatography and supercritical fluid chromatography–mass spectrometry has been developed. The technique has been used to identify paracetamol and stanozolol in spiked plasma extracts and its utility for the analysis of a sample from a process waste stream is illustrated.     

Potential use of secondary products of the agri-food industry for topical formulations and comparative analysis of antioxidant activity of grape leaf polyphenols

The aim of the present study was to develop a phytocosmetic using Vitis waste by-products, for use as a topical formulation for skin protection against ultraviolet radiation damage. The study also evaluates the free radical scavenger activity of the crude extracts of dried leaves of Vitis vinifera and Vitis labrusca, as well as the anthocyanins, flavonoid fraction and isolated compounds. Next, release and permeation studies of hydrogels were performed using Franz-type diffusion cells. Flavonoid acted more intensively in TRAP and conjugated dienes antioxidant assays, whereas anthocyanins had higher antioxidant activity in hydroxyl and nitric oxide assay. Only quercetin-3-O-glucuronide (5) was released from hydrogels, and the flavonoid retention in porcine ear skin after eight hours of permeation was below of limit of quantification for this compound. The polyphenols present in Vitis are capable of absorbing UV and visible light, justifying their potential as sunscreens for the development of a phytocosmetic.     

Radial and longitudinal profiles of the electron paramagnetic resonance signal intensity of a single TE102 rectangular cavity: A three-dimensional surface plot for a point-like sample

Radial and longitudinal profiles of the electron paramagnetic resonance (EPR) signal intensity of a point-like sample inserted into a Bruker single TE₁₀₂ rectangular cavity were computed and the three-dimensional surface plots presented for the set of the point-like samples situated, (i) at any available points, P(ρ∈〈0, b/2〉, φ∈〈0, 2π〉, x=0), of a circle with a radius, ρ_max=b/2 (5.5 mm), which is located in the horizontal, central (y-z)-plane of the microwave cavity (a radial profile), and (ii) at any available points, P(ρ=b/4, φ∈〈0, 2π〉, x∈〈−a/2, a/2〉), of the cylindrical surface with a radius, ρ=b/4, and length, L=a (23.5 mm), which is concentric with the vertical, central x-axis of the microwave cavity (a longitudinal profile). The three-dimensional surface plots of the EPR signal intensity can be used for the theoretical prediction of the experimental response of the microwave cavity to a bulky sample: (i) for movement along (the longitudinal response); and (ii) for rotation around (the radial response) the vertical, central cavity x-axis.     

Characterization of the dispersion process for NiFe2O4 nanocrystals in a silica matrix with infrared spectroscopy and electron paramagnetic resonance

The structural development of the NiFe₂O₄ nanocrystals dispersed in a silica matrix was followed by IR and EPR spectroscopies of the dried gel 10NiO–10Fe₂O₃–90SiO₂ after heat treatment. The dried gel obtained at 200°C was amorphous, in which Fe³⁺ and Ni²⁺ ions were distributed in the pores of silica matrix. When the dried gel was heat treated at 400°C, NiFe₂O₄ clusters were partially formed, showing an enhanced interaction with the silica matrix. NiFe₂O₄ clusters were completely formed in silica matrix when the heat treatment was increased to 600°C, at which the interactions between the clusters and silica matrix reached a maximum. The formation reaction of NiFe₂O₄ clusters was accompanied by a rearrangement of the silica matrix network. Further increase of the heat treatment temperature to 800°C led to superparamagnetic single domain NiFe₂O₄ nanocrystals (ca. 4 nm) dispersed in the silica matrix with the elimination of the interactions between magnetic nanocrystals and silica matrix.     

Comparison of different extraction methods for the analysis of volatile secondary metabolites of Lippia alba (Mill.) N.E. Brown, grown in Colombia, and evaluation of its in vitro antioxidant activity

Hydrodistillation (HD), simultaneous distillation solvent extraction (SDE), microwave-assisted hydrodistillation (MWHD), and supercritical fluid (CO2) extraction (SFE) were employed to isolate volatile secondary metabolites from fresh leaves and stems of Colombian Lippia alba (Mill.) N.E. Brown. Kovàts indices, mass spectra or standard compounds were used to identify around 40 components in the various volatile fractions. Carvone (40-57%) was the most abundant component, followed by limonene (24-37%), bicyclosesquiphellandrene (5-22%), piperitenone (1-2%), piperitone (ca. 1.0%), and beta-bourbonene (0.6-1.5%), in the HD, SDE, MWHD, and SFE volatile fractions. Static headspace (S-HS), simultaneous purge and trap in solvent (CH2Cl2) (P&T), and headspace solid-phase microextraction (HS-SPME) were used to sample volatiles from fresh L. alba stems and leaves. The main components isolated from the headspace of the fresh plant material were limonene (27-77%), carvone (14-30%), piperitone (0.3-0.5%), piperitenone (ca. 0.4%), and beta-bourbonene (0.5-6.5%). The in vitro antioxidant activity of L. alba essential oil, obtained by hydrodistillation was evaluated by determination of hexanal, the main carbonyl compound released by linoleic acid subjected to peroxidation (1 mm Fe2+, 37 degrees C, 12 h), and by quantification of this acid as its methyl ester. Under the same conditions, L. alba HD-essential oil and Vitamin E exhibited similar antioxidant effects.     

Characterization of carbon nanotubes and analytical methods for their determination in environmental and biological samples: A review

In the present paper, a critical overview of the most commonly used techniques for the characterization and the determination of carbon nanotubes (CNTs) is given on the basis of 170 references (2000–2014). The analytical techniques used for CNT characterization (including microscopic and diffraction, spectroscopic, thermal and separation techniques) are classified, described, and illustrated with applied examples. Furthermore, the performance of sampling procedures as well as the available methods for the determination of CNTs in real biological and environmental samples are reviewed and discussed according to their analytical characteristics. In addition, future trends and perspectives in this field of work are critically presented.