Polar Phenolic Compounds Research Articles

Allelopathic potential of Psychotria leiocarpa, a dominant understorey species of subtropical forests

Psychotria leiocarpa is an understorey woody shrub native to the forests of southern Brazil, which occurs in groups of relatively high density. Leaves of field-grown plants contain approximately 2.5% of their dry weight as the N-glycosylated indolic alkaloid N,β- d-glucopyranosyl vincosamide (GPV). To find out if allelopathy could play a role in the distribution pattern of the species, several assays were performed. Aqueous extracts of dried powdered leaves at 4% (w/v) collected during the winter of 2004 inhibited the germination and/or early growth of three different test species. Lactuca sativa plantlets were affected when grown in soil containing dried P. leiocarpa leaves and on plates containing aqueous extracts of leaves of the same species. Partial chemical characterization of the extract was carried out and an allelopathic effect of the purified major leaf alkaloid GPV was not observed at the highest concentration tested of 10 ppm. Experiments with different organic extracts and sequential extractions were also performed. The data suggested that polar phenolic compounds or iridoids are responsible for the phytotoxic effect observed.

Phenolic Molecules in Virgin Olive Oils: a Survey of Their Sensory Properties, Health Effects, Antioxidant Activity and Analytical Methods. An Overview of the Last Decade Alessandra

Among vegetable oils, virgin olive oil (VOO) has nutritional and sensory characteristics that to make it unique and a basic component of the Mediterranean diet. The importance of VOO is mainly attributed both to its high content of oleic acid a balanced contribution quantity of polyunsaturated fatty acids and its richness in phenolic compounds, which act as natural antioxidants and may contribute to the prevention of several human diseases. The polar phenolic compounds of VOO belong to different classes: phenolic acids, phenyl ethyl alcohols, hydroxy-isochromans, flavonoids, lignans and secoiridoids. This latter family of compounds is characteristic of Oleaceae plants and secoiridoids are the main compounds of the phenolic fraction. Many agronomical and technological factors can affect the presence of phenols in VOO. Its shelf life is higher than other vegetable oils, mainly due to the presence of phenolic molecules having a catechol group, such as hydroxytyrosol and its secoiridoid derivatives. Several assays have been used to establish the antioxidant activity of these isolated phenolic compounds. Typical sensory gustative properties of VOO, such as bitterness and pungency, have been attributed to secoiridoid molecules. Considering the importance of the phenolic fraction of VOO, high performance analytical methods have been developed to characterize its complex phenolic pattern. The aim of this review is to realize a survey on phenolic compounds of virgin olive oils bearing in mind their chemical-analytical, healthy and sensory aspects. In particular, starting from the basic studies, the results of researches developed in the last ten years will be focused.

Changes occurring in phenolic content, tocopherol composition and oxidative stability of Camelina sativa oil during storage

Changes occurring during storage in the content of polar phenolic compounds, the composition of tocopherols (T), the presence of primary and secondary oxidative products and titratable acidity in oil obtained from the seeds of Camelina sativa were studied. In fresh oil the content of polar phenolic compounds amounted to 128 mg/kg (expressed as chlorogenic acid), the content of α-T was (41 ± 8) mg/kg, of γ-T (710 ± 19) mg/kg and of δ-T (12 ± 3) mg/kg. β-T and tocotrienols were not detected. In oil stored at 50 °C the concentration of total tocopherols decreased to a value of (440 ± 13) mg/kg in 15 days. In that time the content of polar phenolic compounds in the oil stored at 50 °C was reduced to 72% of its initial value. The content of polar phenolic compounds in oil stored at 65 °C for 15 days was reduced to 21% of its initial value. The content of polar phenolic compounds in the C. sativa oil investigated decreased linearly with peroxide value and with p-anisidine value. The antioxidative activity of polar phenolic compounds extracted from camelina oil was also elucidated. Analysis revealed that the phenolic extract obtained from camelina oil added to a model lipid system for a certain time significantly retarded the process of autooxidation.

Antioxidant Effect of Two Virgin Olive Oils Depends on the Concentration and Composition of Minor Polar Compounds

In vitro studies show that some individual minor polar phenolic compounds (MPC) present in virgin olive oil prevent oxidation of human low-density lipoproteins (LDL), but few data are available on the antioxidant effect of whole oil extract. Thus, whole virgin olive extracts were studied to determine whether they maintain the antioxidant activity and whether this last is linked to MPC composition of a single virgin oil. Using HPLC-DAD the MPC content in Taggiasca and Seggianese virgin olive oils was measured. Taggiasca oil was less rich in total MPC (208.5 mg/L) than Seggianese oil (441.9 mg/L). In addition, the major compounds of Taggiasca oil were lignan derivatives, whereas the major compounds in Seggianese oils were secoiridoid derivatives. Moreover, Taggiasca oil was practically free of 5-hydroxytyrosol and 5-hydroxytyrosol derivatives, deacetoxy-oleuropein aglycone and oleuropein aglycone. The antioxidant activity of the oils on human LDL was evaluated by measuring malondialdehyde and conjugate diene generation induced by copper ions. In both tests, the oil extracts dose-dependently reduced malondialdehyde and conjugate diene generation. Moreover, antioxidant potency correlated with total MPC; thus, Seggianese extract was more active. The two oils differed quantitatively and qualitatively, and these differences influenced their biological activities; thus clinical trials focused on studying the effects of olive oils should specify the oils used.

Functional characterization of pressurized liquid extracts of Spirulina platensis

Three different parameters (temperature, solvent, and extraction time) were studied regarding to pressure liquid extraction (PLE) of antioxidant and antimicrobial compounds from Spirulina platensis. Two different antioxidant methods, β-carotene bleaching method and DPPH• (2,2-Diphenyl-1-picrylhydrazyl hydrate) free radical scavenging assay, were used to determine the optimal PLE conditions for antioxidants extraction. The selected conditions were as follows: extraction temperature equal to 115 °C, extraction time equal to 15 min and ethanol as extracting solvent. The main antioxidant compounds found in this extract were identified as zeaxanthin, a myxoxanthophyll-like compound and very polar phenolic compounds. Moreover, antimicrobial activity of different PLE fractions was tested against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 11775, Candida albicans ATCC 60193, and Aspergillus niger ATCC 16404. Data obtained showed the hexane and petroleum ether extracts were slightly more active than ethanolic extracts. As for water extracts, none of them were active against the microorganisms tested. Data indicated that both 115 and 170 °C were the best extraction temperatures conditions in order to optimize the extraction of antimicrobial compounds, whereas 9 min was the optimal extraction time. Besides, C. albicans was the most sensitive microorganism to all Spirulina PLE extracts.

Preparation and application of poly(dimethylsiloxane)/β-cyclodextrin solid-phase microextraction membrane

A novel poly(dimethylsiloxane)/β-cyclodextrin (PDMS/β-CD) coating was prepared for solid-phase microextraction (SPME) in the form of membrane instead of fiber. The surface of the membrane was uniform and has not gel cracking after dipped into methanol, acetonitrile and acetone. Non-polar polycyclic aromatic hydrocarbons (PAHs) and polar phenolic compounds were used to evaluate the character of the PDMS/β-CD solid-phase microextraction membrane by direct extraction and solvent desorption, followed by GC–MS analysis. Parameters that affect the membrane extraction process were investigated, which included the matrix of sample, extraction time, desorption solvent and time. For PAHs, the linearity was from 0.10 to 1000 μg 1 −1. The limit of detection (LOD) was in the range of 0.01–0.2 μg 1 −1. The repeatability was in the range of 5.4–9.3%. For phenolic compounds, the linearity was from 0.10 to 5000 μg 1 −1 and LOD varied from 0.02 to 1.5 μg 1 −1. Compared with the SPME fiber, the SPME membrane has a large extraction capacity, low cost of preparation. The sensitivity can be further increased by developing large-volume-injection or thermal desorption technique.

Novel benzo-15-crown-5 sol–gel coating for solid-phase microextraction

A novel dihydroxy-terminated benzo-15-crown-5 was synthesized and applied to prepare a solid-phase microextraction (SPME) fiber coating with sol–gel technology. The optimization of the sol–gel process was studied. The coating method with sol–gel was improved and completed in one run, which economized materials and allowed easier control of the fiber thickness. The repeatability of coating fiber to fiber was better than 4.94% (RSD). The surface of the fiber coating was well-distributed and an electron microscopy experiment suggested a porous structure for crown ether coating, providing high surface areas and allowing for high extraction efficiency. The coating has a high thermal stability (350 °C), long lifetime and can stand solvent (organic and inorganic) rinsing due to the chemical binding between the coating and the fiber surface. Non-polar benzene, toluene, ethylbenzene, xylenes, chlorobenzenes, polar phenolic compounds and arylamines were used to evaluate the character of the fiber coating by headspace SPME–gas chromatography technology. For phenols, the linear concentrations ranged from 5 to 1000 μg/l, the detection limits were between 0.05 and 1 μg/l, and the RSD was less than 5%. The addition of benzo-crown ether not only increases the thermal stability of the fiber coating, but also enhances the selectivity of the fiber coating. Compared with commercially available SPME fibers poly(dimethylsiloxane) and polyacrylate, the new phases showed better selectivity and sensitivity towards non-polar and polar aromatic compounds.

Use of porous graphitic carbon coupled with mass detection for the analysis of polar phenolic compounds by liquid chromatography

Phenolic compounds present in olive mill wastewater (OMW) need to be quantified because of their pollution capacity toward the environment. In the present study, six representative phenolic compounds of OMW were chosen to develop a LC–MS method. The high polarity of the compounds caused problems when using traditional reversed-phase liquid chromatography (RPLC). Consequently, a method was developed on another kind of chromatographic phase: Porous Graphitic Carbon (PGC) involving the use of a tetrahydrofuran (THF) gradient. The influence of THF as mobile phase in LC–MS coupling, which is not common practice, was evaluated. In Atmosperic Pressure Chemical Ionisation (APCI) in the negative ion mode, the presence of THF in the mobile phase did not degrade the MS signal of the target compounds in the conditions studied. On the contrary, an improvement was even observed when the percentage of THF increased. The proposed PGC-LC–MS method was selective and linear for the six phenolic compounds analysed with limits of quantification lower than 5 ppm in all cases. The precision was satisfactory (pooled RSD around 6%). The analyses of OMW matrix spiked sample confirmed the good performance of the proposed method

Solid-phase microextraction using fused-silica fibers coated with sol-gel-derived hydroxy-crown ether.

A novel solid-phase microextraction (SPME) fiber containing hydroxydibenzo-14-crown-4 (OH-DB14C4)/hydroxy-terminated silicone oil (OH-TSO) was first prepared by a sol-gel method and investigated for the determination of phenols. The possible mechanism is discussed and confirmed by IR spectra. The coating has stable performance in high temperature (to 350 degrees C) and solvents (organic and inorganic) due to the chemical binding between the coating and the fiber surface. The addition of crown ether enhances the polarity of the coating compared with that of the sol-gel OH-terminated silicone oil fiber and, accordingly, provides higher extraction efficiency for polar phenolic compounds. On the other hand, OH-terminated silicone oil in the coating can not only increase the length of network but also help to spread the stationary phase on the silica surface uniformly. The fluorescence microscopy experiment suggests the benefit the more uniform surface of the sol-gel-derived OHDB14C4/OH-TSO fiber in comparison with sol-gelderived OH-DB14C4 fiber. Some parameters of the SPME fiber for the determination of phenols were investigated. Limits of detection of the phenols are below 1.0 ng/mL, and the precisions are from 2.9 to 4.6% (n = 6). Linear ranges were found to be 0.1-10 microg/mL The sensitivity of the method is enhanced at a low-pH level (pH approximately 1) and with the addition of salt. The method was applied to the analysis of wastewater sample from a paper mill.

Antioxidant capacity of oat (Avena sativa L.) extracts. 1. Inhibition of low-density lipoprotein oxidation and oxygen radical absorbance capacity.

Milled oat groat pearlings, trichomes, flour, and bran were extracted with methanol and the fractions tested in vitro for antioxidant capacity against low-density lipoprotein (LDL) oxidation and R-phycoerythrin protein oxidation in the oxygen radical absorbance capacity (ORAC) assay. The oxidative reactions were generated by 2,2'-azobis(2-amidinopropane) HCl (AAPH) or Cu(2+) in the LDL assay and by AAPH or Cu(2+) + H(2)O(2) in the ORAC assay and calibrated against a Trolox standard to calculate Trolox equivalents (1 Trolox equivalent = 1 TE = activity of 1 micromol of Trolox). The antioxidant capacity of the oat fractions was generally consistent with a potency rank of pearlings (2.89-8.58 TE/g) > flour (1.00-3.54 TE/g) > trichome (1.74 TE/g) = bran (1.02-1.62 TE/g) in both LDL and ORAC assays regardless of the free radical generator employed. A portion of the oat antioxidant constituents may be heat labile as the greatest activity was found among non-steam-treated pearlings. The contribution of oat tocols from the fractions accounted for <5% of the measured antioxidant capacity. AAPH-initiated oxidation of LDL was inhibited by the oat fractions in a dose-dependent manner, although complete suppression was not achieved with the highest doses tested. In contrast, Cu(2+)-initiated oxidation of LDL stimulated peroxide formation with low oat concentrations but completely inhibited oxidation with higher doses. Thus, oats possess antioxidant capacity most of which is likely derived from polar phenolic compounds in the aleurone.

Determination of polar priority phenols at parts per trillion levels in water using on-line liquid-solid extraction followed by liquid chromatography with coulimetric detection

A high-sensitivity method for the determination of polar phenolic compounds in water samples was developed. Water samples were preconcentrated using on-line solid-phase extraction with LiChrolut EN sorbent and afterwards were analyzed by liquid chromatography and dual coulimetric detection. The first electrode was set at low potential (250 mV) for sample clean up whereas the second one was used for analytical purposes. The system could not be used in its reductive form due to the lack of reversibility on the electrochemical behaviour of nitrophenols. Detection limits at part per trillion level were obtained using only 5 ml of water. Additionally, the large cell constant of the coulimetric detector lead to low values of coefficients of variation (±6) when working with river water.

Quantification of 2,4-Diacetylphloroglucinol Produced by Fluorescent Pseudomonas spp. In Vitro and in the Rhizosphere of Wheat

The broad-spectrum antibiotic 2,4-diacetylphloroglucinol (Phl) is a major determinant in the biological control of a wide range of plant diseases by fluorescent Pseudomonas spp. A protocol was developed to readily isolate and quantify Phl from broth and agar cultures and from the rhizosphere environment of plants. Extraction with ethyl acetate at an acidic pH was suitable for both in vitro and in situ sources of Phl. For soil samples, the addition of an initial extraction step with 80% acetone at an acidic pH was highly effective in eliminating polar organic soil components, such as humic and fulvic acids, which can interfere with Phl detection by high-performance liquid chromotography. The efficiency of Phl recovery from soil by a single extraction averaged 54.6%, and a second extraction added another 6.1%. These yields were substantially greater than those achieved by several standard protocols commonly used to extract polar phenolic compounds from soil. For the first time Phl was isolated from the rhizosphere environment in raw soil. Following application of Pseudomonas fluorescens Q2-87 and the Phl-overproducing strain Q2-87(pPHL5122) to the seeds of wheat, 2.1 and 2.4 (mu)g of Phl/g of root plus rhizosphere soil, respectively, were isolated from wheat grown in a Ritzville silt loam; 0.47 and 1.3 (mu)g of Phl/g of root plus rhizosphere soil, respectively, were isolated from wheat grown in a Shano silt loam. However, when the amount of Phl was calculated on the basis of cell density, Q2-87(pPHL5122) produced seven and six times more antibiotic than Q2-87 in Ritzville silt loam, and Shano silt loam, respectively.

Comparison of the effects of condensed tannin and pectin on cecal fermentations and lipid metabolism in the rat

The aim of the study was to compare the effect of a soluble fiber (citrus pectin) and prefermented condensed tannin (Quebracho) on the cecal fermentations, bile acids excretion and lipid metabolism in rats fed semi-purified diets. Analysis of the fermented tannin established than it is rich in monomers and trimers with little highly condensed polymers. Food intake and weight gain were not affected by addition of 5% citrus pectin or 1% Quebracho tannin in the diet. In the cecum, there was evidence of a depolymerization of polymers and of degradation of monomers, together with an accumulation of polar phenolic compounds. There was a significant enlargement of the cecum and of the volatile fatty acids (VFA) pool in rat fed the pectin diet; the Quebracho diet depressed the cecal VFA concentrations, compared to controls. The 1% Quebracho diet enhanced bile acids excretion, but the 5% pectin diet did not. In contrast, plasma cholesterol was depressed more effectively by pectin than by Quebracho. Both diets increased the activity of liver HMG-CoA reductase, a rate limiting enzyme of cholesterogenesis. The data show that, at a relatively low level in the diet, condensed tannins and soluble fibers may affect lipid metabolism by distinct mechanisms, which could be complementary in natural product diets.

Trace-level determination of polar phenolic compounds in aqueous samples by high-performance liquid chromatography and on-line preconcentration on porous graphitic carbon

The use of porous graphitic carbon (PGC) was investigated for the trace enrichment and the on-line liquid chromatographic separation of polar phenolic compounds (phenol, di- and trihydroxybenzenes, aminophenols, etc.) from aqueous samples. Comparison between retentions obtained with PGC and with the copolymer-based sorbent PRP-1 showed similar variations of the capacity factors with the mobile phase composition, but an inverse retention order. The capacity factor of a very polar analyte, such as 1,3,5-trihydroxybenzene (phloroglucinol), is 1000 in pure water, whereas this analyte is not retained by C 18-silica and is poorly retained by PRP-1 ( k′ = 3 in water). A precolumn packed with PGC can be coupled to a PGC analytical column for simple separation in the reversed-phase mode. This methodology has been applied to the direct determination of pyrocatechol, resorcinol and phloroglucinol below the 0.1 μg/1 level in a 50-ml sample.

Untersuchungen über das Wachstum des Pilzstammes Mucor circinelloides (1 M) III. Chemische Bestandteile der Wachstumsformen

Summary Of the fungus strain Mucor circinelloides (1 M) with its filamentous (F) and cellular (Z) growth forms, cultured in glucose (Glc) and n-alkanes (KW) medium, the cell wall fraction of the biomass, the chemical substances of the cell wall, and the intra-cellular cAMP level were determined. The pigments of the gemmae mycelium and the yeast-like budding cells were isolated and identified with thin-layer chromatography. The isolation of the cell wall was carried out with lyophilized dry matter, starting first by physical methods with ultrasonic treatment and with Ballotinis in a vibration homogenizer, followed by chemical methods according to Mitchell and Taylor (1) or White et al. (2). On comparing the two methods by the chemical components of the isolated cell wall, it was found that the cell wall substances of the experimental variants quantitatively were chiefly the same, but the cell wall treated according to method 1 contained RNA and a relatively high protein content. The relation of cell wall: biomass was with all the experimental variants 40 : 60. A significant difference between the filamentous and the cellular growth form was detected in the carbohydrate fractions of the cell wall, independent of the C and energy source of the culture medium. In comparison with the blastospores the mycelium contained about the 0.5-fold quantity of glucose, mannose, and alkaline-soluble carbohydrates and about the two-fold quantity of glucosamine and glucuronic acid. The protein content was higher in the cellular growth form and the lipid content was higher in the filamentous one. The cAMP level was higher in the mycelium than in the blastospores. In continuous culture, with a limiting value in the diluting rate for the transformation from cellular growth to hyphal growth, the experimental variant Gflc-Z had a cAMP value between that of the mycelium and that of the blastospores. For the extraction of pigments from the yellow-coloured gemmae mycelium and the green-coloured blastospores different solvents were tested. The pigments were easily soluble in formic acid or methanol. The separation of the pigment solution by thin-layer chromatography resulted in yellow, orange, and violet-coloured components, in their Rf-values to a high degree identical with those of the filamentous and cellular growth forms. It is supposed that there are strong polar phenolic compounds of the flavone type. The results were discussed.