Optimizing Microwave‐Assisted Extraction Conditions to Obtain Phenolic‐Rich Extract from Chromolaena odorata Leaves

Phenolic compounds are secondary metabolites that are mainly responsible for different pharmacological activities of plant extracts. In this study, microwave‐assisted extraction (MAE) variables were optimized for the extraction of phenolic compounds from Chromolaena odorata leaves by using a Box‐Behnken design of response surface methodology. The concentration of polyphenols and functional characteristics of the extracts were identified by using liquid chromatography quadrupolar time‐of‐flight mass spectrometry and FTIR analyses, respectively. The obtained results indicated the MAE conditions for the optimal recoveries of the total phenolic content and total flavonoid content from C. odorata leaves. The results reveal that the C. odorata leaf is enriched with phenolic compounds.     

Growth Inhibitory Effects of Nutgrass (Cyperus rotundus) on Rice (Oryza sativa) Seedlings

Growth inhibitory effects of aqueous extracts and leachates of leaves and tubers of Cyperus rotundus L. were investigated by using rice (Oryza sativa L.) seedling as a bioassay material. Both the extracts and leachates of Cyperus were inhibitory to the growth of rice seedlings. Growth inhibition was more pronounced in the presence of aqueous extracts than the leachates. The extract and leachate of leaves had higher total phenolic contents than those of the tubers. Soil amendment with fresh leaves of Cyperus reduced plant height, leaf area, and root and shoot weight of rice seedlings. Total phenolic content was higher in soil amended with fresh Cyperus leaves than the unamended control soil. Nineteen compounds were tentatively identified from the aqueous extracts of leaves and tubers by ethyl acetate extraction followed by gas chromatography–mass spectroscopy (GC-MS). Dicarboxylic, phenolic, and fatty acids were the major compounds. Our results suggest that Cyperus may affect the growth and establishment of rice seedlings after sowing or transplanting, especially when Cyperus plants are mixed in soil during land preparation by ploughing in rain-fed rice culture.     

Extraction of phenolic compounds from sour cherry pomace with supercritical carbon dioxide: Impact of process parameters on the composition and antioxidant properties of extracts

Sour cherry (Prunus cerasus) is rich in biologically active phenolic compounds. These compounds are concentrated in fruit skin and most of them remain in the leftovers during the production of juice. Supercritical carbon dioxide extraction was used to separate phenolic compounds from sour cherry pomace. The effects of temperature, pressure and the addition of ethanol on anthocyanin and the total phenolic content and radical scavenging activity of the extracts were investigated. The best results were acquired for 35°C, 10 MPa and 80% ethanol addition. A strong correlation was found between the phenolic content and other features of the extracts.     

Extraction of antioxidant compounds from blackberry (Rubus sp.) bagasse using supercritical CO2 assisted by ultrasound

Supercritical carbon dioxide extraction (SFE) was performed to recover bioactive components from blackberry (Rubus sp.) industrial residues. Ultrasound was applied during the extractions in order to enhance rate and yield. Moreover, water and ethanol at different proportions were used as cosolvents to improve the extraction of polar compounds from the residues. The extraction global yields were measured at all performed conditions (pressure, temperature, ultrasound power and cosolvent). The extracts were evaluated in terms of their antioxidant activity, measured using two methods, phenolic content, monomeric anthocyanins, and anthocyanin profile. The application of ultrasound in SFE helped increasing the extraction rate at the beginning of the process, which could be observed on the extraction curves at 15 MPa, the lowest pressure applied. Scanning electron microscopy (FESEM) was used to analyze the blackberry bagasse undergoing SFE with and without ultrasounds and showed that ultrasound disturbs the cell walls, enhancing the release of the extractable compounds. The extracts have shown high antioxidant activity and phenolic contents when obtained at higher temperatures. Regarding anthocyanins, the use of water as cosolvent resulted in a significant increase. Four major anthocyanins were identified and quantified by ultra performance liquid chromatography (UPLC).     

Extracts from pitanga (Eugenia uniflora L.) leaves: Influence of extraction process on antioxidant properties and yield of phenolic compounds

Different extraction processes were employed to extract the polyphenolic compounds from pitanga (Eugenia uniflora L.) leaves: a one-step process using water, ethanol or supercritical CO₂ as solvents, and a two-step process using supercritical CO₂ followed by either water or ethanol. The total polyphenolic compounds, total flavonoids and antioxidant activity were determined in all the extracts obtained. The process performance was evaluated with respect to three variables: global extraction yield, concentration and yield of both polyphenols and flavonoids in the extracts. For the one-step extraction, the results showed that the extraction yield increased with solvent polarity. For the two-step process, the results suggested that water was more efficient in extracting the phenolic compounds from E. uniflora when the matrix was previously extracted with scCO₂. With respect to the antioxidant activity, the ethanolic extracts obtained from both processes, using either the DPPH radical scavenging method or the β-carotene bleaching method, presented high antioxidant activities.     

Extraction of phenolic compounds and anthocyanins from blueberry (Vaccinium myrtillus L.) residues using supercritical CO2 and pressurized liquids

This work explored the potential of subcritical liquids and supercritical carbon dioxide (CO₂) in the recovery of extracts containing phenolic compounds, antioxidants and anthocyanins from residues of blueberry (Vaccinium myrtillus L.) processing. Supercritical CO₂ and pressurized liquids are alternatives to the use of toxic organic solvents or extraction methods that apply high temperatures. Blueberry is the fruit with the highest antioxidant and polyphenol content, which is present in both peel and pulp. In the extraction with pressurized liquids (PLE), water, ethanol and acetone were used at different proportions, with temperature, pressure and solvent flow rate kept constant at 40 °C, 20 MPa and 10 ml/min, respectively. The extracts were analyzed and the highest antioxidant activities and phenolic contents were found in the extracts obtained with pure ethanol and ethanol + water. The highest concentrations of anthocyanins were recovered with acidified water as solvent. In supercritical fluid extraction (SFE) with CO₂, water, acidified water, and ethanol were used as modifiers, and the best condition for all functional components evaluated was SFE with 90% CO₂, 5% water, and 5% ethanol. Sixteen anthocyanins were identified and quantified by ultra performance liquid chromatography (UPLC).     

Composition and Antioxidant Activity of Olive Leaf Extracts from Greek Olive Cultivars

The olive leaf phenolic composition of the Greek cultivars koroneiki, megaritiki and kalamon was determined using LC/MS. Furthermore, the antioxidant activity of olive leaf extracts from the above three cultivars, using solvents of increasing polarity (petroleum ether, dichloromethane, methanol and methanol/water: 60/40) was evaluated using the stable free radical diphenylpicrylhydrazyl (DPPH) test. Furthermore the oxidative stability index (OSI) was compared to that of the synthetic antioxidant TBHQ and commercial oleoresin (rosemary extract). The ability of phenolic compounds to inhibit the lipoxygenase (LOX) activity was also investigated. The ten main components determined in the olive tree leaf extracts for the cultivars koroneiki and kalamon were: secologanoside, dimethyloleuropein, oleuropein diglucoside, luteolin-7-O-glucoside, rutin, oleuropein, oleuroside, quercetin, ligstroside and verbascoside. Respective compounds for the cultivar megaritiki were: secologanoside, dimethyloleuropein, oleuropein diglucoside, luteolin7-O-glucoside, oleuropein, oleuroside, quercetin and ligstroside. In all three cultivars, oleuropein represented the main phenolic component. The solvent polarity influenced the total amount of the phenolic compounds determined. When methanol/water (60/40) was used, as solvent, more phenolic compounds were determined. The total amounts of phenols determined in the extracts, obtained by successive extractions using the above solvents, were 6,094, 5,579 and 6,196 mg/kg (mg gallic acid/kg dried olive leaves) for the cultivars megaritiki, kalamon and koroneiki, respectively. Among all extracts, methanol/water extracts exhibited the highest antioxidant activity as shown through the application of the DPPH and OSI methods. The OSI antioxidant activity followed the sequence: synthetic antioxidant TBHQ > commercial oleoresin > olive tree leaf extracts > control. Likewise, methanol/water olive leaf extracts significantly inhibited soybean lipoxygenase, although some small differences in the activity among the olive leaf extracts of the different cultivars were observed. The solvent polarity as well as the amount of the extract influenced the inhibitory activity. A positive correlation was shown between the antioxidant activity of leaf extracts and the total phenol content.     

Quantitative Analysis of UV-B Radiation Interception in 3D Plant Structures and Intraindividual Distribution of Phenolic Contents

Ultraviolet-B (UV-B) acts as a regulatory stimulus, inducing the dose-dependent biosynthesis of phenolic compounds such as flavonoids at the leaf level. However, the heterogeneity of biosynthesis activation generated within a whole plant is not fully understood until now and cannot be interpreted without quantification of UV-B radiation interception. In this study, we analyzed the spatial UV-B radiation interception of kales (Brassica oleracea L. var. Acephala) grown under supplemental UV-B LED using ray-tracing simulation with 3-dimension-scanned models and leaf optical properties. The UV-B-induced phenolic compounds and flavonoids accumulated more, with higher UV-B interception and younger leaves. To distinguish the effects of UV-B energy and leaf developmental age, the contents were regressed separately and simultaneously. The effect of intercepted UV-B on flavonoid content was 4.9-fold that of leaf age, but the effects on phenolic compound biosynthesis were similar. This study confirmed the feasibility and relevance of UV-B radiation interception analysis and paves the way to explore the physical and physiological base determining the intraindividual distribution of phenolic compound in controlled environments.     

The Effect of Olive Leaf Addition on Antioxidant Content and Antioxidant Activity of “Memecik” Olive Oils at Two Maturity Stages

In this study, the effects of leaf addition, maturity stage and storage on the antioxidant content and activity of olive oils (cv. Memecik) were investigated in the 2008/09 and 2009/10 crop seasons. Olive fruits were harvested at two different maturity stages (early and late), and the leaves of the same cultivar were added at different rates (0, 1, and 3 %) prior to oil extraction. After extraction, the oil samples were stored for 18 months and total chlorophyll, α-tocopherol, total phenolic content and the antioxidant activity [DPPH^· (2,2-diphenyl-1-picrylhydrazyl) and ABTS^·+ (2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid) radical scavenging] were determined at 6 month-intervals. Olive leaf addition induced a significant increase in total chlorophyll, α-tocopherol, total phenolic content, and antioxidant activities in both years (P < 0.001). During the storage period antioxidant content and antioxidant activities in the oils significantly decreased in both years (P < 0.001). However, the oils to which leaf material was added had higher antioxidant contents and activities than those without leaf material addition at the end of the 18-month storage period. After storage, the antioxidant content and DPPH^· radical scavenging activity of control (0 %) samples were lower than those in the leaf added samples (3 %). The data obtained from this study suggested that the addition of olive leaf to oils allowed more functional olive oils with higher antioxidant contents.     

Effect of extraction conditions on total phenolic content and antioxidant capacity of pretreated wild Peumus boldus leaves from Chile

We studied the effect of both heat-drying and freeze-drying on the recovery of total phenolic compounds (TPCs) and antioxidant capacity from leaves of Peumus boldus Molina (Boldo), an endemic tree of Chile, using DPPH (2,2-diphenyl-1-picrylhydrazyl radical scavenging), FRAP (ferric reducing antioxidant power) and ORAC (oxygen radical absorbance capacity) methods. The results indicated that infusions prepared using commercial boldo tea bags had similar or higher TPCs, DPPH, FRAP and ORAC values in comparison with those of the infusions prepared using heat- or freeze-dried leaves. The extraction experiments showed that hydro-alcoholic mixtures are the best solvents to extract antioxidants from boldo leaves, favoring the use of freeze-dried leaves. Considering the alkaloid profile of the extracts of freeze-dried leaves and herbal tea bags, the latter exhibited higher amounts of the alkaloids tested, including boldine, which is well correlated with the results obtained using the ORAC method. These results indicate a great potential to develop commercial boldo extracts and could encourage improved applications of this endemic Chilean plant.     

Phenolic Metabolites in Leaves of the Invasive Shrub, Lonicera maackii, and Their Potential Phytotoxic and Anti-Herbivore Effects

Lonicera maackii is an invasive shrub in North America for which allelopathic effects toward other plants or herbivores have been suspected. We characterized the major phenolic metabolites present in methanol extracts of L. maackii leaves. In addition, we examined the effects of methanol–water extracts of L. maackii leaves on seed germination of a target plant species and on feeding preference and growth rate of a generalist insect herbivore. A total of 13 individual major and minor compounds were detected in crude leaf extracts by high-performance liquid chromatography coupled to electronspray ionization-tandem mass spectrometry (ESI-MS/MS). Extracts were dominated by two major flavones, apigenin and luteolin, and their glucoside derivatives, apigenin-7-glucoside and luteolin-7-glucoside. Quantities of these compounds, along with chlorogenic acid, varied between two sampling points. Leaf extracts that contained these compounds were inhibitory to seed germination of Arabidopsis thaliana. In addition, treatment of artificial diet with leaf extracts deterred feeding of the generalist herbivore, Spodoptera exigua, in choice experiments but had no effect on growth rate in short-term no-choice bioassays. Purified apigenin tended to deter feeding by S. exigua and inhibited seed germination of A. thaliana. We conclude that leaves of L. maackii contain phenolic compounds, including apigenin and chlorogenic acid, capable of having biological effects on other plants and insects.     

Rosmarinus Officinalis Leaves as a Natural Source of Bioactive Compounds

In an extensive search for bioactive compounds from plant sources, the composition of different extracts of rosemary leaves collected from different geographical zones of Serbia was studied. The qualitative and quantitative characterization of 20 rosemary (Rosmarinus officinalis) samples, obtained by microwave-assisted extraction (MAE), was determined by high performance liquid chromatography coupled to electrospray quadrupole-time of flight mass spectrometry (HPLC–ESI-QTOF-MS). The high mass accuracy and true isotopic pattern in both MS and MS/MS spectra provided by the QTOF-MS analyzer enabled the characterization of a wide range of phenolic compounds in the extracts, including flavonoids, phenolic diterpenes and abietan-type triterpenoids, among others. According to the data compiled, rosemary samples from Sokobanja presented the highest levels in flavonoids and other compounds such as carnosol, rosmaridiphenol, rosmadial, rosmarinic acid, and carnosic acid. On the other hand, higher contents in triterpenes were found in the extracts of rosemary from Gložan (Vojvodina).     

The role of leaf lipids in food selection by larvae of the tobacco hornworm,Manduca sexta

The role of leaf lipids in food plant selection by larvae ofManduca sexta was investigated by measuring preference responses in a two-choice preference test using glass fiber filter paper disks laced with extract (test) or water (control). The larvae respond to the petroleum ether extract of whole leaves of the host-plantLycopersicon esculentum (tomato) extract in a concentration-dependent manner. At natural concentration it is the most strongly stimulating extract or compound yet tested using the disk test. This response is affected by food plant experience of the larvae, suggesting stimulation by plant-specific compounds in the extract. The extract contains volatile compounds that attract the larvae. In contrast, it does not promote continued feeding on an agar-cellulose diet that incorporates the extract. Also stimulating are the extracts of leaf surfaces of two hosts,L. esculentum andSolanum pseudocapsicum, and two acceptable nonhosts,Brassicae napus andVigna sinensis, indicating the presence of nonpolar feeding stimulants at the leaf surface. However, similar leaf-surface extracts of the unacceptable plantCanna generalis were inactive, although the surface extraction process renders this plant acceptable. Leaf-surface extracts ofL. esculentum, S. pseudocapsicum, andB. napus evoke feeding responses that are qualitatively comparable to those of their corresponding leaves. However, no such parallel is found for surface extracts ofV. sinensis andC. generalis. Thus, nonpolar compounds at the leaf surface of host and some acceptable non-host-plant species strongly stimulate feeding and hence must play an important role in food selection by the tobacco hornworm.     

Feeding stimulatory and inhibitory chemicals from an acceptable nonhost plant forManduca sexta: Improved detection by larvae deprived of selected chemosensory organs

The chemical basis of feeding responses to the acceptable nonhost plantVigna sinensis (cowpea) by larvae ofManduca sexta was investigated using chemical isolation techniques directed by a novel chemosensory-based bioassay. The presence of feeding stimulatory and inhibitory compounds in leaves or leaf extracts was determined in a two-choice preference test using leaf disks or glass fiber filter paper disks laced with leaf extract as test substrate and filter paper disks laced with water as control. Larvae strongly prefer the control disks over leaf disks, indicating the presence of feeding inhibitory compounds in the leaf. An ethanol extract of both fresh and dried leaves neither stimulated nor inhibited feeding. The cause of this inactivity was examined by using larvae that respond strongly to either feeding stimulatory or inhibitory compounds due to selective chemosensory deprivation. Larvae having chemosensory organs remaining only on the maxillary palps are stimulated to feed by whole leaf disks and by the ethanol extracts. In contrast, larvae having only the medial and lateral maxillary sensilla styloconica and the epipharyngeal sensilla remaining are strongly inhibited by whole leaf disks and the ethanol extract of fresh leaves. Thus, the ethanol extract contains both feeding stimulatory and inhibitory compounds, which elicit opposite behavioral effects in unoperated larvae, therefore nullifying any stimulatory and inhibitory activity. These compounds can only be demonstrated by using discrimination-enhanced larvae in the choice tests. Further isolation of the feeding stimulatory principle inV. sinensis yielded two separate fractions of neutral compounds, suggesting at least two different chemicals belonging to two different classes: nonpolar and polar lipids. Feeding inhibitory chemicals have apparently polar properties because strong activity was found in the ethyl acetate and methanol extracts of dried leaves. The role of feeding stimulatory and inhibitory compounds in food selection ofM. sexta larvae is discussed.     

Improvement of quality and antioxidant properties of dried mulberry leaves with combined far-infrared radiation and air convection in Thai tea process

Combined far-infrared radiation with hot-air convection (FIR-HA) drying was used for improving colour and antioxidant properties of mulberry leaf tea. Antioxidant properties and phenolic compounds of FIR-HA dried mulberry tea were determined and compared with the commercial product and with fresh leaves. We found that a smaller decrease in L and b values of the FIR-HA dried tea than those of commercial tea was observed. FIR-HA tea was found to have similar colour to fresh leaf while the commercial tea had darker colour. A significant decrease in total phenolic acid content (TPC) and total flavonoid content (TFC) was found in hot-air (HA) dried commercial tea compared to fresh leaves, while TPC in FIR-HA dried tea was significantly increased. Similar results were found in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical activities. However, the results were different for ferric reducing antioxidant power (FRAP). Both teas had lower FRAP values compared to fresh leaves. Eleven phenolic compounds were identified in fresh leaf and in mulberry tea, namely p-coumaric acid, benzoic acid, (+)-catechin, chlorogenic acid, vanillic acid, syringic acid, sinapic acid, protocatechuic acid, ferulic acid, gallic acid and caffeic acid. The total content of phenolic compounds (TPCC) increased in FIR-HA dried samples compared to those of HA dried tea, except for chlorogenic and syringic acids, which were found in greater amounts in HA dried commercial tea. Our results have demonstrated that FIR-HA should be considered as a suitable drying method for mulberry tea with respect to preserving its antioxidant properties and phenolic compounds.     

Optimization of the Process for Recovering Phenolic Antioxidant Compounds from Low-Quality Eggplant (Solanum melongena L.) Pulp by Modified Supercritical Carbon Dioxide Extraction

The extraction of biologically active compounds from eggplant pulp by modified supercritical CO₂ extraction was investigated. Response surface methodology was used to optimize the extraction of phenolic compounds and antioxidant capacity by assessing the pressure, temperature, and cosolvent percentage. The results demonstrated that the maximum phenolic content (3,530.79 mg CAE/100 g extract) and antioxidant capacity (4,593.22 μmol TE/g extract) were observed at 56.8°C, 280 bar, and 1.22% of ethanol and were higher than those obtained by conventional solvent extraction. Four phenolic acids were identified in the supercritical extracts and not in the conventional extracts using HPLC-DAD analysis, suggesting that modified supercritical CO₂ extraction is more efficient and selective.     

Screening the Antioxidant and Antimicrobial Properties of the Extracts from Plantain (Plantago Major L.) Leaves

Abstract

Antioxidant and antimicrobial activities of the extracts obtained by classical (maceration) and ultrasonic (40 kHz) extraction from dry Plantago major leaves were compared. The antioxidant activities of extracts obtained by ultrasonic and classical extraction were 0.87±0.02 and 0.85±0.02 µg/µg DPPH, respectively. Ultrasound positively affected the extractive substance yield and the kinetics of extraction, but the extract obtained by classical extraction contained higher total contents of phenolic compounds and flavonoids than that obtained by ultrasonic extraction. Extracts of P. major showed better antimicrobial activity against the yeasts than against the bacteria.     

Extraction of low-molar-mass phenolics and lipophilic compounds from Pinus pinaster wood with compressed CO2

Near-supercritical and supercritical CO₂ was used to extract low-molar-mass phenolics and lipophilic compounds from Pinus pinaster wood. Extraction of samples containing sapwood and knotwood was carried out at 10⿿25 MPa and 30⿿50 °C to assess the influence of the operational conditions on the yields of total extracts and phenolics, as well as on the radical scavenging capacity of extracts. The use of ethanol as a co-solvent increased both the extraction yields and the concentration of phenolics in extracts. Operating under selected conditions (25 MPa, 50 °C, 10% ethanol), the extraction yield accounted for 4.1 wt% of the oven-dry wood. The extracts contained up to 7.6 g of phenolic compounds (measured as gallic acid equivalents) per 100 g extract, and showed one third of the radical scavenging capacity of Trolox. Native resin acids accounted for about 24 g per 100 g extracts, whereas flavonoids, lignans, stilbenes and juvabiones were found at lower proportions.     

Insights into the 3D In Vitro Permeability and In Vivo Antioxidant Protective Effects of Kiwiberry Leaf Extract: A Step Forward to Human Nutraceutical Use

Actinidia arguta (Siebold & Zucc.) Planch. ex Miq. (kiwiberry) leaves are a source of phenolic compounds with pro-health biological effects, such as antioxidant and anti-inflammatory activities. Despite the huge number of studies reporting the composition of A. arguta leaves, no in vitro or in vivo studies explore its potential use as nutraceutical ingredient based on these activities. Therefore, this study aims to characterize the safety profile of kiwiberry leaf extracts using in vitro and in vivo approaches through the assessment of intestinal cell viability (Caco-2 and HT29-MTX), 3D intestinal permeation, and, most important, the redox markers, biochemical profile and liver and kidney function effects after the animal assays. Briefly, wistar rats were orally treated for 7 days with kiwiberry leaf extracts (50 and 75 mg/kg bw), water (negative control), or vitamin C (positive control). The cell viability was above 90% at 1000 μg/mL for both cells. Coumaroyl quinic acid and rutin achieved a permeation higher than 25% in the 3D intestinal model. The animal studies confirmed the extracts’ ability to increase superoxide dismutase, glutathione peroxidase, and catalase content in animals’ livers and kidneys while simultaneously decreasing the triglycerides content. This study highlighted the antioxidant capacity of kiwiberry leaf extracts, ensuring their efficacy and safety as a nutraceutical ingredient.     

Antioxidant activity of extracts from six different Sudanese plant materials

Methanolic extracts obtained by manual solvent extraction (MSE) and accelerated solvent extraction (ASE) of different Sudanese plant materials (Sclerocarya birrea leaves, Salvadora persica bark and leaves, Combretum hartmannianum leaves, Guiera senegalensis leaves and roots) were investigated for their antioxidant activity. There was no significant difference between the two extraction methods (p < 0.01) regarding the total amount of phenolic compounds expressed as gallic acid equivalents (GAE) (52.6–166.7 mg GAE/g total extractable compounds for MSE and 53.1–169.3 mg GAE/g for ASE). In comparison to a control without extract, the extracts were remarkably effective in the β‐carotene bleaching method, whereas the effectiveness was half or less in comparison to Trolox as standard antioxidant. Also using the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) method antioxidant activity could be shown in comparison to a control, however, the extracts were less effective than Trolox. No significant difference was found between the two extraction methods. The increase of the peroxide value of sunflower oil during storage at 70°C was markedly lower after addition of the extracts in comparison to the control, but in the Rancimat test (120°C) the extracts showed only a small stabilization factor (F = 0.9–1.4) especially in comparison to Trolox (F = 5.8).