Characterization of the interglycosidic linkage in di-, tri-, tetra- and pentaglycosylated flavonoids and differentiation of positional isomers by liquid chromatography/electrospray ionization tandem mass spectrometry

The LC/UV-DAD/ESI-MSn negative fragmentation mode of 23 O-glycosylated flavonoids with two, three, four and five hexoses was studied. The results show that it is possible to differentiate the (1-->2) and (1-->6) interglucosidic linkages and also to discern between the flavonoid isomers with two glucoses (sophorosides, gentiobiosides and X,Y-diglucosides), three glucoses (sophorotriosides and X-sophoroside-Y-glucoside) and four glucoses (X-sophorotriosides-Y-glucoside and X-sophoroside-Y-sophoroside). In the characterization of the (1-->2) and (1-->6) interglycosidic linkages, the Y1- (-162 u) and Z1- (-180 u) ions play a relevant role. In the first case ions with high relative abundance (13-79%) are found, whereas in the other cases they are in very low abundance or absent. X,Y-di-O-glucoside flavonoids can be differentiated from the O-diglucoside flavonoids by the presence of Y1- (base peak) and Y0- (approximately 30%) ions and the absence of Z1- ions. Regarding flavonoids glycosylated with three glucoses, X-sophoroside-Y-glucoside flavonoids show the Y7(0-) (-162 u) ion as the only peak in MS2 events whereas in sophorotrioside flavonoids various ions due to intermediate fragmentations are observed. These ions are characteristic of a (1-->2) interglucosidic linkage. In MS2 experiments on flavonoids with four glucoses (X-sophorotrioside-Y-glucoside and X-sophoroside-Y-sophoroside), the base peak indicated the total loss of the sugar moieties in position 7. In addition, the characterization of the type of interglycosidic linkage in flavonoids glycosylated with five sugars can be achieved. On the other hand, in tetra- and pentaglycosylated flavonoids, the ions that characterize the (1-->2) interglucosidic linkage formed by intermediate fragmentation of the oligosacharide residues (sophorosides and sophorotriosides) are found in much higher relative abundance in MS3 than in MS2 experiments, where they are almost not detected.

Simultaneous determination of catechin, rutin, quercetin kaempferol and isorhamnetin in the extract of sea buckthorn (Hippophae rhamnoides L.) leaves by RP-HPLC with DAD

A rapid and specific reversed-phase high performance liquid chromatography (RP-HPLC) method with diode array detection (DAD) at room temperature was used and validated for the simultaneous determination of five flavonoids (catechin, CA; rutin, RU; quercetin, QU; kaempferol, KA; isorhamnetin, IS) in the extract of sea buckthorn (Hippophae rhamnoides L.) leaves. The sample pretreatment process involved ultrasonic extraction with 85% ethanol under the frequency of 80 kHz, at a temperature of 45 degrees C for 30 min and with the ratio of liquor to material of 15 mL g-1, followed by separation on HIQ SIL C18V column with methanol-acetonitrile-water (40:15:45, v/v/v) containing 1.0% acetic acid as a mobile phase. The extract was detected by DAD at the wavelength of 279 nm for CA, 257 nm for RU, 368 nm for QU, KA and IS. Calibration curves were found to be linear with the ranges of 0.011-0.520 mg ml-1 (CA), 0.007-0.500 mg ml-1 (RU), 0.019-0.280 mg ml-1 (QU), 0.010-0.440 mg ml-1 (KA) and 0.008-0.400 mg ml-1 (IS). The correlation coefficients of linear regression analysis and detection limits were between 0.9963-0.9999 and 0.00079-0.00290 mg ml-1. The contents of CA, RU, QU, KA and IS in sea buckthorn leaves were successfully determined with 3.8, 5.2, 7.3, 10.9 and 11.9 min with satisfactory reproducibility and recovery. Recoveries of the five flavonoids were between 97.27 and 99.98%. The method was applied to the determination of flavonoids in sea buckthorn leaves and was found to be simple, rapid and efficient.

Phenolic profiling of Portuguese propolis by LC-MS spectrometry: uncommon propolis rich in flavonoid glycosides

INTRODUCTION

Propolis is a chemically complex resinous substance collected by honeybees (Apis mellifera) from tree buds, comprising plant exudates, secreted substances from bee metabolism, pollen and waxes. Its chemical composition depends strongly on the plant sources available around the beehive, which have a direct impact in the quality and bioactivity of the propolis. Being as Portugal is a country of botanical diversity, the phenolic characterisation of propolis from the different regions is a priority.

OBJECTIVE

Extensive characterisation of the phenolic composition of Portuguese propolis from different continental regions and islands.

METHOD

Forty propolis ethanolic extracts were analysed extensively by liquid chromatography with diode-array detection coupled to electrospray ionisation tandem mass spectrometry (LC-DAD-ESI-MS(n) ).

RESULTS

Seventy-six polyphenols were detected in the samples and two groups of propolis were established: the common temperate propolis, which contained the typical poplar phenolic compounds such as flavonoids and their methylated/esterified forms, phenylpropanoid acids and their esters, and an uncommon propolis type with an unusual composition in quercetin and kaempferol glycosides - some of them never described in propolis.

CONCLUSION

The method allowed the establishment of the phenolic profile of Portuguese propolis from different geographical locations, and the possibility to use some phenolic compounds, such as kaempferol-dimethylether, as geographical markers. Data suggest that other botanical species in addition to poplar trees can be important sources of resins for Portuguese propolis.

Characterization and quantification of flavonoids and hydroxycinnamic acids in curly kale (Brassica oleracea L. Convar. acephala Var. sabellica) by HPLC-DAD-ESI-MSn

Kale is a leafy green vegetable belonging to the Brassicaceae family, a group of vegetables including cabbage, broccoli, cauliflower, and Brussels sprouts, with a high content of health-promoting phytochemicals. The flavonoids and hydroxycinammic acids of curly kale ( Brassica oleracea L. ssp. oleracea convar. acephala (DC.) Alef. var. sabellica L.), a variety of kale, were characterized and identified primarily through HPLC-DAD-ESI-MS(n) analysis. Thirty-two phenolic compounds including glycosides of quercetin and kaempferol and derivatives of p-coumaric, ferulic, sinapic, and caffeic acid were tentatively identified, providing a more complete identification of phenolic compounds in curly kale than previously reported. Moreover, three hydroxycinnamic acids and one flavonoid with an unusual high grade of glycosylation, quercetin-3-disinapoyl-triglucoside-7-diglucoside, have been tentatively identified for the first time. The influence of different extraction conditions (extraction method, solvent type, solvent/solid ratio, and duration of extraction) was investigated. The total flavonol and hydroxycinnamic acid contents in curly kale determined as rutin equivalents (RE) were 646 and 204 mg of RE/100 g of fresh weight (fw), respectively. The contents of individual flavonoids ranged from 2 to 159 mg of RE/100 g of fw, with main compounds kaempferol-3-sinapoyl-diglucoside-7-diglucoside (18.7%) and quercetin-3-sinapoyl-diglucoside-7-diglucoside (16.5%). After acidic hydrolysis, two flavonol aglycones were identified in curly kale, quercetin and kaempferol, with total contents of 44 and 58 mg/100 g of fw, respectively.

The anti-obesity and anti-diabetic effects of kaempferol glycosides from unripe soybean leaves in high-fat-diet mice

The present study investigated the anti-obesity and anti-diabetic effects of kaempferol glycoside (KG) fractions which were composed of four kaempferol glycosides and purified from unripe Jindai-soybean (Edamame) leaves in C57BL/6J mice. High fat-fed mice treated with 0.15% dietary KG for 92 days had reduced body weight, adipose tissue and TG levels compared to the high fat-fed control group. KG-treatment also decreased fasting blood glucose, serum HbA1c (hemoglobin A(1c)) levels and improved insulin resistance. Gene expression analysis of the liver showed that KG decreased peroxisome proliferator-activated receptor (PPAR-γ) and sterol regulatory element-binding protein (SREBP-1c) expression. These results suggest that KG reduced the accumulation of adipose tissue, improving hyperlipidemia as well as diabetes in obese mice by increasing lipid metabolism through the downregulation of PPAR-γ and SREBP-1c. Thus, KG may have an anti-obesity and anti-diabetic potential.

Matrix-free UV-laser desorption/ionization (LDI) mass spectrometric imaging at the single-cell level: distribution of secondary metabolites of Arabidopsis thaliana and Hypericum species

The present paper describes matrix-free laser desorption/ionisation mass spectrometric imaging (LDI-MSI) of highly localized UV-absorbing secondary metabolites in plant tissues at single-cell resolution. The scope and limitations of the method are discussed with regard to plants of the genus Hypericum. Naphthodianthrones such as hypericin and pseudohypericin are traceable in dark glands on Hypericum leaves, placenta, stamens and styli; biflavonoids are also traceable in the pollen of this important phytomedical plant. The highest spatial resolution achieved, 10 microm, was much higher than that achieved by commonly used matrix-assisted laser desorption/ionization (MALDI) imaging protocols. The data from imaging experiments were supported by independent LDI-TOF/MS analysis of cryo-sectioned, laser-microdissected and freshly cut plant material. The results confirmed the suitability of combining laser microdissection (LMD) and LDI-TOF/MS or LDI-MSI to analyse localized plant secondary metabolites. Furthermore, Arabidopsis thaliana was analysed to demonstrate the feasibility of LDI-MSI for other commonly occurring compounds such as flavonoids. The organ-specific distribution of kaempferol, quercetin and isorhamnetin, and their glycosides, was imaged at the cellular level.

Flavonoid composition and antioxidant activity of tree peony (Paeonia section moutan) yellow flowers

Tree peony flowers are edible and traditional Chinese medicine materials. In the present study, 26 flavonoids were identified and quantified in yellow flowers of tree peony by high-performance liquid chromatography with diode array detector (HPLC-DAD) and by HPLC-electrospray ionization-mass spectrometry (HPLC-ESI-MS). Seventeen of them were first reported in flowers of tree peony, and glycosides of kaempferol, luteolin, and apigenin as well as isosalipurposide were the main flavonoids investigated. Furthermore, the petal extracts showed high antioxidant activity according to DPPH*, ABTS*(+), and OH* scavenging assays and ferric reducing antioxidant power assay. There were significant correlations between antioxidant activity and both the total polyphenol content (determined by Folin-Ciocalteu method) and the total content of quercetin, kaempferol, and luteolin glycosides. This work is valuable for elucidation of phenolic composition in tree peony flowers and for further utilization of them as functional food and medicine materials.

Determination of flavonoids in Portulaca oleracea L. by capillary electrophoresis with electrochemical detection

A general method based on capillary electrophoresis with electrochemical detection (CE-ED) was developed for identification and determination of five flavonoids (kaempferol, apigenin, myricetin, quercetin and luteolin) in plant species. Running buffer, pH and concentration, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. The working electrode was a 500 microm diameter carbon disc electrode positioned opposite the outlet of capillary. At room temperature, the five flavonoids could be well separated within 21 min in a 60 cm length capillary at a separation voltage of 19.5 kV with 50 mM Na2B4O7-100 mM NaH2PO4 (pH 8.50) as the running buffer. The relationship between peak currents and analyte concentrations was linear over about two orders of magnitude, and the detection limits (S/N=3) were ranging from 0.12 to 0.21 microg/ml for all analytes. The optimized CE-ED method was employed to analyze the above flavonoids in different parts of Portulaca oleracea L.

Three-year comparison of the content of antioxidant microconstituents and several quality characteristics in organic and conventionally managed tomatoes and bell peppers

Understanding how the environment and production and cultivation practices influence the composition and quality of food crops is fundamental to the production of high-quality nutritious foods. In this 3-year study, total phenolics, percent soluble solids, ascorbic acid, and the flavonoid aglycones quercetin, kaempferol, and luteolin were measured in two varieties of tomato (Lycopersicon esculentum L. cv. Ropreco and Burbank) and two varieties of bell peppers (Capsicum annuum L. cv. California Wonder and Excalibur) grown by certified organic and conventional practices in a model system. Significantly higher levels of percent soluble solids (17%), quercetin (30%), kaempferol (17%), and ascorbic acid (26%) were found in Burbank tomatoes (fresh weight basis; FWB), whereas only levels of percent soluble solids (10%) and kaempferol (20%) were significantly higher in organic Ropreco tomatoes (FWB). Year-to-year variability was significant, and high values from 2003 influenced the 3-year average value of quercetin reported for organic Burbank tomatoes. Burbank tomatoes generally had higher levels of quercetin, kaempferol, total phenolics, and ascorbic acid as compared to Ropreco tomatoes. Bell peppers were influenced less by environment and did not display cropping system differences.

HPLC/MS analysis and anxiolytic-like effect of quercetin and kaempferol flavonoids from Tilia americana var. mexicana

AIM OF THE STUDY

Around the world, Tilia species have been used in traditional medicine for their properties as tranquilizer. Furthermore, Mexican species of Tilia have been grouped as Tilia americana var. mexicana, but their specific content in flavonoids is poorly described. In this study, inflorescences of Mexican Tilia were collected in three different regions of Mexico to compare their flavonoid content and anxiolytic-like response.

MATERIALS AND METHODS

Flavonoid content was analyzed by using an HPLC-MS technique. For anxiolytic-like response, Tilia inflorescences extracts (from 10 to 300 mg/kg, i.p.) were tested in experimental models (open-field, hole-board and plus-maze tests, as well as sodium pentobarbital-induced hypnosis) in mice.

RESULTS

HPLC-MS analysis revealed specific peaks of flavonoid composition demonstrating some differences in these compounds in flowers and bracts depending on the region of collection. No differences in the neuropharmacological activity among these samples of Tilia were found. Moreover, their effects were associated with quercetin and kaempferol glycosides.

CONCLUSIONS

Dissimilarities in the flavonoid composition of Mexican Tilias might imply that these species must be re-classified in more than one species, not as a unique Tilia americana var. mexicana. Since quercetin and kaempferol aglycons demonstrated anxiolytic-like response and that no difference in the pharmacological evaluation was observed between these three Mexican Tilias, we suggest that this pharmacological effect of Tilia inflorescences involves these flavonoids occurrence independently of the kind of glycosides present in the samples reinforcing their use in traditional medicine in several regions of Mexico.

Determination of Flavonoids, Tannins and Ellagic acid in leaves fromRubus L. species

This paper describes the quantitative determination of flavonoids, tannins and ellagic acid in the leaves from wild and cultivated variations of Rubus L. species (Rosaceae): raspberry (2 wild and 13 cultivars) and blackberry (3 wild and 3 cultivars). The content of flavonoids was analyzed using spectrophotometric (the Christ-Mullers method) and HPLC analysis after acid hydrolysis. The content of tannins was determined by the weight method, with hide powder, described by German Pharmacopoeia 10 (DAB 10). Ellagic acid content was examined using the HPLC method after acid hydrolysis. Flavonoid content, determined using the Christ-Muller's method was higher for the blackberry leaves than for the raspberry leaves and varied between 0.46% and 1.05%. Quercetin and kaempferol were predominant in all samples analyzed using the HPLC method. The highest flavonoid content was found in the leaves of R. nessensis (1.06%); with results in all of the examined samples varying between 0.27% and 1.06%. The concentration of ellagic acid in all species was determined after acid hydrolysis and ranged from 2.06% to 6.89%. The leaves of raspberries are characterized by greater amounts of tannins (varying between 2.62% and 6.87%) than the leaves of other species. The results from this study indicate that the analyzed species are a rich source of flavonoids, ellagic acid and tannins, which may be used for the quality assessment of Rubus L. species leaves.

Complete 1H NMR spectral analysis of ten chemical markers of Ginkgo biloba

The complete and unambiguous (1)H NMR assignments of ten marker constituents of Ginkgo biloba are described. The comprehensive (1)H NMR profiles (fingerprints) of ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, bilobalide, quercetin, kaempferol, isorhamnetin, isoquercetin, and rutin in DMSO-d(6) were obtained through the examination of 1D (1)H NMR and 2D (1)H,(1)H-COSY data, in combination with (1)H iterative full spin analysis (HiFSA). The computational analysis of discrete spin systems allowed a detailed characterization of all the (1)H NMR signals in terms of chemical shifts (δ(H)) and spin-spin coupling constants (J(HH)), regardless of signal overlap and higher order coupling effects. The capability of the HiFSA-generated (1)H fingerprints to reproduce experimental (1)H NMR spectra at different field strengths was also evaluated. As a result of this analysis, a revised set of (1)H NMR parameters for all ten phytoconstituents was assembled. Furthermore, precise (1)H NMR assignments of the sugar moieties of isoquercetin and rutin are reported for the first time.

(Poly)phenolic fingerprint and chemometric analysis of white (Morus alba L.) and black (Morus nigra L.) mulberry leaves by using a non-targeted UHPLC-MS approach

This study reports the (poly)phenolic fingerprinting and chemometric discrimination of leaves of eight mulberry clones from Morus alba and Morus nigra cultivated in Spain. UHPLC-MS(n) (Ultra High Performance Liquid Chromatography-Mass Spectrometry) high-throughput analysis allowed the tentative identification of a total of 31 compounds. The phenolic profile of mulberry leaf was characterized by the presence of a high number of flavonol derivatives, mainly glycosylated forms of quercetin and kaempferol. Caffeoylquinic acids, simple phenolic acids, and some organic acids were also detected. Seven compounds were identified for the first time in mulberry leaves. The chemometric analysis (cluster analysis and principal component analysis) of the chromatographic data allowed the characterization of the different mulberry clones and served to explain the great intraspecific variability in mulberry secondary metabolism. This screening of the complete phenolic profile of mulberry leaves can assist the increasing interest for purposes related to quality control, germplasm screening, and bioactivity evaluation.

Phytochemical phenolics in organically grown vegetables

Fruit and vegetable intake is inversely correlated with risks for several chronic diseases in humans. Phytochemicals, and in particular, phenolic compounds, present in plant foods may be partly responsible for these health benefits through a variety of mechanisms. Since environmental factors play a role in a plant's production of secondary metabolites, it was hypothesized that an organic agricultural production system would increase phenolic levels. Cultivars of leaf lettuce, collards, and pac choi were grown either on organically certified plots or on adjacent conventional plots. Nine prominent phenolic agents were quantified by HPLC, including phenolic acids (e. g. caffeic acid and gallic acid) and aglycone or glycoside flavonoids (e. g. apigenin, kaempferol, luteolin, and quercetin). Statistically, we did not find significant higher levels of phenolic agents in lettuce and collard samples grown organically. The total phenolic content of organic pac choi samples as measured by the Folin-Ciocalteu assay, however, was significantly higher than conventional samples (p < 0.01), and seemed to be associated with a greater attack the plants in organic plots by flea beetles. These results indicated that although organic production method alone did not enhance biosynthesis of phytochemicals in lettuce and collards, the organic system provided an increased opportunity for insect attack, resulting in a higher level of total phenolic agents in pac choi.

Phenolic antioxidants of foxtail and little millet cultivars and their inhibitory effects on α-amylase and α-glucosidase activities

Evaluation of phenolic contents and their in vitro bioactivities of six diverse cultivars of foxtail and little millets revealed that their total phenolic content ranged from 19.42 to 24.12 µmol ferulic acid equivalents/g. The soluble fraction accounted for more than 80% of the total phenolic and flavonoid contents. Ferulic, caffeic and sinapic acids were the predominant phenolic acids, and luteolin and kaempferol were major flavonoids in the soluble fractions of millets. However, ferulic and p-coumaric acids were abundant in the bound fractions. Millet cultivars exhibited relevant changes in antioxidant activities in different mechanisms. Little millet cultivars showed superior inhibition of α-amylase and α-glucosidase than foxtail millet cultivars. The soluble and bound fractions of CO7 cultivar of foxtail millet (IC₅₀, 22.37 and 57.26 µg/ml) and CO4 cultivar of little millet (IC₅₀, 18.97 and 55.69 µg/ml) displayed strong inhibition towards α-glucosidase. These results suggest the potential application of underutilized millets as functional food ingredients for regulating postprandial hyperglycemia.

Construction of hydrophilic hypercrosslinked polymer based on natural kaempferol for highly effective extraction of 5-nitroimidazoles in environmental water, honey and fish samples

A series of novel hydroxyl-functional hypercrosslinked polymers (named as HCPs-Kae) were fabricated using natural and environmentally benign kaempferol as monomer via one-step Friedel-Crafts reaction. The prepared HCP-Kae1-24 h exhibited large surface area, good hydrophilicity and excellent adsorption performance to 5-nitroimidazoles (5-NDZs). Thus, by applying HCP-Kae1-24 h as a solid-phase extraction adsorbent, a sensitive method was developed for enrichment of 5-NDZs including metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole prior to high performance liquid chromatography analysis. Under the optimum conditions, good linearities were achieved in the range of 0.10-100.0 ng mL^-1 for water, 1.3-500.0 ng g^-1 for honey, and 1.7-100.0 ng g^-1 for fish meat. The detection limits of the method were 0.03-0.05 ng mL^-1, 0.4-1.0 ng g^-1, 0.5-1.0 ng g^-1 for water, honey and fish meat, respectively. High method recovery was obtained in the range of 84-118% with relative standard deviations lower than 8.9%. The established method was successfully applied to the detection of 5-NDZs in environmental water, honey and fish samples. This work provides a new strategy for constructing hydroxyl-functional HCPs by using natural resource as robust adsorbent for adsorption/extraction applications.

The Phenolic Contents and Antioxidant Activities of Infusions of Sambucus nigra L

The aim of this work was to evaluate the antioxidant potential of teas prepared from twenty-four commercially available berries and flowers of Sambucus nigra L. in relation to their phenolic profile, as reflected by the most representative phenolic acids (caffeic, chlorogenic, p-coumaric, ferulic, gallic and syringic acids); flavonols (quercetin, kaempferol, myricetin and rutin); and total phenolic (TPC), phenolic acid (TAC) and flavonoid (TFC) contents. The infusions prepared from elderflowers contained more abundant phenolic compounds than the elderberry infusions. The TPC of these infusions ranged from 19.81 to 23.90 mg of gallic acid equivalents/g dry weight of sample (GAE/g DW) for elderberries and from 15.23 to 35.57 mg GAE/g DW for elderflowers, whereas the TFC ranged from 2.60 to 4.49 mg of rutin equivalents/g dry weight of sample (RUTE/g DW) in elderberry infusions and from 5.27 to 13.19 mg RUTE/g DW in elderflower infusions. Among the phenolic compounds quantified in this study, quercetin (2.07-9.48 mg/g DW) and myricetin (1.17-9.62 mg/g DW) had the highest concentrations in the teas prepared from berries and flowers, respectively. Moreover, the antioxidant potential of elder infusions assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and ferric reducing antioxidant power (FRAP) assays revealed that the teas prepared from flowers had higher mean DPPH and FRAP activities than the teas prepared from berries. Therefore, elder beverages could be important dietary sources of natural antioxidants that contribute to the prevention of diseases caused by oxidative stress.

Phenolics and antioxidant activity of mulberry leaves depend on cultivar and harvest month in Southern China

To elucidate the effects of cultivar and harvest month on the phenolic content and antioxidant activity of mulberry leaves, four major phenolics, including chlorogenic acid (ChA), benzoic acid (BeA), rutin (Rut) and astragalin (Ast), were quantified using an HPLC-UV method. Leaves from six mulberry cultivars, collected from April to October, were analyzed. The antioxidant activity of mulberry leaves was assessed by ferric reducing antioxidant power (FRAP), hydroxyl radical scavenging activity (HSA) and superoxide radical scavenging activity (SSA) assays. The results showed that the total values of the four phenolic compounds ranged from 2.3 dry weight (DW) to 4.2 mg/g DW, with ChA being the major compound. The mean total phenol (TP) content of the six cultivars ranged from 30.4 equivalents (GAE) mg/g DW to 44.7 GAE mg/g DW. Mulberry leaves harvested in May had the highest TP content. Moreover, the antioxidant activities of mulberry leaves harvested from April to October differed noticeably. In general, Kq 10 and May were considered to be a better cultivar and harvest month concerning phenolic content and antioxidant activity, respectively.

Massive accumulation of gallic acid and unique occurrence of myricetin, quercetin, and kaempferol in preparing old oolong tea

Old oolong tea, tasting superior and empirically considered beneficial for human health, is prepared by long-term storage accompanied with periodic drying for refinement. Analyzing infusions of three old and one newly prepared oolong teas showed that significant lower (-)-epigallocatechin gallate (EGCG) but higher gallic acid contents were detected in the old teas compared to the new one. The possibility of releasing gallic acid from EGCG in old tea preparation was supported by an in vitro observation of gallic acid degraded from EGCG under heating conditions mimicking the drying process. Moreover, three minor flavonols, myricetin, quercetin, and kaempferol, that were undetectable in the new tea occurred in all of the three old teas. Converting the new oolong tea into an old one by periodic drying revealed the same characteristic observation, i.e., massive accumulation of gallic acid presumably released from EGCG and unique occurrence of flavonols putatively decomposed from flavonol glycosides.

Metabolome classification of Brassica napus L. organs via UPLC-QTOF-PDA-MS and their anti-oxidant potential

INTRODUCTION

Brassica napus L. is a crop widely grown for its oil production and other nutritional components in the seed. In addition to the seed, other organs contain a wide range of phenolic metabolites although they have not been investigated to the same extent as in seeds.

OBJECTIVE

To define and compare the phytochemical composition of B. napus L. organs, namely the root, stem, leaf, inflorescence and seeds.

METHOD

Non-targeted metabolomic analysis via UPLC-QTOF-MS was utilised in order to localise compounds belonging to various chemical classes (i.e. oxygenated fatty acids, flavonols, phenolic acids and sinapoyl choline derivatives).

RESULTS

The vast majority of identified metabolites were flavonol glycosides that accumulated in most of the plant organs. Whereas other classes were detected predominantly in specific organs, i.e. sinapoyl cholines were present uniquely in seeds. Furthermore, variation in the accumulation pattern of metabolites from the same class was observed, particularly in the case of quercetin, kaempferol and isorhamnetin flavonols. Anti-oxidant activity, based on 2,2-diphenyl-1-picrylhdrazyl analysis was observed for all extracts, and correlated to some extent with total flavonoid content.

CONCLUSION

This study provides the most complete map for polyphenol composition in B. napus L. organs. By describing the metabolites profile in B. napus L., this study provides the basis for future investigations of seeds for potential health and/or medicinal use.

¹H-NMR simultaneous identification of health-relevant compounds in propolis extracts

INTRODUCTION

Propolis is a resinous substance collected by bees from exudates of different plants that is rich in well-known health-relevant phenolic compounds such as flavonoids and phenolic acids. Propolis extracts are very complex matrices difficult to study. Different analytical methods are usable to analyse propolis extracts and to obtain chemical fingerprint but to our knowledge NMR has not previously been used for this purpose.

OBJECTIVE

This study aims to demonstrate that it is possible to use ¹H-NMR for the simultaneous recognition of phenolic compounds in complex matrices, such as propolis extracts, using appropriate tools for spectra pre-treatment and analysis.

METHODOLOGY

In this work 12 typical phenolic propolis compounds (apigenin, chrysin, galangin, kaempferol, quercetin, naringenin, pinocembrin, pinostrobin, caffeic acid, cinnamic acid, p-coumaric acid and ferulic acid) were considered as reference compounds and their presence in samples was verified by HPLC-MS. A simple ¹H-NMR sequence was used to obtain spectra of samples. Spectra were pre-treated by using an appropriate tool for spectra alignment and analysed by using software for the study of spectra originated from complex matrices. Sixty-five propolis samples were used to test the proposed identification procedure.

RESULTS

Ten out of 12 considered compounds were identified as statistically significant in most of the samples.

CONCLUSION

This work suggests that it is possible to efficiently use ¹H-NMR, coupled with appropriate spectral analytical tools, for the simultaneous detection of phenolic compounds in complex matrices.

Antidiabetic components of Cassia alata leaves: identification through α-glucosidase inhibition studies

CONTEXT

Cassia alata Linn. [syn. Senna alata (L.) Roxb.] (Caesalpiniaceae) is used for treating various disease conditions including diabetes but its mechanism(s) of action and active principles remain to be elucidated.

OBJECTIVE

The antidiabetic principles were identified using an in vitro α-glucosidase inhibition study.

MATERIALS AND METHODS

The methanol extract of leaves of C. alata, which showed potent α-glucosidase inhibitory activity (IC₅₀, 63.75 ± 12.81 µg/ml), was fractionated. Active fractions were taken for further analysis by a variety of techniques including HPLC and Combiflash chromatography. The identity of the isolated compounds was established by spectroscopic analysis while their potential antidiabetic activity was assessed by in vitro enzyme inhibition studies.

RESULTS

The α-glucosidase inhibitory effect of the crude extract was far better than the standard clinically used drug, acarbose (IC₅₀, 107.31 ± 12.31 µg/ml). A subsequent fractionation of the crude extract was made using solvents of ascending polarity (petroleum ether, chloroform, ethyl acetate, n-butanol and water). The ethyl acetate (IC₅₀, 2.95 ± 0.47 µg/ml) and n-butanol (IC₅₀, 25.80 ± 2.01 µg/ml) fractions which contained predominantly kaempferol (56.7 ± 7.7 µM) and kaempferol 3-O-gentiobioside (50.0 ± 8.5 µM), respectively, displayed the highest carbohydrate enzyme inhibitory effect.

DISCUSSION

One of the possible antidiabetic mechanisms of action of C. alata is by inhibiting carbohydrate digestion. This is the first report on α-glucosidase activity of kaempferol 3-O-gentiobioside.

CONCLUSION

Considering the activity profile of the crude extract and isolated bioactive compounds, further in vivo and clinical studies on C. alata extracts and compounds are well merited.

Quantitative determination of major active components in Ginkgo biloba dietary supplements by liquid chromatography/mass spectrometry

A reversed-phase high-performance liquid chromatography/electrospray ionisation mass spectrometry (RP-HPLC/ESI-MS) method was developed and validated for the simultaneous determination of ten major active components in Ginkgo biloba extract (bilobalide, ginkgolides A, B, C, quercetin, kaempferol, isorhamnetin, rutin hydrate, quercetin-3-beta-D-glucoside and quercitrin hydrate) which have not been previously reported to be quantified in a single analysis. The ten components exhibit baseline separation in 50 min by C18 chromatography using a water/1:1 (v/v) methanol/acetonitrile gradient. Quantitation was performed using negative ESI-MS in selected ion monitoring (SIM) mode. Good reproducibility and recovery were obtained by this method. The sensitivity of both UV and different mass spectrometry modes (full scan, selected ion monitoring (SIM), and selected reaction monitoring (SRM)) were compared and both quantitation with and without internal standard were evaluated. The analysis of Ginkgo biloba commercial products showed remarkable variations in the rutin and quercetin content as well as the terpene lactone contents although all the products satisfy the conventional quality control method.

Antioxidant activity in extracts of 27 indigenous Taiwanese vegetables

The objectives of this study were to identify the antioxidants and antioxidant axtivity in 27 of Taiwan's indigenous vegetables. Lycium chinense (Lc), Lactuca indica (Li), and Perilla ocymoides (Po) contained abundant quercetin (Que), while Artemisia lactiflora (Al) and Gynura bicolor (Gb) were rich in morin and kaempferol, respectively. Additionally, Nymphoides cristata (Nc) and Sechium edule (Se)-yellow had significantly higher levels of myricetin (Myr) than other tested samples. Cyanidin (Cyan) and malvidin (Mal) were abundant in Gb, Abelmoschus esculentus Moench (Abe), Po, Anisogonium esculentum (Retz.) Presl (Ane), Ipomoea batatas (Ib)-purple, and Hemerocallis fulva (Hf)-bright orange. Relatively high levels of Trolox equivalent antioxidant capacity (TEAC), oxygen radical absorption capacity (ORAC), and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenger were generated from extracts of Toona sinensis (Ts) and Po. Significant and positive correlations between antioxidant activity and polyphenols, anthocyanidins, Que, Myr, and morin were observed, indicating that these phytochemicals were some of the main components responsible for the antioxidant activity of tested plants. The much higher antioxidant activity of Po, Ts, and Ib (purple leaf) may be related to their higher Cyan, Que, and polyphenol content.

Phenolic compounds in blackcurrant (Ribes nigrum L.) leaves relative to leaf position and harvest date

Blackcurrant leaves are an essential source of phenolic compounds and this study investigated their variation relative to leaf positions and harvest date. The phenolic content varied between harvest dates, although leaf position on the shoot and interactions also played an important role. The contents of quercetin-malonyl-glucoside, kaempferol-malonyl-glucoside isomer and kaempferol-malonyl-glucoside were higher than that of the other identified phenolic compounds, whereas epigallocatechin was the lowest for all investigated leaf positions and harvest dates. The content of several of the compounds was highest in June, while quercetin-glucoside, kaempferol-glucoside and total phenols, increased towards the end of the season. Leaf position influenced the content of myricetin-malonyl-glucoside, myricetin-malonyl-glucoside isomer, quercetin-malonyl-glucoside and kaempferol-glucoside at the end of the season. Knowledge relating to the influence of ontogenetic and harvest time on the content of specific phenolic compounds might contribute in tailoring functional foods or pharmaceutical products using blackcurrant leaves as natural ingredients.