FLAVONOL GLYCOSIDES OF THE CULTIVATED STRAWBERRY

SUMMARY— Alter extraction and separation by thin-layer chromatography (TLC) on cellulose, nine flavonol glycosides were detected and purified in the fruit of strawberry from various sources. The structures of these were investigated by TLC, spectral properties and several types of hydrolysis. Four of them mere completely identified as the -3-ß-monoglucosides and -3-ß-glucuronides of quercetin and kaempferol. Three others were characterized less fully as kaempferol-7-monogluco-side, a kaempferol-7-glucoside and an unreported quercetin-3-glucoside which was not the -3-ß-monoglucoside or a diglucoside. A comparison between the flavonol glycosides and anthocyanins of this fruit was made with respect to the amounts and types present.     

HPLC-DAD-ESIMS analysis of phenolic compounds in bayberries (Myrica rubra Sieb. et Zucc.)

Qualitative analysis of the ethyl acetate extracts from three bayberry cultivars, Xiangshan, Biqi and Dongkui, was performed by means of a hyphenated technique of HPLC coupled to photodiode array detection and electrospray ionization mass spectrometry (HPLC-DAD-ESIMS). Three phenolic compounds were identified (gallic acid, protocatechuic acid, and quercetin 3-glucoside) and seven others (two myricetin hexoside and two myricetin deoxyhexoside derivatives; quercetin hexoside and quercetin deoxyhexoside derivatives; kaempferol hexoside derivative) partially identified. Quantification of phenolic compounds was performed by HPLC-DAD, which revealed that gallic acid (2.6–7.0 mg/kg FW) was the major phenolic acid in all analysed cultivars. Myricetin glycosides (71.1 mg/kg FW) were the major flavonol glycosides in cultivar Xiangshan and quercetin glycosides (117.8 mg/kg FW) were the major ones in cultivar Biqi. Cultivar Dongkui had medium contents of quercetin glycosides (48.0 mg/kg FW) and myricetin glycosides (53.2 mg/kg FW). Kaempferol glyosides (3.1–4.6 mg/kg FW) were the lowest contents of flavonol glycosides in the assayed bayberries. These results are relevant not only from a nutritional point of view, but also in the control of color stability and haze formation during bayberry juice processing and storage.     

Antioxidant flavonol glycosides in mulberry (Morus alba L.) leaves isolated based on LDL antioxidant activity

Oxidation of low-density lipoprotein (LDL) has been implicated in atherogenesis. Antioxidants that prevent LDL from oxidation may reduce atherosclerosis. We investigated LDL antioxidant activity and extracted compounds of mulberry (Morus alba L.) leaves. The LDL antioxidant activity of 60% ethanol extracted of mulberry leaves, which inhibits human LDL oxidation induced by copper ion, was determined on the basis of oxidation lag time and calculated as epigallocatechin 3-gallate equivalents (58.3 μmol of EGCG equivalent/g of dry weight). Three flavonol glycosides [quercetin 3-(6-malonylglucoside), rutin (quercetin 3-rutinoside) and isoquercitrin (quercetin 3-glucoside)] were identified as the major LDL antioxidant compounds by LC-MS and NMR. The amounts of these flavonol glycosides in mulberry leaves and mulberry-leaf tea were determined by HPLC. Our results showed that quercetin 3-(6-malonylglucoside) and rutin were the predominant flavonol glycosides in the mulberry leaves.     

绿茶茶汤中黄酮醇及其苷类的测定方法以及对茶汤色度的影响

黄酮醇及其苷类物质是构成绿茶汤色的重要组分。绿茶中含有20多种黄酮醇及其苷类物质,其中以槲皮素、杨梅素、山柰素的3种苷类物质为主。文中采用高效液相色谱法研究了绿茶茶汤酸水解前后槲皮素、杨梅素、山柰素的含量变化,建立了黄酮醇及其苷类含量的检测方法。利用正交实验方法得到茶汤水解的优化条件为:5 mL的茶汤中加15 mL纯甲醇、5 mL 6 mol/L HCl,在75℃下水解时间2h,芦丁的平均水解率为82.74%。对不同贮藏期间茶汤色度与黄酮醇及其苷类的相关性进行了研究,结果表明:茶汤贮藏过程中随着茶汤的红绿度(a)和黄蓝度(b)不断升高,杨梅素苷含量逐步下降,杨梅素苷与茶汤的红绿度、黄蓝度的相关系数分别为:-0.982 1、-0.882 6,但与茶汤明亮度(L)的相关性不显著。槲皮素和山柰素及其苷类与茶汤色泽变化关系不密切。     

Flavonol glycosides and antioxidant capacity of various blackberry and blueberry genotypes determined by high‐performance liquid chromatography/mass spectrometry

Flavonol glycoside composition and content in blueberry and blackberry extracts were determined using a high‐performance liquid chromatographic (HPLC) separation method coupled with photodiode array (PDA) and mass spectrometric (MS) detection. The hydrophilic antioxidant capacities of crude and fractionated flavonol extracts were also determined by the oxygen radical‐absorbing capacity (ORAC_FL) and photochemiluminescence (PCL) assays. Eight flavonols of quercetin and quercetin–sugar conjugates were identified in Kiowa blackberry, namely rutinoside, galactoside, methoxyhexoside, glucoside, pentoside, [6″‐(3‐hydroxy‐3‐methylglutaroyl)]‐β‐galactoside, glucosylpentoside and oxalylpentoside. Thirteen flavonols were detected in Ozarkblue blueberry. Of these, myricetin 3‐hexoside and 12 quercetin–sugar conjugates, namely rutinoside, galactoside, methoxyhexoside, glucoside, pentoside, glucosylpentoside, caffeoylglucoside, oxalylpentoside, rhamnoside, dimethoxyrhamnoside, acetylgalactoside and acetylglucoside, were identified. In Bluecrop blueberry, two additional quercetin–sugar conjugates were identified, namely glucuronide and caffeoylgalactoside. Quercetin glycosides accounted for 75% of total flavonols in the blueberry genotypes. Total flavonol contents ranged from 99 to 150 mg kg^?1 for blackberries and from 192 to 320 mg kg^?1 for blueberries. Quenching of peroxyl and superoxide anion radicals by the flavonol fractions ranged from 1.5 to 2.3 mmol Trolox equivalents (TE) kg^?1 and from 0.5 to 0.7 mmol TE kg^?1 respectively for blackberries and from 2.9 to 5.2 mmol TE kg^?1 and from 0.8 to 1.4 mmol TE kg^?1 respectively for blueberries. The HPLC method allowed for complete separation and identification of flavonols commonly found in blackberries, and blueberries. Our results showed that blueberry and blackberry genotypes varied significantly in flavonol content and antioxidant capacity. Even though total flavonol content did not correlate well with antioxidant capacity, their ability to scavenge peroxyl and superoxide anion radicals was apparent. Copyright © 2005 Society of Chemical Industry     

Identification of phenolic compounds in strawberries by liquid chromatography electrospray ionization mass spectroscopy

Strawberry (Fragaria x ananassa Duch.) fruits contain phenolic compounds that have antioxidant, anticancer, antiatherosclerotic and anti-neurodegenerative properties. Identification of food phenolics is necessary since their nature, size, solubility, degree and position of glycosylation and conjugation influence their absorption, distribution, metabolism and excretion in humans. Freeze-dried whole strawberry fruit powder and strawberry fruit extracts were analyzed by liquid chromatography electrospray ionization mass spectrometry (LC–ESI–MS) methods. Phenolics were identified as ellagic acid (EA), EA-glycosides, ellagitannins, gallotannins, anthocyanins, flavonols, flavanols and coumaroyl glycosides. The anthocyanidins were pelargonidin and cyanidin, found predominantly as their glucosides and rutinosides. The major flavonol aglycons were quercetin and kaempferol found as their glucuronides and glucosides. LC–ESI–MS/MS methods differentiated EA from quercetin conjugates since both aglycons have identical molecular weights (302 g/mol). The identification of strawberry phenolics is necessary to generate standardized materials for in vitro and in vivo studies and for the authentication of strawberry-based food products.     

Flavonol composition of Australian red and white wines determined by high‐performance liquid chromatography

Background and Aims: Flavonols are present in Vitis vinifera L. wine grapes as glycosides and are found in wines in both their glycosidic and aglycone forms. Flavonols and their glycosides are important components in wine because of their impact on colour, taste and health properties. An assessment of the flavonols and flavonol glycosides present in a wide selection of Australian red and white wines (n = 121 and 44, respectively) was undertaken. Methods and Results: Analyses were performed using HPLC, with compound identification being aided by HPLC‐MS. In the red wines, quercetin and myricetin dominated the flavonol profile, and quercetin‐3‐glucuronide was by far the most abundant glycoside present. White wines had considerably lower levels of flavonols and their glycosides, in most cases, being below the detection limit of the HPLC method. Conclusions: There appeared to be no correlation between the flavonol profile and wine variety or region in either white or red wines. Contrary to literature reports of rutin in wine, rutin was not found in any of the wines we analysed, and spiking experiments showed rutin rapidly degraded to the aglycone quercetin. Furthermore, changes in elution order for some quercetin glycoside standards were observed depending upon the acid used in the mobile phase. Significance of the Study: This is the first time the flavonol contents of an extensive cross section of Australian wines have been reported. The concentrations are consistent with those reported in wines from other countries. In light of the instability of rutin in wine, critical review should be given to reports discussing its presence.     

The effect of temperature and radiation on flavonol aglycones and flavonol glycosides of kale (Brassica oleracea var. sabellica)

The winter crop kale has a complex profile of different glycosylated and acylated flavonol glycosides which may be affected by global warming. To the best of our knowledge, compound–climate relationships for flavonol aglycones and flavonol glycosides were established for the first time. The investigated 10 major flavonol glycosides responded structure-dependent in the investigated temperature range between 0 and 12 °C and the photosynthetic active radiation range between 4 and 20 mol m⁻² d⁻¹, e.g. the decrease in temperature led to an increase in sinapic acid monoacylated and diacylated quercetin glycosides, while the sinapic acid monoacylated kaempferol glycosides showed a maximum at 4.5 °C. Furthermore, the hydroxycinnamic acid residues and the different number of glucose moieties in the 7-O position affected the response of kaempferol triglucosides. Consequently, global warming would result in lower concentrations of antioxidant-relevant quercetin glycosides in winter crops, suggesting a production at e.g. higher altitudes due to lower temperature.     

A remarkable influence of microwave extraction: Enhancement of antioxidant activity of extracted onion varieties

Four (red, yellow, white and grelot onion) varieties of Allium cepa, a rich source of quercetin (flavonol) glycosides, were studied for their total content of reducing compounds (TCRC), flavonol content and antioxidant activity evaluation. Extracts obtained by solvent free microwave hydrodiffusion and gravity (MHG) technique and conventional solvent extraction (CSE) were analysed with high performance liquid chromatography (HPLC) for quantification of flavonoids. Three different methods were selected for evaluating the antioxidant capacity of the different onion varieties (after the determination of their phenolic content by the Folin–Ciocalteu method): the reduction of the stable DPPH (2,2-diphenyl-1-picrylhydrazyl) radical, the ORAC (oxygen radical absorbance capacity) method, and the inhibition of the AAPH-induced peroxidation of linoleic acid in SDS micelles. The highest antioxidant capacity was observed for red onion, followed by yellow, white and grelot onion. In spite of the low recovery of extractable flavonoids (quercetin 3,4′-diglucoside, 4′-glucoside and 3-glucoside), MHG remained the preferred extraction method in comparison to the conventional method, as all the samples obtained under microwave-assisted extraction (MAE) exhibited the highest antioxidant activities in all the tests. Also the microscopic observations of extracted tissues showed that at cellular level, microwaves induced disruptions of vacuoles and cell walls thus promoting the effectiveness of this method.     

Polyphenols in greenhouse and open-air-grown lettuce

Lactuca sativa L. plants (cv. Audran) developed in greenhouse or in open air, were analysed for their polyphenol compounds (caffeic acid derivatives, quercetin and kaempferol glycosides) to verify whether these two different growing environments affected both the qualitative and quantitative phenol patterns. The lettuce extracts from greenhouse and open-air samples were compared and directly analysed by HPLC/DAD, HPLC/MS and HPTLC. All open-air samples had higher flavonol contents than the greenhouse ones. The applied rapid and sensitive HPTLC method could be routinely employed to determine the leaf flavonol content of a large number of lettuce samples.     

Antioxidative properties and flavonoid composition of Chenopodium quinoa seeds cultivated in Japan

To evaluate the nutritional advantages of quinoa seeds (Chenopodium quinoa Willd.) cultivated in Japan, antioxidative properties and flavonoid composition were determined and compared to corresponding data for conventionally-used cereals and pseudo-cereals, including quinoa seeds from South America. The antioxidant activities of these grains against DPPH radicals were strongly associated with the total phenolic content of the tested samples. The crude extracts of quinoa seeds cultivated in Japan exhibited higher antioxidative effects than those from South America and other cereals, excluding buckwheat. Four flavonol glycosides were isolated and identified from the Japanese quinoa seeds, and the chemical composition of the flavonoids – quercetin and kaempferol 3-O-(2″,6″-di-O-α-rhamnopyranosyl)-β-galactopyranosides (1 and 4), quercetin 3-O-(2″,6″-di-O-α-rhamnopyranosyl)-β-glucopyranoside (2), and quercetin 3-O-(2″-O-β-apiofuranosyl-6″-O-α-rhamnopyranosyl)-β-galactopyranoside (3) – was evaluated through quantitative determination. Trioside 2 was isolated for the first time from quinoa seeds. These glycosides were not detected in extracts from any of the tested grains except quinoa. The aglycone quercetin content of the Japanese quinoa seeds is higher than in the seeds from South America and buckwheat. The amounts of quercetin and kaempferol formed via acidic hydrolysis in quinoa are much higher than those of conventionally-used edible plants. The quinoa seeds cultivated in Japan are the most effective functional foodstuff – in terms of being a source of antioxidative and bioactive flavonoids – among cereals and pseudo-cereals.     

Quantification of Quercetin Glycosides in 6 Onion Cultivars and Comparisons of Hydrolysis-HPLC and Spectrophotometric Methods in Measuring Total Quercetin Concentrations

ABSTRACT: This study was performed to purify and quantify quercetin glycosides (QG) and aglycone (free) quercetin (Q) in 6 selected onion cultivars and to compare analytical approaches based on high-performance liquid chromatography (HPLC) and spectrophotometry for the quantification of total quercetin (TQ) concentrations. Individual mono- and di-glycoside Q compounds were purified using a semipreparative HPLC and identified by comparing spectral data and by confirming corresponding peaks of QG and Q after incomplete enzyme-hydrolysis. Purified QG were quantified as Q by enzyme-hydrolysis/HPLC. TQ concentrations obtained from 20 onion bulbs with enzyme-hydrolysis/HPLC, no-hydrolysis/HPLC, and a spectrophotometric method without prior hydrolysis were significantly correlated (r²= 0.99) and were about 15% higher, identical, or 10% less than those concentrations by a standard acid-hydrolysis/HPLC method, respectively. During enzyme-hydrolysis of onion extracts, progressive reduction of the QG and formation of the corresponding mono-glycosides and Q were monitored using an analytical HPLC. TQ ranged from 83 to 330 μg/g F.W. in 6 selected cultivars of long-day or short-day onions. Q3,4′G and Q4′G were the 2 major compounds and comprised approximately between 94% and 97% of TQ in onions.     

Comparison of phenolic composition and antioxidant properties of two native Chilean and one domestic strawberry genotypes

The phenolic composition of extracts from the forms chiloensis and patagonica of Fragaria chiloensis were compared with that of the commercial strawberry Fragaria × ananassa cv. Chandler by high performance liquid chromatography with diode-array detector (HPLC–DAD) and high performance liquid chromatography with electrospray ionization mass spectroscopy detector (HPLC–ESI–MS). The phenolic constituents in the three species were mainly proanthocyanidins, hydrolysable tannins, anthocyanins and flavonol glycosides. In both native strawberry species the main flavonol glycoside was quercetin 3-O-glucuronide and the minor anthocyanins identified were cyanidin-malonyl-glucoside and pelargonidin-malonyl-glucoside. The highest anthocyanin content was found in the commercial red strawberry while ellagic acid was the main phenolic in the native white strawberry. From the methanolic fruit extract of the native Chilean strawberry Fragaria chiloensis ssp. chiloensis f. chiloensis four known antioxidants were isolated by selective fractionation using the bleaching of the free radical scavenger 1,1-diphenyl-2-picrylhydrazyl (DPPH) as the guiding assay. The antioxidant properties (measured as the bleaching of the DPPH radical) were determined for methanol extracts of the three fruits, for fractions of F. chiloensis ssp. chiloensis f. chiloensis, and for the isolated compounds cyanidin-3-glucoside, pelargonidin-3-glucoside, quercetin-3-glucuronide and ellagic acid. This study allows a clear chemical differentiation between the commercial strawberry and the Chilean white strawberry.     

Flavonol Glycosides in Cranberries

SUMMARY The yellow flavonol glycosides were isolated from cranberries ( Vaccinium macrocarpon , Ait.) and identified by chromatographic, chemical, and spectral studies. The major pigment was quercetin-3-galactoside, followed by quercetin-3-hamnoside, quercetin-3-arabinoside, quercetin, myri-cetin-3.arabinoside, and myricetin-3-digalactoside.     

Identification and quantification of flavonol aglycons in cactus pear (Opuntia ficus indica) fruit using a commercial pectinase and cellulase preparation

The applicability of pectinases and cellulases as soft hydrolysing agents on flavonol glycosides was investigated for identification and quantification of flavonol aglycons in cactus pear fruit. Freeze-dried samples of cactus pear fruit’s peel (cactus pear peels) and onions were treated with commercial pectinase and cellulase preparations at 50 °C for different time periods (up to 16 h). Additionally isorhamnetin-3-O-rutinoside and quercetin-3,4′-O-diglucoside were used as model compounds. In parallel, samples of cactus pear peels and onions were treated by the traditional acidic hydrolysis using HCl. Following hydrolysis, flavonols were characterised using HPLC–DAD. Enzymatically, all model compounds and plant material were highly hydrolysable. Flavonol glycosides were completely hydrolysed after 16 h (cactus pear) and 4 h (onion), respectively. While the acidic hydrolysis caused degradation of the flavonols and produced protocatechuic acid as a degradation product, the enzymatic hydrolysis gave gentle effects and did not produce any protocatechuic acid at all.     

Identification of phenolics in the fruit of emblica (Phyllanthus emblica L.) and their antioxidant activities

An activity-directed fractionation and purification process was used to identify the antioxidative components of emblica fruit. Dried fruit of emblica was extracted with methanol and then partitioned by ethyl ether, ethyl acetate, butanol and water. The ethyl acetate fraction showed the strongest 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity among four fractions. The ethyl acetate fraction was then subjected to separation and purification using Sephadex LH-20 chromatography and reverse-phase high-performance liquid chromatography (HPLC). Six compounds were identified to be geraniin (1), quercetin 3-β-d-glucopyranoside (2), kaempferol 3-β-d-glucopyranoside (3), isocorilagin (4), quercetin (5), and kaempferol (6), respectively, by spectral methods, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, ultraviolet–visible (UV–Vis) spectrophotometry and mass spectroscopy (MS), and comparison with literatures. Compounds 2–4 and 6 were identified from emblica fruit for the first time. Furthermore, the antioxidant activities of purified compounds were screened for their antioxidative potential using lipid peroxidation and DPPH systems. All the purified compounds showed strong antioxidant and radical scavenging activities. Amongst, geraniin showed the highest antioxidant activity (4.7 and 65.7 μM of IC₅₀ values for DPPH and lipid peroxidation assay, respectively) than other purified compounds.     

Flavonol content in the water extract of the mulberry (Morus alba L.) leaf and their antioxidant capacities

Abstract: The biological activities of the mulberry (Morus alba L.) leaf have been attributed to its flavonoid content. The water extract of the mulberry leaf (WEML) was prepared by autoclaving at 121 °C for 15 min, and the flavonol content of the WEML was determined by HPLC The WEML contained 4 flavonols in the following order: quercetin‐3‐β‐D‐glucose (QT‐G) > quercetin‐3‐O‐glucose‐6″‐acetate (QT‐GA) > rutin (RT) > quercetin (QT). In the oxygen radical absorbance capacity (ORAC) assay, QT had the highest peroxyl radical‐scavenging capacity and a similar hydroxyl radical‐scavenging capacity as its glycosides (QT‐G, QT‐GA, and RT). QT exhibited a stronger cellular antioxidant capacity (CAC) against 2,2′‐Azobis(2‐amidinopropane) dihydrochloride (AAPH)‐ and Cu²⁺‐induced oxidative stress in HepG2 cells compared to its glycosides, indicating that the intracellular antioxidant capacity of QT and its glycosides may depend upon both the permeability across the cell membrane and the peroxyl or hydroxyl radical‐scavenging capacity. Practical Application: The information presented might be used for developing mulberry leaf‐based functional foods.     

Human intestinal hydrolysis of phenol glycosides - a study with quercetin and p-nitrophenol glycosides using ileostomy fluid

In order to study the influence of sugar moiety, aglycon structure and microflora concentration on the human ileal hydrolysis of phenol glycosides, various quercetin and p-nitrophenol glycosides were incubated under anaerobic conditions (37 degrees C for 0, 0.5, 1, 2, 4, 6, 8, 10 and 24 h) with ileostomy fluids from three different donors. The glycosides, i.e. beta-D-glucopyranosides, beta-D-galactopyranosides, alpha-L-arabinofuranosides, beta-D-xylopyranosides and alpha-L-rhamnopyranosides as well as the liberated aglycones were identified by HPLC-DAD and HPLC-ESI-MS/MS. Among the quercetin glycosides under study, the 3-O-beta-D-glucopyranoside showed with 0.22 micromol/h the highest hydrolysis rate, followed by the 3-O-beta-D-galactopyranoside, the 3-O-beta-D-xylopyranoside and the 3-O-alpha-L-arabinofuranoside (0.04 and each 0.03 micromol/h, respectively). Quercetin 3-O-alpha-L-rhamnopyranoside was found to be stable for the entire incubation period. Using quercetin 3-O-beta-D-glucopyranoside as a representative example, linear hydrolysis rate was observed from 75 to 2500 microL ileostomy fluid corresponding to its microflora content (log 0.68 up to 21.9 colony forming units). Studies performed in the presence of antibiotics did not reveal any hydrolysis. The p-nitrophenol glycosides were hydrolyzed faster than the corresponding quercetin glycosides. The hydrolysis rate decreased from the beta-D-glucopyranoside (0.41 micromol/h), to the beta-D-galactopyranoside (0.21 micromol/h), the beta-D-xylopyranoside (0.12 micromol/h), the alpha-L-arabinofuranoside (0.09 micromol/h) to the alpha-L-rhamnopyranoside (0.06 micromol/h). These results demonstrate that the human ileal hydrolysis of phenol glycosides depends on the sugar and the aglycon structure as well as the microflora.