Determination of flavonoids and ascorbic acid in grapefruit peel and juice by capillary electrophoresis with electrochemical detection

Evaluation of Citrus aurantifolia peel and leaves extracts for their chemical composition, antioxidant and anti-cholinesterase activities

BACKGROUND

The replacement of synthetic antioxidants by safe natural antioxidants fosters research on the screening of vegetables and food as sources of new antioxidants. Moreover, oxidative degeneration of cells is associated with neurodegenerative diseases such as Alzheimer's disease. On the basis of these considerations this work aimed to investigate the antioxidant properties [by using the diphenyl picryl hydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and ferric reducing ability of plasma assays, and the β-carotene bleaching test] and the anti-cholinesterase activity of Citrus aurantifolia peel and leaves from different areas of growth.

RESULTS

Methanol extracts of the peel and leaves demonstrated the strongest radical scavenging activity. A similar trend was observed with the reducing ability, with values from 112.1 to 146.0 µmol L(-1) Fe(II) g(-1). The relationship between phenol and flavonoid contents and antioxidant activity was statistically investigated. Based on analysis by high-performance liquid chromatography, the most abundant flavonoids found in C. aurantifolia extracts were apigenin, rutin, quercetin, kaempferol and nobiletin. n-Hexane fractions of both peel and leaves showed a good acetylcholinesterase inhibitory activity with IC(50) values in the range 91.4-107.4 µg mL(-1). Gas chromatography-mass spectrometry analysis revealed the presence of monoterpenes and sesquiterpenes as most common components.

CONCLUSION

The findings of this study suggest a potential use of C. aurantifolia peel and leaves for supplements for human health.

Simultaneous quantification of capsaicinoids and ascorbic acid from pungent peppers

The development of simultaneous extraction and determination of bioactive molecules from natural products is becoming more popular. The present study reports the development of a method for the simultaneous extraction and determination of both capsaicinoids and ascorbic acid in peppers. Capsaicin (341.61 µg/g), dihydrocapsaicin (119.91 µg/g) and ascorbic acid (2,109.60 µg/g) were extracted with 3% metaphosphoric acid-ethanol (2:8) as a solvent. The efficient extraction of capsaicinoids (412.61 µg/g) and ascorbic acid (2,785.93 µg/g) was achieved at a sample-to-solvent ratio of 1:8 after 30 minutes of sonication. Simultaneous separation of capsaicinoids and ascorbic acid was achieved using a Gemini C18 column with a gradient elution of 0.03M phosphoric acid and methanol. Capsaicinoids and ascorbic acid were simultaneously detected at 282 and 254 nm, respectively. The recovery of capsaicinoids ranged from 96.21 to 108.71%, and the recovery of ascorbic acid ranged from 97.01 to 98.83%. The limits of detection for capsaicin, dihydrocapsaicin and ascorbic acid were 0.24, 0.21 and 0.26 µg, respectively. Relative standard deviation for the intra-day and inter-day variability in the results was less than 3%, indicating that the method produced highly reproducible results. Therefore, this method enables the reproducible, simultaneous separation and quantification of capsaicinoids and ascorbic acid from peppers.

Separation/determination of flavonoids and ascorbic acid in rat serum and excrement by capillary electrophoresis with electrochemical detection

A capillary electrophoresis with electrochemical detection was developed for the simultaneous determination of three flavonoids (naringenin, rutin, quercetin) and ascorbic acid. It was found that naringenin, rutin, quercetin and ascorbic acid were well separated within 5 min in borate buffer solution (pH 8.6, 24 mM). The detection limit was 1.0 microM for naringenin, 8.0 microM for rutin, 2.0 microM for ascorbic acid and 0.5 microM for quercetin. The protocol was successfully applied for the determination of the analytes in rat serum and excrement. Recovery results ranged from 90.9 to 108.6%.

Use of different buffers for detection and separation in determination of physio-active components in oolong tea infusion by CZE with amperometric detection

With a view of simultaneous determination of physio-active ingredients in oolong tea infusion: sugars, amino acids, epigallocatechin gallate and ascorbic acid, a novel CZE with amperometric detection method was studied. Operated in a wall-jet configuration, 100 mmol/L NaOH was used in detecting cell to lead the electrocatalysis oxidation behaviors of the analytes on a 300 mum diameter copper-disc electrode (working electrode), while in separating capillary, a mild alkaline running buffer consisting in a mixture of 30 mmol/L borate and 40 mmol/L phosphates charged and carried analytes to detecting end. The methodology research was performed for system stability and suitability. Under the optimal CE conditions, analytes could be separated within moderate time period. Good linearity between peak area and concentration existed over three orders of magnitude; lower RSD and LOD were achieved. The oolong tea infusion was assayed and result was satisfactory.

Application and potential of capillary electroseparation methods to determine antioxidant phenolic compounds from plant food material

Antioxidants are one of the most common active ingredients of nutritionally functional foods which can play an important role in the prevention of oxidation and cellular damage inhibiting or delaying the oxidative processes. In recent years there has been an increased interest in the application of antioxidants to medical treatment as information is constantly gathered linking the development of human diseases to oxidative stress. Within antioxidants, phenolic molecules are an important category of compounds, commonly present in a wide variety of plant food materials. Their correct determination is pivotal nowadays and involves their extraction from the sample, analytical separation, identification, quantification and interpretation of the data. The aim of this review is to provide an overview about all the necessary steps of any analytical procedure to achieve the determination of phenolic compounds from plant matrices, paying particular attention to the application and potential of capillary electroseparation methods. Since it is quite complicated to establish a classification of plant food material, and to structure the current review, we will group the different matrices as follows: fruits, vegetables, herbs, spices and medicinal plants, beverages, vegetable oils, cereals, legumes and nuts and other matrices (including cocoa beans and bee products). At the end of the overview, we include two sections to explain the usefulness of the data about phenols provided by capillary electrophoresis and the newest trends.

Natural bioactive compounds of Citrus limon for food and health

Citrus genus is the most important fruit tree crop in the world and lemon is the third most important Citrus species. Several studies highlighted lemon as an important health-promoting fruit rich in phenolic compounds as well as vitamins, minerals, dietary fiber, essential oils and carotenoids. Lemon fruit has a strong commercial value for the fresh products market and food industry. Moreover, lemon productive networks generate high amounts of wastes and by-products that constitute an important source of bioactive compounds with potential for animal feed, manufactured foods, and health care. This review focuses on the phytochemistry and the analytical aspects of lemon compounds as well as on the importance for food industry and the relevance of Citrus limon for nutrition and health, bringing an overview of what is published on the bioactive compounds of this fruit.

Vitamin C and the Role of Citrus Juices as Functional Food

The literature on the content and stability of vitamin C (ascorbic acid, AA) in citrus juices in relation to industrial practices is reviewed. The role of vitamin C from citrus juices in human diet is also reviewed. Citrus fruits and juices are rich in several types of bioactive compounds. Their antioxidant activity and related benefits derive not only from vitamin C but also from other phytochemicals, mainly flavonoids. During juice processing, temperature and oxygen are the main factors responsible for vitamin C losses. Nonthermal processed juices retain higher levels of vitamin C, but economic factors apparently delay the use of such methods in the citrus industry. Regarding packing material, vitamin C in fruit juice is quite stable when stored in metal or glass containers, whereas juice stored in plastic bottles has a much shorter shelf-life.

The limiting step for vitamin C absorption in humans is transcellular active transport across the intestinal wall where AA may be oxidized to dehydroascorbic acid (DHAA), which is easily transported across the cell membrane and immediately reduced back to AA by two major pathways. AA bioavailability in the presence of flavonoids has yielded controversial results. Whereas flavonoids seem to inhibit intestinal absorption of AA, some studies have shown that AA in citrus extract was more available than synthetic ascorbic acid alone. DHAA is reported to possess equivalent biological activity to AA, so recent studies often consider the vitamin C activity in the diet as the sum of AA plus DHAA. However, this claimed equivalence should be carefully reexamined.

Humans are one of the few species lacking the enzyme (L-gulonolactone oxidase, GLO) to convert glucose to vitamin C. It has been suggested that this is due to a mutation that provided a survival advantage to early primates, since GLO produces toxic H2O2. Furthermore, the high concentration of AA (and DHAA) in neural tissues could have been the key factor that caused primates (vertebrates with relative big brain) to lose the capacity to synthesize vitamin C.

Oxidative damage has many pathological implications in human health, and AA may play a central role in maintaining the metabolic antioxidant response. The abundance of citrus juices in the Mediterranean diet may provide the main dietary source for natural vitamin C.

Amperometric determination of ascorbic acid in real samples using a disposable screen-printed electrode modified with electrografted o-aminophenol film

Ascorbic acid (AA) is an antioxidant considered to play a crucial role in human health. Therefore, diverse methods for the determination of AA in foods have been developed, most of them time-consuming and requiring costly instrumentation. A simple and sensitive method for the quantification of AA in fresh fruits and vegetables and commercial juices using an amperometric sensor is presented on the basis of disposable screen-printed carbon electrodes (SPEs) modified with an o-aminophenol (o-AP) film selective for the detection of AA. The sensor exhibited a linear response for AA from 2-20 microM, with a correlation coefficient r2 = 0.998 and a limit of detection of 0.86 microM. Common possible interferents of the sample matrices were tested, and results showed high selectivity of the o-AP SPEs toward AA. The sensor exhibited an excellent reproducibility (RSD% = 1.98, n = 8) and surface stability. The method was validated by a comparison to a reference method, and excellent correlation is obtained.

Determination of Vitamin C (Ascorbic Acid) Using High Performance Liquid Chromatography Coupled with Electrochemical Detection

Vitamin C (ascorbic acid, ascorbate, AA) is a water soluble organic compound that participates in many biological processes. The main aim of this paper was to utilize two electrochemical detectors (amperometric - Coulouchem III and coulometric - CoulArray) coupled with flow injection analysis for the detection of ascorbic acid. Primarily, we optimized the experimental conditions. The optimized conditions were as follows: detector potential 100 mV, temperature 25 °C, mobile phase 0.09% TFA:ACN, 3:97 (v/v) and flow rate 0.13 mL·min-1. The tangents of the calibration curves were 0.3788 for the coulometric method and 0.0136 for the amperometric one. The tangent of the calibration curve measured by the coulometric detector was almost 30 times higher than the tangent measured by the amperometric detector. Consequently, we coupled a CoulArray electrochemical detector with high performance liquid chromatography and estimated the detection limit for AA as 90 nM (450 fmol per 5 μL injection). The method was used for the determination of vitamin C in a pharmaceutical preparations (98 ± 2 mg per tablet), in oranges (Citrus aurantium) (varied from 30 to 56 mg/100 g fresh weight), in apples (Malus sp.) (varied from 11 to 19 mg/100 g fresh weight), and in human blood serum (varied from 38 to 78 μM). The recoveries were also determined.

A new method for determination of myricetin and quercetin using solid phase microextraction-high performance liquid chromatography-ultra violet/visible system in grapes, vegetables and red wine samples

A new approach for the extraction and determination of myricetin and quercetin by using SPME-HPLC-UV system has been developed. The method involves adsorption of flavonoids on CAR/TPR fiber followed by desorption in the desorption chamber of SPME-HPLC interface using citrate buffer (0.001 M):acetonitrile (70:30) as mobile phase and UV detection at 372 nm. The detection limits for myricetin and quercetin are 48.3 and 24.7 pgmL(-1), respectively. The proposed method was validated by determining myricetin and quercetin in tomato, onion, grapes and red wine samples.

Comparison of the contents of various antioxidants of sea buckthorn berries using CE

The increased interest in sea buckthorn (Hippophae rhamnoides L.) made it possible to investigate the antioxidant content in it. To address this issue, the presence of following antioxidant compounds were analyzed: trans-resveratrol, catechin, myricetin, quercetin, p-coumaric acid, caffeic acid, L-ascorbic acid (AA), and gallic acid (linear range of 50-150 micromol/L) in six different varieties of sea buckthorn berries extracts (sea buckthorn varieties: "Trofimovskaja (TR)," "Podarok Sadu (PS)," and "Avgustinka (AV),") received from two local Estonian companies. Trans-Resveratrol, catechin, AA, myricetin, and quercetin were found in extracts of sea buckthorn. Moreover, AA, myricetin, and quercetin contents were quantified. The biggest average AA content was found in TR (740 mg/100 g of dried berries, respectively). Furthermore, the same varieties gave the biggest quercetin content 116 mg/100 g of dried berries, respectively. For analysis, CZE was used and the results were partly validated by HPLC. Statistically no big differences in levels of antioxidants were consistently found in different varieties of sea buckthorn extracts investigated in this work.

Advances of modern chromatographic and electrophoretic methods in separation and analysis of flavonoids

Flavonoids, one of the largest groups of secondary metabolites, are widespread in vegetable crops such as herbs, fruits, vegetables, grains, seeds and derived foods such as juices, wines, oils, etc. They receive considerable attention due to their biological and physiological importance. Hundreds of publications on the analysis of flavonoids have appeared over the past decade. Traditional and more advanced techniques have come to prominence for sample preparation, separation, detection, and identification. This review intends to provide an updated, concise overview on the recent development and trends of separation, identification and quantification for flavonoids by modern chromatographic and spectrophotometric analytical techniques, including gas chromatography (GC), liquid chromatography (LC), and capillary electrophoresis (CE). The sample preparation before analysis is also briefly summarized.

Analysis of inorganic and small organic ions by CE with amperometric detection

Capillary electrophoresis has become a widely useful analytical technology. Amperometric detection is extensively employed in capillary electrophoresis for its many inherent virtues, such as rapid response, remarkable sensitivity, and low cost of both detectors and instrumentations. Analysis of inorganic and small organic ions by capillary electrophoresis is an important research field. This review focuses on the recent developments of capillary electrophoresis coupled with amperometric detection for analysis of inorganic and small organic ions. Advancements in electrophoresis separation modes, amperometric detection modes, working electrodes, and applications of inorganic ions, amino acids, phenols, and amines are discussed.

The simultaneous separation and determination of six flavonoids and troxerutin in rat urine and chicken plasma by reversed-phase high-performance liquid chromatography with ultraviolet–visible detection

The method of high-performance liquid chromatography (HPLC) with UV-vis detection was used and validated for the simultaneous determination of six flavonoids (puerarin, rutin, morin, luteolin, quercetin, kaempferol) and troxerutin in rat urine and chicken plasma. Chromatographic separation was performed using a VP-ODS column (150 mm x 4.6 mm, 5.0 microm) maintained at 35.0 degrees C. The mobile phase was a mixture of water, methanol and acetic acid (57:43:1, v/v/v, pH 3.0) at the flow rate of 0.8 mL/min. Six flavonoids and troxerutin were analyzed simultaneously with good separation. On optimum conditions, calibration curves were found to be linear with the ranges of 0.10-70.00 microg/mL (puerarin, rutin, morin, luteolin, quercetin, kaempferol) and 0.50-350.00 microg/mL (troxerutin). The detection limits were 0.010-0.050 microg/mL. The method was validated for accuracy and precision, and it was successfully applied to determine drug concentrations in rat urine and chicken plasma samples from rat and chicken that had been orally administered with six flavonoids and troxerutin.

Comparison of two sample preconcentration strategies for the sensitivity enhancement of flavonoids found in Chinese herbal medicine in micellar electrokinetic chromatography with UV detection

Two on-column preconcentration techniques named stacking with reverse migrating micelles (SRMM) and anion selective electrokinetic injection and a water plug-sweeping with reverse migrating micelles (ASIW-sweep-RMM) were used and compared for concentration and separation of flavonoids in Chinese herbs using reverse migration micellar electrokinetic chromatography (RM-MEKC). The optimal background electrolyte (BGE) used for separation and preconcentration was a solution composed of 20mM phosphoric acid (H(3)PO(4))-100mM sodium dodecyl sulfate (SDS)-20% (v/v) acetonitrile (ACN) buffer (pH 2.0), the applied voltage was -15kV. To achieve reasonable results of the two techniques, the conditions which affected preconcentration were examined. A comparison of used techniques with normal hydrodynamic injection (5s), concerning enhancement factors and limits of detection (LODs) was presented. Under the optimum stacking conditions, about 27-37- and 45-194-fold improvement in the detection sensitivity was obtained for SRMM and ASIW-sweep-RMM, respectively, compared to usual hydrodynamic sample injection (5s). The LODs (S/N=3) for SRMM and ASIW-sweep-RMM in terms of peak height, can reach down to 1.15 x 10(-2) microg/ml for hesperetin and 2.4 x 10(-3) microg/ml for nobiletin, respectively. Finally, the amounts of the six flavonoids in extract of Fructus aurantii Immaturus were successfully determined using ASIW-sweep-RMM. The six analytes were baseline separated with sample matrix under the optimum ASIW-sweep-RMM conditions and the experimental results showed that preconcentration was well achieved after the dilution of sample solutions.

Simultaneous determination of sugars and ascorbic acid by capillary zone electrophoresis with amperometric detection at a carbon paste electrode modified with polyethylene glycol and Cu2O

In this paper, a kind of novel carbon paste electrode modified with double modifiers-polyethylene glycol (PEG) and Cu(2)O (PEG/Cu(2)O CPME) in capillary zone electrophoresis with amperometric detection (CZE-AD) was applied to simultaneously determine three sugars: glucose, sucrose, fructose and ascorbic acid (AA). The catalytic electrochemical properties of PEG/Cu(2)O CPME could enhance sensitivity obviously compared with carbon paste electrode modified with only PEG or Cu(2)O at a relatively lower detection potential (+0.3 V versus SCE). Especially, the electrochemical detection response of AA increased obviously to the same level of saccharides by adding PEG into the Cu(2)O carbon paste modified electrode. The four analytes could be perfectly separated within 22 min, the linear ranges were from 1.0 x 10 (-6) to 5.0 x 10(-5) mol L(-1) and the detection limits were at 10(-7) mol L(-1) magnitude (S/N=3). The present working electrode was successfully employed to analyse beverage samples with recoveries in the range 93-107% and RSDs less than 4%. Above results demonstrated that capillary zone electrophoresis coupled with the PEG/Cu(2)O carbon paste modified electrode was of convenient preparation, high sensitivity, good repeatability and could be used in the rapid determination of practical samples.

Continuous determination of total flavonoids in Platycladus orientalis (L.) Franco by dynamic microwave-assisted extraction coupled with on-line derivatization and ultraviolet–visible detection

This paper describes a new method for the determination of total flavonoids in Platycladus orientalis (L.) Franco. The method was based on dynamic microwave-assisted extraction (DMAE) coupled with on-line derivatization and ultraviolet-visible (UV-vis) detection. The influence of the experimental conditions was tested. Maximum extraction yield was achieved using 80% aqueous methanol of extraction solvent; 80 W of microwave output power; 5 min of extraction time; 1.0 mL min(-1) of extraction solvent flow rate. The derivatization reaction between aluminium chloride and flavonoid is one of the most sensitive and selective reactions for total flavonoids determination. The optimized derivatization conditions are as follows: derivatization reagent 1.5% aluminium chloride methanol solution; reaction coil length 100 cm; derivatization reagent flow rate 1.5 mL min(-1). The detection and quantification limits obtained are 0.28 and 0.92 mg g(-1), respectively. The intra-day and inter-day precisions (R.S.D.) obtained are 1.5% and 4.6%, respectively. Mean recovery is 98.5%. This method was successfully applied to the determination of total flavonoids in P. orientalis (L.) Franco and compared with heat reflux extraction. The results showed that the higher extraction yield of total flavonoids was obtained by DMAE with shorter extraction time (5 min) and small quantity of extraction solvent (5 mL).