Measurement of food flavonoids by high-performance liquid chromatography: A review

Phenolic compounds and bioactivities of pigmented rice

The pigmented rice has been consumed in China, Japan, and Korea for a long time. It has been used for strengthening kidney function, treating anemia, promoting blood circulation, removing blood stasis, treating diabetes, and ameliorating sight in traditional Chinese medicine. The extracts from pigmented rice are used as natural food colorants in bread, ice cream, and liquor as well as functional food. The pigmented rice is mainly black, red, and dark purple rice, and contains a variety of flavones, tannin, phenolics, sterols, tocols, γ-oryzanols, amino acids, and essential oils. Anthocyanins are thought as major functional components of pigmented rice. Several anthocyanins have been isolated and identified from the pigmented rice, including cyanidin 3-glucoside, cyanidin 3-galactoside, cyanidin 3-rutinoside, cyanidin 3,5-diglucoside, malvidin 3-galactoside, peonidin 3-glucoside, and pelargonidin 3,5-diglucoside. This review provides up-to-date coverage of pigmented rice in regard to bioactive constituents, extraction and analytical methods, and bioactivities. Special attention is paid to the bioactivities including antioxidant and free radical scavenging, antitumor, antiatherosclerosis, hypoglycemic, and antiallergic activities.

High-performance liquid chromatographic phenolic compound fingerprint for authenticity assessment of honey

BACKGROUND

Phenolic compound profiles of 20 honeys of different botanical origin (eucalyptus, citrus, chestnut and linden) were obtained by high-performance liquid chromatography with ultraviolet detection after solid phase extraction, in order to evaluate the effectiveness of the fingerprint method for monofloral honey discrimination.

RESULTS

A total of 58 peaks were detected at λ = 280 nm. Distinctive phenolic compound profiles were obtained in which both the nature and the relative amount of the detected compounds were characteristic for different botanical source honeys. In order to detect sample groupings, chromatographic peak areas were submitted to principal component analysis. Then linear discriminant analysis was carried out on the first three principal components. In addition, linear discriminant analysis was carried out on the 58 variables, allowing the selection of five variables able to discriminate honeys of different botanical origin.

CONCLUSION

The chemometric evaluation of the phenolic compound profiles yielded classification models able to group honey samples according to their floral source with an excellent degree of agreement. The main advantage of the fingerprint approach with respect to traditional methods is that it does not require time-consuming identification and quantification of the analytes. The method proved to be effective for the assessment of honey authenticity.

Analysis of Naturally Occurring Phenolic Compounds in Aromatic Plants by RP-HPLC Coupled to Diode Array Detector (DAD) and GC-MS after Silylation

The following aromatic plants of Greek origin, Origanum dictamnus (dictamus), Eucalyptus globulus (eucalyptus), Origanum vulgare L. (oregano), Mellisa officinalis L. (balm mint) and Sideritis cretica (mountain tea), were examined for the content of phenolic substances. Reversed phase HPLC coupled to diode array detector (DAD) was used for the analysis of the plant extracts. The gas chromatography-mass spectrometry method (GC-MS) was also used for identification of phenolic compounds after silylation. The most abundant phenolic acids were: gallic acid (1.5–2.6 mg/100 g dry sample), ferulic acid (0.34–6.9 mg/100 g dry sample) and caffeic acid (1.0–13.8 mg/100 g dry sample). (+)-Catechin and (−)-epicatechin were the main flavonoids identified in oregano and mountain tea. Quercetin was detected only in eucalyptus and mountain tea.

Techniques for analysis of plant phenolic compounds

Phenolic compounds are well-known phytochemicals found in all plants. They consist of simple phenols, benzoic and cinnamic acid, coumarins, tannins, lignins, lignans and flavonoids. Substantial developments in research focused on the extraction, identification and quantification of phenolic compounds as medicinal and/or dietary molecules have occurred over the last 25 years. Organic solvent extraction is the main method used to extract phenolics. Chemical procedures are used to detect the presence of total phenolics, while spectrophotometric and chromatographic techniques are utilized to identify and quantify individual phenolic compounds. This review addresses the application of different methodologies utilized in the analysis of phenolic compounds in plant-based products, including recent technical developments in the quantification of phenolics.

Evolution of analysis of polyhenols from grapes, wines, and extracts

Grape and wine phenolics are structurally diverse, from simple molecules to oligomers and polymers usually designated as tannins. They have an important impact on the organoleptic properties of wines, that's why their analysis and quantification are of primordial importance. The extraction of phenolics from grapes and from wines is the first step involved in the analysis. Then, several analytical methods have been developed for the determination of total content of phenolic, while chromatographic and spectrophotometric analyses are continuously improved in order to achieve adequate separation of phenolic molecules, their subsequent identification and quantification. This review provides a summary of evolution of analysis of polyphenols from grapes, wines and extracts.

Application of response surface methodology to optimise extraction of flavonoids from fructus sophorae

Response surface methodology (RSM) based on a central composite design (CCD) was applied to optimise the extraction conditions for flavonoids from fructus sophorae with advantages in terms of resisting flavonoids during the whole process and maximising of extraction yield. Three aglycon forms of the flavonoids, namely, quercetin, kaempferol and isorhamnetin were quantified by high-performance liquid chromatography with ultraviolet detection (HPLC-UV) to estimate extraction yield. The combined effects of independent variables were studied and the optimal extraction conditions were obtained as ethanol concentration, 74.47%; solid-liquid ratio, 17.99 ml/g; temperature, 89.13°C; and extraction time, 2.10h. The reliability of the method was confirmed by recovery experiments, performed under optimal conditions. Recoveries indicated that flavonoids resisted the extraction conditions. The experimental extraction yield under optimal conditions was found to be 10.459%, which was well matched with the predicted values of 10.461%.

Evaluation of the ion trap MS performance for quantification of flavonoids and comparison to UV detection

The application of an ion trap mass spectrometer, usually employed for identification, has been here systematically evaluated for quantitative analysis of various conjugated forms of flavonoids and compared with UV quantification. Three MS methods were tested to assess the potential and limits of the ion trap for quantification of flavonoids: full-scan experiment MS(2) , isolated ion experiment MS, and full-scan experiment MS. The test was performed using nine reference standards of flavonoids with six different aglycones: luteolin, apigenin, hypolaetin, 4'-O-methylhypolaetin, isoscutellarein and 4'-O-methylisoscutellarein in the form of 7-O-glucosides and diglucosides, mono or diacetylated, isolated from Sideritis scardica. The analytical characteristics of the tested MS methods were shown to be comparable to UV with regards to precision and accuracy, and superior for selectivity and sensitivity especially when using extracted ion chromatograms. Detection limits did not differ significantly between the MS methods but were significantly lower than those obtained with UV detection by one order of magnitude. Another issue addressed by these results was the choice of most suitable standard substances for quantification of flavonoids with various substituents attached when using MS. In UV detection, the nature of the aglycone is crucial for the absorbance properties, and various derivatives can be quantified with the available one with the same aglycone. Here, it was shown that in MS detection, one flavone derivative can be quantified using other available derivatives with similar substitution pattern with regards to attached and acetylated sugars, whereas the nature of the aglycone is not crucial.

Rapid identification of molecular changes in tulsi (Ocimum sanctum Linn) upon ageing using leaf spray ionization mass spectrometry

Tulsi or Holy Basil (Ocimum sanctum Linn) is a medicinally important plant. Ursolic acid (UA) and oleanolic acid (OA) are among its major constituents which account for many medicinal activities of the plant. In the present work, we deployed a new ambient ionization method, leaf spray ionization, for rapid detection of UA, OA and their oxidation products from tulsi leaves. Tandem electrospray ionization mass spectrometry (ESI-MS) has been performed on tulsi leaf extracts in methanol to establish the identity of the compounds. We probed changes occurring in the relative amounts of the parent compounds (UA and OA) with their oxidized products and the latter show an increasing trend upon ageing. The findings are verified by ESI-MS analysis of tulsi leaf extracts, which shows the same trend proving the reliability of the leaf spray method.

A review on antioxidants, prooxidants and related controversy: natural and synthetic compounds, screening and analysis methodologies and future perspectives

Many studies have been conducted with regard to free radicals, oxidative stress and antioxidant activity of food, giving antioxidants a prominent beneficial role, but, recently many authors have questioned their importance, whilst trying to understand the mechanisms behind oxidative stress. Many scientists defend that regardless of the quantity of ingested antioxidants, the absorption is very limited, and that in some cases prooxidants are beneficial to human health. The detection of antioxidant activity as well as specific antioxidant compounds can be carried out with a large number of different assays, all of them with advantages and disadvantages. The controversy around antioxidant in vivo benefits has become intense in the past few decades and the present review tries to shed some light on research on antioxidants (natural and synthetic) and prooxidants, showing the potential benefits and adverse effects of these opposing events, as well as their mechanisms of action and detection methodologies. It also identifies the limitations of antioxidants and provides a perspective on the likely future trends in this field.

Chromolithic Method Development, Validation and System Suitability Analysis of Ultra-Sound Assisted Extraction of Glycyrrhizic Acid and Glycyrrhetinic Acid from Glycyrrhiza glabra

An ultrasound-assisted extraction and chromolithic LC method was developed for simultaneous determination of glycyrrhizic acid (GA) and glycyrrhetinic acid (GL) from the root extract of Glycyrrhiza glabra using RPLC-PDA. The developed method was validated according to the International Conference on Harmonisation. The method exhibited good linearity (r2 >0.9989) with high precision and achieved good accuracies between 97.5 to 101.3% of quantitative results. The method is more sensitive and faster (resolved within ten minutes) than the earlier developed methods using normal LC columns.

Simultaneous determination of anthocyanins, coumarins and phenolic acids in fruits, kernels and liqueur of Prunus mahaleb L

In the fresh tissues of Prunus mahaleb L., three classes of phenolics were characterised: phenolic acid derivatives (main compound being o-coumaric acid glucoside), quercetin glycosides, and anthocyanins (cyanidin 3,5-diglucoside, cyanidin 3-sambubioside, cyanidin 3-xylosyl-rutinoside and cyanidin 3-rutinoside). Coumarin was also identified. The kernels showed a high content of coumarin (0.87 mgg(-1)) which is the main class of metabolites in this sample, but present in pitted berries as well (0.63 mgg(-1)). Flavonoids are mainly concentrated in the skin and pulp (0.55 mgg(-1)). In 'Mirinello di Torremaggiore' liqueur, produced from P. mahaleb L. in accordance with traditional procedures, anthocyanins make up 16.5%, phenolic acids 43.3%, coumarin 36.2% and flavonoids 4% of total compounds. Anthocyanins are the main class in solid residues from liqueur production (70%). These findings point out that solid residues of P. mahaleb can be considered an interesting and innovative source of appreciable amounts of cyanidin glycosides (3.3 mgg(-1)).

Evaluation of matrix effect in determination of some bioflavonoids in food samples by LC-MS/MS method

In the present work the LC-MS/MS method with solid phase extraction for simultaneous determination of bioflavonoids rutin, quercetin, hesperidin, hesperetin and kaempferol in some food samples (red onion, orange peel and honey) was developed and the matrix effect accompanying this determination was quantified. The matrix effect evaluated using a postextraction addition method was found to be negative in the range -44 to -0.5%, indicating ionization suppression and strongly depended on bioflavonoid concentration. The observed matrix effect was explained taking into account the co-elution of phenolic acids, in terms of their acid-base and hydrophilic properties. The efficacy of extraction expressed as the absolute recoveries of flavonoids were 88-96%, indicating very good efficiency of extraction. The extracts of food samples obtained either by Soxhlet or ultrasonic extraction were analyzed for bioflavonoid content by the LC-MS/MS method in selected reaction monitoring mode using a triple quadrupole detector and standard addition method, which was found to be the most suitable calibration approach for these samples. The optimized separation was achieved on a Phenomenex Gemini C18 column with gradient elution and mobile phase composition A: 2% acetic acid in water and B: acetonitrile. R(s) values were in the range from 1.3 to 3.1, indicating good selectivity of the method. The obtained results (mg/100g fresh weight) for different bioflavonids were for rutin 0.16, for quercetin in the range 0.65-56, for hesperidin 0.016-24, for hesperetin 0.0068-36.4 and for kaempferol 0.14-1.63 and generally show good agreement with published data. Low detection limits (0.014-0.063 μg/mL) were obtained with acceptable recoveries (86-114%). Total time of analysis was less than 40 min, therefore the proposed method represents significant improvement over existing methods.

Application of dietary phenolic biomarkers in epidemiology: past, present, and future

Phenolics are a large group of plant compounds that have been associated with protective health effects against several chronic diseases due to their potential antioxidant, anti-inflammatory, and anticarcinogenic properties. Consequently, in nutritional epidemiology it is essential to make an accurate assessment of phenolic exposure to evaluate their protective activities against human diseases. Self-reported questionnaires and biomarkers are the two main methods used for estimating dietary phenolics. Despite the limitations of self-reported methods, they are still an acceptable and useful measure. Meanwhile, nutritional biomarkers provide an alternative, more accurate measure, but they are expensive, and to date there are few validated biomarkers of phenolic intake. Nowadays, new analytical techniques, using both targeted and untargeted metabolomic approaches, play an important part in the rapid increase in the understanding of phenolic bioavailability and, consequently, have provided new potential biomarkers in small trials. In the near future, these dietary biomarkers should be tested in large epidemiological studies. Furthermore, the use of two independent measures-questionnaires and biomarkers-together provides a more thorough analysis of true phenolic exposure. Indeed, the challenge in the long term is to combine the information from biomarkers and self-reported questionnaires to clarify the relationship between dietary phenolics and disease.

Evolution of phenolic compounds from color and flavor problems to health benefits

Early studies focused on the negative effects on color and flavor of foods, followed by exploration of the antioxidant properties and the associated health benefits. The growing body of evidence suggests that plant-based polyphenols may help prevent or delay the onset of a multiplicity of diseases. Newer work suggests that a variety of polyphenols can alter the expression of genes in the inflammatory pathway. Data also show that the absorption of the polyphenols is very limited. Insulin resistance and endothelial and mitochondrial dysfunction are hallmarks of the metabolic syndrome and aging and occur at the early stages of the disease. There is limited clinical evidence that certain polyphenolic metabolites by virtue of their anti-inflammatory activities can improve insulin sensitivity and endothelial and mitochondrial function, suggesting that polyphenols are good for disease prevention. The goal of this review is to summarize the evolution and emphasize the potential benefits of polyphenols.

A review of the chemistry of the genus Crataegus

Since the 1800s, natural health products that contain hawthorn (Crataegus spp.) have been used in North America for the treatment of heart problems such as hypertension, angina, arrhythmia, and congestive heart failure. Traditionally, Native American tribes used hawthorn (Crataegus spp.) to treat gastrointestinal ailments and heart problems, and consumed the fruit as food. Hawthorn also has a long history of use in Europe and China for food, and in traditional medicine. Investigations of Crataegus spp. typically focus on the identification and quantification of flavonoids and anthocyanins, which have been shown to have pharmacological activity. The main flavonoids found in Crataegus spp. are hyperoside, vitexin, and additional glycosylated derivatives of these compounds. Reviewed herein are the botany, ethnobotany, and traditional use of hawthorn while focusing on the phytochemicals that have been reported in Crataegus species, and the variation in the described chemistry between individual species.

Anti-inflammatory and anti-apoptotic effects of strawberry and mulberry fruit polysaccharides on lipopolysaccharide-stimulated macrophages through modulating pro-/anti-inflammatory cytokines secretion and Bcl-2/Bak protein ratio

This study is the first to isolate strawberry (SP) and mulberry fruit polysaccharides (MP) and assess their anti-inflammatory and anti-apoptotic activities using lipopolysaccharide (LPS)-stimulated mouse primary macrophages. Pro-/anti-inflammatory cytokine levels secreted by LPS-stimulated macrophages cultured with SP and MP for 48 h were determined using ELISA method to evaluate anti-inflammatory effects of SP and MP. The Bcl-2/Bak (anti-/pro-apoptotic) protein levels in the cells were determined using Western blotting method to evaluate anti-apoptotic effects of SP and MP. The results showed that the maximum absorption peak of SP and MP appeared at 240 nm with a small shoulder around 280∼310 nm, suggesting that SP and MP might be glycoproteins. SP- and MP-treatment significantly (P<0.05) decreased pro-inflammatory cytokines including interleukin (IL)-1β and IL-6, whereas the anti-inflammatory cytokine IL-10 was markedly increased, suggesting that SP and MP have anti-inflammation potential via modulating pro-/anti-inflammatory cytokine secretion profiles. Both SP and MP modulated Bak and Bcl-2 protein levels in the cells, suggesting that the SP and MP protected LPS-stimulated macrophages from apoptotic cell death. A negative correlation between cytokine secretion levels and Bcl-2 protein levels suggested that pro-inflammatory IL-1β and IL-6 cytokines decreased Bcl-2 levels in the LPS-stimulated macrophages.

Release of flavonoids from lupin globulin proteins during digestion in a model system

Lupin seed globulin proteins form complexes with flavonoids, predominantly apigenin C-glycosides. Enzymes typical for the gastrointestinal tract were used to hydrolyze lupin seed globulins. Release of native flavonoids as a result of the proteolysis reaction was observed. Different analytical methods such as size exclusion chromatography, HPLC-MS, and fluorescence spectroscopy (steady-state fluorescence, fluorescence anisotropy, fluorescence lifetimes) were used for a detailed characterization of this phenomenon. Flavonoids liberated from lupin globulin proteins as a result of pancreatin-catalyzed digestion were bound by γ-conglutin resistant to this enzyme. Two possible mechanisms of this interaction may be suggested: hydrogen bonding between oligosaccharide chains of glycoproteins and the sugar moieties of the flavonoid glycosides or electrostatic attraction between positively charged γ-conglutin and flavonoids partially ionized at pH 7.5.

Quantitation of the hydroxycinnamic acid derivatives and the glycosides of flavonols and flavones by UV absorbance after identification by LC-MS

A general approach was developed to quantify hydroxycinnamic acid derivatives and the glycosides of flavonols and flavones using UV molar relative response factors (MRRFs). More than 90 standards were analyzed by LC-MS and divided into five groups based on the λ(max) of their band I absorbance profiles. For each group, a commercially available standard was chosen as the group reference standard. Response factors were determined for each standard in each group as purchased (MRRF) and, when possible, after vacuum drying (MRRF(D)). The MRRF(D) values for 17 compounds whose λ(max) values fell within ±2 nm of the group reference standard were 1.01 ± 0.03. MRRF values for compounds whose λ(max) values fell within ±10 nm of the group reference standard were 0.96 ± 0.13. Group reference standards were used to quantify 44 compounds in Chinese lettuce, red onion, and white tea. This approach allows quantitation of numerous compounds for which there are no standards.

Identification of phenolic compositions and the antioxidant capacity of mandarin juices and wines

This research was undertaken to determine the phenolic composition and antioxidant capacity of juices and wines obtained from Robinson, Fremont and Satsuma mandarins. High-performance liquid chromatography coupled with diode-array detection was used for identifying and quantifying phenolic compounds. The total amount of phenolic compounds ranged from 36.6 to 132.6 mg/L for the mandarin juice, and from 14.1 to 54.5 mg/L for the wines. In the juices and wines, the major hydroxybenzoic acid was vanillic acid; the major hydroxycinnamic acid was ferulic acid; and the major flavanone was hesperidin. The antioxidant activity was measured using the DPPH and ABTS radical scavenging assays, and the antioxidant capacity of mandarin juices was found to be higher than that of wines. Results of this study indicated that these mandarin wines had a composition similar to other beverages, thus demonstrating that these fruits have the potential to be used to produce fermented beverages.

Effect of rootstock on mango fruit susceptibility to infestation by Anastrepha obliqua

The effect of the use of rootstock Criollo on the susceptibility of Manila mango fruit to infestation by Anastrepha obliqua (Macquart) was determined in the present investigation. Growth, quality parameters (Soluble solids content (%), citric acid content (%), firmness, monoterpene volatiles (3-carene, limonene, alpha-pinene, and beta-myrcene), main flavonoids content (milligrams/100 g fresh pulp), and larvicidal activity of methanolic extracts, as well as the degree of infestation during preharvest development of the fruits were analyzed. The results indicated that the rootstock did not have any significant effect on growth, soluble solids content, or citric acid content; although it increased firmness as well as 3-carene levels and main flavonoids content, resulting in a greater resistance to infestation by A. obliqua. The obtained results support the use of this rootstock because of the beneficial effects observed on the resistance of mango fruit to infestation by this fruit fly.

Simultaneous determination of free amino acid content in tea infusions by using high-performance liquid chromatography with fluorescence detection coupled with alternating penalty trilinear decomposition algorithm

In this paper, a novel application of alternating penalty trilinear decomposition (APTLD) for high-performance liquid chromatography with fluorescence detection (HPLC-FLD) has been developed to simultaneously determine the contents of free amino acids in tea. Although the spectra of amino acid derivatives were similar and a large number of water-soluble compounds are coextracted, APTLD could predict the accurate concentrations together with reasonable resolution of chromatographic and spectral profiles for the amino acids of interest owing to its "second-order advantage". An additional advantage of the proposed method is lower cost than traditional methods. The results indicate that it is an attractive alternative strategy for the routine resolution and quantification of amino acids in the presence of unknown interferences or when complete separation is not easily achieved.

A fast method coupling ultrahigh performance liquid chromatography with diode array detection for flavonoid quantification in citrus fruit extracts

Flavonoids are a widely distributed group of polyphenolic compounds present in an extensive range of edible plants, notably Citrus species. This article reports a rapid, optimized, and validated method for the separation and quantification of flavonoids in three Citrus fruit extracts by ultrahigh performance liquid chromatography (UHPLC) using a photodiode array detector. This new procedure allowed the simultaneous separation and quantification of 11 selected flavonoids in 5.5 min, 8.2 times faster than that by HPLC analysis. The solvent consumption for each individual analysis was also reduced almost 6.2-fold. The most abundant component in the analyzed samples was naringin (299.06-544.36 mg 100 g⁻¹), followed by rutin (116.60-256.33 mg 100 g⁻¹) and quercetin (7.78-251.49 mg 100 g⁻¹). Isoquercitrin was found in a lower proportion (60.05-81.88 mg 100 g⁻¹). The method was completely validated, providing a sensitive analysis for flavonoid detection and showing satisfactory data for all the parameters tested. This methodology is cheaper, more environmentally friendly, and easier to perform than others previously described.

Total phenolic content and antioxidant activity of plants used in traditional Romanian herbal medicine

A number of herbal plants from Romania widely used as natural food additives or for health promotion in traditional medicine were investigated for their antioxidant activity. Methanol extracts were obtained from plants belonging to the Lamiaceae family (lavender Lavandula angustifolia L.; lemon balm Melissa officinalis; sage Salvia officinalis; oregano Origanum vulgare L.; rosemary Rosmarinus officinalis L.; thyme Thymus vulgaris L.; mullein Verbascum phlomoides; mint Mentha longifolia), Clusiaceae family (St John’s wort Hypericum perforatum L.), and Compositae family (elecampane Inula helenium). Total phenolic concentration was determined using the Folin-Ciocalteu phenol reagent method, while total flavonoids were measured using the aluminium chloride colorimetric method. Relationships between total antioxidant activity and composition of plant extracts were evaluated. Origanum vulgare extract showed the highest antioxidant activity and total phenolic content compared to the other plants extracts. A positive correlation was observed between total antioxidant activity and total phenolic content of the analyzed extracts.

Arctic mustard flower color polymorphism controlled by petal-specific downregulation at the threshold of the anthocyanin biosynthetic pathway

Intra- and interspecific variation in flower color is a hallmark of angiosperm diversity. The evolutionary forces underlying the variety of flower colors can be nearly as diverse as the colors themselves. In addition to pollinator preferences, non-pollinator agents of selection can have a major influence on the evolution of flower color polymorphisms, especially when the pigments in question are also expressed in vegetative tissues. In such cases, identifying the target(s) of selection starts with determining the biochemical and molecular basis for the flower color variation and examining any pleiotropic effects manifested in vegetative tissues. Herein, we describe a widespread purple-white flower color polymorphism in the mustard Parrya nudicaulis spanning Alaska. The frequency of white-flowered individuals increases with increasing growing-season temperature, consistent with the role of anthocyanin pigments in stress tolerance. White petals fail to produce the stress responsive flavonoid intermediates in the anthocyanin biosynthetic pathway (ABP), suggesting an early pathway blockage. Petal cDNA sequences did not reveal blockages in any of the eight enzyme-coding genes in white-flowered individuals, nor any color differentiating SNPs. A qRT-PCR analysis of white petals identified a 24-fold reduction in chalcone synthase (CHS) at the threshold of the ABP, but no change in CHS expression in leaves and sepals. This arctic species has avoided the deleterious effects associated with the loss of flavonoid intermediates in vegetative tissues by decoupling CHS expression in petals and leaves, yet the correlation of flower color and climate suggests that the loss of flavonoids in the petals alone may affect the tolerance of white-flowered individuals to colder environments.

Chromatographic separations and liquid phase extraction/concentration of some polyphenolic compounds: a comparison between reverse phase and cation-exchange chromatography

Chromatographic performance based on the use of a C18 reverse phase and a LC-SCX cation-exchange column associated with UV absorption at 280 nm is optimized and compared for the simultaneous determination of resveratrol and other polyphenolic compounds with the aim to establish the best experimental conditions for the trace analysis of these substances. Under the optimized chromatographic conditions using a gradient acid mobile phase and acetonitrile as a modifier solvent, the elution of all injected compounds was completed in about 30 min of analysis and the detection limits (LOD) ranged between 20 nM and 120 nM. The regression analysis for most of the analyzed compounds shows linear ranges spanning over five orders of magnitude with correlation coefficients always ≥0.98. A liquid-liquid extraction procedure was optimized using three different extracting solvents such as methyl ethyl ketone, diethyl ether, and dichloromethane. The hydrophilic/hydrophobic character of the water/organic solvent was modulated by addition of NaCl salt. In order to ascertain the analytical potentialities of the investigated method, and in particular the performance of the extraction procedure, a wide variety of selected red wines were analysed. The average recoveries ranged between 73% and 103% for the analysed molecules, indicating both the practical absence of interfering peaks on the chromatographic separation and an appreciable capacity of extraction of polyphenolic acids from the wine matrices.