High-speed counter-current chromatography of apple procyanidins

Preparative isolation of apple flavan-3-ols monomers and oligomers using pH-zone-refining centrifugal partition chromatography combined with reversed-phase liquid chromatography

Flavan-3-ols (catechin monomers and procyanidins) are the main class of polyphenols in apples and are found in high concentrations in cider apple varieties. They are known to be involved in bitterness and astringency in apple-based beverages, and also contribute to polyphenol nutritional intake.Therefore, highly purified flavan-3-ol fractions isolated from raw materials are needed to study their various properties. For this purpose, a gentle strategy combining pH-zone-refining centrifugal partition chromatography (pH-ZRCPC) and preparative reversed-phase liquid chromatography (Prep-RPLC) was developed to recover one hundred milligrams of a high purity apple flavan-3-ol fraction. First, pH-ZRCPC fractionation in descending mode was optimized to remove hydroxycinnamic acid derivatives using a biphasic mixture composed of ethyl acetate/n-butanol/water (3/2/5, v/v). Trifluoroacetic acid and sodium hydroxide were used as retainer and eluter, in the upper and lower phases, respectively. Secondly, Prep-RPLC separation was carried out in isocratic mode at 20% ACN to remove dihydrochalcones. Finally, from one gram of a crude polyphenol extract, four hundred and nine milligrams of a highly purified fraction of flavan-3-ols with an average degree of polymerization close to 3.1 was obtained with 73% recovery.

Centrifugal partition chromatography enables selective enrichment of trimeric and tetrameric proanthocyanidins for biomaterial development

Proanthocyanidins (PACs) find wide applications for human use including food, cosmetics, dietary supplements, and pharmaceuticals. The chemical complexity associated with PACs has triggered the development of various chromatographic techniques, with countercurrent separation (CCS) gaining in popularity. This study applied the recently developed DESIGNER (Depletion and Enrichment of Select Ingredients Generating Normalized Extract Resources) approach for the selective enrichment of trimeric and tetrameric PACs using centrifugal partition chromatography (CPC). This CPC method aims at developing PAC based biomaterials, particularly for their application in restoring and repairing dental hard tissue. A general separation scheme beginning with the depletion of polymeric PACs, followed by the removal of monomeric flavan-3-ols and a final enrichment step produced PAC trimer and tetramer enriched fractions. A successful application of this separation scheme is demonstrated for four polyphenol rich plant sources: grape seeds, pine bark, cinnamon bark, and cocoa seeds. Minor modifications to the generic DESIGNER CCS method were sufficient to accommodate the varying chemical complexities of the individual source materials. The step-wise enrichment of PAC trimers and tetramers was monitored using normal phase TLC and Diol-HPLC-UV analyses. CPC proved to be a reliable tool for the selective enrichment of medium size oligomeric PACs (OPACs). This method plays a key role in the development of dental biomaterials considering its reliability and reproducibility, as well as its scale-up capabilities for possible larger-scale manufacturing.

Apple phenolics as nutraceuticals: assessment, analysis and application

Humankind is presently engulfed by convenience quench, modern life style and urbanized diet system leading to progression in array of health disorders. The past decade confronted cardiometabolic disorder (21.8 %), lower respiratory and chronic obstructive lung disease (12.5 %) as the major causes of death world over. In anticipation, scientific communities' have demonstrated the role of healthy diets, especially those rich in fruits and vegetables, for management of such health related issues. These horticultural  crops are considered as a good source of polyphenols such as dihydrochalcones, flavanols, flavonols, anthocyanins and phenolic acids. The present article reviews the efforts made to assess the potential of apple phenolic compounds present in fresh fruits, leaves, bark and pomace as dietary polyphenols. Considering the positive impact of such phytochemicals on human health, various nutraceuticals, dietary supplements and phenolic-rich food products are presently available on market shelves. On analytical front, improved instrumentation based on liquid chromatography (HPLC, UPLC, LC/MS/MS) have made the assessment of phenolics more rapid and reliable. Thus, owing to the emergent interest in natural compounds, it is pertinent to discuss the latest significant research findings on therapeutic aspects along with probable metabolic mechanisms of dietary polyphenols found in apples and their implications on human health.

Extraction and isolation of phenolic compounds

Phenolic compounds constitute a major class of plant secondary metabolites that are widely distributed in the plant kingdom and show a large structural diversity. These compounds occur as aglycones or glycosides, as monomers or constituting highly polymerized structures, or as free or matrix-bound compounds. Furthermore, they are not uniformly distributed in the plant and their stability varies significantly. This greatly complicates their extraction and isolation processes, which means that a single standardized procedure cannot be recommended for all phenolics and/or plant materials; procedures have to be optimized depending on the nature of the sample and the target analytes, and also on the object of the study. In this chapter, the main techniques for sample preparation, and extraction and isolation of phenolic compounds have been reviewed-from classical solvent extraction procedures to more modern approaches, such as the use of molecularly imprinted polymers or counter-current chromatography.

Strategies of solvent system selection for the isolation of flavonoids by countercurrent chromatography

Flavonoids form a large class of important naturally occurring bioactive compounds. Their isolation and purification from natural sources can sometimes be very difficult and time-consuming when traditional phytochemical techniques are used. Countercurrent chromatography (CCC), a support-free liquid-liquid partition chromatography technique, is very useful for the isolation of polar compounds and its use is increasing in the natural products field. In this paper, we propose strategies of solvent system selection for the isolation of flavonoids by CCC, based on data from the literature, plus incorporation of own practical experiences. The selected references report the isolation of over 300 different flavonoid compounds from more than 100 plant species, using 40 different solvent systems, showing the versatility of this technique. The solvent system hexane-ethylacetate-methanol-water is proposed as a starting point for the separation of samples containing free flavonoids, as it was cited in more than 60% of the papers. A "fine tuning" step is proposed at each level of this solvent family. Other modifications include exchanging the alcohol in the system as well as introducing a fifth solvent. The solvent system ethyl-acetate-butanol-water is proposed as the starting point for glycosylated flavonoids. Other solvent systems are also discussed. The use of gradients is proposed for samples containing both free and glycosylated flavonoids, as the polarity window is larger in these cases. High-speed countercurrent chromatography was used in 89% of the reviewed data.

Preparative isolation and purification of alkannin/shikonin derivatives from natural products by high-speed counter-current chromatography

Alkannin and shikonin (A/S) and their derivatives have been found in the roots of several Boraginaceous species and are also produced through plant tissue cultures. The chiral compounds A/S are potent pharmaceutical substances with a wide spectrum of biological and pharmacological activities like wound healing, antimicrobial, anti-inflammatory, anticancer and antioxidant activity. High-speed counter-current chromatography (HSCCC) was applied for the first time to the separation, preparative isolation and purification of A/S and their esters from extracts of Alkanna tinctoria roots, as well as commercial samples. The constituents of HSCCC fractions and their purity were determined by high-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS), since DAD cannot detect oligomeric A/S derivatives that are present in most of the samples containing the respective monomeric derivatives. The purity of HSCCC fractions was compared with the one of fractions isolated by column chromatography (CC) using as stationary phases silica gel and Sephadex LH-20. As shown, the purity of monomeric alkannin/shikonin was greater by HSCCC than CC separation of commercial A/S samples.

Separation and identification of polyphenols in apple pomace by high-speed counter-current chromatography and high-performance liquid chromatography coupled with mass spectrometry

Apple pomace, a by-product in the processing of apple juice, was investigated as a potential source of polyphenols. Two methods of separation and purification of polyphenols from apple pomace extract were established by combination of gel chromatography with high-speed counter-current chromatography (HSCCC) and solvent extraction with HSCCC, respectively. The optimal separation was performed on a Sephadex LH-20 column using gradient aqueous ethanol as eluting solvent from 0% to 100% in increments of 10%. HPLC analysis indicated that main polyphenols existed in fractions eluted between 40% and 50% aqueous ethanol. The fractions of interest from column were separated by HSCCC with the solvent system hexane-ethyl acetate-1% aqueous acetic acid (0.5:9.5:10, v/v/v). Ethyl acetate fractionation of the apple pomace extract followed by direct HSCCC separation by the same solvent system in the volume ratio of 1:9:10 also produced a good separation of the main polyphenols of interest. Six high-purity polyphenols were achieved tentatively and identified by HPLC/MS: chlorogenic acid (1, m/z 354), quercetin-3-glucoside/quercetin-3-glacaside (2, m/z 464), quercetin-3-xyloside (3, m/z 434), phloridzin (4, m/z 436), quercetin-3-arabinoside (5, m/z 434), and quercetin-3-rhamnoside (6, m/z 448). These results provided a preliminary foundation for further development and exploration of apple pomace.

Countercurrent chromatography in analytical chemistry (IUPAC Technical Report)

Countercurrent chromatography (CCC) is a generic term covering all forms of liquid-liquid chromatography that use a support-free liquid stationary phase held in place by a simple centrifugal or complex centrifugal force field. Biphasic liquid systems are used with one liquid phase being the stationary phase and the other being the mobile phase. Although initiated almost 30 years ago, CCC lacked reliable columns. This is changing now, and the newly designed centrifuges appearing on the market make excellent CCC columns. This review focuses on the advantages of a liquid stationary phase and addresses the chromatographic theory of CCC. The main difference with classical liquid chromatography (LC) is the variable volume of the stationary phase. There are mainly two different ways to obtain a liquid stationary phase using centrifugal forces, the hydrostatic way and the hydrodynamic way. These two kinds of CCC columns are described and compared. The reported applications of CCC in analytical chemistry and comparison with other separation and enrichment methods show that the technique can be successfully used in the analysis of plants and other natural products, for the separation of biochemicals and pharmaceuticals, for the separation of alkaloids from medical herbs, in food analysis, etc. On the basis of the studies of the last two decades, recommendations are also given for the application of CCC in trace inorganic analysis and in radioanalytical chemistry.

Metabolic fingerprinting using direct flow injection electrospray ionization tandem mass spectrometry for the characterization of proanthocyanidins from the barks of Hancornia speciosa

Direct flow injection electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS) was used to investigate the polyphenolic compounds present in an infusion from the barks of Hancornia speciosa Gom. (Apocynaceae), a native Brazilian plant popularly known as 'mangabeira', used as a source of nutrition and against gastric disorders. After a simple sample filtration pretreatment the characteristic fingerprint of the infusion was performed in negative ion ESI mode in a few minutes. At low capillary-voltage activation, the deprotonated molecules ([M--H]-) were observed and using collision-induced dissociation the product ion spectra showed the presence of a homologous series of B-type proanthocyanidins, as well as another series containing their respective C-glycosylated derivatives, with a degree of polymerization from 1 up to 6 units of interlinked catechins. Therefore, direct flow injection allowed us to identify the key compounds without preparative isolation of the components.

Apple (Malus pumila) procyanidins fractionated according to the degree of polymerization using normal-phase chromatography and characterized by HPLC-ESI/MS and MALDI-TOF/MS

Our previously reported method for the fractionation of apple procyanidins was modified successfully to achieve the separation of (epi)catechins and procyanidins (ranging from dimers to octamers) according to the degree of polymerization. Normal-phase chromatography was employed, using a hexane-methanol-ethyl acetate mixture as the mobile phase. Each fraction was characterized using high-performance liquid-chromatography electrospray-ionization mass spectrometry (HPLC-ESI/MS) and matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS). This method will be useful for the evaluation of the physiological functions of proanthocyanidins and for the elucidation of their individual structures.

Purification of paeoniflorin from Paeonia lactiflora Pall. by high-speed counter-current chromatography

High-speed counter-current chromatography was successfully used for the first time for the preparative separation and purification of paeoniflorin from the Chinese medicinal plant Paeonia lactiflora Pall. using a two-phase solvent system composed of n-butanol-ethyl acetate-water (1:4:5, v/v) in a single run. From 160 mg of the crude sample containing 22.0% paeoniflorin, 33.2 mg of paeoniflorin was yielded at 98.2% purity as determined by HPLC analysis. The recovery of paeoniflorin was 94.3%.

Separation of proanthocyanidins by degree of polymerization by means of size-exclusion chromatography and related techniques

The molecular masses of polyphenols in plants and food vary greatly up to the order of 10 kDa. Polymerized polyphenols are not only natural antioxidants but also strong inhibitors of numerous physiological enzymatic activities. Several useful methods for the determination and separation of these high-molecular-mass polyphenols have recently been developed. In this review, details of the methods and applications of size-exclusion chromatographic separation of polymerized polyphenols, particularly those of proanthocyanidins, are described and compared with other related chromatographic or mass spectrometric analyses.

Separation of apple procyanidins into different degrees of polymerization by high-speed counter-current chromatography

Apple procyanidins were fractionated by high-speed counter-current chromatography in a one-step operation from apple condensed tannins using a type-J multilayer coil planet centrifuge. The separation of procyanidins was performed with a two-phase solvent system composed of methyl acetate-water (1:1) by eluting the upper phase at a flow-rate of 1.0 ml/min. Each fraction was examined by time-of-flight mass spectrometry. Procyanidins were separated according to their degrees of polymerization.