Aleksandra Sentkowska

Recent Developments in the HPLC Separation of Phenolic Food Compounds

Phenolic compounds, as an important class of natural products, are the main bioactive constituents of many dietary and medicinal plants. They have been reported to show extensive benefits to human health, including antioxidant, anti-inflammatory, and anticancer activities. In most cases, phenolic compounds are present in plants as a series of analogues with similar structures and physico-chemical properties. Rapid, accurate, and sensitive analytical techniques for their analysis in different kinds of food samples are becoming increasingly important from a nutritional standpoint. HPLC is the most widely used separation technique for these purposes. New techniques like ultrahigh-pressure liquid chromatography (UHPLC), hydrophilic interaction liquid chromatography (HILIC), and multidimensional LC have found increasing application. This review summarizes these developments for chemical analysis of phenolic compounds in food samples.

Effects of the operation parameters on HILIC separation of flavonoids on zwitterionic column.

The hydrophilic interaction chromatography (HILIC) coupled to mass spectrometry was employed to study retention behavior of several flavonoids from their different groups using the polymeric zwitterionic stationary phase (ZIC-pHILIC). It contains sulfobetaine-bonded ligand with an inner positively charged quaternary ammonium and an outer negatively charged sulfonate functional groups. Two organic solvents - acetonitrile (ACN) and methanol (MeOH) - were compared as a component of mobile phase. Separation parameters such as a content of organic modifier, pH of an eluent and a column temperature were studied. Retention of flavonoids is controlled primarily by a partition between the mobile phase eluent and a water-enriched layer on the hydrophilic stationary phase with some contribution from hydrogen bonding formation. Using MeOH, in contrast to ACN, strongly retained compounds (myricetin, morin, rutin and quercetrin) could be eluted under isocratic conditions. A better sensitivity was achieved with MeOH as mobile phase component, particularly for quercetin, naringenin and kaempferol. The method was applied to the determination of flavonoids in fruit juices.

Comparison of three modifications of fused-silica capillaries and untreated capillaries for protein profiling of maize extracts by capillary electrophoresis.

In this work, capillary electrophoresis was applied to protein profiling of fractionated extracts of maize. A comparative study on the application of uncoated fused-silica capillaries and capillaries modified with hydroxypropylmethylcellulose, ω-iodoalkylammonium salt and a commercially available neutral capillary covalently coated with polyacrylamide is presented. The coating stability, background electrolyte composition, and separation efficiency were investigated. It was found that for zeins separation, the most stable and efficient was the capillary coated with polyacrylamide. Finally, the usefulness of these methods was studied for the differentiation of zein fraction in transgenic and nontransgenic maize. Zeins extracted from maize standards containing 0 and 5% m/m genetic modification were successfully separated, but slight differences were observed in terms of the zein content. Albumin and globulin fractions were analyzed with the use of unmodified fused-silica capillary with borate buffer pH 9 and the capillary coated with polyacrylamide with phosphate buffer pH 3. In the albumin fraction, additional peaks were found in genetically modified samples.

Polyphenolic Composition and Antioxidative Properties of Lemon Balm (Melissa officinalis L.) Extract Affected by Different Brewing Processes

Polyphenolic composition of lemon balm (Mellisa officinalis L.) aqueous extracts prepared as infusion and decoction were evaluated by high performance liquid chromatography/tandem mass spectrometry. All the samples showed a similar phenolic profile but presenting differences in the quantities found of each compound. Higher content was found in plant infusion extract compared to decoction process. During the prolonged time of extractions the contents of some compounds were changed. Rutin and caffeic acid contents were decreased in the infusion mode, while increased concentration was observed during decoction process. The antioxidant activities measured by Folin-Ciocalteu and CUOPRAC assays were higher for the extract prepared in decoction mode (1245 mg/g GAE and 4.91 mmol/g TRE, respectively) in comparison to infusion process (267 mg/g GAE and 2.62 mmol/g TRE).

Retention Study of Flavonoids Under Different Chromatographic Modes.

The goal of this study was to investigate the chromatographic behavior of selected flavonoids from their different subgroups (flavonols, flavanones, flavones and isoflavones) in hydrophilic interaction liquid chromatography (HILIC). Chromatographic measurements were made on two different HILIC columns: cross-linked DIOL (Luna HILIC) and zwitterionic sulfoalkylbetaine (SeQuant ZIC-HILIC). Separation parameters such as the content of acetonitrile and pH of an eluent were studied. On the ZIC column, the retention factors of flavonoids increased with decreasing water content in the mobile phase. The increase in pH of the aqueous component mainly affects the polarity of the analytes. DIOL stationary phase shows more or less apparent dual retention mechanism, HILIC at the acetonitrile (ACN) content ≥75% and reversed phase (RP) with lower content of organic modifier. In the presence of ammonium acetate in the mobile phase, the retention of flavonoids onto the DIOL column increases without change in the selectivity of the separations. The similar effect, but considerably smaller was observed for aglycones on the ZIC column. The retention of studied glycosides (hesperidin, rutin) decreases in the presence of salt in the mobile phase. The significantly higher mass spectrometry sensitivity was observed under HILIC conditions in comparison with the most often used RP LC due to much higher content of ACN in the mobile phase. Finally, under optimal chromatographic conditions, the method was validated and applied for the determination of flavonoids in chamomile (Matricaria chamomilla L.) infusion.

Biophenols and antioxidant activity in wild and cultivated heather.

Abstract Over the last decade, there has been an increasing interest to study the antioxidants from natural sources which can be applied to replace the synthetic compounds commonly used in food or as cosmetic ingredients. Calluna vulgaris (L.) Hull (heather), a plant grown in most parts of Europe and Northern America, has been used in ethnopharmacology. The content of selected biophenols and the antioxidant capacity of the extracts of wild heather collected from natural environmental localities of central Poland were assessed in this study and compared with cultivated plant. Chlorogenic acid was the major biophenolic compound present in the extracts, followed by a high amount of catechins. The reducing power of the extracts evaluated by Folin–Ciocalteau assay was in the range of 75.7–89.1 mg GA/g dry flowers. The cultivated plant extract showed the largest radical scavenging on 1,1-diphenyl-2-pirylhydrazyl (DPPH) radicals.

Effects of brewing process on phenolic compounds and antioxidant activity of herbs

Traditionally used medicinal plants contain a wide range of polyphenolic compounds that act as powerful antioxidants. The content of phenolic compounds in the infusions and decoctions of chamomile (Matricaria chamomilla L.) and St. John’s wort (Hypericum perforatum), which are traditionally used medicinal herbs, was evaluated via liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. To obtain relevant antioxidant/reducing capacity of the prepared extracts, cupric reducing antioxidant capacity and Folin-Ciocalteu assay were applied. Rutin and apigenin were the major flavonoids in the aqueous extract of chamomile, whereas the predominant phenolic compounds of St. John’s wort water extracts were rutin and catechin followed by chlorogenic acid. A longer time of infusion and decoction of St. John’s wort herb significantly affected the rutin content. The increase of extraction time had very little impact on the antioxidant activities for chamomile but considerably higher impact on those for St. John’s wort.

Potentilla erecta (L.) rhizomes as a source of phenolic acids

Abstract The aim of this study was to evaluate the content of major phenolic acids from Potentilla erecta rhiozomes. Water and ethanol-water mixture was used for extraction of these compounds. The extracts were also evaluated for the quantification of total phenolic content and the antioxidant capacity. The contents of phenolic acids and resulting antioxidant activities are dependent on the nature of extracting solvent due to the presence of different antioxidant compounds. Results showed that P. erecta rhiozomes contained high amount of gallic and p-HBA acids. The contents of chlorogenic and protocatechuic acids in the extracts of Potentilla species have not been reported yet. The results suggested that the extracts could be used as the active cosmetics ingredients and nutraceuticals. Graphical Abstract

Investigation of antioxidant interaction between Green tea polyphenols and acetaminophen using isobolographic analysis

Graphical abstract Figure. No caption available. HighlightsIsobolgraphic analysis was performed to investigate the interactions between APAP and green tea polyphenols.Interactions between green tea polyphenols and APAP have impact on antioxidant capacity of green tea.Proved the need of caution in the consumpion of green tea while APAP is taken. ABSTRACT The antioxidant interactions between acetaminophen (APAP) and green tea polyphenols were investigated using 1,1‐diphenyl‐ 2‐picryl‐hydrazyl (DPPH) radicals and cupric reducing antioxidant capacity (CUPRAC). The results obtained experimentally for the mixtures were compared with theoretical values calculated by adding up the effects of both individual components analyzed separately. The potential antagonistic, additive or synergistic effects were also evaluated using the isobolographic analysis and interaction indexes. The results obtained for DPPH assays suggest the antagonistic type of interaction, while the results from CUPRAC method showed synergism. The observed differences in the type of interactions were probably a result of different reaction mechanisms between two used assays.

Hydrophilic interaction liquid chromatography in the speciation analysis of selenium

The hydrophilic interaction liquid chromatography (HILIC) coupled to mass spectrometry was employed to study retention behavior of selected selenium compounds using two different HILIC stationary phases: silica and zwitterionic. Two organic solvents - acetonitrile and methanol - were compared as a component of mobile phase. Separation parameters such as a content of organic modifier, the eluent pH and inorganic buffer concentration were investigated. Based on all observations, methanol seems to be beneficial for the separation of studied compounds. The optimal HILIC separation method involved silica column and eluent composed of 85% MeOH and CH3COONH4 (8 mM, pH 7) was compared to RP method in terms of time of the single run, the separation efficiency and limit of detection.