Identification of triterpene saponins in Quercus robur L. and Q. petraea Liebl. Heartwood by LC-ESI/MS and NMR

Mass spectrometry in the study of wood compounds released in the barrel-aged wine and spirits

Aging of wines and spirits in wooden barrels is an industrial process used to stabilize the color, to improve the limpidity and to enrich the sensorial characteristics of the products. In red wines, the oxygen that permeates through the wood staves promotes the oxidization of polyphenols and the formation of new pigments with consequent stabilization of the wine color. Barrel aging of spirits, such as brandy, whisky, rum, and grappa is finalized to enrich their aroma and improve their sensorial characteristics by the contribute of the compounds released by the wood. Oak is the wood type mostly used in making barrels; however, an increasing interest in the use of chestnut, cherry, acacia, and in less extent, ash and mulberry, has been observed in the recent years. Gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry are the main techniques used to characterize respectively the volatile and polar metabolites released by the wood barrels in the products. In this article are reported the recent advancements in this field.

Antioxidants in Animal Nutrition: UHPLC-ESI-QqTOF Analysis and Effects on In Vitro Rumen Fermentation of Oak Leaf Extracts

The genus Quercus supplies a large amount of residual material (e.g., bark, acorns, leaves, wood), the valorization of which can favor a supply of antioxidant polyphenols to be used in the pharmaceutical, nutraceutical, or cosmeceutical sector. The recovery of specialized metabolites could also benefit livestock feeding, so much so that polyphenols have gained attention as rumen fermentation modifiers and for mitigating the oxidative imbalance to which farm animals are subject. In this context, leaves of Quercus robur L. from Northern Germany were of interest and the alcoholic extract obtained underwent an untargeted profiling by means of ultra-high-performance liquid chromatography/high-resolution tandem mass spectrometry (UHPLC-HRMS/MS) techniques. As triterpenes and fatty acids occurred, the alcoholic extract fractionation pointed out the obtainment of a polyphenol fraction, broadly constituted by coumaroyl flavonol glycosides and condensed tannins. Total phenol, flavonoid and condensed tannins content assays, as well as antiradical (DPPH^● and ABTS^+●) and reducing activity (PFRAP) were carried out on the alcoholic extract and its fractions. When the effects on rumen liquor was evaluated in vitro in terms of changes in fermentation characteristics, it was observed that oak leaf extract and its fractions promoted an increase in total volatile fatty acids and differently modulated the relative content of each fatty acid.

Oak Species Quercus robur L. and Quercus petraea Liebl. Identification Based on UHPLC-HRMS/MS Molecular Networks

Two species of oak are dominant in French forests: pedunculate oak (Quercus robur L.) and sessile oak (Quercus petraea Liebl.). Their differentiation is not straightforward but is essential to better understand their respective molecular content in order to better valorize them. Thus, to improve oak species identification, an untargeted UHPLC-HRMS/MS method associated with a two-step data treatment was developed to analyze a wide range of specialized metabolites enabling the comparison of both species of oak extracts. Pooled extracts from sessile and pedunculate oaks, composed of extracts from several trees of pure species from various origins, were compared using first the Venn diagram, as a quick way to get an initial idea of how close the extracts are, and then using a molecular network to visualize, on the one hand, the ions shared between the two species and, on the other hand, the compounds specific to one species. The molecular network showed that the two species shared common clusters mainly representative of tannins derivatives and that each species has specific molecules with similar fragmentation patterns, associated in specific clusters. This methodology was then applied to compare these two pooled extracts to unknown individuals in order to determine the species. The Venn diagram allowed for the quick presumption of the species of the individual and then the species could be assigned more precisely with the molecular network, at the level of specific clusters. This method, developed for the first time, has several interests. First, it makes it possible to discriminate the species and to correctly assign the species of unknown samples. Moreover, it gave an overview of the metabolite composition of each sample to better target oak tree utilization and valorization.

Untargeted UHPLC-Q-TOF-HRMS based determination of discrimating compounds for oak species Quercus robur L. and Quercus petraea Liebl. identification

INTRODUCTION

Two species of oak are dominant in French forests: pedunculate oak (Quercus robur L.) and sessile oak (Quercus petraea Liebl.). Differentiating oak species is difficult, since features such as morphological characters, geographical origin and grain are not always relevant. Even if the former is generally richer in tannin compounds while the latter is often richer in aromatic compounds, the intra-species variability is high. The characterisation of the oak species remains a suitable indicator of the molecular composition and quality of the wood.

OBJECTIVES

The aim of this study was to determine differentiating molecules allowing oak species identification in order to assist in a suitable wood selection for a better oak tree valorisation since the selection of the oak wood to be used in the production of barrels plays an essential role in wine ageing.

MATERIALS AND METHODS

Oak wood samples were collected both in forests and in cooperage timber yards. An untargeted metabolomic approach using ultra-high-pressure liquid chromatography qualitative time-of-flight high-resolution mass spectrometry (UHPLC-Q-TOF-HRMS) associated to multivariate statistical analyses (hierarchical ascendant clustering and partial least squares discriminant analysis) was implemented to determine molecular markers of oak species.

RESULTS

Heartwood was identified as the suitable wood part to distinguish oak species. Discriminating molecules did not depend on the sample set. The pedunculate species showed overexpression of bartogenic derivatives while sessile oak presented a higher content in oak lactone precursors and in quercotriterpenosids.

CONCLUSION

The developed method allowed the identification of relevant compounds for oak species identification to a better wood valorisation and selection.

Isolation of Taste-Active Triterpenoids from Quercus robur: Sensory Assessment and Identification in Wines and Spirit

Six new triterpenoids (1-6), two known genins (7 and 8), and five known functionalized triterpenoids (9-13) were isolated from a Quercus robur heartwood extract. The purification protocol was guided by LC-HRMS by searching for structural analogues of bartogenic acid on the basis of their putative empirical formula. The structures of the new compounds were unequivocally elucidated using HRESIMS and 1D/2D NMR experiments. Sensory analyses were performed in water and in a non-oaked white wine on the pure compounds 1-13 at 5 mg/L. All molecules were perceived as bitter in water and wine, but they were mostly reported as modifying the wine taste balance. Using LC-HRMS, compounds 1-13 were observed in oaked red wine and cognac and were semiquantified in oak wood extracts. The influence of two cooperage parameters, oak species and toasting process, on compounds 1-13 content was studied. All compounds were found in quantities significantly higher in pedunculate than in sessile oak wood. Toasting is a key step in barrel manufacture and modulates the concentration of the discussed compounds. Significantly higher quantities were observed in untoasted wood compared to medium or highly toasted wood. These findings provide new insights into the molecular origin of taste changes due to oak aging.

Triterpenoid Components from Oak Heartwood (Quercus robur) and Their Potential Health Benefits

For centuries oak wood (Quercus robur) has been used in aging of wines and spirits, which is based on pleasant flavors given to beverages by phenolics transferred to the liquid during the maturation process. Other metabolites, such as triterpenoids, can also be released. Searching for extractable triterpenoids in oak heartwood, 12 new, 1-12, and five known, 13-17, oleanane types were isolated and characterized. Their cytotoxicities were tested against cancer cells (PC3 and MCF-7) and lymphocytes. Breast cancer cells (MCF-7) were the most affected by triterpenoids, with roburgenic acid, 4, being the most active compound (IC₅₀ = 19.7 μM). Selectivity was observed for compounds 1-3, 8, 9, and 16, exhibiting an IC₅₀ > 200 μM against lymphocytes, while active against cancer cells. A galloyl unit attached to the triterpenoid moiety was established as the key feature for such effect. These results highlight the occurrence of triterpenoids in oak heartwood and their relevance for chemoprevention of breast cancer.

Cytotoxic triterpenoids isolated from sweet chestnut heartwood (Castanea sativa) and their health benefits implication

For centuries wood containers have been used in aging of wines and spirits, due to the pleasant flavors they give to the beverages. Together with oak, sweet chestnut wood (Castanea sativa) have been often used for such purpose. The maturation process involves the transfer of secondary metabolites, mainly phenolics, from the wood to the liquid. At the same time, other metabolites, such as triterpenoids and their glycosides, can also be released. Searching for the extractable triterpenoids from sweet chestnut heartwood (C. sativa), two new ursane-type triterpenoid saponins named chestnoside A (1) and chestnoside B (2), together with two known oleanen-type analogs (3 and 4) were isolated and characterized. The cytotoxicity of isolated compounds was tested against two cancer cell lines (PC3 and MCF-7), and normal lymphocytes. Breast cancer cells (MCF-7) were more affected by tested compounds than prostate cancer cells (PC3). Chestnoside B (2) exhibited the strongest cytotoxicity with an IC₅₀ of 12.3 μM against MCF-7 cells, lower than those of positive controls, while it was moderately active against normal lymphocytes (IC₅₀ = 67.2 μM). These results highlight the occurrence of triterpenoid saponins in sweet chestnut heartwood and their potential for the chemoprevention of breast cancer.

α-Glucosidase inhibition and antioxidant activity of an oenological commercial tannin. Extraction, fractionation and analysis by HPLC/ESI-MS/MS and (1)H NMR

Two batches of the oenological tannin Tan'Activ R, (toasted oak wood - Quercus robur), were extracted with ethanol. A fractionation on XAD-16 afforded four fractions for each extract. Extracts and fractions were evaluated for antioxidant activity (DPPH), polyphenol content (GAE) and yeast α-glucosidase inhibitory activity. Comparable results were obtained for both columns, fractions X1B and X2B showing the highest antioxidant activity. Fractions X1C and X2C notably inhibited α-glucosidase, with IC50=9.89 and 8.05μg/mL, respectively. Fractions were subjected to HPLC/ESI-MS/MS and (1)H NMR analysis. The main phenolic constituents of both X1B and X2B were a monogalloylglucose isomer (1), a HHDP-glucose isomer (2), castalin (3) gallic acid (4), vescalagin (5), and grandinin (or its isomer roburin E, 6). X1C and X2C showed a complex composition, including non-phenolic constituents. Fractionation of X2C gave a subfraction, with enhanced α-glucosidase inhibitory activity (IC50=6.15μg/mL), with castalagin (7) as the main constituent.

Anti-inflammatory activity of bartogenic acid containing fraction of fruits of Barringtonia racemosa Roxb. in acute and chronic animal models of inflammation

The fruits of Barringtonia racemosa are traditionally used in Indian medicine for the treatment of pain and inflammatory conditions. In this study, a fraction of ethyl acetate extract of fruits of B. racemosa (BREAF) was investigated for anti-inflammatory activity in experimental models of acute and chronic inflammation. Activity against acute inflammation was evaluated in inflammogens induced rat paw edema models. Whereas, effect in chronic inflammation was evaluated in cotton pellet granuloma and oxazolone induced delayed type hypersensitivity (DTH) model in mice. The BREAF exhibited dose dependent anti-inflammatory activity in both acute and chronic models at oral doses of 5, 10 and 20 mg/kg. BREAF inhibited both phases of carrageenan induced rat paw inflammation. The reduction in paw inflammation by BREAF was also evident in histamine and serotonin induced inflammation in rats. Effect of BREAF on DTH indicates inhibition of immune mediated inflammation. The reduction in cotton pellet granuloma by BREAF treatment shows inhibition of proliferative changes associated with chronic inflammation. Analysis of BREAF after chromatographic separations showed presence of bartogenic acid as a major constituent. Hence, it is proposed that anti-inflammatory effects of BREAF can be partially attributed to its bartogenic acid content. The minute doses at which this fraction shows anti-inflammatory effects emphasizes the need for further investigations on its efficacy in the immuno-inflammatory conditions.

New Approach for Differentiating Sessile and Pedunculate Oak: Development of a LC-HRMS Method To Quantitate Triterpenoids in Wood

Oak aging is a crucial step in winemaking during which the organoleptic properties of wine are modified. Various parameters affect the chemical composition of oak wood including botanical origin, which has been previously shown to be a determinant factor. This study focused on the development of a LC-HRMS method to assay four recently discovered taste-active triterpenes (three sweet and one bitter). The method was applied to evaluate the effect of oak species (Quercus petraea and Quercus robur) on the concentration of these molecules in wood. The results showed that sessile oak was richer in sweet triterpenes and poorer in the bitter one than pedunculate oak, with high interindividual variations within species. Furthermore, a triterpenoid index was calculated to reveal the triterpenoid composition of oak wood. This index appears to be a promising tool for the unambiguous discrimination of oak species and could offer new insights into oak wood selection by coopers and the monitoring of oak aging by winemakers.

Oleanane-type isomeric triterpenoids from Barringtonia racemosa

Two new isomeric acylated oleanane-type triterpenoids along with three known compounds were isolated from the MeOH extract of the dried fruits of Barringtonia racemosa. On the basis of spectroscopic methods, with special emphasis on 1D and 2D NMR techniques as well as chemical methods, the structures were characterized as racemosol A (1) [22alpha-acetoxy-3beta,15alpha,16alpha,21beta-tetrahydroxy-28-(2-methylbutyryl)olean-12-ene] and isoracemosol A (2) [21beta-acetoxy-3beta,15alpha,16alpha,28-tetrahydroxy-22alpha-(2-methylbutyryl)olean-12-ene]. The isolated compounds (1-5) were not active against HeLa and P388 D1 carcinoma cell lines.

Natural product isolation

Since the 1990s, interest in natural product research has increased considerably. Following several outstanding developments in the areas of separation methods, spectroscopic techniques, and sensitive bioassays, natural product research has gained new attention for providing novel chemical entities. This updated review deals with sample preparation and purification, recent extraction techniques used for natural product separation, liquid-solid and liquid-liquid isolation techniques, as well as multi-step chromatographic operations. It covers examples of papers published since the NPR review 'Modern separation methods' by Marston and Hostettmann,1 with major emphasis on methods developed and the research undertaken since 2000.

Inhibition of alpha-glucosidase and amylase by bartogenic acid isolated from Barringtonia racemosa Roxb. seeds

Barringtonia racemosa presents a wide range of therapeutic applications. In the course of identifying bioactives from Indian medicinal plants it was observed that the hexane, ethanol and methanol extracts of B. racemosa seeds displayed potent yeast and intestinal alpha-glucosidase inhibitory activities. The methanol extract was found to be superior among them. However, none of the extracts exhibited pancreatic alpha-amylase inhibitory activity, rather the ethanol and methanol extracts accelerated the alpha-amylase enzyme activity. Interestingly, however, bartogenic acid isolated from the methanol extract inhibited alpha-amylase also. This is the first report identifying alpha-glucosidase inhibitory activity in B. racemosa seed extracts and assigning to bartogenic acid an alpha-glucosidase and amylase inhibitory property. The presence of bartogenic acid in B. racemosa seeds as a major compound is also reported for the first time in this communication.

ESI-QqTOF-MS/MS and APCI-IT-MS/MS analysis of steroid saponins from the rhizomes of Dioscorea panthaica

Using high-resolution quadrupole time-of-flight mass spectrometry along with an electrospray ionization source (ESI-QqTOF-MS), accurate molecular weights of 13 steroid saponins extracted from the rhizomes of Dioscorea panthaica were acquired and the corresponding molecular formulae obtained. In order to elucidate the fragmentation pathways of steroid saponins in D. panthaica, 10 authentic samples were investigated using ESI-QqTOF-MS/MS. In addition, atmospheric pressure chemical ionization mass spectrometry combined with ion trap tandem mass spectrometry (APCI-IT-MS/MS) was used to analyze the structures of 13 steroid saponins in D. panthaica. Through the analysis of their tandem mass data, diagnostic fragment ions of the spirostanol and furostanol steroid saponins in D. panthaica were detected as m/z 271.2056 and 253.1951. In addition, four pairs of isomers were detected and the possible structures of four unknown steroid saponins in D. panthaica speculated. ESI-TOF and APCI-MS(n) have proved to be effective tools for research on fragmentation mechanism of steroid saponins and the rapid determination of native steroid saponins in extract mixture, thereby avoiding tedious derivation and separation steps.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, lanostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleannes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins. The literature from January to December 2002 is reviewed and 221 references are used.