Fast Sampling, Analyses and Chemometrics for Plant Breeding: Bitter Acids, Xanthohumol and Terpenes in Lupulin Glands of Hops (Humulus lupulus)

Fingerprinting and chemotyping approaches reveal a wide genetic and metabolic diversity among wild hops (Humulus lupulus L.)

Hop (Humulus lupulus L.) is an emblematic industrial crop in the French North East region that developed at the same time as the brewing activity. Presently, this sector, especially microbreweries, are interested in endemic wild hops, which give beer production a local signature. In this study, we investigated the genetic and metabolic diversity of thirty-six wild hops sampled in various ecological environments. These wild accessions were propagated aeroponically and cultivated under uniform conditions (the same soil and the same environmental factors). Our phytochemical approach based on UHPLC-ESI-MS/MS analysis led to the identification of three metabolic clusters based on leaf content and characterized by variations in the contents of twelve specialized metabolites that were identified (including xanthohumol, bitter acids, and their oxidized derivatives). Furthermore, molecular characterization was carried out using sixteen EST-SSR microsatellites, allowing a genetic affiliation of our wild hops with hop varieties cultivated worldwide and wild hops genotyped to date using this method. Genetic proximity was observed for both European wild and hop varieties, especially for Strisselspalt, the historical variety of our region. Finally, our findings collectively assessed the impact of the hop genotype on the chemical phenotype through multivariate regression tree (MRT) analysis. Our results highlighted the 'WRKY 224' allele as a key discriminator between high- and low-metabolite producers. Moreover, the model based on genetic information explained 40% of the variance in the metabolic data. However, despite this strong association, the model lacked predictive power, suggesting that its applicability may be confined to the datasets analyzed.

Quantitative Raman chemical imaging of intracellular drug-membrane aggregates and small molecule drug precipitates in cytoplasmic organelles

Raman confocal microscopes have been used to visualize the distribution of small molecule drugs within different subcellular compartments. This visualization allows the discovery, characterization, and detailed analysis of the molecular transport phenomena underpinning the Volume of Distribution - a key parameter governing the systemic pharmacokinetics of small molecule drugs. In the specific case of lipophilic small molecules with large Volumes of Distribution, chemical imaging studies using Raman confocal microscopes have revealed how weakly basic, poorly soluble drug molecules can accumulate inside cells by forming stable, supramolecular complexes in association with cytoplasmic membranes or by precipitating out within organelles. To study the self-assembly and function of the resulting intracellular drug inclusions, Raman chemical imaging methods have been developed to measure and map the mass, concentration, and ionization state of drug molecules at a microscopic, subcellular level. Beyond the field of drug delivery, Raman chemical imaging techniques relevant to the study of microscopic drug precipitates and drug-lipid complexes which form inside cells are also being developed by researchers with seemingly unrelated scientific interests. Highlighting advances in data acquisition, calibration methods, and computational data management and analysis tools, this review will cover a decade of technological developments that enable the conversion of spectral signals obtained from Raman confocal microscopes into new discoveries and information about previously unknown, concentrative drug transport pathways driven by soluble-to-insoluble phase transitions occurring within the cytoplasmic organelles of eukaryotic cells.

Successful combination of benchtop nuclear magnetic resonance spectroscopy and chemometric tools: A review

Low-field nuclear magnetic resonance (NMR) has three general modalities: spectroscopy, imaging, and relaxometry. In the last twelve years, the modality of spectroscopy, also known as benchtop NMR, compact NMR, or just low-field NMR, has undergone instrumental development due to new permanent magnetic materials and design. As a result, benchtop NMR has emerged as a powerful analytical tool for use in process analytical control (PAC). Nevertheless, the successful application of NMR devices as an analytical tool in several areas is intrinsically linked to its coupling with different chemometric methods. This review focuses on the evolution of benchtop NMR and chemometrics in chemical analysis, including applications in fuels, foods, pharmaceuticals, biochemicals, drugs, metabolomics, and polymers. The review also presents different low-resolution NMR methods for spectrum acquisition and chemometric techniques for calibration, classification, discrimination, data fusion, calibration transfer, multi-block and multi-way.

Metabolomic Approach Based on Analytical Techniques for the Detection of Secondary Metabolites from Humulus lupulus L. Dried Leaves

Currently, the leaves of the hop plant (Humulus lupulus L.) are an unexploited and still little-investigated agricultural by-product. In our study, with the aim of exploring the metabolome of dried hop leaves (Chinook cultivar), a metabolomic approach was applied using multiple analytical tools such as SPME/GC-MS, GC-MS, PTR-ToF-MS, and NMR to identify the secondary metabolites. The obtained results showed the presence of a high number of components belonging to different chemical classes. In fact, thanks to the multi-methodological approach, volatile organic compounds (VOCs) with low molecular weight, terpenic compounds, fatty acids, sugars, amino acids, organic acids, and alcohols have been detected and identified. Among the revealed terpenes in the untreated matrix, the sesquiterpenes α-humulene, β-caryophyllene, and α-copaene were the most abundant. Among the saturated and unsaturated fatty acids, palmitic and linolenic acids, respectively, were those with the highest relative percentages. Particularly relevant was the sugar content, where sucrose was the main exponent while glutamate and asparagine were the principal detected amino acids. Conversely, alcohols and organic acids were the least abundant compound classes, and xanthohumol was also identified in the methanolic extract.

Halimane Diterpenes in the Alpine Daisy Celmisia viscosa: Absolute Configuration, 2,6-Dideoxyhexopyran-3-ulosides, Conformational Flexibility, and Intraspecific Variation

The methyl-migrated bicyclic skeleton of the halimane diterpenes has been found in a wide range of organisms, including flowering plants, liverworts, marine animals, and bacteria. The discovery of halima-1(10),14-dien-13-ol (3) from the Aotearoa New Zealand endemic alpine daisy Celmisia viscosa is now reported. The full configuration was assigned for the first time by X-ray crystallography, enantiomeric to that of a liverwort isolate. The absolute configuration at C-5 of the halimane is opposite to that at C-5 of the labdane epimanool (1) found in some C. viscosa specimens. Two new 2,6-dideoxyhexopyran-3-uloside halimane derivatives (4 and 5) were also found, and the absolute configuration of 5 was determined by ¹H NMR analysis of the Mosher esters. Line broadening in the ¹³C NMR spectra of these halim-1(10)-enes was due to conformational exchange in the decalin ring A, as shown by molecular modeling and DFT calculations. ¹H NMR and GC analyses of leaf extracts of individual plants from across the full geographic range of C. viscosa revealed intraspecific variation of diterpenes: 37 samples had halimadienol as the main diterpene in large amounts and 2 specimens had predominantly epimanool, again in large amounts. Three other viscid (sticky leaved) Celmisia species also contained diterpenes, but none was detectable in four nonviscid Celmisia species.

Analytical artefacts: H2 carrier gas hydrogenation of plant volatiles during headspace solid-phase microextraction gas chromatography

INTRODUCTION

Hydrogen is the most efficient and economical carrier gas for gas chromatography (GC). However, there are rare reports of artefact formation by hydrogenation of unsaturated compounds on GC. Head space solid-phase microextraction (HS-SPME) GC conditions for hydrogenation were studied.

METHODOLOGY

HS-SPME-GC-mass spectrometry (MS) analyses of common classes of plant volatiles were carried out using hydrogen (H₂ ) and helium (He) carrier gases with different SPME fibre coatings, GC inlet temperatures, and desorption times.

RESULTS

Common phenylpropanoids, monoterpenes, and green leaf volatiles were hydrogenated to varying degrees on HS-SPME-GC with H₂ carrier gas and SPME fibres coated with polydimethylsiloxane (PDMS)/Carboxen (CAR), PDMS/divinylbenzene (DVB), and PDMS/CAR/DVB. No artefacts were detected using PDMS-only coated fibres or He carrier gas.

CONCLUSION

Unsaturated plant volatiles may be hydrogenated on HS-SPME-GC when using H₂ carrier gas with SPME fibre coatings containing DVB polymer or CAR porous particles. Parallel analyses with He and H₂ carrier gases are recommended when developing HS-SPME-GC methods for plant volatiles, or use of PDMS-only coated fibres.

Chemical diversity of kānuka: Inter- and intraspecific variation of foliage terpenes and flavanones of Kunzea (Myrtaceae) in Aotearoa/New Zealand

Kunzea (Myrtaceae) trees and shrubs, generally called kānuka, grow across most of Aotearoa/New Zealand (NZ). With the exception of K. sinclairii, an offshore island endemic, kānuka had been treated as an Australasian species K. ericoides. However, a 2014 taxonomic revision recognized ten species, all endemic to NZ. Kānuka chemistry is less studied than that of its closest relative in NZ, mānuka (Leptospermum scoparium), which shows very distinct regional foliage chemotypes. We have used a miniaturized method with GC and ¹H NMR to analyze foliage chemistry of voucher specimens from across the geographic ranges of the ten NZ Kunzea species. We found common mono- and sesquiterpenes, with α-pinene dominant in all samples, but only traces of antimicrobial triketones. Two unusual flavanones, with unsubstituted B-rings and known bioactivity against Phytophthora, did distinguish some of the samples. 5,7-Dihydroxy-6,8-dimethyl flavanone was only found at high concentrations in the three K. sinclairii samples in this study's sample set, but this compound has separately been reported in K. robusta samples from a nearby region. Therefore none of the NZ Kunzea species was distinguished by the chemistry analyzed in this study, but there is a possibility of regional flavonoid chemotypes cutting across the species boundaries.

Low-field benchtop NMR spectroscopy: status and prospects in natural product analysis†

INTRODUCTION

Since a couple of years, low-field (LF) nuclear magnetic resonance (NMR) spectrometers (40-100 MHz) have re-entered the market. They are used for various purposes including analyses of natural products. Similar to high-field instruments (300-1200 MHz), modern LF instruments can measure multiple nuclei and record two-dimensional (2D) NMR spectra.

OBJECTIVE

To review the commercial availability as well as applications, advantages, limitations, and prospects of LF-NMR spectrometers for the purpose of natural products analysis.

METHOD

Commercial LF instruments were compared. A literature search was performed for articles using and discussing modern LF-NMR. Next, the articles relevant to natural products were read and summarised.

RESULTS

Seventy articles were reviewed. Most appeared in 2018 and 2019. Low costs and ease of operation are most often mentioned as reasons for using LF-NMR.

CONCLUSION

As the spectral resolution of LF instruments is limited, they are not used for structure elucidation of new natural products but rather applied for quality control (QC), forensics, food and health research, process control and teaching. Chemometric data handling is valuable. LF-NMR is a rapidly developing niche and new instruments keep being introduced.

Differentiation of aromatic, bittering and dual-purpose commercial hops from their terpenic profiles: An approach involving batch extraction, GC-MS and multivariate analysis

Terpenes are one of the main classes of compounds in hops (Humulus lupulus, L). They play an important role in brewing due to their central function, which is related to beer aroma. A screening of terpenes in several commercial hop varieties was carried out by gas chromatography coupled to mass spectrometry after employing a simple, straightforward and high throughput extraction method. A single batch extraction, using hexane as solvent, was employed to obtain the terpenic fraction of the hop samples. Nineteen terpenes were identified in analyzed samples with β-myrcene (2.22-45.30%), α-humulene (20.20-67.64%), and β-caryophyllene (9.97-24.62%) being the major terpenes in all samples. The studied system was multivariate modeled by principal component analysis. Based on the proposed approach, it was possible to correlate the terpenic hop profiles to their specific purpose in the brewing industry and to distinguish aromatic hops (high α-humulene content), bittering hops (high β-myrcene content), and dual-purpose hops (more complex and intermediate terpenic profile) among the samples.

Gas-phase volatilomic approaches for quality control of brewing hops based on simultaneous GC-MS-IMS and machine learning

For the first time, a prototype HS-GC-MS-IMS dual-detection system is presented for the analysis of volatile organic compounds (VOCs) in fields of quality control of brewing hop. With a soft ionization and drift time-based ion separation in IMS and a hard ionization and m/z-based separation in MS, substance identification in the case of co-elution was improved, substantially. Machine learning tools were used for a non-targeted screening of the complex VOC profiles of 65 different hop samples for similarity search by principal component analysis (PCA) followed by hierarchical cluster analysis (HCA). Partial least square regression (PLSR) was applied to investigate the observed correlation between the volatile profile and the α-acid content of hops and resulted in a standard error of prediction of only 1.04% α-acid. This promising volatilomic approach shows clearly the potential of HS-GC-MS-IMS in combination with machine learning for the enhancement of future quality assurance of hops.

Comparison of antioxidant activity of extracts of hop leaves harvested in different years

Introduction: Hop (Humulus lupulus L.) is a common plant in Europe, with many beneficial health effects. In addition to the use in brewing, hops are a valuable source of active substances used in conventional and folk medicine, such as humulones and lupulones, as well as antioxidants, including phenolic compounds.

Objective: The aim of the study was to evaluate and compare the antioxidant activity of alcoholic extracts of fresh hop leaves collected in 2017 and 2018.

Material and methods: The raw material consisting of fresh hop leaves was extracted using ultrasound-assisted extraction. Methyl, ethyl and isopropyl alcohol at three concentrations were used as extractants. The antioxidant activity of extracts was determined using DPPH and FRAP methods. Total phenolic content was evaluated using the Folin-Ciocalteu technique.

Results: All the extracts showed antioxidant potential as well as the phenolic content. Regardless of the harvesting year and methods of evaluation, the highest antioxidant activity and the total polyphenol content were observed for extracts prepared in undiluted methanol, obtained during one hour lasting extraction.

Conclusion: The results of the studies have suggested that hop leaves can be a potential source of health-promoting antioxidants.

Progress in low-field benchtop NMR spectroscopy in chemical and biochemical analysis

The employment of spectroscopically-resolved NMR techniques as analytical probes have previously been both prohibitively expensive and logistically challenging in view of the large sizes of high-field facilities. However, with recent advances in the miniaturisation of magnetic resonance technology, low-field, cryogen-free "benchtop" NMR instruments are seeing wider use. Indeed, these miniaturised spectrometers are utilised in areas ranging from food and agricultural analyses, through to human biofluid assays and disease monitoring. Therefore, it is both intrinsically timely and important to highlight current applications of this analytical strategy, and also provide an outlook for the future, where this approach may be applied to a wider range of analytical problems, both qualitatively and quantitatively.

Non-volatile natural products in plant glandular trichomes: chemistry, biological activities and biosynthesis

The investigation methods, chemistry, bioactivities, and biosynthesis of non-volatile natural products involving 489 compounds in plant glandular trichomes are reviewed.

The R2R3 transcription factor HlMYB8 and its role in flavonoid biosynthesis in hop (Humulus lupulus L.)

Hop is an important source of medicinally valuable secondary metabolites including bioactive prenylated chalcones. To gain in-depth knowledge of the regulatory mechanisms of hop flavonoids biosynthesis, full-length cDNA of HlMyb8 transcription factor gene was isolated from lupulin glands. The deduced amino acid sequence of HlMyb8 showed high similarity to a flavonol-specific regulator of phenylpropanoid biosynthesis AtMYB12 from Arabidopsis thaliana. Transient expression studies and qRT-PCR analysis of transgenic hop plants overexpressing HlMyb8 revealed that HlMYB8 activates expression of chalcone synthase HlCHS_H1 as well as other structural genes from the flavonoid pathway branch leading to the production of flavonols (F3H, F'3H, FLS) but not prenylflavonoids (PT1, OMT1) or bitter acids (VPS, PT1). HlMyb8 could cross-activate Arabidopsis flavonol-specific genes but to a much lesser extent than AtMyb12. Reciprocally, AtMyb12 could cross-activate hop flavonol-specific genes. Transcriptome sequence analysis of hop leaf tissue overexpressing HlMyb8 confirmed the modulation of several other genes related to flavonoid biosynthesis pathways (PAL, 4CL, ANR, DFR, LDOX). Analysis of metabolites in hop female cones confirmed that overexpression of HlMyb8 does not increase prenylflavonoid or bitter acids content in lupulin glands. It follows from our results that HlMYB8 plays role in a competition between flavonol and prenylflavonoid or bitter acid pathways by diverting the flux of CHS_H1 gene product and thus, may influence the level of these metabolites in hop lupulin.

Desktop NMR and Its Applications From Materials Science To Organic Chemistry

NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small-molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen-containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state-of-the-art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed.