Characterization of Natural and Alkaline-Oxidized Proanthocyanidins in Plant Extracts by Ultrahigh-Resolution UHPLC-MS/MS

Exploring the Interactions between Plant Proanthocyanidins and Thiabendazole: Insights from Isothermal Titration Calorimetry

Anthelmintic resistance in gastrointestinal nematodes produces substantial challenges to agriculture, and new strategies for nematode control in livestock animals are called for. Natural compounds, including tannins, with proven anthelmintic activity could be a functional option as structurally diverse complementary compounds to be used alongside commercial anthelmintics. However, the dual use of two anthelmintic components requires an understanding of the pharmacological effects of the combination, while information concerning the interactions between plant-based polyphenols and commercial anthelmintics is scarce. We studied the direct interactions of proanthocyanidins (PAs, syn. condensed tannins) and a commercial anthelmintic thiabendazole, as a model substance of benzimidazoles, by isothermal titration calorimetry (ITC). Our results show evidence of a direct interaction of an exothermic nature with observed enthalpy changes ranging from 0 to -30 kJ/mol. The strength of the interaction between PAs and thiabendazole is mediated by structural characteristics of the PAs with the strongest positive correlation originating from the presence of galloyl groups and the increased degree of polymerization.

Polyphenols and Phenolic Glucosides in Antibacterial Twig Extracts of Naturally Occurring Salix myrsinifolia (Salisb.), S. phylicifolia (L.) and S. starkeana (Willd.) and the Cultivated Hybrid S. x pendulina (Wender.)

(1) Background: Salix species occurring in Finland have not been well studied for their antimicrobial potential, despite their frequent use for lung and stomach problems in traditional medicine. Thus, twig extracts of three species of Salix that are found naturally in Finland and one cultivated species were screened for their antimicrobial properties against human pathogenic bacteria. S. starkeana and S. x pendulina were screened for antibacterial effects for the first time. (2) Methods: An agar diffusion and a microplate method were used for the screenings. Time-kill effects were measured using a plate-count and a microplate method. A DPPH-method using a qualitative TLC-analysis was used to detect antioxidant compounds in antimicrobial extracts. Metabolites from a S. myrsinifolia extract showing good antibacterial effects were identified using UPLC/QTOF-MS. (3) Results: A methanol extract of S. starkeana was particularly active against B. cereus (MIC 625 µg/mL), and a methanol extract of S. myrsinifolia showed good activity against S. aureus and B. cereus (MIC 1250 µg/mL) and showed bactericidal effects during a 24 h incubation of B. cereus. Moreover, a decoction of S. myrsinifolia resulted in good growth inhibition against P. aeruginosa. Our UPLC/QTOF-MS results indicated that proanthocyanidins (PAs), and especially the dimer procyanidin B1 (m/z 577) and other procyanidin derivatives, including highly polymerized proanthocyanidins, were abundant in S. myrsinifolia methanol extracts. Procyanidin B1 and its monomer catechin, as well as taxifolin and p-hydroxycinnamic acid, all present in S. myrsinifolia twigs, effectively inhibited B. cereus (MIC 250 µg/mL). (4) Conclusions: This study indicates that Finnish Salix species contain an abundance of antibacterial condensed tannins, phenolic acids and other polyphenols that deserve further research for the antibacterial mechanisms of action.

Synthesis and Isolation of Phenol- and Thiol-Derived Epicatechin Adducts Prepared from Avocado Peel Procyanidins Using Centrifugal Partition Chromatography and the Evaluation of Their Antimicrobial and Antioxidant Activity

Polyphenols from agro-food waste represent a valuable source of bioactive molecules that can be recovered to be used for their functional properties. Another option is to use them as starting material to generate molecules with new and better properties through semi-synthesis. A proanthocyanidin-rich (PACs) extract from avocado peels was used to prepare several semi-synthetic derivatives of epicatechin by acid cleavage in the presence of phenol and thiol nucleophiles. The adducts formed by this reaction were successfully purified using one-step centrifugal partition chromatography (CPC) and identified by chromatographic and spectroscopic methods. The nine derivatives showed a concentration-dependent free radical scavenging activity in the DPPH assay. All compounds were also tested against a panel of pathogenic bacterial strains formed by Listeria monocytogenes (ATCC 7644 and 19115), Staphylococcus aureus (ATCC 9144), Escherichia coli (ATCC 11775 and 25922), and Salmonella enterica (ATCC 13076). In addition, adducts were tested against two no-pathogenic strains, Limosilactobacillus fermentum UCO-979C and Lacticaseibacillus rhamnosus UCO-25A. Overall, thiol-derived adducts displayed antimicrobial properties and, in some specific cases, inhibited biofilm formation, particularly in Listeria monocytogenes (ATCC 7644). Interestingly, phenolic adducts were inactive against all the strains and could not inhibit its biofilm formation. Moreover, depending on the structure, in specific cases, biofilm formation was strongly promoted. These findings contribute to demonstrating that CPC is a powerful tool to isolate new semi-synthetic molecules using avocado peels as starting material for PACc extraction. These compounds represent new lead molecules with antioxidant and antimicrobial activity.

Willow (Salix spp.) bark hot water extracts inhibit both enveloped and non-enveloped viruses: study on its anti-coronavirus and anti-enterovirus activities

Introduction

Recurring viral outbreaks have a significant negative impact on society. This creates a need to develop novel strategies to complement the existing antiviral approaches. There is a need for safe and sustainable antiviral solutions derived from nature.

Objective

This study aimed to investigate the antiviral potential of willow (Salix spp.) bark hot water extracts against coronaviruses and enteroviruses. Willow bark has long been recognized for its medicinal properties and has been used in traditional medicines. However, its potential as a broad-spectrum antiviral agent remains relatively unexplored.

Methods

Cytopathic effect inhibition assay and virucidal and qPCR-based assays were used to evaluate the antiviral potential of the bark extracts. The mechanism of action was investigated using time-of-addition assay, confocal microscopy, TEM, thermal, and binding assays. Extracts were fractionated and screened for their chemical composition using high-resolution LC-MS.

Results

The native Salix samples demonstrated their excellent antiviral potential against the non-enveloped enteroviruses even at room temperature and after 45 s. They were equally effective against the seasonal and pandemic coronaviruses. Confocal microscopy verified the loss of infection capacity by negligible staining of the newly synthesized capsid or spike proteins. Time-of-addition studies demonstrated that Salix bark extract had a direct effect on the virus particles but not through cellular targets. Negative stain TEM and thermal assay showed that antiviral action on enteroviruses was based on the added stability of the virions. In contrast, Salix bark extract caused visible changes in the coronavirus structure, which was demonstrated by the negative stain TEM. However, the binding to the cells was not affected, as verified by the qPCR study. Furthermore, coronavirus accumulated in the cellular endosomes and did not proceed after this stage, based on the confocal studies. None of the tested commercial reference samples, such as salicin, salicylic acid, picein, and triandrin, had any antiviral activity. Fractionation of the extract and subsequent MS analysis revealed that most of the separated fractions were very effective against enteroviruses and contained several different chemical groups such as hydroxycinnamic acid derivatives, flavonoids, and procyanidins.

Conclusion

Salix spp. bark extracts contain several virucidal agents that are likely to act synergistically and directly on the viruses.

Affinity of Tannins to Cellulose: A Chromatographic Tool for Revealing Structure-Activity Patterns

Food, feed and beverage processing brings tannins into contact with macromolecules, such as proteins and polysaccharides, leading to different chemical and physical interactions. The interactions of tannins with proteins are well known but less is known about the affinity of tannins to polysaccharides. We used bacterial cellulose from nata de coco as a model compound to investigate how tannins and cellulose interact by adsorption measurements using UPLC-DAD. We also explored how the structure of tannins influences these interactions. The model tannins included nine individual structurally different hydrolysable tannins (HTs) and eight well-defined proanthocyanidin (PA) fractions with different monomeric units, mean degree of polymerization and both A- and B-type linkages. Tannins were found to have both strong and weak interactions with bacterial cellulose, depending on the exact structure of the tannin. For HTs, the main structural features affecting the interactions were the structural flexibility of the HT molecule and the number of free galloyl groups. For PAs, prodelphinidins were found to have a higher affinity to cellulose than procyanidins. Similarly to HTs, the presence of free galloyl groups in galloylated PAs and the flexibility of the PA molecule led to a stronger interaction. Adsorption measurements by UPLC-DAD proved to be a sensitive and rapid tool to evaluate the affinity of tannins to cellulose.

Dragon's Blood Sap Microencapsulation within Whey Protein Concentrate and Zein Using Electrospraying Assisted by Pressurized Gas Technology

Dragon's blood sap (DBS) obtained from the bark of Croton lechleri (Müll, Arg.) is a complex herbal remedy of pharmacological interest due to its high content in polyphenols, specifically proanthocyanidins. In this paper, electrospraying assisted by pressurized gas (EAPG) was first compared with freeze-drying to dry natural DBS. Secondly, EAPG was used for the first time to entrap natural DBS at room temperature into two different encapsulation matrices, i.e., whey protein concentrate (WPC) and zein (ZN), using different ratios of encapsulant material: bioactive compound, for instance 2:1 w/w and 1:1 w/w. The obtained particles were characterized in terms of morphology, total soluble polyphenolic content (TSP), antioxidant activity, and photo-oxidation stability during the 40 days of the experiment. Regarding the drying process, EAPG produced spherical particles with sizes of 11.38 ± 4.34 µm, whereas freeze-drying produced irregular particles with a broad particle size distribution. However, no significant differences were detected between DBS dried by EAPG or freeze-drying in TSP, antioxidant activity, and photo-oxidation stability, confirming that EAPG is a mild drying process suitable to dry sensitive bioactive compounds. Regarding the encapsulation process, the DBS encapsulated within the WPC produced smooth spherical microparticles, with average sizes of 11.28 ± 4.28 µm and 12.77 ± 4.54 µm for ratios 1:1 w/w and 2:1 w/w, respectively. The DBS was also encapsulated into ZN producing rough spherical microparticles, with average sizes of 6.37 ± 1.67 µm and 7.58 ± 2.54 µm for ratios 1:1 w/w and 2:1 w/w, respectively. The TSP was not affected during the encapsulation process. However, a slight reduction in antioxidant activity measured by DPPH was observed during encapsulation. An accelerated photo-oxidation test under ultraviolet light confirmed that the encapsulated DBS showed an increased oxidative stability in comparison with the non-encapsulated DBS, with the stability being enhanced for the ratio of 2:1 w/w. Among the encapsulating materials and according to the ATR-FTIR results, ZN showed increased protection against UV light. The obtained results demonstrate the potential of EAPG technology in the drying or encapsulation of sensitive natural bioactive compounds in a continuous process available at an industrial scale, which could be an alternative to freeze-drying.

Alkaline oxidization can increase the in vitro antiparasitic activity of proanthocyanidin-rich plant extracts against Ascarissuum

Proanthocyanidins (PAs) are a class of plant specialized metabolites with well-documented bioactivities such as antiparasitic effects. However, little is known about how the modification of PAs influences their bioactivity. The objective of this study was to investigate a wide range of PA-containing plant samples to determine if extracts containing PAs modified by oxidation had altered antiparasitic activities, compared to the original extracts that had not been modified in alkaline conditions. We extracted and analyzed samples from 61 proanthocyanidin-rich plants. The extracts were then oxidized under alkaline conditions. We used these non-oxidized and oxidized proanthocyanidin-rich extracts to conduct a detailed analysis of direct antiparasitic effects against the intestinal parasite Ascaris suum in vitro. These tests showed that the proanthocyanidin-rich extracts had antiparasitic activity. Modification of these extracts significantly increased the antiparasitic activity for the majority the extracts, suggesting that the oxidation procedure enhanced the bioactivity of the samples. Some samples that showed no antiparasitic activity before oxidation showed very high activity after the oxidation. High levels of other polyphenols in the extracts, such as flavonoids, was found to be associated with increased antiparasitic activity following oxidation. Thus, our in vitro screening opens up the opportunity for future research to better understand the mechanism of action how alkaline treatment of PA-rich plant extracts increases their biological activity and potential as novel anthelmintics.

Inspired by nature: Fiber networks functionalized with tannic acid and condensed tannin-rich extracts of Norway spruce bark show antimicrobial efficacy

This study demonstrated the antibacterial and antiviral potential of condensed tannins and tannic acid when incorporated into fiber networks tested for functional material purposes. Condensed tannins were extracted from industrial bark of Norway spruce by using pressurized hot water extraction (PHWE), followed by purification of extracts by using XADHP7 treatment to obtain sugar-free extract. The chemical composition of the extracts was analyzed by using HPLC, GC‒MS and UHPLC after thiolytic degradation. The test matrices, i.e., lignocellulosic handsheets, were produced and impregnated with tannin-rich extracts, and tannic acid was used as a commercial reference. The antibacterial and antiviral efficacy of the handsheets were analyzed by using bioluminescent bacterial strains (Staphylococcus aureus RN4220+pAT19 and Escherichia coli K12+pCGLS11) and Enterovirus coxsackievirus B3. Potential bonding of the tannin-rich extract and tannic acid within the fiber matrices was studied by using FTIR-ATR spectroscopy. The deposition characteristics (distribution and accumulation patterns) of tannin compounds and extracts within fiber networks were measured and visualized by direct chemical mapping using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and digital microscopy. Our results demonstrated for the first time, how tannin-rich extracts obtained from spruce bark side streams with green chemistry possess antiviral and antibacterial properties when immobilized into fiber matrices to create substitutes for plastic hygienic products, personal protection materials such as surgical face masks, or food packaging materials to prolong the shelf life of foodstuffs and prevent the spread of infections. However, more research is needed to further develop this proof-of-concept to ensure stable chemical bonding in product prototypes with specific chemistry.

Tackling the Future Pandemics: Broad-Spectrum Antiviral Agents (BSAAs) Based on A-Type Proanthocyanidins

A-type proanthocyanidins (PAC-As) are plant-derived natural polyphenols that occur as oligomers or polymers of flavan-3-ol monomers, such as (+)-catechin and (-)-epicatechin, connected through an unusual double A linkage. PAC-As are present in leaves, seeds, flowers, bark, and fruits of many plants, and are thought to exert protective natural roles against microbial pathogens, insects, and herbivores. Consequently, when tested in isolation, PAC-As have shown several biological effects, through antioxidant, antibacterial, immunomodulatory, and antiviral activities. PAC-As have been observed in fact to inhibit replication of many different human viruses, and both enveloped and non-enveloped DNA and RNA viruses proved sensible to their inhibitory effect. Mechanistic studies revealed that PAC-As cause reduction of infectivity of viral particles they come in contact with, as a result of their propensity to interact with virion surface capsid proteins or envelope glycoproteins essential for viral attachment and entry. As viral infections and new virus outbreaks are a major public health concern, development of effective Broad-Spectrum Antiviral Agents (BSAAs) that can be rapidly deployable even against future emerging viruses is an urgent priority. This review summarizes the antiviral activities and mechanism of action of PAC-As, and their potential to be deployed as BSAAs against present and future viral infections.

Chemical characterisation by UPLC-Q-ToF-MS/MS and antibacterial potential of Coffea arabica L. leaves: A coffee by-product

INTRODUCTION

Coffea arabica L. leaves are considered a by-product of the coffee industry however they are sources of several bioactive compounds.

OBJECTIVES

This study aimed to evaluate the chemical composition and the in vitro antibacterial activity of the lyophilised ethanol extract of arabica coffee leaves (EE-CaL).

MATERIAL AND METHODS

The chemical characterisation of EE-CaL was performed using ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-ToF-MS/MS). The in vitro antibacterial effect of EE-CaL was evaluated using the broth microdilution method and the adapted drop plate agar method to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC), respectively.

RESULTS

The chemical analysis of EE-CaL revealed the presence of compounds from the alkaloid class, such as trigonelline and caffeine, in addition to the phenolic compounds such as quinic acid, 5-caffeoylquinic acid, caffeic acid-O-hexoside, mangiferin, (epi)catechin, (epi)catechin monoglucoside and procyanidin trimer. Regarding the antibacterial potential, EE-CaL was active against Gram-positive and Gram-negative bacteria, being more effective against Escherichia coli (ATCC 25922) (MIC = 2500 μg/mL and bactericidal effect).

CONCLUSION

The results of this research suggest that coffee leaves, a by-product, possess compounds with antibacterial properties. Thus, further studies with coffee leaf extracts must be carried out to relate the compounds present in the extract with the antibacterial activity and find the mechanisms of action of this extract against bacteria.

Identification of Oxindoleacetic Acid Conjugates in Quinoa (Chenopodium quinoa Willd.) Seeds by High-Resolution UHPLC-MS/MS

Quinoa (Chenopodium quinoa Willd.) has a high nutritional value and it contains a high number and high amounts of specialized metabolites. These metabolites include, for example, phenolic acids, flavonoids, terpenoids and steroids. In addition, it is known to contain N-containing metabolites, such as betalains. Here, we report the presence and identification of 14 new oxindoleacetate conjugates in quinoa by high-resolution ultrahigh-performance liquid chromatography quadrupole-time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS) and ultrahigh-resolution UHPLC-QOrbitrap-MS/MS. The oxindoleacetate conjugates were extracted from dried and ground quinoa seeds using either methanol/water or acetone/water (4:1, v/v) and were further concentrated into aqueous phase and analyzed by UHPLC with reverse-phase chromatography using acetonitrile and 0.1% aqueous formic acid as eluents. High-resolution hybrid LC-MS/MS techniques, including full scan MS with in-source collision, induced dissociation, and data dependent-MS2(TopN) with stepped normalized collision energies using N2 as collision gas and data-independent acquisition (MSE) using ramped collision energies and argon as collision gas enabled their analysis directly from the crude quinoa seed extract. The oxindoleacetate conjugates were found to be present in both conventional and organic farmed seeds. According to our best knowledge, this is the first time hydroxy-oxindoles have been reported in quinoa.

Geographical origin of guarana seeds from untargeted UHPLC-MS and chemometrics analysis

Guarana is one of the most popular functional foods in the Amazon and widely used in the world. This work aimed to study the chemical composition of guarana produced by the main producing states and try to associate their geographical origin. We report an untargeted metabolomic analytical method performed by UHPLC-ESI-IT-MS and multivariate analysis (chemometrics) of guarana seeds, which was able to separate the samples according to their geographical origin. Previously, full chromatogram range was analyzed, and it could be observed that the two main compounds, catechin and epicatechin, have introduced large data variance in PCA analysis not related to the geographical origin of samples. After exclusion of the corresponding peaks, it was possible to obtain three main clusters corresponding to samples from Amazonas, Bahia and Mato Grosso. Thirteen dimers and trimers of procyanidins type A and B were identified by PCA and UHPLC-ESI-Q-TOF-MS/MS, as chemical markers of geographic origin.