Structural characterization of red wine rhamnogalacturonan II

Influence of Grape Flesh on the Retention and Composition of Polyphenols from Skins and Seeds

This study examined the impact of grape flesh polysaccharide, protein, and amino acid contents on polyphenol retention from skins and seeds in Pinot noir (Vitis vinifera) and cold-hardy interspecific cultivars Marquette and Frontenac (Vitis spp.). After isolating grape tissues (skin, seed, and flesh), they were soaked either individually or combined with other tissues in a wine-like solution for up to 7 days. Findings revealed that flesh significantly reduces the concentration of condensed tannin, and mono- and diglucoside forms of anthocyanins in the supernatants, due to its rich content in polysaccharides and proteins. Frontenac skin and flesh tissues were the main sources of soluble proteins, amino acids, and soluble polysaccharides. Surprisingly, Marquette exhibited a higher retention of skin tannin than Pinot noir, likely due to its smaller tannin molecular mass, and a potential competitive effect with anthocyanins for the binding sites of flesh.

Bifidobacterial GH146 β-L-arabinofuranosidase for the removal of β1,3-L-arabinofuranosides on plant glycans

L-Arabinofuranosides with β-linkages are present in several plant molecules, such as arabinogalactan proteins (AGPs), extensin, arabinan, and rhamnogalacturonan-II. We previously characterized a β-L-arabinofuranosidase from Bifidobacterium longum subsp. longum JCM 1217, Bll1HypBA1, which was found to belong to the glycoside hydrolase (GH) family 127. This strain encodes two GH127 genes and two GH146 genes. In the present study, we characterized a GH146 β-L-arabinofuranosidase, Bll3HypBA1 (BLLJ_1848), which was found to constitute a gene cluster with AGP-degrading enzymes. This recombinant enzyme degraded AGPs and arabinan, which contain Araf-β1,3-Araf structures. In addition, the recombinant enzyme hydrolyzed oligosaccharides containing Araf-β1,3-Araf structures but not those containing Araf-β1,2-Araf and Araf-β1,5-Araf structures. The crystal structures of Bll3HypBA1 were determined at resolutions up to 1.7 Å. The monomeric structure of Bll3HypBA1 comprised a catalytic (α/α)6 barrel and two β-sandwich domains. A hairpin structure with two β-strands was observed in Bll3HypBA1, to extend from a β-sandwich domain and partially cover the active site. The active site contains a Zn2+ ion coordinated by Cys3-Glu and exhibits structural conservation of the GH127 cysteine glycosidase Bll1HypBA1. This is the first study to report on a β1,3-specific β-L-arabinofuranosidase. KEY POINTS: • β1,3-l-Arabinofuranose residues are present in arabinogalactan proteins and arabinans as a terminal sugar. • β-l-Arabinofuranosidases are widely present in intestinal bacteria. • Bll3HypBA1 is the first enzyme characterized as a β1,3-linkage-specific β-l-arabinofuranosidase.

Pectic polysaccharides from Lilium brownii and Polygonatum odoratum exhibit significant antioxidant effects in vitro

Two pectic polysaccharides (WLBP-A3-c and WPOP-A-c) were isolated from traditional Chinese medicines Lilium brownii and Polygonatum odoratum, respectively. Monosaccharide composition, FT-IR, NMR and enzymatic analyses indicated that both WLBP-A3-c (59 kDa) and WPOP-A-c (33 kDa) contained homogalacturonan (HG), rhamnogalacturonan I (RG-I), and rhamnogalacturonan II (RG-II) domains, with mass ratios of 76.0: 17.2:6.8 and 76.8:10.6:12.6, respectively. Two RG-I domains WLBP-A3-c-DE1 and WPOP-A-c-DE1, correspondingly obtained from WLBP-A3-c and WPOP-A-c by enzymatic hydrolysis, were composed of repeating units of [→2)-α-L-Rhap-(1 → 4)-α-D-GalpA-(1→] with highly branched neutral sugar side chains at the O-4 position of Rhap, which contained arabinan, galactan, arabinogalactan I and II (AG-I and AG-II) side chains in different proportions. By comparison, WPOP-A-c exhibited higher scavenging effects against DPPH, ABTS and hydroxy radicals than WLBP-A3-c, probably because WPOP-A-c had higher contents of GalA residues and HG domains and lower molecular weight. Among three domains of WPOP-A-c, HG domain possessed the strongest activity in decreasing ROS production and promoting SOD activity, resulting in the effective protection of HepG2 cells against H2O2-induced oxidative stress. Our study provides evidence that pectins rich in HG domains from Lilium brownii and Polygonatum odoratum exhibit significant antioxidant effects, which hold potential for the application in the field of healthcare products.

Effect of Pre-fermentative Treatments on Polysaccharide Composition of White and Rosé Musts and Wines

This paper studied the effect of conventional pre-fermentative techniques (direct pressing "CP" and cold maceration "CM") and an innovate technique (high power ultrasounds "S"), applied to Viogner and Monastrell grapes on the polysaccharide content of the musts, white and rosé wines, and after six months of bottle aging. The results showed that the longer pre-fermentation maceration time applied with the CM technique compared to the short ultrasonic maceration was key in the extraction of polysaccharides from the grape to the must. CP treatment produced wines with the lowest content of total soluble polysaccharide families since it was the least intense pretreatment for the disruption of the grape berry cell wall polysaccharides. Ultrasonic pretreatment could be used as a new tool to increase the solubilization of polysaccharides in wines, positively affecting the wine colloidal properties. During bottle aging, there wasn't a clear effect of pretreatments on the evolution of polysaccharides.

Composition, ζ Potential, and Molar Mass Distribution of 20 Must and Wine Colloids from Five Different Cultivars Obtained during Four Consecutive Vintages

Colloids are responsible for undesirable haze formation in wine. Here, we characterized 20 colloid batches after isolation by ultrafiltration of musts and wines from five cultivars obtained from four consecutive vintages. Polysaccharide and protein concentrations of the colloids ranged from 0.10 to 0.65 and 0.03 to 0.40 mg/L, respectively. Protein profiling in must and wine colloids by fast protein liquid chromatography (FPLC) and liquid chromatography-high-resolution tandem mass spectrometry (LC-HR-MS/MS) analyses indicated a lower number of proteins in wine than in must colloids. Molar mass distribution analyses revealed all colloids to consist of two carbohydrate- (424-33,390 and 48-462 kg/mol) and one protein-rich (14-121 kg/mol) fractions. The observed barely negative ζ potentials (-3.1 to -1.1 mV) in unstable wines unraveled that colloid instability might be partly related to their poor electrostatic repulsion in the wine matrix. ζ potentials of the colloids from pH 1 to 10 are also presented. Our data support future developments to eliminate haze-forming colloids from wine.

Ultrasound and microwave techniques for assisting ageing on lees of red wines

Ageing on lees is a slow process that carries microbiological and economic risks in the wineries. This study evaluates the possibility of enhancing the extraction of different compounds from the lees, using combined strategies, such as ultrasound (US) or microwaves (MW) and the addition of inactive dry yeasts (IDY), to reduce the lees ageing time. The complete chemical analysis of the wine was done, amino acids, polysaccharides, colour and volatile compounds, together with the sensory analysis. The combined treatments increased the release of total polysaccharides, mannoproteins and total monosaccharides in the wines, and some amino acids like proline. However, wines treated with US and MW, with and without lees, showed a decrease in tannins and colour intensity, and in some volatile compounds like fatty acid esters, acetates and terpenes. The wines treated with IDY and MW were the best valued for their floral and red berry flavours and less astringency.

A critical review of RG-I pectin: sources, extraction methods, structure, and applications

In recent years, RG-I pectin isolated by low-temperature alkaline extraction methods has attracted the attention of a large number of researchers due to its huge health benefits. However, studies on other applications of RG-I pectin are still lacking. In this study, we summarized the sources (e.g. potato pulp, sugar beet pulp, okra, apple pomace, citrus peel, pumpkin, grapefruit, ginseng, etc.), extraction methods, fine structure and applications of RG-I pectin in physiological activities (e.g. anti-cancer, anti-inflammatory, anti-obesity, anti-oxidation, immune regulation, prebiotics, etc.), emulsions, gels, etc. These neutral sugar side chains not only endow RG-I pectin with various physiological activities but the entanglement and cross-linking of these side chains also endow RG-I pectin with excellent emulsifying and gelling properties. We believe that this review can not only provide a comprehensive reading for new workers interested in RG-I pectin, but also provide a valuable reference for future research directions of RG-I pectin.

Making and breaking of boron bridges in the pectic domain rhamnogalacturonan-II at apoplastic pH in vivo and in vitro

Cross-linking of the cell-wall pectin domain rhamnogalacturonan-II (RG-II) via boron bridges between apiose residues is essential for normal plant growth and development, but little is known about its mechanism or reversibility. We characterized the making and breaking of boron bridges in vivo and in vitro at 'apoplastic' pH. RG-II (13-26 μm) was incubated in living Rosa cell cultures and cell-free media with and without 1.2 mm H3 BO3 and cationic chaperones (Ca2+ , Pb2+ , polyhistidine, or arabinogalactan-protein oligopeptides). The cross-linking status of RG-II was monitored electrophoretically. Dimeric RG-II was stable at pH 2.0-7.0 in vivo and in vitro. In-vitro dimerization required a 'catalytic' cation at all pHs tested (1.75-7.0); thus, merely neutralizing the negative charge of RG-II (at pH 1.75) does not enable boron bridging. Pb2+ (20-2500 μm) was highly effective at pH 1.75-4.0, but not 4.75-7.0. Cationic peptides were effective at approximately 1-30 μm; higher concentrations caused less dimerization, probably because two RG-IIs then rarely bonded to the same peptide molecule. Peptides were ineffective at pH 1.75, their pH optimum being 2.5-4.75. d-Apiose (>40 mm) blocked RG-II dimerization in vitro, but did not cleave existing boron bridges. Rosa cells did not take up d-[U-14 C]apiose; therefore, exogenous apiose would block only apoplastic RG-II dimerization in vivo. In conclusion, apoplastic pH neither broke boron bridges nor prevented their formation. Thus boron-starved cells cannot salvage boron from RG-II, and 'acid growth' is not achieved by pH-dependent monomerization of RG-II. Divalent metals and cationic peptides catalyse RG-II dimerization via co-ordinate and ionic bonding respectively (possible and impossible, respectively, at pH 1.75). Exogenous apiose may be useful to distinguish intra- and extra-protoplasmic dimerization.

Grape-derived pectic polysaccharides alter the tannin and pigment composition of Cabernet Sauvignon red wines

Tannins, anthocyanins, and polymeric pigments are essential phenolic constituents of red wine because they provide color, color stability, and mouthfeel properties like astringency. The behavior of these compounds is significantly affected by pectic polysaccharides, whereby the extent of their influence on red wine quality depends on their structural features and their interactions with the polyphenols. In the present study, the composition of the pectic polysaccharides of commercially available Cabernet Sauvignon wines and their impact on anthocyanin, tannin, and polymeric pigment analyses was characterized. This was accomplished by preparation of polysaccharide deprived wines and comparison of the polyphenolic composition of both, the wines and their corresponding polysaccharide-free counterparts. The results show that the cell wall fragments enhance the spectral absorbance of anthocyanins by facilitating anthocyanin self-association, leading to a co-pigmentation-like effect. Low molecular weight pectins like rhamnogalacturonan II and polygalacturonic acids with a low degree of esterification are assumed to form soluble complexes with anthocyanins and also prevent protein precipitation of tannins, which was reduced by 6-13%. High molecular weight pectins with a high degree of esterification lead to the increased precipitability of pigments and tannins by a factor of 1.3 to 32.4 and 1.1 to 1.9, respectively, seemingly impairing the incorporation of anthocyanins in tannins to form precipitable polymeric pigments that are responsible for the longevity of red wine color. The increased precipitability of the pigments due to the interactions with the polysaccharides may indicate the formation of pigmented yet non-covalent aggregates that show comparable properties to the covalently formed precipitable pigments. The formation of those non-covalent structures may affect red wine color stability and astringency.

Biochemical Characterization of a Pectate Lyase AnPL9 from Aspergillus nidulans

Pectinolytic enzymes have diverse industrial applications. Among these, pectate lyases act on the internal α-1,4-linkage of the pectate backbone, playing a critical role in pectin degradation. While most pectate lyases characterized thus far are of bacterial origin, fungi can also be excellent sources of pectinolytic enzymes. In this study, we performed biochemical characterization of the pectate lyase AnPL9 belonging to the polysaccharide lyase family 9 (PL9) from the filamentous fungus Aspergillus nidulans. Recombinant AnPL9 was produced using a Pichia pastoris expression system and purified. AnPL9 exhibited high activity on homogalacturonan (HG), pectin from citrus peel, pectin from apple, and the HG region in rhamnogalacturonan-I. Although digalacturonic acid and trigalacturonic acid were not degraded by AnPL9, tetragalacturonic acid was converted to 4,5-unsaturated digalacturonic acid and digalacturonic acid. These results indicate that AnPL9 degrades HG oligosaccharides with a degree of polymerization > 4. Furthermore, AnPL9 was stable within a neutral-to-alkaline pH range (pH 6.0-11.0). Our findings suggest that AnPL9 is a candidate pectate lyase for biotechnological applications in the food, paper, and textile industries. This is the first report on a fungal pectate lyase belonging to the PL9 family.

Structure and function of non-digestible carbohydrates in the gut microbiome

Together with proteins and fats, carbohydrates are one of the macronutrients in the human diet. Digestible carbohydrates, such as starch, starch-based products, sucrose, lactose, glucose and some sugar alcohols and unusual (and fairly rare) α-linked glucans, directly provide us with energy while other carbohydrates including high molecular weight polysaccharides, mainly from plant cell walls, provide us with dietary fibre. Carbohydrates which are efficiently digested in the small intestine are not available in appreciable quantities to act as substrates for gut bacteria. Some oligo- and polysaccharides, many of which are also dietary fibres, are resistant to digestion in the small intestines and enter the colon where they provide substrates for the complex bacterial ecosystem that resides there. This review will focus on these non-digestible carbohydrates (NDC) and examine their impact on the gut microbiota and their physiological impact. Of particular focus will be the potential of non-digestible carbohydrates to act as prebiotics, but the review will also evaluate direct effects of NDC on human cells and systems.

Plant-microbe interactions in the apoplast: Communication at the plant cell wall

The apoplast is a continuous plant compartment that connects cells between tissues and organs and is one of the first sites of interaction between plants and microbes. The plant cell wall occupies most of the apoplast and is composed of polysaccharides and associated proteins and ions. This dynamic part of the cell constitutes an essential physical barrier and a source of nutrients for the microbe. At the same time, the plant cell wall serves important functions in the interkingdom detection, recognition, and response to other organisms. Thus, both plant and microbe modify the plant cell wall and its environment in versatile ways to benefit from the interaction. We discuss here crucial processes occurring at the plant cell wall during the contact and communication between microbe and plant. Finally, we argue that these local and dynamic changes need to be considered to fully understand plant-microbe interactions.

Application of Elicitors at Two Maturation Stages of Vitis vinifera L. cv Monastrell: Changes in Skin Cell Walls

The aim of this study was to evaluate whether the application of two pre-harvest elicitors—methyl-jasmonate (MeJ) and benzothiadiazole (BTH)—to Monastrell grapes, at two maturation stages, affected the composition and structure of the skin cell walls (SCWs) to differing extents. This study was conducted in 2016–2017 on Vitis vinifera L. cv Monastrell. A water suspension of MeJ and BTH, and a mixture of both, was applied at veraison and mid-ripening. The composition of the berry SCW was analyzed. Environmental conditions caused substantial changes in SCW composition, especially at high temperatures. Indeed, a reduction of approximately 50% in the biosynthesis of hemicellulose, proteins and total phenols was observed, accompanied by a slight increase in cellulose and lignin. However, the application of the treatments also caused changes in some SCW constituents: increases in the concentration of phenols, proteins and lignin were observed, especially when the MeJ and MeJ + BTH treatments were applied at veraison. Likewise, a reduction in uronic acids was observed in the MeJ + BTH treatment applied at veraison. These changes in the SCWs could affect their structural characteristics, and therefore influence grape handling in the field and in the winery. Further studies are needed to determine the extent to which MeJ and BTH treatments affect other skin characteristics.

Grape polysaccharides: compositional changes in grapes and wines, possible effects on wine organoleptic properties, and practical control during winemaking

Polysaccharides present in grapes interact with wine sensory-active compounds (polyphenols and volatile compounds) via different mechanisms and can affect wine organoleptic qualities such as astringency, color and aroma. Studies on the role that grape polysaccharides play in wines are reviewed in this paper. First, the composition of grape polysaccharides and their changes during grape ripening, winemaking and aging are introduced. Second, different interaction mechanisms of grape polysaccharides and wine sensory-active compounds (flavanols, anthocyanins and volatiles) are introduced, and the possible effects on wine astringency, color and aroma caused by these interactions are illustrated. Finally, the control of the grape polysaccharide content in practice is discussed, including classical winemaking methods (applying different maceration enzymes, temperature control, co-fermentation, blending), modern vinification technologies (pulsed electric field, ultrasound treatment), and the development of new grape polysaccharide products.

Effect of Sonication Treatment and Maceration Time in the Extraction of Polysaccharide Compounds during Red Wine Vinification

The application of high-power ultrasounds (US) at 28 kHz to the crushed grapes and the use of different pomace contact times caused changes in the content and composition of monosaccharides and polysaccharides in the musts and wines. These differences were maintained from the moment of pressing (end of maceration) until the end of the alcoholic fermentation. The US increased the content of monosaccharides and polysaccharides in the musts by facilitating their extraction from the solid parts during maceration. The application of medium maceration time (3 days) to sonicated grapes led to an extraction of polysaccharides rich in arabinose and galactose, rhamnogalacturonan type II (RG-II) and mannoproteins (MP), similar to that observed in the control wines made with an extended maceration of 7 days (968.21 vs. 1029.45; 895.04 vs. 1700.50; 356.81 vs. 343.95, respectively). This fact was attributed to a higher extraction in the must during the sonication process and to an important release of pectic polysaccharides during the pressing of the sonicated pomace, which is reported here for the first time. Therefore, the US technology could be useful for increasing the polysaccharide content in the wines or for reducing the maceration time needed to achieve certain levels of wine polysaccharides.

Protocols for isolating and characterizing polysaccharides from plant cell walls: a case study using rhamnogalacturonan-II

BACKGROUND

In plants, a large diversity of polysaccharides comprise the cell wall. Each major type of plant cell wall polysaccharide, including cellulose, hemicellulose, and pectin, has distinct structures and functions that contribute to wall mechanics and influence plant morphogenesis. In recent years, pectin valorization has attracted much attention due to its expanding roles in biomass deconstruction, food and material science, and environmental remediation. However, pectin utilization has been limited by our incomplete knowledge of its structure. Herein, we present a workflow of principles relevant for the characterization of polysaccharide primary structure using nature's most complex polysaccharide, rhamnogalacturonan-II (RG-II), as a model.

RESULTS

We outline how to isolate RG-II from celery and duckweed cell walls and from red wine using chemical or enzymatic treatments coupled with size-exclusion chromatography. From there, we applied mass spectrometry (MS)-based techniques to determine the glycosyl residue and linkage compositions of the intact RG-II and derived oligosaccharides including special considerations for labile monosaccharides. In doing so, we demonstrated that in the duckweed Wolffiella repanda the arabinopyranosyl (Arap) residue of side chain B is substituted at O-2 with rhamnose. We used electrospray-MS techniques to identify non-glycosyl modifications including methyl-ethers, methyl-esters, and acetyl-esters on RG-II-derived oligosaccharides. We then showed the utility of proton nuclear magnetic resonance spectroscopy (¹H-NMR) to investigate the structure of intact RG-II and to complement the RG-II dimerization studies performed using size-exclusion chromatography.

CONCLUSIONS

The complexity of pectic polysaccharide structures has hampered efforts aimed at their valorization. In this work, we used RG-II as a model to demonstrate the steps necessary to isolate and characterize polysaccharides using chromatographic, MS, and NMR techniques. The principles can be applied to the characterization of other saccharide structures and will help inform researchers on how saccharide structure relates to functional properties in the future.

Ultrasound treatment of crushed grapes: Effect on the must and red wine polysaccharide composition

This paper studied the effect on the molecular weight and polysaccharide composition of musts and wines of the application of high-power ultrasound (US) at 20 and 28 kHz on crushed grapes. Two different pomace maceration times (short and mid) were tested for sonicated and control vinifications. A long pomace maceration time was also tested for non-treated wines. In must samples, US significantly increased the content of monosaccharides and polysaccharides rich in arabinose and galactose (PRAG), and the average molecular weight of smaller PRAG, mannoproteins (MP) or mannans. The 28 kHz had a major effect on most wine monosaccharides and grape polysaccharides. The wine obtained from sonicated grapes at 28 kHz and with mid maceration had higher rhamnogalacturonans type II and PRAG content than its control, and closer polysaccharide and monosaccharide content to long maceration control wines. No significant differences were obtained in the MP content between sonicated and control wines.

Pectic polysaccharides from Radix Sophorae Tonkinensis exhibit significant antioxidant effects

Two pectic polysaccharides (WRSP-A2b and WRSP-A3a) have been obtained from Radix Sophorae Tonkinensis and comparatively investigated in terms of their physical properties and antioxidant activities. Monosaccharide composition, FT-IR, NMR and enzymatic analyses indicate that both WRSP-A2b (13.6 kDa) and WRSP-A3a (44.6 kDa) consist of homogalacturonan (HG), rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II) domains, with mass ratios of 0.9:1.8:1 and 2.3:2.9:1, respectively. The RG-I domains were further purified and characterized. Results show that WRSP-A2b contains a highly branched RG-I domain, primarily substituted with α-(1→5)-linked arabinans, whereas WRSP-A3a contains a small branched RG-I domain mainly composed of β-(1→4)-linked galactan side chains. WRSP-A3a exhibits stronger antioxidant activity in scavenging different radicals than WRSP-A2b, a finding that may be due to its higher content of GalA residues and HG domains. Our results provide useful information for screening natural polysaccharide-based antioxidants from Radix Sophorae Tonkinensis.

Post-Synthetic Reduction of Pectin Methylesterification Causes Morphological Abnormalities and Alterations to Stress Response in Arabidopsis thaliana

Pectin is a critical component of the plant cell wall, supporting wall biomechanics and contributing to cell wall signaling in response to stress. The plant cell carefully regulates pectin methylesterification with endogenous pectin methylesterases (PMEs) and their inhibitors (PMEIs) to promote growth and protect against pathogens. We expressed Aspergillus nidulans pectin methylesterase (AnPME) in Arabidopsis thaliana plants to determine the impacts of methylesterification status on pectin function. Plants expressing AnPME had a roughly 50% reduction in methylester content compared with control plants. AnPME plants displayed a severe dwarf phenotype, including small, bushy rosettes and shorter roots. This phenotype was caused by a reduction in cell elongation. Cell wall composition was altered in AnPME plants, with significantly more arabinose and significantly less galacturonic acid, suggesting that plants actively monitor and compensate for altered pectin content. Cell walls of AnPME plants were more readily degraded by polygalacturonase (PG) alone but were less susceptible to treatment with a mixture of PG and PME. AnPME plants were insensitive to osmotic stress, and their susceptibility to Botrytis cinerea was comparable to wild type plants despite their compromised cell walls. This is likely due to upregulated expression of defense response genes observed in AnPME plants. These results demonstrate the importance of pectin in both normal growth and development, and in response to biotic and abiotic stresses.

Tannins in Food: Insights into the Molecular Perception of Astringency and Bitter Taste

Astringency and bitterness are organoleptic properties widely linked to tannin compounds. Due to their significance to food chemistry, the food industry, and to human nutrition and health, these tannins' taste properties have been a line of worldwide research. In recent years, significant advances have been made in understanding the molecular perception of astringency pointing to the contribution of different oral key players. Regarding bitterness, several polyphenols have been identified has new agonists of these receptors. This review summarizes the last data about the knowledge of these taste properties perceived by tannins. Ultimately, tannins' astringency and bitterness are hand-in-hand taste properties, and future studies should be adapted to understand how the proper perception of one taste could affect the perception of the other one.

Locating Methyl-Etherified and Methyl-Esterified Uronic Acids in the Plant Cell Wall Pectic Polysaccharide Rhamnogalacturonan II

Rhamnogalacturonan II (RG-II) is a structurally complex pectic polysaccharide that exists as a borate ester cross-linked dimer in the cell walls of all vascular plants. The glycosyl sequence of RG-II is largely conserved, but there is evidence that galacturonic acid (GalA) methyl etherification and glucuronic acid (GlcA) methyl esterification vary in the A sidechain across plant species. Methyl esterification of the galacturonan backbone has also been reported but not confirmed. Here we describe a new procedure, utilizing aq. sodium borodeuteride (NaBD₄)-reduced RG-II, to identify the methyl esterification status of backbone GalAs. Our data suggest that up to two different GalAs are esterified in the RG-II backbone. We also adapted a procedure based on methanolysis and NaBD₄ reduction to identify 3-, 4-, and 3,4-O-methyl GalA in RG-II. These data, together with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF) MS analysis of sidechain A generated from selected RG-IIs and their NaBD₄-reduced counterparts, suggest that methyl etherification of the β-linked GalA and methyl esterification of the GlcA are widespread. Nevertheless, the extent of these modifications varies between plant species. Our analysis of the sidechain B glycoforms in RG-II from different dicots and nonpoalean monocots suggests that this sidechain has a minimum structure of an O-acetylated hexasaccharide (Ara-[MeFuc]-Gal-AceA-Rha-Api-). To complement these studies, we provide further evidence showing that dimer formation and stability in vitro is cation and borate dependent. Taken together, our data further refine the primary sequence and sequence variation of RG-II and provide additional insight into dimer stability and factors controlling dimer self-assembly.

Inhibition Mechanisms of Wine Polysaccharides on Salivary Protein Precipitation

In this work, high-performance liquid chromatography, fluorescence quenching, nephelometry, and sodium dodecyl sulfate polyacrylamide gel electrophoresis were used to study the effect of polysaccharides naturally present in wine [rhamnogalacturonan II (RG II) and arabinogalactan proteins (AGPs)] on the interaction between salivary proteins (SP) together present in saliva and tannins (punicalagin (PNG) and procyanidin B2). In general, the RG II fraction was more efficient to inhibit SP precipitation by tannins, especially for acidic proline-rich proteins (aPRPs) and statherin/P-B peptide, than AGPs. The RG II fraction can act mainly by a competition mechanism in which polysaccharides compete by tannin binding. However, in the presence of Na⁺ ions in solution, no RG II effect was observed on SP-tannin interactions. On the other hand, dependent upon the saliva sample as well as the tannin studied, AGPs can act by both mechanisms, competition and ternary (formation of a ternary complex with SP-tannin aggregates enhancing their solubility).

Utilization of Complex Pectic Polysaccharides from New Zealand Plants (Tetragonia tetragonioides and Corynocarpus laevigatus) by Gut Bacteroides Species

Pectic polysaccharides from New Zealand (NZ) spinach (Tetragonia tetragonioides) and karaka berries (Corynocarpus laevigatus) were extracted and analyzed. NZ spinach polysaccharides comprised mostly homogalacturonan (64.4%) and rhamnogalacturonan I (5.8%), with side chains of arabinan (8.1%), galactan (2.2%), and type II arabinogalactan (7.1%); karaka berry polysaccharides comprised homogalacturonan (21.8%) and rhamnogalacturonan I (10.0%), with greater proportions of side chains (arabinan, 15.6%; galactan, 23.8%; and type II arabinogalactan, 19.3%). Screening of gut commensal Bacteroides showed that six were able to grow on the NZ spinach extract, while five were able to grow on the karaka berry extract. Analysis of the polysaccharides remaining after fermentation, by size-exclusion chromatography and constituent sugar analysis, showed that the Bacteroides species that grew on these two substrates showed preferences for the different pectic polysaccharide types. Our data suggest that, to completely degrade and utilize the complex pectin structures found in plants, members of Bacteroides and other bowel bacteria work as metabolic consortia.

Oral Wine Texture Perception and Its Correlation with Instrumental Texture Features of Wine-Saliva Mixtures

Unlike solid food, texture descriptors in liquid food are scarce, and they are frequently reduced to the term viscosity. However, in wines, apart from viscosity, terms, such as astringency, body, unctuosity and density, help describe their texture, relating the complexity and balance among their chemical components. Yet there is uncertainty about which wine components (and their combinations) cause each texture sensation and if their instrumental assessment is possible. Therefore, the aim of the present work was to study the effect of wine texture on its main components, when interacting with saliva. This was completed by using instrumental measurements of density and viscosity, and by using two types of panels (trained and expert). For that, six different model-wine formulations were prepared by adding one or multiple wine components: ethanol, mannoproteins, glycerol, and tannins to a de-alcoholised wine. All formulations were mixed with fresh human saliva (1:1), and their density and rheological properties were measured. Although there were no statistical differences, body perception was higher for samples with glycerol and/or mannoproteins, this was also correlated with density instrumental measurements (R = 0.971, p = 0.029). The viscosity of samples with tannins was the highest due to the formation of complexes between the model-wine and salivary proteins. This also provided astringency, therefore correlating viscosity and astringency feelings (R = 0.855, p = 0.030). No correlation was found between viscosity and body perception because of the overlapping of the phenolic components. Overall, the present results reveal saliva as a key factor when studying the wine texture through instrumental measurements (density and viscosity).

Single cell fluorescence imaging of glycan uptake by intestinal bacteria

Microbes in the intestines of mammals degrade dietary glycans for energy and growth. The pathways required for polysaccharide utilization are functionally diverse; moreover, they are unequally dispersed between bacterial genomes. Hence, assigning metabolic phenotypes to genotypes remains a challenge in microbiome research. Here we demonstrate that glycan uptake in gut bacteria can be visualized with fluorescent glycan conjugates (FGCs) using epifluorescence microscopy. Yeast α-mannan and rhamnogalacturonan-II, two structurally distinct glycans from the cell walls of yeast and plants, respectively, were fluorescently labeled and fed to Bacteroides thetaiotaomicron VPI-5482. Wild-type cells rapidly consumed the FGCs and became fluorescent; whereas, strains that had deleted pathways for glycan degradation and transport were non-fluorescent. Uptake of FGCs, therefore, is direct evidence of genetic function and provides a direct method to assess specific glycan metabolism in intestinal bacteria at the single cell level.

Biochemistry of complex glycan depolymerisation by the human gut microbiota

The human gut microbiota (HGM) makes an important contribution to health and disease. It is a complex microbial community of trillions of microbes with a majority of its members represented within two phyla, the Bacteroidetes and Firmicutes, although it also contains species of Actinobacteria and Proteobacteria. Reflecting its importance, the HGM is sometimes referred to as an 'organ' as it performs functions analogous to systemic tissues within the human host. The major nutrients available to the HGM are host and dietary complex carbohydrates. To utilise these nutrient sources, the HGM has developed elaborate, variable and sophisticated systems for the sensing, capture and utilisation of these glycans. Understanding nutrient acquisition by the HGM can thus provide mechanistic insights into the dynamics of this ecosystem, and how it impacts human health. Dietary nutrient sources include a wide variety of simple and complex plant and animal-derived glycans most of which are not degraded by enzymes in the digestive tract of the host. Here we review how various adaptive mechanisms that operate across the major phyla of the HGM contribute to glycan utilisation, focusing on the most complex carbohydrates presented to this ecosystem.

Preparing rhamnogalacturonan II domains from seven plant pectins using Penicillium oxalicum degradation and their structural comparison

Rhamnogalacturonan II (RG-II) is a complex pectin with diverse pharmaceutical activities. To assess how RG-II functions, the development of methods for its preparation is required. In this paper, pectin from Codonopsis pilosula was used to evaluate the ability of fungi and bacteria to degrade the pectin. We discovered that the fungus Penicillium oxalicum could efficiently lead to the recovery of RG-II domains by degrading the other pectic domains. Further, six pectin fractions from different medical plants were used as the sole carbon source for the growth of Penicillium oxalicum. The major polymeric products remaining after fungus degradation was RG-II domains. Depending of plant source, side chains A differed with respect to their proportion of L-Gal and L-Fuc and to their degree of methyletherification. Side chains B were made of 8-10 sugar residues and up to 2 acetyl groups. Overall, our method provides an effective way to prepare RG-II pectin domains for investigating their structure-function relationships.

Polysaccharides and Oligosaccharides Produced on Malvar Wines Elaborated with Torulaspora delbrueckii CLI 918 and Saccharomyces cerevisiae CLI 889 Native Yeasts from D.O. "Vinos de Madrid"

Polysaccharides and oligosaccharides released into Malvar white wines elaborated through pure, mixed, and sequential cultures with Torulaspora delbrueckii CLI 918 and Saccharomyces cerevisiae CLI 889 native yeasts from D.O. "Vinos de Madrid" were studied. Both fractions from different white wines were separated by high-resolution size-exclusion chromatography. Glycosyl composition and wine polysaccharide linkages were determined by GC-EI-MS chromatography. Molar-mass distributions were determined by SEC-MALLS, and intrinsic viscosity was determined by differential viscometer. Yeast species and type of inoculation have a significant impact on wine carbohydrate composition and structure. Mannose residues from mannoproteins were significantly predominant in those cultures where T. delbrueckii was present in the fermentation process in comparison with when pure cultures of S. cerevisiae were present in the fermenation process. Galactose residues from polysaccharides rich in arabinose and galactose presented greater values in pure cultures of S. cerevisiae, indicating that S. cerevisiae released fewer mannoproteins than T. delbrueckii. Moreover, we reported structural differences between mannoproteins released by T. delbrueckii CLI 918 and those released by S. cerevisiae CLI 889. These findings help to provide important information about the polysaccharides and oligosaccharides released from the cell walls of Malvar grapes and the carbohydrates released from each yeast species.

Complex pectin metabolism by gut bacteria reveals novel catalytic functions

The metabolism of carbohydrate polymers drives microbial diversity in the human gut microbiota. It is unclear, however, whether bacterial consortia or single organisms are required to depolymerize highly complex glycans. Here we show that the gut bacterium Bacteroides thetaiotaomicron uses the most structurally complex glycan known: the plant pectic polysaccharide rhamnogalacturonan-II, cleaving all but 1 of its 21 distinct glycosidic linkages. The deconstruction of rhamnogalacturonan-II side chains and backbone are coordinated to overcome steric constraints, and the degradation involves previously undiscovered enzyme families and catalytic activities. The degradation system informs revision of the current structural model of rhamnogalacturonan-II and highlights how individual gut bacteria orchestrate manifold enzymes to metabolize the most challenging glycan in the human diet.

Necroptosis mediates the antineoplastic effects of the soluble fraction of polysaccharide from red wine in Walker-256 tumor-bearing rats

Polysaccharides are substances that modify the biological response to several stressors. The present study investigated the antitumor activity of the soluble fraction of polysaccharides (SFP), extracted from cabernet franc red wine, in Walker-256 tumor-bearing rats. The monosaccharide composition had a complex mixture, suggesting the presence of arabinoglactans, mannans, and pectins. Treatment with SFP (30 and 60mg/kg, oral) for 14days significantly reduced the tumor weight and volume compared with controls. Treatment with 60mg/kg SFP reduced blood monocytes and neutrophils, reduced the tumor activity of N-acetylglucosaminidase, myeloperoxidase, and nitric oxide, increased blood lymphocytes, and increased the levels of tumor necrosis factor α (TNF-α) in tumor tissue. Treatment with SFP also induced the expression of the cell necroptosis-related genes Rip1 and Rip3. The antineoplastic effect of SFP appears to be attributable to its action on the immune system by controlling the tumor microenvironment and stimulating TNF-α production, which may trigger the necroptosis pathway.