Structure-antioxidant activity relationship of xylooligosaccharides obtained from carboxyl-reduced glucuronoarabinoxylans from bamboo shoots.

Xylooligosaccharides (XOs) have shown high potential as prebiotics with nutritional and health benefits. In this work, XOs were obtained from highly purified, carboxy-reduced glucuronoarabinoxylans by treatment with Driselase®. The mixtures were fractionated, and the structures were elucidated by methylation analysis and NMR spectroscopy. Antioxidant activity was determined by the methods of DPPH and ß-carotene/linoleic acid. It was found that the most active oligosaccharides (P3 and G3) comprised 4 or 5 xylose units, plus two arabinoses and one 4-O-methylglucose as side chains, their sequence of units was determined. The optimal concentration for their use as antioxidants was 2 mg/mL. The synthetic antioxidant butylated hydroxytoluene (BHT, 0.2 mg/mL) showed a percentage of inhibition 15% higher than P3. Although its concentration was ∼10 times higher, P3 is non-toxic, and could have great advantages as food additive. These results show that pure XOs exert significant antioxidant activity, only due to their carbohydrate nature.

Antioxidant Edible Films Based on Pear Juice and Pregelatinized Cassava Starch: Effect of the Carbohydrate Profile at Different Degrees of Pear Ripeness.

Edible films based on fruit and vegetable purees combined with different food-grade biopolymeric binding agents (e.g., pectin, gelatin, starch, sodium alginate) are recognized as interesting packaging materials that benefit from the physical, mechanical, and barrier properties of biopolymers as well as the sensory and nutritional properties of purees. In the current contribution, edible antioxidant films based on pear juice and pregelatinized cassava starch were developed. In particular, the suitability of using pregelatinized cassava starch for the non-thermal production of these novel edible films was evaluated. In addition, the effects on the films' properties derived from the use of pear juice instead of the complete puree, from the content of juice used, and from the carbohydrate composition associated with the ripening of pears were all studied. The produced films were characterized in terms of their total polyphenol content, water sensitivity, and water barrier, optical, mechanical and antioxidant properties. Results showed that the use of pear juice leads to films with enhanced transparency compared with puree-based films, and that juice concentration and carbohydrate composition associated with the degree of fruit ripeness strongly govern the films' properties. Furthermore, the addition of pregelatinized cassava starch at room temperature discloses a significant and favorable impact on the cohesiveness, lightness, water resistance, and adhesiveness of the pear-juice-based films, which is mainly attributed to the effective interactions established between the starch macromolecules and the juice components.

Complex sulfated galactans from hot water extracts of red seaweed Asparagopsis taxiformis comprise carrageenan and agaran structures.

Hot water extraction from the red seaweed Asparagopsis taxiformis yielded three extracts which showed sulfated galactans with a D:L-galactose ratio non consistent with carrageenan or agaran backbones. The major extract was fractionated by cetrimide precipitation and redissolution with increasing sodium chloride concentrations due to their low solubility. Seven fractions were obtained, and studied by methylation analysis, desulfation-methylation, and NMR spectroscopy of the partially hydrolyzed and the native samples. Fractions with the highest yield were those obtained at high concentrations of NaCl. They comprised both agaran and crageenan structures in considerable amounts. The main agaran structures were ß-D-galactose 4-sulfate and ß-D-galactose 2-sulfate units linked to α-L-galactose 2,3-disulfate residues, and ß-D-galactose linked to α-L-galactose 3-sulfate or 6-sulfate, or substituted with single stubs of ß-D-xylose on C3, while the carrageenan structures comprised ß-D-galactose (2-sulfate) linked to α-D-galactose 3-sulfate or 2,3-disulfate, and ß-D-galactose 2,4-disulfate linked to α-D-galactose 2,3-disulfate. Between the less sulfated fractions, the one obtained by solubilization in 0.5 M NaCl was mainly constituted by agarans, which included 3,6-anhydro-α-L-galactose units. Anticoagulant activity was assayed by general coagulation tests (aPTT and TT), showing a moderate action compared with heparin. This is the first detailed study of the sulfated galactans from the order Bonnemaisoniales.

NMR spectroscopy for structural elucidation of sulfated polysaccharides from red seaweeds.

Some sulfated polysaccharides from red seaweeds are used as hydrocolloids. In addition, it is well known that there are sulfated galactans (carrageenans and agarans) and sulfated mannans, with remarkable biological properties, as antiviral, antitumoral, immunomodulating, antiangiogenic, antioxidant, anticoagulant, and antithrombotic activities, and so on. Knowledge of the detailed structure of the active compound is essential and difficult to acquire. The substitution patterns of the polymer chain, as degree of sulfation and position of sulfate groups, as well as other substituents of the backbone, determine their biological behavior. NMR spectroscopy is a powerful and versatile tool for structural determination. It can be used for elucidation of structures of polysaccharides from new algal sources with novel substitutions or to detect the already known structures from different algal sources, and it could even help to monitor the quality of the active compound on a productive scale. In this review, the available information about NMR spectroscopy of sulfated polysaccharides from red seaweeds is revised and rationalized, to help other researchers working in different fields to study their structures. In addition, considerations about the effects of different structural features, as well as some recording conditions on the chemical shifts of the signals are analyzed.

Salt stress on Lotus tenuis triggers cell wall polysaccharide changes affecting their digestibility by ruminants.

Lotus tenuis is a glycophytic forage legume (Fabaceae) used in feeding ruminants that can grow under salinity and waterlogging stresses. Plants obtained in controlled conditions were affected negatively in their growth by the effect of salt. Results from sequential extraction of plant cell wall polysaccharides and chemical characterization were related to those from nutritional parameters used to assess ruminants feedstuffs (Van Soest detergent system). Shoots and leaves were analyzed, and the most important differences were found for shoots. The salt-stressed shoots gave lower values of neutral detergent fiber and acid detergent fiber; they produced higher amounts of reserve α-glucans, and hemicelluloses (xyloglucans and glucuronoxylans from primary and secondary cell walls, respectively) and pectins, leaving less material resistant to extraction. This effect was clearly confirmed by an in vitro gas production assay. In addition, observations by light microcopy (LM) and transmission electron microscopy (TEM), showed in some tissues thicker walls and more opened cell wall structures in regard to control samples, which could allow easier access of degrading enzymes in the rumen. Although the plant biomass of Lotus tenuis produced under salt stress was lower, its quality as forage improved due to production of increased quantities of more digestible polysaccharides.

Diversity of Sulfated Polysaccharides From Cell Walls of Coenocytic Green Algae and Their Structural Relationships in View of Green Algal Evolution.

Seaweeds biosynthesize sulfated polysaccharides as key components of their cell walls. These polysaccharides are potentially interesting as biologically active compounds. Green macroalgae of the class Ulvophyceae comprise sulfated polysaccharides with great structural differences regarding the monosaccharide constituents, linearity of their backbones, and presence of other acidic substituents in their structure, including uronic acid residues and pyruvic acid. These structures have been thoroughly studied in the Ulvales and Ulotrichales, but only more recently have they been investigated with some detail in ulvophytes with giant multinucleate (coenocytic) cells, including the siphonous Bryopsidales and Dasycladales, and the siphonocladous Cladophorales. An early classification of these structurally heterogeneous polysaccharides was based on the presence of uronic acid residues in these molecules. In agreement with this classification based on chemical structures, sulfated polysaccharides of the orders Bryopsidales and Cladophorales fall in the same group, in which this acidic component is absent, or only present in very low quantities. The cell walls of Dasycladales have been less studied, and it remains unclear if they comprise sulfated polysaccharides of both types. Although in the Bryopsidales and Cladophorales the most important sulfated polysaccharides are arabinans and galactans (or arabinogalactans), their major structures are very different. The Bryopsidales produce sulfated pyruvylated 3-linked ß-d-galactans, in most cases, with ramifications on C6. For some species, linear sulfated pyranosic ß-l-arabinans have been described. In the Cladophorales, also sulfated pyranosic ß-l-arabinans have been found, but 4-linked and highly substituted with side chains. These differences are consistent with recent molecular phylogenetic analyses, which indicate that the Bryopsidales and Cladophorales are distantly related. In addition, some of the Bryopsidales also biosynthesize other sulfated polysaccharides, i.e., sulfated mannans and sulfated rhamnans. The presence of sulfate groups as a distinctive characteristic of these biopolymers has been related to their adaptation to the marine environment. However, it has been shown that some freshwater algae from the Cladophorales also produce sulfated polysaccharides. In this review, structures of sulfated polysaccharides from bryopsidalean, dasycladalean, and cladophoralean green algae studied until now are described and analyzed based on current phylogenetic understanding, with the aim of unveiling the important knowledge gaps that still exist.

Structural Diversity in Galactans From Red Seaweeds and Its Influence on Rheological Properties.

Galactans are important components of many plant cell walls. Besides, they are the major polysaccharides in extracellular matrixes from different seaweeds, and other marine organisms, which have an acidic character due to the presence of sulfate groups in their structures. In particular, most of the red seaweeds biosynthesize sulfated galactans with very special linear backbones, constituted by alternating (1→3)-ß-d-galactopyranose units (A-unit) and (1→4)-α-galactopyranose residues (B-unit). In the industrially significant seaweeds as source of hydrocolloids, B-units belong either to the d-series and they produce carrageenans (as in the order Gigartinales), or to the l-series, and they are sources of agarose and/or structurally related polymers (i.e., Gelidiales, Gracilariales). In both cases, the latter units appear as cyclized 3,6-anhydro-α-galactose in certain amounts, which can be increased by alkaline cyclization of α-galactose 6-sulfate units. Besides, it has been clearly shown that some red algae produce different amounts of both galactan structures, known as d/l-hybrids. It is not yet clear if they comprise both diasteromeric types of units in the same molecule, or if they are mixtures of carrageenans and agarans that are very difficult to separate. It has been reported that the biosynthesis of these galactans, showing that the nucleotide transport for d-galactopyranose units is UDP-d-Gal, while for l-galactose, it is GDP-l-Gal, so, there is a different pathway in the biosynthesis of agarans. However, at least in those seaweeds that produce carrageenans as major galactans, but also agarans, both synthetic pathways should coexist. Another interesting characteristic of these galactans is the important variation in the sulfation patterns, which modulate their physical behavior in aqueous solutions. Although the most common carrageenans are of the κ/ι- and λ-types (with A-units sulfated at the 4- and 2-positions, respectively) and usually in agarans, when sulfated, is at the 6-position, many other sulfate arrangements have been reported, greatly influencing the functional properties of the corresponding galactans. Other substituents can modify their structures, as methyl ethers, pyruvic acid ketals, acetates, and single stubs of xylose or other monosaccharides. It has been shown that structural heterogeneity at some extent is essential for the proper functional performance of red algal galactans.

A cell surface arabinogalactan-peptide influences root hair cell fate.

Root hairs (RHs) develop from specialized epidermal trichoblast cells, whereas epidermal cells that lack RHs are known as atrichoblasts. The mechanism controlling RH cell fate is only partially understood. RH cell fate is regulated by a transcription factor complex that promotes the expression of the homeodomain protein GLABRA 2 (GL2), which blocks RH development by inhibiting ROOT HAIR DEFECTIVE 6 (RHD6). Suppression of GL2 expression activates RHD6, a series of downstream TFs including ROOT HAIR DEFECTIVE 6 LIKE-4 (RSL4) and their target genes, and causes epidermal cells to develop into RHs. Brassinosteroids (BRs) influence RH cell fate. In the absence of BRs, phosphorylated BIN2 (a Type-II GSK3-like kinase) inhibits a protein complex that regulates GL2 expression. Perturbation of the arabinogalactan peptide (AGP21) in Arabidopsis thaliana triggers aberrant RH development, similar to that observed in plants with defective BR signaling. We reveal that an O-glycosylated AGP21 peptide, which is positively regulated by BZR1, a transcription factor activated by BR signaling, affects RH cell fate by altering GL2 expression in a BIN2-dependent manner. Changes in cell surface AGP disrupts BR responses and inhibits the downstream effect of BIN2 on the RH repressor GL2 in root epidermis.

Glucuronoarabinoxylans and other cell wall polysaccharides from shoots of Guadua chacoensis obtained by extraction in different conditions.

Guadua is a genus of woody bamboos, native to the American continent, which comprises economically important species. Cell wall polysaccharides from young shoots of Guadua chacoensis showed glucuronoarabinoxylans (GAX) as the major hemicellulosic components (65%, of the recovered carbohydrates by extraction with aqueous solutions), which were obtained in major quantities with 1 M KOH (molar ratio Xyl:Ara:GlcA, 100:28:8). AGP and pectin polymers, as well as mixed linkage glucans and xyloglucans were present in smaller amounts (16% and 15%, respectively). Alternative extraction of GAX with solutions of DMSO allowed the characterization of alkali labile substituents, in particular, acetyl groups, which were linked mainly to C3 or, to a lesser extent, to C2 of some of the xylose residues. Besides, small amounts of phenolic compounds, released by saponification, were detected, linked to C5 of some α-l-arabinofuranose units. These results could be relevant for their use as a new resource for the food industry.

Gracilariopsis hommersandii, a red seaweed, source of agar and sulfated polysaccharides with unusual structures.

Red seaweed Gracilariopsis hommersandii produces important amounts of non-gelling galactans, which were extracted with hot water (GrC, yield, 37%, viscosity average molecular weight, Mv 109 kDa), comprising agarose and sulfated galactan structures. The alkali modified derivative, GrCTr (Mv 95 kDa), gave a galactose:3,6-anhydrogalactose molar ratio of 1.0:0.9, and a more regular structure, favouring gelation (melting and gelling temperatures 64 and 14 °C, respectively). The rheological properties of this product suggest possible applications as hydrocolloid. G. hommersandii also biosynthesizes non gelling sulfated galactan fractions with diads constituted by ß-d-galactose and partially cyclized α-l-galactose units or non-cyclized α-d-galactose residues. Sulfation was mainly detected on C6 or C4 of the ß-d-galactose units, and on C6 and, in minor amounts, on C3 of the α-l-galactose units. The presence of ß-apiuronic acid was demonstrated for these fractions as side chains of the galactan backbone. Carrageenan structures were found for the first time in an agarophyte of the Gracilariales.

Sulfated Polysaccharides in the Freshwater Green Macroalga Cladophora surera Not Linked to Salinity Adaptation.

The presence of sulfated polysaccharides in cell walls of seaweeds is considered to be a consequence of the physiological adaptation to the high salinity of the marine environment. Recently, it was found that sulfated polysaccharides were present in certain freshwater Cladophora species and some vascular plants. Cladophora (Ulvophyceae, Chlorophyta) is one of the largest genera of green algae that are able to grow in both, seas and freshwater courses. Previous studies carried out on the water-soluble polysaccharides of the marine species C. falklandica established the presence of sulfated xylogalactoarabinans constituted by a backbone of 4-linked ß-L-arabinopyranose units partially sulfated mainly on C3 and also on C2 with partial glycosylation, mostly on C2, with terminal ß-D-xylopyranose or ß-D-galactofuranose units. Besides, minor amounts of 3-, 6- and/or 3,6-linked ß-D-galactan structures, with galactose in the pyranosic form were detected. In this work, the main water soluble cell wall polysaccharides from the freshwater alga Cladophora surera were characterized. It was found that this green alga biosynthesizes sulfated polysaccharides, with a structure similar to those found in marine species of this genus. Calibration of molecular clock with fossil data suggests that colonization of freshwater environments occurred during the Miocene by its ancestor. Therefore, the presence of sulfated polysaccharides in the freshwater green macroalga C. surera could be, in this case, an adaptation to transient desiccation and changes in ionic strength. Retention of sulfated polysaccharides at the cell walls may represent a snapshot of an evolutionary event, and, thus constitutes an excellent model for further studies on the mechanisms of sulfation on cell wall polysaccharides and environmental stress co-evolution.

Glucuronoarabinoxylans as major cell walls polymers from young shoots of the woody bamboo Phyllostachys aurea.

Young shoots of Phyllostachys aurea showed glucuronoarabinoxylans (GAX) as the major hemicellulosic components, being extracted in major amounts with 1M KOH (ratio Xyl:Ara:GlcA, 100:67:8), but also with water, showing a broad structural variability. Mixed linkage glucans were also present, but in minor amounts, mostly concentrated in the 4M KOH extracts, while pectin polymers were very scarce. Arabinogalactan proteins were an important part of water extracts, determined by the presence of the typical arabinogalactan structures (3- and 6-linked Gal p; terminal and 5-linked Ara f), in addition to small amounts of hydroxyproline (2-3% of total protein) and positive reaction to Yariv's reagent. Morphological and anatomical characteristics of young shoots are described, as well as localization of some cell wall components, and related with chemical analysis. A method for determination of uronic acids as their N-propylaldonamide acetates and separation and quantification by GC/MS was adapted for its use with grass cell wall fractions.

Anatomy, nutritional value and cell wall chemical analysis of foliage leaves of Guadua chacoensis (Poaceae, Bambusoideae, Bambuseae), a promising source of forage.

BACKGROUND: The present study combines morphological and anatomical studies, cell wall chemical composition analysis, as well as assessment of the nutritional value of Guadua chacoensis foliage leaves. RESULTS: Foliage leaves of G. chacoensis are a promising source of forage because: (a) as a native woody bamboo, it is adapted to and helps maintain environmental conditions in America; (b) leaf anatomical studies exhibit discontinuous sclerenchyma, scarcely developed, while pilose indumentum, silica cells, prickles and hooks are also scarce; (c) it has a high protein content, similar to that of Medicago sativa, while other nutritional parameters are similar to those of common forages; and (d) glucuronoarabinoxylan, the major extracted polysaccharide, has one-third of the 4-linked ß-d-xylopyranosyl units of the backbone substituted mainly with α-l-arabinofuranose as single stubs or non-reducing end of short chains, but also 5-linked α-l-arabinofuranose units, terminal ß-d-xylopyranose and d-galactopyranose units, as well as α-d-glucuronic acid residues and small amounts of its 4-O-methylated derivative. CONCLUSION: These results constitute the first report on this species, and as culms are utilized in constructions and crafts, the remaining leaves, when used as forage, constitute a byproduct that allows an additional income opportunity. © 2016 Society of Chemical Industry.

Novel sulfated xylogalactoarabinans from green seaweed Cladophora falklandica: Chemical structure and action on the fibrin network.

The water-soluble sulfated xylogalactoarabinans from green seaweed Cladophora falklandica are constituted by a backbone of 4-linked ß-l-arabinopyranose units partially sulfated mainly on C3 and also on C2. Besides, partial glycosylation mostly on C2 with single stubs of ß-d-xylopyranose, or single stubs of ß-d-galactofuranose or short chains comprising (1→5)- and/or (1→6)-linkages, was also found. These compounds showed anticoagulant activity, although much lower than that of heparin. The effect of a purified fraction (F1) on the fibrin network was studied in detail. It modifies the kinetics of fibrin formation, suggesting an impaired polymerization process. Scanning electron microscopy showed a laxer conformation, with larger interstitial pores than the control. Accordingly, this network was lysed more easily. These fibrin properties would reduce the time of permanence of the clot in the blood vessel, inducing a lesser thrombogenic state. One of the possible mechanisms of its anticoagulant effect is direct thrombin inhibition.

Carrageenan and agaran structures from the red seaweed Gymnogongrus tenuis.

The galactan system biosynthesized by the red seaweed Gymnogongrus tenuis (Phyllophoraceae) is constituted by major amounts of κ/ι-carrageenans, with predominance of ι-structures, which were isolated by extraction with hot water in high yield (∼ 45%). A small amount of non-cyclized carrageenans mostly of the ν-type was also obtained. Besides, 12% of these galactans are agaran structures, which were present in major quantities in the room temperature water extracts, but they were also found in the hot water extract. They are constituted by 3-linked ß-D-galactose units partially substituted on C-6 with sulfate or single stubs of ß-D-xylose and 4-linked residues that comprise α-L-galactose units partially sulfated or methoxylated on C-3 or sulfated on C-3 and C-6 and 3,6-anhydro-α-L-galactose. Related structural patterns were previously found for agarans synthesized by other carrageenophytes. Results presented here show that these agarans are low molecular weight molecules independent of the carrageenan structures, with strong interactions between them.

Determination of Substitution Patterns of Galactans from Green Seaweeds of the Bryopsidales.

Sulfated and pyruvylated galactans are the major soluble polysaccharides produced by seaweeds of the Bryopsidales. Their backbones have a complex and variable pattern of substitution which, until now, has only been elucidated for a few species. Methods for determination of sulfate and pyruvic acid content, and chemical strategies to determine their position in the galactan chain are outlined here. These methods can also be applied to other sulfated and/or pyruvylated polysaccharides.

Chemical structure and anticoagulant activity of highly pyruvylated sulfated galactans from tropical green seaweeds of the order Bryopsidales.

Sulfated and pyruvylated galactans were isolated from three tropical species of the Bryopsidales, Penicillus capitatus, Udotea flabellum, and Halimeda opuntia. They represent the only important sulfated polysaccharides present in the cell walls of these highly calcified seaweeds of the suborder Halimedineae. Their structural features were studied by chemical analyses and NMR spectroscopy. Their backbone comprises 3-, 6-, and 3,6-linkages, constituted by major amounts of 3-linked 4,6-O-(1'-carboxy)ethylidene-d-galactopyranose units in part sulfated on C-2. Sulfation on C-2 was not found in galactans from other seaweeds of this order. In addition, a complex sulfation pattern, comprising also 4-, 6-, and 4,6-disulfated galactose units was found. A fraction from P. capitatus, F1, showed a moderate anticoagulant activity, evaluated by general coagulation tests and also kinetics of fibrin formation was assayed. Besides, preliminary results suggest that one of the possible mechanisms involved is direct thrombin inhibition.

Antiviral activity of lambda-carrageenan prepared from red seaweed (Gigartina skottsbergii) against BoHV-1 and SuHV-1.

The antiviral effect of polysaccharides has been known for many years. Carrageenans are considered a good alternative for the prevention of a wide range of diseases, mainly caused by enveloped viruses. The advantages lie on their high availability, low cost and low induction of resistance. The aim of this study was to evaluate the sensitivity of two viral pathogens of veterinary interest to the presence of lambda-carrageenan. This is the first report of a lambda-carrageenan having antiviral activity against animal viruses belonging to the Alphaherpesvirinae subfamily, BoHV-1 (bovine herpesvirus type 1) strain Cooper and SuHV-1 (suid herpesvirus type 1) strain Bartha. Lambda-carrageenan was able to reduce infectivity of both viruses with a more pronounced effect against BoHV-1. These results proved, as previously shown for human herpes virus type 1, that these compounds could be used as potential antiviral agents in the veterinary field.

Polysaccharides from the green seaweed Codium decorticatum. Structure and cell wall distribution.

The cell wall polysaccharides from Codium decorticatum and their assembly were studied and these results were compared with those obtained previously for this genus. The water soluble polysaccharides are: (i) Pyruvylated and sulfated 3- and 6-linked ß-D-galactans with sulfate mainly on C-4 and also on C-6. Pyruvate ketals are linked to O-3 and O-4 of terminal ß-D-galactose or O-4 and O-6 of 3-linked ß-D-galactose. (ii) Sulfated 3-linked ß-L-arabinans substituted on C-2 or C-2 and C-4 predominantly with sulfate, but also with single stubs of arabinose, and (iii) 4-linked ß-D-mannans with a low degree of sulfation on C-2. The whole polysaccharide system comprises 6.9% of sulfated polysaccharides and 32.9% of fibrillar polysaccharides, mostly insoluble mannans. By in situ localization it was possible to detect two similar fibrillar layers separated by a zone rich in charged polymers. Besides, arabinogalactan proteins co-localized with the fibrillar components.