Arabinogalactan-protein Complex Research Articles

Emulsifying properties of biopolymer extracts from Opuntia ficus indica cladodes

The use of natural extracts in the field of cosmetics and pharmaceuticals is increasing due to the growing demand for sustainable and safe products, together with their potential therapeutic benefits. Bioextracts from the parenchyma of Opuntia ficus indica cladodes were characterized and evaluated as emulsifying agents. They contain pectin together with variable amounts of arabinogalactan-protein complex (AGP), as in many polysaccharides of natural origin. Their protein content varies according to the purification steps: 11.4 wt% for the raw mucilage (Mofi), 4.7 wt% for the pectin fraction (Pofi) and less than 0.5 wt% for the filtrated pectin fraction (FPofi). Part of the AGP contained in the Mofi and Pofi extracts precipitates as particles with a ∼5 µm diameter. Mofi at 1.5 wt% concentration is an efficient emulsifier of oil-in-water emulsions of medium-chain triglycerides or sunflower oil with stability against coalescence for more than three months. Pofi is less efficient and FPofi does not allow the stabilization of emulsions. The performance of emulsifiers is directly related to the protein content of the extracts and the role of the insoluble particles is essential. The insoluble particles of AGP are responsible for the stabilization through a Pickering effect. The emulsions have the characteristic properties of Pickering emulsions.

Revisiting the structure of arabinogalactan from Lycium barbarum and the impact of its side chain on anti-ageing activity

In this study, we obtained all the homogeneous LBGP70 (arabinogalactan-protein complex), LBGP70-OL (sugar chain of LBGP70), and LBGP70-OL-I (backbone part of LBGP70-OL) fraction from crude Lycium barbarum polysaccharides (LBP) by stepwise precipitation. The structural features of LBGP70-OL were investigated by a series of analytical techniques and chemical methods, which was identified as a highly branched polysaccharide with an average of 9 branches per 10 sugar backbone units. The backbone was only →6)-β-Galp-(1→ residues, substituted at the C3 position. The side chains contained β-Galp-(1→, α-Araf-(1→, α-Araf-(1 → 3)-β-Araf-(1 → 3)-β-Araf-(1→, α-Araf-(1 → 3)-β-Gap-(1 → 3)-β-Galp-(1→, α-Araf-(1 → [5)-β-Araf-(1]4 → 3)-β-Galp-(1→. LBGP70-OL had the highest anti-ageing activity, with its side chain and backbone exhibiting a synergistic effect. LBGP70-OL exerted the anti-ageing activity by attenuating SA-β-Gal activity, preventing cell cycle arrest, increasing antioxidant enzyme activity, protecting the cell membranes from oxidative damage, and regulating the senescence-related genes Sirt1, NAMPT, and Prx1. These results lay the fundamental for further studies on the structure-function relationships of LBP.

Modification of EDC method for increased labeling efficiency and characterization of low-content protein in gum acacia using asymmetrical flow field-flow fractionation coupled with multiple detectors

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) is widely used as a crosslinker for fluorescence labeling of protein in the fields of biochemistry and food analysis. Many natural polysaccharides often contain some proteins or peptides that are very low in content but play a vital role in their biological function as well as technical applications. Determination of these low-content proteinaceous matters requires a highly sensitive and selective method. In this study, a methodological approach for investigations of the presence of proteinaceous material over the molar mass distribution (MD) of polysaccharides was developed using gum acacia (GA) as a model polysaccharide. EDC fluorescence-labeling method was modified by changing the pH (7, 9, and 11) of the solution for the analysis of low-content protein in food materials. Fluorescence spectroscopy and asymmetrical flow field-flow fractionation (AF4) were employed for characterizing the labeling efficiency and physiochemical properties of unlabeled and fluorescence-labeled GA. AF4 provided molar mass (M) and the radius of gyration (rG) of arabinogalactan (AG) and arabinogalactan protein complex (AGP) and determined the presence of proteinaceous matter over the MD. The labeling efficiencies of GA at pH 7, 9, and 11 determined by fluorescence spectroscopy were 56.5, 68.4, and 72.0%, respectively, with an increment of 15.5% when pH was increased from 7 to 11. The modified EDC fluorescence-labeling method allows highly sensitive and selective analysis of low-content proteinaceous matters and their distribution in natural polysaccharides.Graphical abstract

Arabic gum ameliorates histological and histochemical changes in the renal cortex of rats induced by alloxan injection

Arabic gum (AG) is a natural branched-chain multifunctional hydrocolloid with a highly neutral or slightly acidic, arabinogalactan protein complex containing calcium, magnesium, and potassium. Arabic gum is a dried exudate obtained from the stem and branches of Acacia trees. AG has an anti-inflammatory and antioxidant effect. This study aimed to examine the possible anti-inflammatory and antioxidant effect of AG against the damage induced by alloxan injection on renal tissue of adult male rats using histological and histochemical studies. The current experiment was carried out on 48 adult male Albino rats. Rats were randomly and equally categorized into four groups 12 rats in each group as follows: 1) Control group (C): rats have left without treatment; 2) Diabetic groups (D): rats were injected with 150 mg/kg body weight of alloxan and left for 21 days ; 3) Arabic gum groups (G): rats were orally administrated (25 mg/kg body weight/day) for 21 days and 4) D+G groups: rats were injected with alloxan and treated with 25 mg/kg body weight/day for 21 days. The experimental rats were sacrificed after 7 and 21 days post-treatment. Examination of renal tissue of rats seven and twenty-one days post-alloxan injection revealed many histological and histochemical changes. Highly increased collagen fibres were demonstrated after seven and twenty-one days post alloxan injection. Also, alloxan injection significantly decreased PAS-positive materials, total protein content, and total DNA content, but it significantly increased amyloid β –protein content relative to the control group. While treatment with AG post-alloxan injection showed a trend toward lowering the incidence of renal tissue histological and histochemical changes induced by alloxan injection. According to the results obtained in the current study using AG as a natural agent showed a strong cytoprotective effect against the histological and histochemical changes due to its antioxidant effect.

Effect of arabinogalactan protein complex content on emulsification performance of gum arabic

The emulsification properties of the standard (STD), matured (EM2 and EM10) and fractionated gum arabic samples via phase separation induced molecular fractionation were investigated to find out how the content of arabinogalactan protein (AGP) complex affects the resulting emulsion properties. Phase separation and the accompanying molecular fractionation were induced by mixing with different hydrocolloids including hyaluronan (HA), carboxymethyl cellulose (CMC), and maltodextrin (MD). Increase of AGP content from 11 to 28% resulted in the formation of emulsions with relatively smaller droplet sizes and better stability. Further increase in the AGP content to 41% resulted in the formation of emulsions with larger droplets. In spite of the larger droplets sizes, these emulsions were extremely stable. In addition, the emulsions prepared with GA higher AGP content better stability in the presence of ethanol. The results indicate that AGP content plays a vital role in emulsion stability and droplet size.

Effects of temperature and solvent condition on phase separation induced molecular fractionation of gum arabic/hyaluronan aqueous mixtures

Effects of temperature and solvent condition on phase separation-induced molecular fractionation of gum arabic/hyaluronan (GA/HA) mixed solutions were investigated. Two gum arabic samples (EM10 and STD) with different molecular weights and polydispersity indices were used. Phase diagrams, including cloud and binodal curves, were established by visual observation and GPC-RI methods. The molecular parameters of control and fractionated GA, from upper and bottom phases, were measured by GPC-MALLS. Fractionation of GA increased the content of arabinogalactan-protein complex (AGP) from ca. 11% to 18% in STD/HA system and 28% to 55% in EM10/HA system. The phase separation-induced molecular fractionation was further studied as a function of temperature and solvent condition (varying ionic strength and ethanol content). Increasing salt concentration (from 0.5 to 5 mol/L) greatly reduced the extent of phase separation-induced fractionation. This effect may be ascribed to changes in the degree of ionization and shielding of the acid groups. Increasing temperature (from 4 °C to 80 °C) also exerted a significant influence on phase separation-induced fractionation. The best temperature for GA/HA mixture system was 40 °C while higher temperature negatively affected the fractionation due to denaturation and possibly degradation in mixed solutions. Increasing the ethanol content up to 30% showed almost no effect on the phase separation induced fractionation.

New structural features of Acacia tortuosa gum exudate

Acacia tortuosa produces a clear gum, very soluble in water. Previous reports showed that it was constituted by four fractions, one of them an arabinogalactan–protein complex. The elucidation of the A. tortuosa gum structure by the combination of classical chemical methods, size exclusion chromatography and NMR spectroscopy, was the objective of this investigation. The data obtained show that the heteropolysaccharide is an arabinogalactan type II, highly ramified, with lateral chains at C-2 as well as at C-6 of the galactose 3-O residues; mono-O-substituted galactoses were not detected. There are residues of mannose, the arabinose, pyranose predominantly, is terminal and 2-O-linked. The abundance of the 4-O-methyl-α-d-glucuronic acid was not previously reported. The proteic fraction is probably represented by an arabinogalactan–protein complex that binds poorly with β-glucosyl Yariv reagent, and two glycoproteins. The NMR spectra suggest that the carbohydrate links to hydroxyproline through the galactose (galactosylation).

Gum arabic fractionation using synthetic membranes: The importance of fouling

The fractionation of 2wt% gum arabic using 0.1, 0.5 and 0.8μm polysulfone (PS) flat sheet membranes is investigated. Fluxes of between 35 and 80Lm−2h−1 were achieved during diafiltration experiments at cross-flow velocities of between 1.0 and 1.6ms−1. Although all three membranes rejected a large proportion of the total solids, a high degree of fractionation was seen, particularly for the 0.1μm membrane, which establishes the principle of this novel membrane application. Rejection of high MW arabinogalactan-protein complex (AGP) was observed with selective transmission of lower MW glycoprotein (GP). Multi-cycle experiments showed that flux can be well recovered after cleaning of the membrane, although with the 0.8μm membrane, greater fractionation was seen after some fouling had occurred.

Phase separation induced molecular fractionation of gum arabic—Sugar beet pectin systems

This paper investigates the phase separation and phase separation-induced fractionation of gum arabic (GA)/sugar beet pectin (SBP) mixed solutions. A phase diagram, including cloud and binodal curves, was established by visual observation and phase composition analysis. The deviation of the binodal curve from the cloud curve was a result of phase separation-induced fractionation of polydisperse GA and SBP molecules. Fractionation of GA increased the content of arabinogalactan-protein complex (AGP) from ca. 13% to 27%. The fractionated GA (FGA) showed improved emulsifying functionality, whereas the fractionated SBP (FSBP) had a reduced emulsifying functionality. The changes in emulsifying efficiency can be explained by interfacial adsorption behaviors at the oil–water interface as indicated by interfacial tension measurements.

Molecular heterogeneity of arabinogalactan-protein from Coffea arabica instant coffee

Arabinogalactan-protein complex (AGP), isolated from freeze-dried instant coffee powder of Coffea arabica beans, was subjected to ion-exchange chromatography. Stepwise elution with water and solutions of sodium chloride with increasing ionic strength afforded eight fractions (F1–F8). Chemical analyses have shown that compositions of individual conjugates varied in carbohydrate and protein contents, molecular mass and slightly in monosaccharide composition. Protein content was increasing by increasing ionic strength of the eluent and it was confirmed also by FT-IR spectra. NMR study has shown that carbohydrate moieties in individual ion exchange fractions differed in the degree of backbone and side chains branching. Performed study has confirmed a molecular heterogeneity of arabinogalactan-protein complex present in a commercial instant coffee.

Characterization and properties of Acacia senegal (L.) Willd. var. Senegal with enhanced properties (Acacia ( sen) SUPER GUM ™): Part 5. Factors affecting the emulsification of Acacia senegal and Acacia ( sen) SUPER GUM™

Acacia senegal is the major gum arabic species used in commercial emulsification for the production of beverages and flavor concentrates. This paper examines the effect of gum concentration, molecular weight parameters and homogenization conditions on the droplet size and stability of emulsions prepared using a conventional commercial A. senegal product and a series of A. senegal test gums that were prepared by a controlled maturation process, including a new commercial product produced by this process (Acacia ( sen) SUPER GUM™ EM2). Pressure homogenization after vigorous stirring produced the best results. At concentrations below 20%, commercial gum arabic weight average molecular weight M W ca. 6×10 5 Da produced emulsions which were not stable under accelerated stress conditions. When the weight average M W was increased to a range 1–2.5×10 6 Da, the droplet size was reduced and the stability was greatly increased, even at a 5% gum concentration. After pressure homogenization, sub-micron droplet sizes could be produced which exhibited complete stability during stress testing at 60 °C and after longer-term storage. A model is proposed to account for the greater effectiveness of the matured gums, whereby the arabinogalactan protein complex unfolds as a result of pressure homogenization and occupies a greater volume around the oil droplet, which in turn produces greater stabilization.

X-ray reflectivity studies of liquid films stabilized by mixed β-lactoglobulin—Acacia gum systems

Acacia gum is a complex mixture of three main components, the arabinogalactan (AG), the arabinogalactan-protein complex (AGP) and the glycoprotein (GP). In the present study, the influence of complex formation between the protein β-lactoglobulin and the Acacia gum and its two major components, the AG and AGP, on the formation of vertical macroscopic thin liquid films were investigated by means of X-ray reflectivity measurements. This method allows the determination of the thickness of the formed film and its nano-structural features. The experimental results revealed that the main effect of adding Acacia gum to a 1 g/l β-lg solution at a pH of 5.3, i.e., near the protein's pI value, is related to the formation of soluble and insoluble β-lg – arabinogalactan (AG) complexes. Addition of Acacia gum to the protein solution significantly decreased the film thickness of the formed film before it ruptured. Film experiments with fractionated Acacia gum mixtures (an AG-rich and an AG-poor, i.e., AGP-rich, fraction) or with a dialyzed Acacia gum preparation allowed to conclude that the observed influence of the Acacia gum on the thickness of the β-lg stabilized films and film stability is primarily due to the extent of complex formation between the negatively charged AG component and the β-lg. This complex formation reduces the ‘free’ β-lg concentration in the bulk which is stabilizing the two water-air surfaces in the film. The degree of complex formation considerably depends on the ionic strength in the solution. At low ionic strength, the negative charges on the AG are not screened by the salt ions leading to extensive electrostatic complex formation (formation of soluble and/or insoluble complexes) with the β-lg, even at the isoelectric point of the protein. However, if the ionic strength in the β-lg – Acacia gum mixture is in the sub-millimolar range, significant charge screening effects are occurring keeping the arabinogalactan component away from complexation with the β-lg molecules and allowing the formation of stable thin liquid films up to a β-lg – Acacia gum weight ratio of 2:1. Addition of more Acacia gum under these ionic strength conditions resulted again in the formation of unstable thin films.

Characterization of two Acacia gums and their fractions using a langmuir film balance.

The mechanical properties of monolayers from two Acacia gums [Acacia senegal (L.) Willd. and Acacia seyal Del.] and their three fractions isolated by hydrophobic interaction chromatography were studied with a Langmuir film balance to obtain a more complete understanding of their action mode. The analysis of compression isotherms revealed that A. senegal gums globally exhibit better interfacial properties than A. seyal ones. The behavior of the whole gums appeared to be strongly influenced by their arabinogalactan-protein complex.

Analysis of a complex polysaccharide (gum arabic) by multi-angle laser light scattering coupled on-line to size exclusion chromatography and flow field flow fractionation

The heterogeneous polysaccharide gum arabic has been characterized using size exclusion chromatography (SEC) and flow field flow fractionation (F4) coupled on-line to multi-angle laser light scattering (MALLS). Two distinct populations have been shown. About 80% of the material consist of highly branched arabinogalactan (AG) units. The rest is mainly composed of heterogeneous arabinogalactan–protein complex (AGP) of high molecular weight. The F4/MALLS method is shown to allow the complete analysis of gum arabic whereas SEC gave only partial information. From light-scattering-based radii of gyration ( R g) and F4-based hydrodynamic radii ( R h) we found that the ratio R g/ R h is near 0.8 for AGP. This value is reasonably consistent with a globular conformation and gives further evidence in favour of the “wattle blossom model” proposed by Connolly et al.

An evaluation of methods for characterising and monitoring gum arabic of commerce and related Acacia gums

Three methods that have been suggested as inexpensive for characterisation of gum arabic were evaluated in characterising and monitoring gum arabic of commerce. The methods were; physico-chemical and carbohydrate analysis (analytical), determination of molecular mass by gel permeation chromatography (gpc) and an Enzyme Linked Immunosorbent Assay (ELISA). The results revealed that gpc provides quick and consistent information on gum arabic of commerce from Acacia senegal. It was able to detect the three chemical species; Arabinogalactan protein complex (AGP), Arabinogalactan (AG) and Glycoprotein (GP) fractions that are typical of A. senegal and could differentiate gum from the two varieties of A. senegal, i.e., var. senegal and var. kerensis on the basis of the enhanced UV peaks in the later. It was able to distinguish gums from different Acacia species as well as suspected contaminants. The analytical method could differentiate between the two varieties of A. senegal on the basis of optical rotation, protein content and viscosity which were noted as basic parameters for comparison. However, where the proposed FAO (1990) specifiction was applied in its present form, it failed to adequately characterise gum from var. kerensis as gum arabic. Secondly, natural product variability i.e., the observed between sample variation made the method to have limited application in adequately characterising gum arabic from even a single source. The method was able to distinguish gums from the other Acacia species purely on the basis of optical rotation though information on nitrogen and sugar composition was also invaluable. Generating data on the composition of sugars requires time that militates against the method as a slow process. Because of the overlap in the analytical parameters for some samples, it could be adequately characterise two of the samples that were presented as suspected contaminants. Nonetheless, by combining information of gpc and analytical data, a better evaluation of the gums was achieved. The method of Elisa has a future scope but will require refining it by utilising monoclonal antibodies to be developed for it to be more specifc in characterising gum arabic from A. senegal.

Characterization of commercial samples of gum arabic

Six commercial gum arabic samples and authenticated samples of gum from Acacia senegal and Acaciaseyal have been characterized using a range of chemical and physicochemical techniques including determination of specific rotation, sugar composition, nitrogen and amino acid content, and molecular mass distribution. Although some of the gums have slightly different chemical and physicochemical characteristics, gel permeation chromatography shows that each consists of essentially three molecular mass fractions classified as an arabinogalactan, an arabinogalactan-protein complex, and a glycoprotein

Fractionation and characterization of gum from Acacia senegal

Gum from Acacia senegal has been fractionated using hydrophobic affinity chromatography. Characterization, including identification of sugars and determination of protein and amino acid contents, has been undertaken for each fraction together with measurements of molecular mass and molecular mass distribution using laser light scattering and gel permeation chromatography. The results have indicated that the gum consists of three distinct components. Fraction 1, which represents 88.4% of the total, is an arabinogalactan with molecular mass 2.79 × 10 5 and is deficient in protein. Fraction 2, which represents 10.4% of the total, is an arabinogalactan—protein complex with a molecular mass of 1.45 × 10 6, containing ~50% of the total protein. It is envisaged that on average each molecule of fraction 2 consists of five carbohydrate blocks of molecular mass ~2.8 × 10 5 covalently linked through a chain of amino acid residues. Fraction 3 represents only 1.24% of the total gum but contains ~25% of the total protein and has been shown to consist of one or more glycoproteins. Whereas the proteinaceous components of fractions 1 and 2 contain predominantly hydroxyproline and serine, this is not the case for fraction 3.

Macromolecular distribution of Acacia senegal gum (gum arabic) by size-exclusion chromatography

Fractionation of Acacia senegal gum has been carried out on Sephacryl gels S-400 and S-500. The shape and relative height of the chromatograms are sample dependent. Physicochemical data including circular dichroism and the weight-average molecular weights distribution show that about 70% of the material is composed of homogeneous polysaccharide chains with a very low nitrogen content. The remaining material is a combination of polysaccharide and nitrogen moieties (probably an arabinogalactan-protein complex). Our data are consistent with the new and simplified structural models proposed recently for this polysaccharide.