Characterization of galactomannans isolated from legume endosperms of Caesalpinioideae and Faboideae subfamilies by multidetection aqueous SEC

Galactomannans isolated from legume seed endosperms, including those of commercial interest, have been characterized by multidetection aqueous SEC. Galactomannans derived from seeds of the Faboideae subfamily had substantially higher M_w than those from Caesalpinioideae seeds (M_w,Fab = 2.4–3.1 × 10⁶ g/mol, M_w,Caes. = 0.86–2.1 × 10⁶ g/mol) and within the latter botanical subfamily, an apparent correlation between M_w and the degree of galactose substitution DG was found. The molar mass distributions were unimodal and differed primarily by a scale factor, with distributional widths narrower than a true Flory ‘most-probable distribution’; good fits to Schulz–Zimm model were obtained. Across subfamilies no differences were found in the exponents of [η]–M and R_v–M relationships (0.61 ± 0.02, 0.54 ± 0.01, respectively), the Flory chain stiffness ratio (C_∞ = 20 ± 1 (BSF analysis)), or the persistence length (L_p = 5.5 ± 0.2 nm) obtained from SEC fraction data. However, it was found that prefactors in the [η]–M and R_v–M relationships as well as the unperturbed parameter K_Θ decrease in proportion to DG and therefore chain density. Generalized relationships incorporating galactose-dependent prefactors were therefore developed to model SEC fraction data of native galactomannans ([η]_GM = (1800 ± 200) × M_o^−1.61 × M^0.61±0.02, R_v,GM = 0.63 ± 0.05 × M_o^−0.54 × M^0.54±0.01) as well as lower-M fractions obtained by ultrasonication ([η]_GM = (730 ± 100) × M_o^−1.71 × M_w^0.71±0.02, R_v,GM = 0.49 ± 0.05 × M_o^−0.57 × M_w^0.57±0.01, M ≈ 1 × 10⁵-native). As a consequence of this dependence and the observed patterns in molar mass variation, [η] varies within a narrow range for galactomannans as a whole despite substantial M_w differences.     

One-step synthesis of glucose-branched galactomannan

The synthesis of branched polysaccharides using naturally occurring materials has been reported since 1975, but applications of branched polysaccharides are relatively limited because of the long and complex modification processes. In this work, a practical and efficient procedure is presented that in one step levoglucosan can be grafted to galactomannan (at 115 °C for 15 h) with monochloroacetic acid as catalyst. The structural characteristics of the resulting substances were investigated by NMR spectroscopy. The MS (molar degree of substitution) of glucose was shown to gradually increase with the increase of the ratio of levoglucosan to galactomannan, and the maximal MS is 0.6. Levoglucosan units are mostly grafted to the C6–OH of the galactosyl residues in galactomannan, and the maximal percentage of the substituted C6–OH of galactosyl residues is 42.2%. The resulting levoglucosan tended to graft to the branching glucosyl residues of copolymers with an increase in MS, and the average length of the branching glucose is 3.6 when MS is 0.6.     

Galactomannan thin films as supports for the immobilization of Concanavalin A and/or dengue viruses

The immobilization of the glucose/mannose-binding lectin from Concanavalia ensiformis seeds (ConA) onto a monolayer made of a galactomannan extracted from Leucaena leucocephala seeds (GML), which was adsorbed onto - amino-terminated surfaces, was investigated by means of ellipsometry and atomic force microscopy. The mean thickness of GML monolayer, which polysaccharide consists of linear 1 → 4-linked β-d-mannopyranosil units partially substituted at C-6 by α-d-galactopyranosyl units, amounted to (1.5 ± 0.2) nm. ConA molecules adsorbed onto GML surfaces forming (2.0 ± 0.5) nm thick layers. However, in the presence of mannose the adsorption failed, indicating that ConA binding sites were blocked by mannose and were no longer available for mannose units present in the GML backbone. The GML film was also used as support for the adsorption of three serotypes of dengue virus particles (DENV-1, DENV-2 and DENV-3), where DENV-2 formed the thickest film (4 ± 2) nm. The adsorbed layer of DENV-2 onto ConA-covered GML surfaces presented mean thickness values similar to that determined for DENV-2 onto bare GML surfaces. The addition of free mannose units prevented DENV-2 adsorption onto ConA-covered GML films by ∼50%, suggesting competition between virus and mannose for ConA binding sites. This finding suggests that if ConA is also adsorbed to GML surface and its binding site is blocked by free mannose, virus particles are able to recognized GML mannose unities substituted by galactose. Interactions between polysaccharides thin films, proteins, and viruses are of great relevance since they can provide basis for the development of biotechnological devices. These results indicate that GML is a potential polysaccharide for biomaterials development, as those could involve interactions between ConA in immune system and viruses.     

五种豆科种子胚乳细胞的微观结构的比较

运用光学显微镜和电子显微镜分别对胡芦巴、野皂荚、皂荚、瓜尔豆、塔拉豆等五种豆科种子内胚乳细胞的形态、大小、壁厚等微观结构进行了观察比较。研究结果表明：五种种子内胚乳细胞壁几乎完全由胶状的透明的半乳甘露聚糖所填充,细胞的形态、大小差异较大,瓜尔豆、塔拉豆的内胚乳细胞呈球形或近球形;胡芦巴内胚乳细胞为多角形或多角椭圆形,它们细胞壁界限清晰,细胞排列整齐有规律;皂荚、野皂荚则为不规则的长椭球形,细胞壁彼此连接成片,界限模糊。一般地说：当细胞壁壁厚小于4μm时,胚乳胶粉中的水不溶物含量较低,1％浓度的胶液的粘度较高,而当壁厚大于4μm时,情况反之。本文的研究目的是为植物胶生产、加工提供一定的细胞学方面的依据。     

烘炒法分离提取半乳甘露聚糖型种子胶

种子多糖胶分离提取工艺试验表明,根据种子胚乳坚硬的物理性能,用机械分离方法分离种子胚乳,其多糖胶抽提率大于80％。烘炒法适用于种皮厚而硬一类种子胚乳的分离,正交试验表明烘炒温度对种子多糖胶抽提率和粘度指标影响最大;皂荚胚乳的最优化分离条件是种子在80℃下预热60min,然后在160℃烘炒机中烘炒4min,再进入开片、选片和筛选工序;野皂荚胚乳的分离条件是种子80℃时预热30min,130℃下烘炒3min。     

半乳甘露聚糖胶物理增粘技术的研究

本文对瓜尔胶、胡芦巴胶、皂荚胶、野皂荚胶、田菁胶的水合增粘工艺进行了研究,并比较了螺杆盘磨式和轧辊刨片式两种增粘机。与原胶相比,增粘胶1％胶液粘度提高了50％,水不溶物含量降低了15％。     

NMR-based identification of cell wall galactomannan of Streptomyces sp. VKM Ac-2125

The major cell wall polymer of Streptomyces sp. VKM Ac-2125, the causative agent of potato scab, is galactomannan with the repeating unit of the following structure: [carbohydrate structure in text] The polysaccharide with such a structure is found in the bacterial cell wall for the first time. The cell wall also contains small amount of a teichoic acid of the poly(glycerol phosphate) type and 3-deoxy-D-glycero-D-galacto-non-2-ulopyranosonic acid.     

Testa is involved in the control of storage mobilisation in seeds of <Emphasis Type="Italic">Sesbania virgata</Emphasis> (Cav.) Pers., a tropical legume tree from of the Atlantic Forest

Seeds of Sesbania virgata (Cav.) Pers. (Leguminosae) contain galactomannan as a cell wall storage polysaccharide in the endosperm. After germination, it is hydrolysed by three enzymes: α-galactosidase (EC 3.2.1.22), endo-β-mannanase (EC 3.2.1.78) and β-mannosidase (EC 3.2.1.25). This work aimed at studying the role of the testa (seed coat) on galactomannan degradation during and after germination. Seeds were imbibed in water, with and without the testa, and used to evaluate the effect of this tissue on storage mobilisation, as well as its possible role in the galactomannan hydrolases activities. Immunocytochemistry and immunodotblots were used to follow biochemical events by detecting and localising endo-β-mannanase in different tissues of the seed. Endo-β-mannanase and α-galactosidase activities were found in the testa and latter in the endosperm during galactomannan degradation. The former enzyme was immunologically detected in the testa, mainly during germination. The absence of the testa during imbibition led to the anticipation of protein mobilisation and increased of the α-galactosidase activity and galactomannan degradation. Thus, the testa appears to play a role during storage mobilisation in the legume seed of S. virgata probably by participating in the control of the production, modification and/or storage of the hydrolases.     

Computer modelling of kappa carrageenam-mannan interactions

Molecular modelling has been used as a theoretical approach to investigate the kappa carrageenan structure and its interaction with mannan chains. Calculations revealed the existence of six minima for the kappa carrageenan structure in solution. Two of them were very close to the structure found in the solid state. The methodology allowed the calculation of the theoretical counterpart of the structures based on x-ray fibre diffractions studies. In the second step of this study, we have shown that there is the possibility of interactions between kappa carrageenan double helices and mannan chains. This interacting process is allowed by the flexibility of the mannan chains and structural changes of the kappa carrageenan double helices. The calculations suggest that the disaccaride mannan fragment might be required for recognition. The result of our investigation are in good agreement with a model of gel structure based on experimental data. This approach could be applied to simulate and predict other associations in molecular assemblies.     

Water stress and galactomannan breakdown in germinated fenugreek seeds. Stress affects the production and the activities in vivo of galactomannan-hydrolysing enzymes

Imposition of water stress on germinated fenugreek (Trigonella foenum-graecum L.) seeds and isolated fenugreek endosperms after the beginning of galactomannan mobilisation caused a reduction in the rate of breakdown of the polysaccharide relative to unstressed controls. The activities, measured in vitro, of the three hydrolytic enzymes involved in the breakdown process (-d-galactosidase, EC 3.2.1.22;endo--d-mannanase, EC 3.2.1.78;exo--d-mannanase, EC 3.2.1.25) were not decreased. Although there was some accumulation of galactomannan-hydrolysis products in endosperms under stress, there was no clear correlation between sugar levels and the inhibition of galactomannan breakdown. When water stress was applied to fenugreek seeds after germination but before the beginning of galactomannan hydrolysis, both galactomannan breakdown and the development of the hydrolytic enzyme activities were inhibited. Washing of newly germinated seeds for 2 h in water prior to the imposition of stress gave partial relief of the inhibition of galactomannan mobilisation, partial recovery ofendo--d-mannanase levels, and full recovery of -d-galactosidase levels. It is argued: 1) that water stress after germination but before the beginning of galactomannan hydrolysis inhibits the production of hydrolytic enzymes in the endosperm, probably via decreased removal at lowered water content of diffusible inhibitory substances; and 2) that water stress after the beginning of galactomannan hydrolysis decreases the rate of galactomannan breakdown in vivo principally via decreased diffusion at lowered water content of enzymes from the aleurone layer through the storage tissue of the endosperm.Abbreviation PEG polyethyleneglycol