Fany Reicher

Linear mannan in the endosperm of Schizolobium amazonicum

Abstract The seed endosperm from the Leguminosae Schizolobium amazonicum was shown to consist of three different parts: (i) the embryo side or interior section; (ii) the seed coat side or exterior section; and (iii) an intermediate zone rich in galactomannan with a 3:1 Man/Gal ratio located between the two sides of the seeds. The exterior section was submitted to a series of hot water and alkaline extractions and the remaining product investigated by monosaccharide analysis, 13 C NMR, X-ray and electron diffraction, together with electron microscopy. After an extraction with 16% NaOH, a linear β(1→4) microfibrillar mannan could be isolated in this portion of the seeds. This is the first time that a pure mannan fraction has been found in the seed of a Leguminosae.

Conformational analysis of galactomannans: from oligomeric segments to polymeric chains

Abstract Conformational features of the glycosidic bond linking two mannosyl units of four different oligomeric fragments of galactomannans have been calculated by means of adiabatic mapping of the glycosidic Φ, Ψ torsion angles using the MM3 force field. These fragments differed in their substitution pattern. The aim of this study was to ascertain the role played by the galactosyl side groups on the conformational flexibility of the galactomannan chain backbone. Although the overall features of all the potential energy surfaces created appear similar, these maps show that the position of the lowest energy minimum conformer and the lower energy region change significantly if one or both mannosyl residues are substituted by a galactosyl side group. Thus, these groups lead to significant differences in the accessible conformational space, when compared with that of the mannobiose molecule. Predicted homonuclear and heteronuclear coupling constants averaged over each entire map also reflect the conformational differences. Computed maps were used to predict polymeric unperturbed dimensions, C ∞ , a , 〈 R 〉 and 〈 s 2 〉 1/2 of idealized galactomannan chains by Monte Carlo methods. For low values of Man:Gal ratios, chain extension appears to be strongly dependent on the degree of substitution. For 2:1 and 3:1 Man:Gal ratios, random, alternate and block patterns of substitution have been investigated. It has also been shown that the spatial extension of the polymer chains is dependent on the scheme of substitution. Such studies provide a unique insight into the dependence of these two factors on the stiffness and flexibility of different galactomannan chains.

Study of solution properties of galactomannan from the seeds of Mimosa scabrella

The rheological properties of the galactomannan from the seeds of a member of the Leguminosae have been studied. The sample used had a mannose/galactose ratio close to 1 and an intrinsic viscosity of 900 ml/g. The viscosity results are characteristic of a random coil polymer with a critical concentration c∗ = 2·6/[η] which is similar to the values found for polystyrene and polystyrenesulphonate, but higher than the value obtained for more rigid polysaccharides. The slope of the logarithmic plot of the specific viscosity measured at zero shear rate against c[η] in the semi-dilute regime was 4·2, a value in agreement with the theoretical predictions for linear polymers interacting by purely topological entanglements. The viscoelastic behaviour was lower than that found for solutions of other galactomannans and this and the less severe dependence of the viscosity on the coil overlap parameter is probably due to lower interactions because of the high galactose content.

Galactomannans from Brazilian seeds: characterization of the oligosaccharides produced by mild acid hydrolysis

Galactomannans with Man:Gal ratios ranging from 1.1:1 to 3:1, obtained from the seeds of Mimosa scabrella, Stryphnodendron barbatiman, Schizolobium parahybum and Schizolobium amazonicum, were submitted to mild acid hydrolysis. The products were fractionated by gel permeation chromatography on BioGel P2 yielding fractions with degrees of polymerization (DP) of 1 to 6. Those with DP 2 to 6 from each species were analysed by ion-exchange high-performance liquid chromatography and characterized by 13C- and 1H-nuclear magnetic resonance (NMR) spectroscopy. The distribution of the oligosaccharides of each degree of polymerization was very similar for the products from S. parahybum and S. amazonicum, indicating the same D-galactosyl distribution on the D-mannan backbone, in agreement with the 13C-NMR splitting in the C4 region of the D-mannosyl units in the original polymers. The hydrolytic conditions adopted allowed characterization of compounds that are not generally produced by enzymatic treatments. The results show that the structures of the oligosaccharides, even if there is a preferential hydrolysis of Gal-Man linkages, reflect the composition of the parent polymer.

Viscometric studies on xanthan and galactomannan systems

Abstract The synergistic effect obtained by mixing xanthan and galactomannans from Brazilian seeds ( Mimosa scabrella Bentham and Schizolobium parahybum (Vell) Blake), with mannose:galactose ratios of 1.1:1 and 3:1 respectively, were examined. Viscosity measurements were performed under different conditions. A strong interaction was observed with xanthan:galactomannan ( X : G ) from S. parahybum , in water at 1 and 2g/liter. For the mixture of xanthan:galactomannan from M. scabrella ( X : G 3:1 2 g/liter, in water) despite the latter high galactose content, an increase in viscosity of 32% was observed over that calculated assuming no interaction. The results showed the formation of a gel-like structure with hysteresis between increasing and decreasing shear rate. The interaction occurred mainly when the system was previously subjected to 80 °C in water, independent of the conformation of xanthan. The stronger interactions were obtained in aqueous systems. Since the main chain of the M. scabrella galactomannan is almost completely substituted, the synergistic effect must have an interaction mechanism different from that previously described by Dea and Morrison (1975), Dea et al. (1977), Morris et al. (1977), and Lundin and Hermansson (1995) in which xanthan interacts with galactomannan via the unsubstituted region of the latter.

Role of galactomannan composition on the binary gel formation with xanthan.

The influence of the galactomannan characteristic ratios (M/G) on the temperature of gelation (Tg) and the gel strength of mixtures of galactomannan with xanthan is reported. Two galactomannans were investigated: one highly substituted from the seeds of Mimosa scabrella (M/G = 11), and the other, less substituted, from the endosperm of Schizolobium parahybae, with (M/G = 30) [Ganter JLMS, Zawadzki-Baggio SF, Leitner SC, Sierakowski MR, Reicher F. J Carbohydr Chem 1993;12:753]. The xanthan:galactomannan systems (4:2 g l(-1), in 5 mM NaCl) showed a temperature of gel formation (Tg) of 24 degrees C for that of S. parahybae [Bresolin TMB, Milas M, Rinaudo M and Ganter JLMS. Int J Biol Macromol 1998;23:263] and 20 degrees C for the galactomannan of M. scabrella, determined by viscoelastic measurements and microcalorimetry. A Tg of 40-50 degrees C was found by Shatwell et al. [Shatwell KP, Sutherland IW, Ross-Murphy SB, Dea ICM. Carbohydr Polym 1991;14:29] for locust bean gum-LBG (M/G = 43). Lundin and Hermansson [Lundin L, Hermansson AM. Carbohydr Polym 1995;26:129] reported a difference of 13 degrees C for Tg of two LBG samples with M/G = 3 (40 degrees C) and 5 (53 degrees C), in mixtures with xanthan. It appears that the more substituted galactomannans have lower temperatures of gelation in the presence of xanthan. The mechanism of gelation depends also on the M/G ratio. For the lower values it involves only disordered xanthan chains in contrast to M/G ratios higher than 3. In addition, the presence of the galactomannan from M. scabrella increased slightly the temperature of the conformational change (Tm) of xanthan probably due to the ionic strength contribution of proteins (3.9%) present in the galactomannan. On the other hand, the galactomannans from S. parahybae, with 1.5% of proteins and M. scabrella, with 2.4% of protein, did not show this effect, the Tm of xanthan alone or in a mixture being practically unchanged.

Galactomannans and arabinans from seeds of caesalpiniaceae

Abstract Schizolobium amazonicum and S. parahybae galactomannans yielded the same pattern of oligosaccharides on partial acid hydrolysis. Seed coats of both species furnished unusual linear arabinans providing chemotyping evidence supporting the suggestion that they are not different species. Schizolobium parahybae and S. amazonicum seeds yielded galactomannans with identical 3.0:1 Man:Gal ratios and with the same d -galactose distribution along the main chain. Although the galactomannan from seeds of Cassia fastuosa showed the same Man:Gal ratio, its fine structure differed significantly from that of the two Schizolobium species as shown by the analysis of oligosaccharides (DP 2 to 6) obtained by partial acid hydrolysis. Seed coasts of S. parahybae and S. amazonicum furnished similar unusual neutral linear α- l -arabinofuranan (1 → 5) linked, as determined by methylation analysis, optical rotation and 13 C NMR spectroscopy. On the other hand, C. fastuosa seed coats furnished two acidic arabinans. These results in terms of using galactomannans and arabinans in chemotyping, support the suggestion of Rizzini that S. parahybae and S. amazonicum are not different species.

Location of O-acetyl groups in the acidic d-xylan of mimosa scabrella (bracatinga). A study of O-acetyl group migration

Abstract Extraction with dimethyl sulfoxide of wood-meal of the stem of bracatinga (Mimosa scabrella), a south Brazilian hardwood, that was defatted and delignified by treatment with aqueous chlorine at 0–5° followed by extraction with cold ethanol, gave a soluble O-acetylated 4-O-methyl- d -glucurono- d -xylan having (1→4)-linked β- d -xylopyranosyl residues that were unsubstituted (65%) and 2-O-(14%), 3-O- (16%), and 2,3-di-O-acetylated (5%), as determined by methylation analysis. Another preparation obtained by use of refluxing ethanol in the delignification process showed neither removal nor migration of acetyl groups. By comparison with synthetic, partly O-acetylated d -xylans of known composition, 13C-n.m.r. spectroscopy indicated that O-acetyl group migration does not occur during treatment with cold aqueous chlorine, refluxing ethanol, or water at 70°. Methyl 2-O-acetyl-4-O-methyl-β- d -xylopyranoside (6) was also unaffected by aqueous chlorine. O-Acetyl group migration took place more readily in aqueous and dimethyl sulfoxide solutions of 6 than of O-acetyl- d -xylans. The lowest temperatures at which migration was observed in monosaccharides was at 50 and 70° for solutions in D2O and (CD3)2SO, respectively.

Oligosaccharides derived from the xyloglucan isolated from the seeds of Hymenaea courbaril var. stilbocarpa.

On aqueous extraction, Hymenaea courbaril var. stilbocarpa, known in Brazil as jatobá, furnishes a high yield of viscous xyloglucan (45%) from its seeds. The crude polysaccharide (B1) was hydrolysed and the products, analysed as alditol acetates, were glucose, xylose, galactose and arabinose in the ratio 50:35:13:2. After further fractionation on DEAE-cellulose column (chloride form), the main fraction (70% yield, B2) was obtained. The basic structure of the xyloglucan was determined as a cellulose-type (1-->4)-linked beta-D-glucan backbone partially substituted with side chains at O6 of alpha-D-xylopyranose, some of which were themselves substituted at O2 by the units of beta-D-galactopyranose. Treatment of the xyloglucan (B2) with commercial cellulase from Trichoderma sp. yielded six oligosaccharides. These oligosaccharides were isolated by preparative paper chromatography, and their structures were determined by gas-liquid chromatography-mass spectroscopy of the derived partially O-methylated alditol acetates. These results confirm the structure proposed for jatobá seed xyloglucan.

Structural Studies on Galactomannans From Brazilian Seeds

Abstract Chemical structures of galactomannans from the native Brazilian species, M. scabrella, S. barbatiman and S. parahy-bum were studied. Their seeds, on aqueous extraction, furnished high yields of viscous galactomannans, whose mannose to galactose ratios were 1.1:1, 1.5:1, and 3.0:1, respectively. The polysaccharides were analysed by methylation, periodate oxidation and chromium trioxide oxidation. The results, confirmed by 13C NMR spectroscopy, indicated expected structures of legume galactomannans, namely a polymeric main chain of (l→4) -linked β-D-mannopyranosyl residues substituted at 0–6 by single unit α-D-galactopyranosyl side-chains. 13C NMR spectra showed clear splitting of the O-substituted resonances of C-4 of the β-D-mannosyl residues depending on the nearest-neighbour probabilities, indicating a random arrangement of the D-galactosyl groups in all of the three galactomannans.