Jean-Claude Fenyo

Effect of a proteinase on the macromolecular distribution of Acacia senegal gum

Abstract Molecular size distribution of Acacia senegal gum on Sephacryl gel S-400 is compared before and after incubation with the proteolytic enzyme Pronase. The profile and elution volumes of chromatograms are greatly modified: a rather broad system of high molecular weight peaks near the exclusion volume is resolved into a single peak at lower molecular weight. Physicochemical data from isolated Pronase-treated samples tend to favour, for crude Acacia senegal gum, a structure where varying numbers of polysaccharide units of MW ca 2×105 are linked to a protein core. The effect of Pronase on Acacia mearnsii and Combretum nigricans gums was also investigated. Our results are discussed in relation to structural models proposed for these arabinogalactan-protein complexes.

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

Abstract 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.

Heterogeneity and homogeneity of an arabinogalactan-protein: Acacia senegal gum

Abstract Proteolysis of Acacia senegal gum by pronase leads to subunits of ~200 000 weight-average mol. wt. The origin of gum heterogeneity is discussed and considered to be due to a variable number of sub-units linked to a protein core.

Analysis of aromatic caramel

Abstract Aromatic caramel is composed of saccharides (sucrose, fructose and glucose) and a lot of degradation products which contribute to its aroma and flavour. Identification of these species currently needs preliminary extraction. A new device is presented in this paper to avoid this step using a continuous trapping on adsorbent when heating, followed by a thermal desorption and overall analysis. Fifty-seven compounds were detected by this technique and also by solvent extraction and vapour analysis during cooking. Some unexpected intermediate volatile molecules were noted which can play an important role in the formation of the flavouring compounds.

The characterization of gum arabic from an experimental field of Ferlo (North Senegal)

Abstract Viscosity, specific rotation and nitrogen content of 75 samples exudated by authenticated Acacia senegal trees of the sahelian station of M’Biddi (Ferlo, North Senegal) have been measured closely after their collection. The values of these parameters are largely scattered when compared with data generally accepted for commercial products, and only few fall completely within the specifications proposed by the JECFA-FAO. This behaviour is analyzed mainly in terms of the macromolecular structure of these fresh samples and the inherent heterogeneity of the exudates. Mechanical or moderate heat treatments are able to reduce this discrepancy. Moreover, no correlation has been found between the physico-chemical parameters and external conditions such as the location of the trees, tapping, harvesting or yields.

Meaning of molecular weight measurements of gum arabic

SummaryThe weight-average MW and number-average Mn molecular weights of gum arabic are identical after a proteolysis treatment with pronase. The value (1.8×105) is closed from Mn early reported in the literature whereas MW before treatment are dispersed for a large lot of samples up to more 106. This can be interpreted by the “wattle blossom” model for which some homogeneous chains of molecular weight c.a. 2.105 are still linked to a protein core, the crude gum being a mixture of this complex and free chains.

Separation of Nickel and Cobalt by Electrodialysis Using Ion-Exchange Membranes in the Presence of EDTA

Abstract Electrodialytic separation of Ni2+ and Co2+ cations has been realized by using ion-exchange membranes in the presence of EDTA by preferentially complexing Ni2+(Ni2+ concentration = EDTA concentration). The degree of complexation is calculated as a function of the pH and of the concentration by using data taken from the literature. Due to a systematic study of the influence of the different separation parameters (nature of the membranes, flow rate, electric current intensity, pH), the conditions_of_separation have been optimized on a computer, and then pure solutions of nickel and cobalt ions have been obtained experimentally. The decomplexation of Ni2+ is accomplished in acidic medium by cooling.

Estimation of the charge density of arabic acid by potentiometry and dye binding

SummaryPotentiometric data of arabic acid in salt-free aqueous Solutions can be interpreted by the Lifson-Katchalsky cell model. The best fit between experimental and theoretical titration curves is obtained using a spatial intercharge distance of 11 Å. This value is corroborated by equilibrium dialysis binding of Ethidium Bromide. When compared with already published results, the apparent charge density of arabic acid is four to six times higher than if it was a linear polyelectrolyte.

Compact Conformation of Polyions Stabilized by Non-Electrostatic Short-Range Interactions

The macromolecular behaviour of some hydrophobic polymers has been investigated by various methods, namely potentiometric, viscosimetric and optical measurements. All the reported results are interpreted by the existence of non-electrostatic short-range interactions leading to a partial or nearly complete screening of electrostatic repulsions. In water, the stabilization of compact conformations lies in a more or less wide range of ionization depending on the hydrophobic character of the polymeric chains and/or of the counter-ion. In the peculiar case of a polycondensate between l-lysine and 1,3-benzenedisulfonyl chloride (PLL), the observed transition from a very compact structure to a mean coil-like one is found to be strongly dependent on the length of apolar groups (and hydrophobicity) of n-tetraalkylammonium counter-ions. In the presence of bulky n-tetraalkylammonium (Bu4N+), the cohesive forces are predominant until α is around 0.7. By partial replacement of water by a good organic solvent of the polymeric chains, or in aqueous solution of urea, normal polyelectrolytic behaviour without any discontinuity in both potentiometric and viscosity changes is observed.

Molecular Weight Determination of an Optically Active Polysulfonamide (PLL) Synthetized by Interfacial Polycondensation

SummaryIn order to study their molecular weight, optically active polysulfonamides were investigated by light scattering and viscosity measurements. The corresponding MARK-HOUWINK type relation is established.