M.-R. Sierakowski

Starch films reinforced with mineral clay

Abstract A mineral clay was used as filler in order to improve the mechanical properties of glycerol-plasticized Cara starch films. These were characterized by mechanical and dynamic mechanical analysis, X-ray diffraction (XRD), thermogravimetry, infrared spectroscopy, and scanning electron microscopy. Dynamic mechanical analyses showed that the composite films give rise to three relaxation processes, attributable to a transition of the glassy state of the glycerol-rich phase, to water loss including the interlayer water from the clay structure, and to the starch-rich phase. A film obtained with 30% in w/w of clay showed an increase of more than 70% in the Young modulus compared to non-reinforced plasticized starch. Both XRD and infrared spectroscopy showed that glycerol can be intercalated into the clay galleries and that there is a possible conformational change of starch in the plasticized starch/clay composite films. Clay exfoliation occurred in unplasticized starch/clay mixtures.

Amylose contents, rheological properties and gelatinization kinetics of yam (Dioscorea alata) and cassava (Manihot utilissima) starches

Abstract After defatting yam and cassava starches have amylose contents of 36.2 and 24.2%, respectively. Suspensions of these starches in water were analysed, in an oscillatory rheometer, using a heating rate of 4.0 °C min−1, deformation of 1% and a frequency of 1 Hz, the initial temperatures of gelatinization being 71 and 62 °C for yam and cassava, respectively. A gelatinization study was also carried out by differential scanning calorimetry with different heating rates (2.5, 3.0, 4.0 and 5.0 °C min−1), to give, by the Arrhenius equation, the activation Energy (Ea) of the process. Yam starch showed a more energetic gelatinization process of when compared to cassava starch and also had a lower rate constant (s−1), indicating a relatively slow gelatinization process of at higher temperatures. Yam gels formed by autoclaving a suspension (50 g l−1) showed after 24 h of refrigeration, a stronger structure than for a cassava gel.

A rheological description of mixtures of a galactoxyloglucan with high amylose and waxy corn starches

Abstract A galactoxyloglucan hydrocolloid (HXG) was extracted with water from endosperms of seeds of Hymenaea courbaril and purified (18.5% yield). It contained galactose, xylose, and glucose in a ∼1:3:4 molar ratio. HXG was mixed with a high amylose (66%) (CSM) and waxy corn starch (CSP). Each gel mixture, under static rheological conditions, showed an increase in the paste viscosity, when compared with those of starches or HXG alone. Dynamic rheological analysis showed an interaction occurred in the HXG–CSM mixture resulting in an increased thermal stability of its gel, when compared with that of CSM alone.

Nanocomposites coated with xyloglucan for drug delivery: In vitro studies

Enalaprilate (Enal), an active pharmaceutical component, was intercalated into a layered double hydroxide (Mg/Al-LDH) by an ion exchange reaction. The use of a layered double hydroxide (LDH) to release active drugs is limited by the low pH of the stomach (pH approximately 1.2), in whose condition it is readily dissolved. To overcome this limitation, xyloglucan (XG) extracted from Hymenaea courbaril (jatobá) seeds, Brazilian species, was used to protect the LDH and allow the drug to pass through the gastrointestinal tract. All the materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, elemental analyses, transmission electronic microscopy, thermal analyses, and a kinetic study of the in vitro release was monitored by ultraviolet spectroscopy. The resulting hybrid system containing HDL-Enal-XG(3) slowly released the Enal. In an 8-h of test, the system protected 40% (w/v) of the drug. The kinetic profile showed that the drug release was a co-effect behavior, involving dissolution of inorganic material and ion exchange between the intercalated anions in the lamella and those of phosphate in the buffer solution. The nanocomposite coated protection with XG was therefore efficient in obtaining a slow release of Enal.

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.

Electrospinning of commercial guar-gum: Effects of purification and filtration

Guar gums of two different commercial sources were successfully electrospun on both mica and copper tape at several concentrations starting from 1% (w/w). The electrospun fibers formed with the raw materials were not uniform and presented aggregates and beads within the fibers. Two different purification procedures and a filtration sequence with different pore size membranes were applied to enhance galactomannan solution homogeneity and solubility. The consequence was improved fiber morphology. We observed that the precipitation step, within the purification procedure, produced changes in the molar mass distribution and yielded different fiber diameter. Furthermore, spherical aggregates between fibers and within them disappeared after the sequential filtration. The resulting electrospun fiber diameter decreased with membrane pore diameter reduction. We conclude that the filtration process is responsible for molecular disentanglement, as well as disaggregation, which leads to improved electrospun galactomannan fiber morphology.

Adsorption behavior of oxidized galactomannans onto amino-terminated surfaces and their interaction with bovine serum albumin

Galactomannans extracted from Cassia fastuosa (CF) and Leucaena leucocephala (LL) seeds were purified and oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) to form the uronic acid-containing polysaccharides CFOX with a degree of oxidation (DO) of 0.22 and LLOX with DO of 0.66, respectively. The adsorption behavior of CFOX and LLOX onto amino-terminated surfaces was studied by means of ellipsometric measurements. The influence of pH and ionic strength on the adsorption was investigated. A strong dependence of pH on the adsorbed amount of CFOX and LLOX was observed. At pH 4, there was a maximum in the adsorbed amount caused by strong electrostatic attraction between the substrate and the oxidized galactomannans. On the other hand, no ionic strength effect on the adsorption of CFOX and LLOX was observed. The immobilization of bovine serum albumin onto LLOX and CFOX was studied as a function of pH. LLOX proved to be a more attractive substrate for BSA than CFOX, indicating that the favorable interactions between the carboxylate groups and the BSA segments have driven the adsorption process. At the isoelectric point of BSA a maximum in the adsorbed amount was found for both surfaces.

Physico–chemical aspects of galactoxyloglucan from the seeds of Hymenaea courbaril and its tetraborate complex

A galactoxyloglucan hydrocolloid (HXGRP) (Glu:Xyl:Gal molar ratio, ∼4:3:1) was obtained from cotyledons of seeds of Hymenaea courbaril by aqueous extraction and then purified (33% yield). Rheological measurements showed that HXGRP, in aqueous systems, interacts with tetraborate ions increasing both, viscosity and G′ values, also increasing the viscoelasticity of the system, but not forming a gel, as shown by Cox-Merz experiments. This interaction dependent of the amount of sodium tetraborate and the pH, and was analyzed in terms of hindered reptation. A temperature sweep of the HXGRP-tetraborate complex showed a characteristic cleavage of cross-links between polysaccharide and borate ions at high temperatures. An aqueous solution of HXGRP after heating at 85 °C for 2 h showed a decrease in its absolute viscosity.

Effect of the oxidation level on the thermogravimetric kinetics of an oxidized galactoxyloglucan from Hymenaea courbaril (Jatobá) seeds

Abstract A natural hydrocolloid extracted from Hymenaea courbaril seeds contains Glc:Xyl:Gal:Ara in a molar ratio of 51:27:21:1. Selective TEMPO radical oxidation (2,2,6,6-tetramethylpiperidine-1-oxyl) at C-6 of the polysaccharide gave products with 3.0, 5.1 and 9.5% of carboxyl groups as determined colorimetrically. Molecular mass analyses showed a decrease in the M w of the oxidized galactoxyloglucans and an increase in angular fit from the RMS ratio versus molar mass plot. This indicated that the oxidation process generated a more rigid structure, going from a random coil in the native polymer to a rod conformation in the oxidized samples, probably due to the polyanionic structure. Thermogravimetric kinetics of degradation was obtained using the Arrhenius equation and an increase in the degradation rate, was apparently directly dependent on the oxidation level.

Equilibrium studies of galactomannan of Cassia fastuosa and Leucaena leucocephala and Cu2+ using potentiometry and EPR spectroscopy

Abstract The binding constants of Cu 2+ and galactomannans composed of sugar units of mannose and galactose from the seeds of Cassia fastuosa and Leucaena leucocephala were determined by potentiometric titrations and inspected by EPR spectroscopy. Two complexed species were found in both systems, one moiety being the metal ion (M) and the other moiety a sugar monomer of the polysaccharide (L), non-protonated, ML, and protonated, MHL. The values for the logarithms of the binding constants are in the range of 15 units for ML for both employed galactomannans, and 8.0 for MHL for Man:Gal medium average ratio 4:1 galactomannan ( C. fastuosa ) and 6.8 for Man:Gal medium average ratio 2.6:1 one ( L. leucocephala ). The EPR spectra have shown one octahedral complex species linked through the oxygen atoms of the hydroxyl groups of the monomer with tetragonal deformation. The A and g obtained values were A ∥ = 178G, g ∥ = 2.260, and g ⊥ = 2.050 and A ⊥ = 30G for CU 2+ with the galactomannans. This was assigned to be ML 2 complex which was only detected in the solid state due to the formation of insoluble products in solution, above pH value of 7.0. The extension of formation of complexed species of galactomannans with Cu 2+ is probably much more affected by the pH variation than by the degree of substitution of monomers of the chain of the biopolymers studied so far.