Cristina T. Andrade

Solution properties of the galactomannans extracted from the seeds of Caesalpinia pulcherrima and Cassia javanica: comparison with locust bean gum

The galactomannans from the seeds of Caesalpinia pulcherrima and Cassia javanica were extracted from the milled seeds in water at room temperature. Both products, as well as a commercial sample of locust bean gum (LBG), were purified by precipitation in isopropyl alcohol. The intrinsic viscosity determined for LBG, [eta] = 15.2 dl/g, was slightly higher than those for the other two galactomannans. The dependence of the specific viscosity at zero shear rate on the coil overlap parameter, C[eta], revealed a similar behaviour for the three galactomannans. A master curve was obtained with a critical concentration, C*, at C*[eta] = 3.3. The slope of the curve in the concentrated regime is higher than the values in the range of 3.9-6.6, obtained for the generalized behaviour of several random coil polysaccharides. Dynamic experiments showed that, at the concentrations studied, the behaviour of the galactomannans was typical of systems with predominant entanglement networks in the region between the terminal and plateau zones of frequency response. The correlation between dynamic and steady shear properties (Cox Merz rule) was satisfactory for the three galactomannans.

High resolution imaging of the microstructure of maize starch films

Glycerol-plasticised and non-plasticised cast films were prepared from maize starch suspensions that had been heated under reflux for different periods of time. Light microscopy (LM) and atomic force microscopy (AFM) have been used to observe the morphology of the starch films. In general, LM and AFM topographic images of corresponding non-plasticised films were similar. AFM topographic images of plasticised films revealed differences associated with the retarding effect of glycerol on the gelatinisation process. Relatively high B-type crystallinity indices were determined for plasticised films, independently of the heating conditions to which the suspensions had been submitted. AFM topographic images of plasticised films at higher magnifications revealed smooth and rough domains, that were detailed by phase contrast imaging.

Role of conformation and acetylation of xanthan on xanthan-guar interaction

The synergistic effect obtained by mixing xanthan and guar solutions were examined by low shear viscosity measurements in relation to the temperature. Native and deacetylated xanthan samples were used in mixtures in which the total polymer concentrations were 1 g/litre and 0·5 g/litre. Gelation was observed for temperatures lower than 15°C for the native xanthan-guar system (weight ratio 11) in 10−2 m NaCl and at 22–24°C for the same system in water; in this last case, it is known that the xanthan is in the disordered conformation. For a mixture of deacetylated xanthan-guar, gelation was observed at a temperature below 26°C in water. The results confirm that there is a stronger interaction between deacetylated xanthan and guar than native xanthan and guar because of enhanced xanthan-guar gum backbone association in the former case.

Investigação dos Processos de Gelatinização e Extrusão de Amido de Milho

Resumo: Os processos de gelatinizacao e de extrusao de amido de milho foram estudados. Calorimetria diferencial de varredura e miscroscopia optica foram utilizadas na determinacao da temperatura de gelatinizacao, T(G), em funcao do grau de umidade. Misturado a plastificantes, o amido foi processado em extrusoras mono- e dupla-rosca para obtencao de termoplasticos. As propriedades mecânicas dos filmes obtidos por processamento em extrusora dupla-rosca foram investigadas. A analise termo-dinâmico-mecânica do filme de amido termoplastico com 33% (p/p) de plastificantes revela a presenca de duas transicoes distintas, atribuidas as transicoes das duas macromoleculas constituintes do amido. Palavras-chave: Gelatinizacao, amidos termoplasticos, extrusao, propriedades fisicas. Investigation of corn starch gelatinization and extrusion processes Abstract: The gelatinization and extrusion processes of corn starch were studied. Differential scanning calorimetry and optical microscopy were used to determine the gelatinization temperature, as a function of the water content. Plasticized corn starch was processed in single- and twin-screw extruders to produce thermoplastic materials. The mechanical properties of the films obtained in the twin-screw extruder were evaluated. The thermo-dynamical-mechanical analysis of the thermoplastic starch with 33% (w/w) plasticizers showed two transitions, attributed to the starch constituents.

Characterisation of Prosopis juliflora seed gum and the effect of its addition to kappa-carrageenan systems

The galactomannan from Prosopis juliflora (PJ galactomannan) was extracted from milled seeds in water at 50 oC. Its structural and solution properties were characterised in comparison with a commercial sample of guar gum (GG galactomannan). After partial degradation, the resulting samples were submitted to 13C-NMR spectroscopy. The mannose to galactose (M/G) ratios of PJ (M/G = 1.64) and GG (M/G = 1.85) galactomannans were estimated from the relative peak areas of the corresponding C-1 lines. Expansion of the C-4 lines revealed differences in the fine structure of the two galactomannans. The intrinsic viscosity determined for the GG sample, [h] = 10.3 dL g-1, was slightly higher than that determined for PJ galactomannan, [h] = 9.4 dL g-1. Dynamic experiments carried out at the same concentrations showed similar viscoelastic behaviours for the two gums. No enhancement in the storage modulus (G¢) was observed for k-carrageenan/PJ mixed solution in 0.1 mol L-1 KCl at 1.0 g L-1 total polymer concentration, in relation to k-carrageenan alone. Self-supporting gels obtained by mixing k-carrageenan and PJ or GG galactomannans in 0.25 mol L-1 KCl at 10 g L-1 total polymer concentration displayed similar mechanical properties.

Rheological study of the effect of Cassia javanica galactomannans on the heat-set gelation of a whey protein isolate at pH 7

Abstract The effect of Cassia gum galactomannan on the thermal gelation of a whey protein isolate (WPI) at 80 °C has been monitored by rheological dynamic measurements at fixed frequency and the mechanical spectra of the gels have been recorded at 80 °C and after quenching to 20 °C. The mechanical spectra were analysed quantitatively by fitting a Cole–Cole model to the storage and loss compliance versus frequency data. The concentration of WPI was 110 g/l and that of Cassia gum varied from 0 to 11 g/l. At low concentration, the presence of the galactomannan enhanced the aggregation rate and the strength of the protein gel but did not modify intrinsically the gelation process and the structure of the system. At higher galactomannan concentrations, the gels displayed substantially lower moduli values and the shape of the mechanical spectra was modified. This was tentatively interpreted as the consequence of a depletion-induced liquid–liquid phase separation occurring during the course of the aggregation process, responsible for the downturn observed on the loss modulus versus time curves monitored at 80 °C.

Properties of poly(methyl methacrylate-g-propylene oxide) in solution

SummaryGraft copolymers of poly(methyl methacrylate) backbone and uniform poly(propylene oxide) branches were synthesized by the macromonomer technique and characterized by VPO, GPC and 1H-NMR. Viscometric investigations of unfractionated samples were carried out at 25°C in chloroform and toluene (non-selective solvents) and in carbon tetrachloride (a selective solvent for the branches). The coefficients of the Huggins, Kraemer, Martin and Schulz-Blaschke equations were calculated. According to the values obtained for the Huggins coefficient, kh, the best solvent for the copolymer seems to be chloroform. The positive values of the Kraemer coefficient, kk, determined in carbon tetrachloride, suggest that the copolymer assumes a star-like conformation in this solvent.

Effect of melt-processing and ultrasonic treatment on physical properties of high-amylose maize starch

High-amylose maize starch (Hylon VII) was submitted to melt-processing in an internal mixer at 100 degrees C and 40 rpm for 8 min. Glycerol was used as a plasticiser at different polymer/glycerol ratios. Torque and temperature curves were obtained. After glycerol extraction with ethyl alcohol, the samples were dispersed at 5 g/L, and treated by ultrasound radiation at the same conditions for 30 min. Samples were characterised by (1)H NMR spectrometry, viscosity measurements, and X-ray diffractometry. The results revealed that both glycerol and water had an important role on the crystallinity properties of the resulting products. Melt-processed and sonicated samples showed similar (1)H NMR spectra. Ultrasound treatment caused a significant reduction in intrinsic viscosity for the sample previously processed with the highest glycerol content, probably because of its higher solubility in water.

UV‐light induced crosslinking reaction of cinnamate natural rubbers: Effect of the spacer length, counter‐ion nature, and content

Maleated natural rubber was modified by introducing different contents of cinnamate groups, separated from the main chain by —(CH2)n— spacers (n = 2 to 6). Residual carboxylic acid groups were neutralized as Li, Na, and K-salts. The kinetic behavior of these materials towards ultraviolet-induced crosslinking reaction was investigated and correlated with Tg.

Complex coacervates obtained from peptide leucine and gum arabic: Formation and characterization

In this study, interactions between polypeptide-leucine (0.2% w/w) and gum arabic (0.03, 0.06, 0.09, 0.12, and 0.15% w/w) were examined at concentrations of NaCl (0, 0.01, 0.25, 0.3, 0.5mol/l) and at different pH values (from 1.0 to 12.0). Formation of insoluble complex coacervates was highest at pH 4.0. At pH 2.0, which is the pKa of the gum Arabic, the dissociation of precipitate occurred. The pHØ2 positively shifted with the addition of higher concentrations of salt. Samples containing 0.2% PL and 0.03% GA and no salt had higher turbidity and increased formation of precipitates showing greater turbidity and particle sizes. The Fourier transform infrared spectroscopy confirms the complex coacervate formation of leucine and gum arabic, and rheological measurements suggest the elastic behavior of 0.2% PL and 0.03% GA complex. Overall, the study suggests that complex coacervates of PLs could be one feasible ways of incorporating amino acids in food products.