Effect of solvent composition on the association behavior of pectin in methanol-water mixtures

Turbidity, small-angle neutron scattering (SANS), and dynamic light scattering measurements have been carried out on semidilute systems of pectin in methanol-water media of various composition ratios. Structural and dynamical properties of pectin dissolved in water-methanol mixtures (case I) are compared with the corresponding conditions when pectin was dissolved in water before the prescribed amounts of methanol were added (case II). The turbidity rises as the percentage of methanol in the mixture increases and this trend is much stronger when the first procedure is used to dissolve pectin. The wavelength dependence of the turbidity indicates that larger association complexes are formed for the samples prepared according to case I. These findings indicate that at a given methanol-water composition, the preparation procedure in case I gives rise to poorer thermodynamic conditions of the system. Local structures probed by SANS experiments do not reveal any significant differences between the systems prepared by the two different procedures. The dynamic light scattering (DLS) results show that increasing methanol concentration in the mixture promotes the formation of association complexes and the disengagement relaxation time of individual chains or clusters is longer at higher percentage of methanol for case II. This can be attributed to stronger entanglement effects in case II. The features from DLS can be rationalized in the framework of the coupling model for constrained and interconnecting systems.     

Structural and dynamical properties of aqueous mixtures of pectin and chitosan

In this study phase separation, structure, and dynamics of aqueous pectin-chitosan mixtures of different ratios and a pure aqueous pectin sample have been investigated under various conditions by turbidimetry, SANS and dynamic light scattering (DLS). Only the mixture with r = 0.75 gelled upon decreasing the temperature ((r ≡ m_pectin/(m_pectin + m_chitosan), where m denotes the mass of the considered component). The pure pectin sample (r = 1) did not gel and the decrease in temperature seemed to promote phase separation. The addition of chitosan reduced the tendency of pectin to phase separate in the mixtures of pectin and chitosan. The general trend when cooling the samples was that the turbidity and the growth of the turbidity became more pronounced as the amount of pectin in the mixture was increased. The wavelength dependence of the turbidity indicated a change of the conformation of pectin chains from an extended form to a more compact structure in pectin solutions without chitosan as the temperature decreased. This was not observed for the mixture of pectin and chitosan. SANS measurements revealed excess scattered intensity in the low wave vector area with the strongest upturn for the pure pectin sample (r = 1). DLS experiments showed longer slow relaxation times after a temperature quench for all samples, with the most pronounced effect for the mixture of pectin and chitosan with r = 0.75. The synergism between pectin and chitosan at high pectin contents (r = 0.75) generated large association complexes over time.     

Porous nano-minerals substituted apatite/chitin/pectin nanocomposites scaffolds for bone tissue engineering

In the current study, a porous 3D scaffold using Gallium-Apatite/chitin/pectin (Ga-HA/C/P) nanocomposites scaffolds (NCS) were fabricated by freeze-drying process with applications in orthopedics (bone tissue engineering). Various NCSs (0%, 30%, 50 and 70%) were prepared and characterized for its chemical structure, crystalline phase, surface texture by using various techniques such as FT-IR, XRD and SEM-EDX, respectively. The analyses of physicochemical properties proved that the formulated scaffolds were highly porous, and mechanically stable with superior density. The nanocomposite scaffolds also presented with increased swelling ability, lower biodegradation rate and higher mechanical strength. Further, biocompatibility and cytotoxicity of Ga-HA/C/P nanocomposite scaffolds were studied using NIH3T3 cells and MG-63 cells revealed no toxicity and cells attached and proliferated on scaffolds. Further implantation of prepared NCS showed mature bone formation through formation of new bone cells and osteoblast differentiation. Also, Ga-HA/C/P nanocomposites scaffolds proved to be more effective than chitin-pectin composite scaffolds. Taking results together it can be inferred that the prepared nanocomposite scaffolds possesses the prerequisites and showed great potential for treating orthopedic applications.     

Kinetics and mechanism of permanganate oxidation of pectin polysaccharide in acid perchlorate media

The kinetics of oxidation of pectin polysaccharide as a natural polymer by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction time curves showed two distinct stages, the initial stage was relatively slow, followed by an increase in the rate of oxidation at longer times. The results of the initial rates reveal first-order kinetics in permanganate ion and fractional-order with respect to pectin concentration. Kinetic evidence for the formation of an intermediate complex between the polysaccharide and the oxidant is presented. The results obtained at various hydrogen ion concentrations showed that the reaction is acid catalyzed. The added salts lead to the prediction that Mn⁴⁺ and/or Mn³⁺ play an important role in the autoaccleration period kinetics. A tentative reaction mechanism consistent with the kinetic results is discussed.     

Effect of high intensity ultrasound on the structure and solubility of soy protein isolate-pectin complex

In this study, a soy protein isolate (SPI)-pectin (PC) complex was prepared, and the effects of different high intensity ultrasound (HIU) powers on the structure and solubility of the complex were studied. Fourier transform infrared (FTIR) spectroscopy analysis exhibited that with increasing HIU power, the α-helix content of the SPI in the complex was significantly reduced, and the random coil content increased; however, an opposite trend appeared after higher power treatments. Fluorescence spectra showed that HIU treatment increased the fluorescence intensity of the complex, and the surface hydrophobicity was increased. The trend of the protein structure studied by Raman spectroscopy was similar to that of FTIR and fluorescence spectroscopy. When the HIU treatment was performed for 15 min and at 450 W power, the particle size of the complex was 451.85 ± 2.17 nm, and the solubility was 89.04 ± 0.19 %, indicating that the HIU treatment caused the spatial conformation of the protein to loosen and improved the functional properties of the complex. Confocal laser scanning microscopy (CLSM) revealed that the complex after HIU treatment exhibited improved dispersibility in water and smaller particle size. Gel electrophoresis results indicated that HIU treatment did not affect the protein subunits of the complex. Therefore, the selection of a suitable HIU treatment power can effectively improve the structural properties and solubility of SPI in the complex, and promote the application of the SPI-PC complex in food processing and industries.     

A single sorbent for tetracycline enrichment and subsequent solid-matrix time-resolved luminescence

The aim of this study was to search for a sorbent that could act as an extraction phase and as a support for solid-matrix time-resolved luminescence (SMTRL). Four potential sorbents were investigated for this purpose using tetracycline (TC) as a model analyte. Sorbents prepared from C18 silica gel or calcium cross-linked pectin gel were able to extract TC from dilute solutions. Europium(III)-TC complex adsorbed on the surface of C18 generated the most intense TRL signal when measured at λ_ex = 388 nm and λ_em = 615 nm. This method achieved a 1 ng/ml limit of detection (LOD) with a 100 μl sample solution in a repeated spotting mode. Hyphenation of sorbent extraction and SMTRL was demonstrated using C18. This method is suitable for screening of TC in foods or aqueous solutions and can be extended to other luminescent lanthanide-chelating analytes in physiological or environmental samples.     

Photodegradation studies of novel biodegradable blends based on poly(ethylene oxide) and pectin

Blends of two biodegradable polymers: natural pectin and synthetic poly(ethylene oxide) at different weight-ratios were obtained by physical mixing in aqueous solutions, and evaporation of the solvent. The macromolecular order in the composites was investigated by applying X-ray diffraction, while the surface morphology was observed using atomic force microscopy. The photooxidative degradation of the blends was studied by viscometry, FTIR spectroscopy and UV-vis spectroscopy. It has been found that the susceptibility of the studied composites to UV radiation depends on an appropriate ratio of components, and the most sensitive to UV-irradiation among the samples studied was the equal weight-ratio blend of poly(ethylene oxide)/pectin.     

Pectin- and gelatin-based film: effect of gamma irradiation on the mechanical properties and biodegradation

Agricultural by-products, pectin and gelatin, were used to prepare a biodegradable film. The film casting solution including the pectin and gelatin was irradiated at 0, 10, 20, and 30 kGy to investigate the irradiation effect on the mechanical properties of the film. The tensile strength of the 10 kGy-irradiated film was the highest among the treatments but the elongation at break, water vapour permeability, and swelling ratio were the lowest. Hunter color L^*- and a^*-values decreased but the b^*-value increased as the irradiation dose increased. The total organic carbon content produced from the Paenibacillus polymyxa and Pseudomonas aeruginosa also showed that the film of 10 kGy-irradiated was lower than those of 0, 20, and 30 kGy-irradiated films. In conclusion, irradiation of the film casting solution at 10 kGy increased the mechanical properties of the pectin and gelatin based film. To manufacture the film by agricultural by-products, however, the irradiation dose of the film casting solution should be determined to achieve better mechanical properties.     

Association under shear flow in aqueous solutions of pectin

Effects of oscillatory and steady shear flows on intermolecular associations in dilute and semidilute aqueous solutions of pectin in the absence and presence of the hydrogen bond breaking agent urea are reported. A weak oscillatory shear perturbation builds up, depending on polymer concentration, multichain aggregates or networks in the course of time and these association structures are mainly stabilized through hydrogen bonds. The association effect is more pronounced at higher concentrations, and the growth of intermolecular interactions is inhibited by the addition of urea. Steady shear measurements on the pectin-water solutions reveal shear thickening at low shear rates for all the concentrations, except the lowest one, and disruption of intermolecular junctions at high shear rates. In the presence of urea, no shear thickening is detected. The polymer concentration dependence of the viscosity at a low shear rate can be described by a power law η ∼ c^x, with x = 1.9 and 1.4 without and with urea, respectively. When a low constant shear rate is applied to pectin solutions and this monitoring shear rate is interrupted periodically by transitory high shear rates perturbations during a short time, prominent association structures evolve upon return to the monitoring shear rate. This effect is more evident at a lower polymer concentration, and in the presence of urea, the growth of the association complexes is damped. The shear-induced alignment and stretching of polymer chains and the formation of hydrogen-bonded structures are analyzed in the framework of a model, where cooperative zipping of stretched chains play an important role. Viscosity enhancement is found for a semidilute pectin-water solution in the presence of moderate levels of salt addition (NaCl), suggesting that partial screening of electrostatic interactions promotes growth of energetic cross-links.     

Shear induced aggregation of a pectin stabilised emulsion in two dimensions

Shear induced aggregation of a Pectin stabilised emulsion trapped at the air-liquid interface was studied in a Couette system by video enhanced microscopy. From dimension analysis, Brownian motion was identified to enhance the probability of bond formation. The characteristic time scale of aggregation was found to scale as t_c ∼ η/φ rather than t_c ∼ 1/γ˙φ as expected for orthokinetic aggregation. The structure of very large clusters showed strongly rearranged strands and fractal scaling for low γ˙ and φ, analysed by density auto-correlation. At high γ˙ and φ, the cluster was dominated by larger drops and no fractal scaling could be determined for the accessible length scales. Received: 7 June 2000 Accepted: 1 August 2000