Formation Of Gel-like Structures Research Articles

Reactivity and Aggregative Stability of Colloidal Silica

The properties of colloidal silica taking into account the reactivity of silica, as well as the kinetics of polycondensation and depolymerization, are analyzed. The breaking of siloxane bonds during depolymerization leads to the appearance of reactive Si–OH and Si–O–Me+ groups, destruction of the silica structure, formation of gel-like layers on the surface and in the volume of particles (at a high level of alkalinity), growth of their hydrophilicity, and the dissolution of silica (limiting depolymerization). The formation of gel-like structures is accompanied by an increase in the hydrodynamic radii of the particles, an increase in the viscosity of aggregative stable sols, a decrease in their turbidity upon transition from acidic to alkaline media, sol dilution, and the introduction of electrolytes. Alkalis affect the solid phase depolymerization process by increasing the cation basicity in the series K+ > Na+ > Li+. The formation of gel-like structures causes an increase in the aggregative stability of the sol at pH> 5.5–6.0. Upon reaching pH 9.0–9.5, the quasi-equilibrium of the polycondensation rates and depolymerization reactions ensures the high aggregative stability of the sol. The further increase in alkalinity (increase in pH, silica modulus) in the aqueous phase increases the concentration of depolymerization products and silicate anions containing ionized and non-ionized silanol groups. Under these conditions, the oligo- and polymeric molecules of silicic acids are formed in the aqueous medium during the secondary polycondensation, and, based on them, linear supramolecular structures, the viscosity of the colloidal system grows, and gels are formed.

Mechanism of Thermal Degradation-Induced Gel Formation in Polyamide 6/Ethylene Vinyl Alcohol Blend Nanocomposites Studied by Time-Resolved Rheology and Hyphenated Thermogravimetric Analyzer Fourier Transform Infrared Spectroscopy Mass Spectroscopy: Synergistic Role of Nanoparticles and Maleic-anhydride-Grafted Polypropylene.

In this study, polyamide 6 (PA) is blended with ethylene vinyl alcohol (EVOH) to yield packaging materials with a balance of mechanical and gas barrier properties. However, the formation of gel-like structures in both polymers because of thermal degradation at high temperatures leads to a processing challenge, particularly during thin-gauge film extrusion. To address this challenge, nanoclays are introduced either directly or via a masterbatch of maleic-anhydride-grafted polypropylene to the PA/EVOH blend and time-resolved rheometry is used to study the effect of different modes of nanoclay incorporation on the kinetics of thermo-oxidative degradation of PA/EVOH blend and its nanocomposites. Time-resolved rheometry measurements allow the acquisition of accurate frequency-dependent linear viscoelastic behavior and offer insights into the rate of degradation or gel formation kinetics and cross-link density. The thermal degradation was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy, allowing the prediction of the possible reactions that take place during the rheological property measurements. The results show that when nanoclays are incorporated directly, the oxidative reactions occur faster. In contrast, in the masterbatch method, oxidative degradation is hindered. The difference in the behaviors is shown to lie in the different nanoclay distributions in the blends; in the blends prepared by the masterbatch method, the nanoclays are dispersed at the interface. In conclusion, the masterbatch-containing blend nanocomposite would benefit processing and product development.

Effects of the Application of Dense Phase Carbon Dioxide Treatments on Technological Parameters, Physicochemical and Textural Properties and Microbiological Quality of Lamb Sausages

The effects of different dense phase carbon dioxide (DPCD) treatments were evaluated on technological parameters, physicochemical and textural properties and microbiological quality of lamb sausages. Sausages were prepared using lamb meat (Longissimus dorsii, 68.6 % w/w), lamb fat (17.2 % w/w), water (12.9 % w/w) and NaCl (1.37 % w/w). Raw sausages were subjected to different CO2 pressures (10, 20 and 30 MPa) at 60 °C–30 min and treatment times (2, 14 and 25 min) at 55 °C–10 MPa. Weight loss, pH and total expressible fluid increased significantly (p < 0.05) as pressure increased from 0 to 30 MPa. These parameters also increased significantly (p < 0.05) as treatment time increased (at 10 MPa). The increase in CO2 pressure and treatment time significantly (p < 0.05) modified internal and surface color parameters. Lightness and b* values increased, whereas redness (a*) decreased. Also, the increase in CO2 pressure and treatment time significantly (p < 0.05) increased Warner–Bratzler shear force and textural parameters values. DPCD treatments may modify meat proteins, which may lead to weak interactions among proteins and formation of gel-like structures. Regarding microbial inactivation, the highest reductions in microbiological counts (2 Log CFU g−1) were obtained applying a CO2 pressure of 20 MPa at 60 °C for 30 min.

Manipulation of the Repertoire of Digestive Enzymes Secreted into the Gastrointestinal Tract of Transgenic Mice

In non-ruminant livestock the energy which can be derived from dietary cellulose and xylan is limited by the inefficient microbial fermentation of these polymers in the hind-gut. Furthermore, in poultry, cereal-derived plant structural polysaccharides impair normal digestive function through the formation of gel-like structures, which trap nutrients rendering them unavailable to the animal. The nutrition of non-ruminant livestock could be significantly improved by the depolymerization of plant structural polysaccharides, through the introduction of cellulase activity into the small intestines of these animals. Here we describe the expression of Clostridium thermocellum endoglucanase E in the exocrine pancreas of transgenic mice. A non-glycosylated active enzyme is secreted into the small intestines, and is resistant to proteolytic inactivation, demonstrating the feasibility of generating non-ruminant animals with the endogenous capacity to depolymerize plant structural polysaccharides in the small intestines.

The generation of non-ruminant transgenic animals with cellulolytic capacity.

In non-ruminant livestock the energy which can be derived from dietary cellulose and xylan is limited by the inefficient microbial fermentation of these polymers in the hind-gut. Furthermore, in poultry, cereal-derived plant structural polysaccharides impair normal digestive function through the formation of gel-like structures that trap nutrients which are therefore unavailable to the animal. The nutrition of non-ruminant livestock could be significantly improved by the depolymerization of plant structural polysaccharides, through the introduction of cellulase activity in the small intestines of these animals. This report describes the generation of transgenic animals with the capacity to express and secrete a functional endoglucanase from the exocrine pancreas.The gene encoding endoglucanase E (celE) from Clostridium thermocellum was fused to the exocrine pancreas specific enhancer of the elastase I gene and the (β-globin polyadenylation signal, and used to create 14 lines of transgenic mice. A range of tissues were assayed for cellulase activity, using β-glucan and 4-methylumbelliferyl-β-D-cellobioside as substrates. The pancreas was also subjected to immunohistochemistry and in situ hybridization.

Light Scattering of Protein Reactivity of Polysaccharides Especially of Carrageenans

The protein reactivity of various polysaccharides was studied by a simple light scattering technique. The formation of gel-like structures could be readily demonstrated. In agreement with the results of previous investigators we have observed that the milk reactivity of polysaccharides is closely related to their solubility in cold milk ultrafiltrate. κ-Casein and calcium are specifically involved in the interaction. The gel was set at 32.8 C±0.7. The setting and melting curves of the gels show considerable hysteresis.The method presented in this paper is simple and has the advantage of leaving the highly thixotropic structures unchanged during the measurement. It can be used for the screening of polysaccharides which differ in milk reactivity.Prospects for a quantitative characterization of the gel structure are discussed.