Felipe Cordobés

Water−Ethylene Glycol Cationic Dimeric Micellar Solutions: Aggregation, Micellar Growth, and Characteristics As Reaction Media

Effects of ethylene glycol (EG) addition on the micellization and on the micellar growth in two aqueous didodecyl dicationic dibromide surfactant, 12-s-12,2Br- (s=2, 6) solutions, with the weight percentage of EG up to 50%, have been investigated. An increment in the amount of EG makes the aggregation process less spontaneous due to the water-EG mixtures being better solvents for the cationic dimeric surfactant molecules than pure water (solvophobic effect). Results show that C*, the surfactant concentration where the sphere-to-rod transition occurs, increases when EG content in the bulk phase increases. The amount of the organic solvent influences C* principally through the decrease in the hydrocarbon/bulk phase interfacial tension (air/bulk phase surface tension) caused by its presence. Changes in the aggregation number, in the micropolarity, in the microviscosity, and in the rheological behavior accompanying micellar growth were studied in the water-EG micellar solutions. Kinetic studies provide information about the characteristics of the dimeric micelles as microreactors. Kinetic data also show that an increase in the surfactant concentration leads to micellar growth.

Interfacial and oil/water emulsions characterization of potato protein isolates.

Interfacial and emulsifying properties of potato protein isolate (PPI) have been studied to evaluate its potential application to stabilize oil/water emulsions at two pH values (2 and 8). The amount, type, and solubility of proteins and the size of aggregates have been determined in aqueous dispersion. Air-water and oil-water interfacial properties (adsorption, spreading, and viscoelastic properties) have been determined as a function of concentration and pH using soluble phases of PPI. The behavior of PPI stabilized oil/water emulsions has been then analyzed by droplet size distribution measurements and interfacial concentration. PPI exhibits low solubility over a wide range of pH values, with the presence of submicrometer aggregates. The pH value exerts a negligible effect on interfacial tension (oil-water) or surface pressure (air-water) but displays very important differences in viscoelastic properties of the interfacial films formed between oil and water. In this sense, pH 8 provides a major elastic response at oil-water interfaces as compared to pH 2. In relation with this result, a much higher ability to produce fine and stable emulsions is noticed at pH 8 as compared to pH 2. Consequently, there is an evident relationship between the rheological properties of the oil-water interfacial films and the macroscopic emulsion behavior.

Enhancement of gel strength by application of thermal treatments in highly flocculated emulsions

Thermal-induced changes of the rheological behavior of flocculated emulsions through the optimization of in situ thermorheological treatments, as well as the effect that several compositional variables (oil fraction, egg yolk concentration or cholesterol reduction level) exert on the enhancement of gel strength, were investigated. With this aim, oil-in-water emulsions were prepared using a spray-dried egg product. Different temperature ramps under oscillatory shear and droplet size distribution measurements were carried out. An increase in temperature produces, first of all, an increase in the storage modulus up to a critical temperature, which depends on heating rate. Subsequently, a dramatic decrease in the viscoelastic functions occurs, due to emulsion breakdown. However, the application of upward/downward temperature cycles, setting the maximum temperature at 67 °C, avoids emulsion breakdown and yield significantly higher values of the rheological functions in comparison to those found with fresh emulsions, in spite of the thermal-induced droplet coalescence observed. The final values of linear viscoelastic functions and droplet size depend on the type of cycles applied, which are based on different heating rates or times at the maximum temperature, and emulsion composition.

Development of crayfish bio-based plastic materials processed by small-scale injection moulding.

BACKGROUND Protein has been investigated as a source for biodegradable polymeric materials. This work evaluates the development of plastic materials based on crayfish and glycerol blends, processed by injection moulding, as a fully biodegradable alternative to conventional polymer-based plastics. The effect of different additives, namely sodium sulfite or bisulfite as reducing agents, urea as denaturing agent and L-cysteine as cross-linking agent, is also analysed. RESULTS The incorporation of any additive always yields an increase in energy efficiency at the mixing stage, but its effect on the mechanical properties of the bioplastics is not so clear, and even dampened. The additive developing a greater effect is L-cysteine, showing higher Youngs modulus values and exhibiting a remnant thermosetting potential. Thus, processing at higher temperature yields a remarkable increase in extensibility. CONCLUSION This work illustrates the feasibility of crayfish-based green biodegradable plastics, thereby contributing to the search for potential value-added applications for this by-product.

Influence of Protein Concentration on the Properties of Crayfish Protein Isolated Gels

Crayfish protein, present in the wastes from crayfish processing, has been investigated as an ingredient of surimi-like gel products, which may be regarded as a renewable, available, and low-cost raw material. The aim of this study was to evaluate the influence of protein concentration on the gelation behaviour and gel properties of crayfish protein isolate-based systems. Gelation was performed by heating crayfish protein isolate dispersions at 90°C for 30 min. Then, gels were cooled at 4°C and the evolution of linear viscoelastic properties upon setting was analysed for 24 h. An increase in both linear viscoelasticity and water holding capacity was found as protein concentration increased, although an asymptotic evolution was found at the highest CFPI concentrations. Scanning electron microscopy revealed occurrence of an extended cross-linked network for crayfish protein isolate gels. These results suggest that crayfish protein can be properly used as a valuable ingredient in food gels, where protein concentration may be modulated to enhance gel strength.

Linear Viscoelasticity of Concentrated Polyethylene Glycol tert-Octylphenyl Ether Solutions

Linear viscoelastic studies were carried out on concentrated polyethylene glycol tert-octylphenyl ether solutions over a range of temperatures and concentrations comprising the lamellar and hexagonal liquid-crystalline phases and the isotropic surfactant-rich phase. The generalized or a simple Maxwell model fits the frequency dependence of the dynamic functions for the hexagonal and isotropic surfactant-rich phases, respectively. The combined influence of temperature and concentration on both the zero-shear rate-limiting viscosity and the relaxation time for isotropic samples follows an exponential dependence. The results are discussed according to the phase behaviour of these systems.

Thermal gelation of mixed egg yolk/kappa-carrageenan dispersions

This study aims to evaluate the effect of gum content and pH on the thermal gelation of mixed egg yolk/κ-carrageenan (EY/κC) dispersions, monitored by linear viscoelastic measurements. Heat processing induces dramatic changes in the microstructure and viscoelastic properties of EY/κC systems, which may be attributed to a multistage mechanism that yields an interparticle gel network. An increase in κC content generally induces an enhancement in viscoelasticity. A reduction in pH hinders this enhancement and causes an anticipation of the multistage process, which confirms the importance of the electrostatic interactions of EY/κC dispersions. The viscoelastic properties of EY/κC gels generally fit a master mechanical spectrum, which suggests that the protein matrix generally dominates the microstructure of EY/κC gels. However, SEM images reveal formation of a κC network at low pH, at which some κC autohydrolysis may also play a role. Electrostatic attractions seem to favour interactions among EY aggregates and κC into the carrageenan network.

Rheological Behaviour of the Hexagonal Liquid Crystalline Phase for a Heptane/Nonionic Surfactant/Water System

Lyotropic surfactant liquid crystals are typically formed by surfactants, water, and/or an organic compound. They can be considered as ordered networks of giant micelles, and find interesting applications in different fields: detergents, cosmetics, Pharmaceuticals, emulsions, etc. The structure of hexagonal liquid cristalline phases consists of long cylindrical micelles which are parallel to each other within a hexagonal array, although this liquid crystal is polycrystalline, being the cylinder aggregates orientated within compact packs of microscopic domains. This microstructure yields a very complex rheological response.