Textural Properties of Beta-lactoglobulin - Sodium Alginate Mixed Gels at Large Scale Deformation.

The denaturation and gelling properties of mixed systems of ß-lactoglobulin and sodium-alginate have been investigated as a function of alginate molecular weight, chemical composition, concentration, pH and ionic strength. Differential scanning calorimetry and small strain oscillatory measurements showed that denaturation temperature were lower than the gelling temperatures under the conditions examined. The denaturation temperatures were dependent on both pH and ionic strength, but unaffected by alginate concentration and type. The mechanical and textural properties of mixed gels of ß-lactoglobulin and sodium alginate were dependent on several factors; the gel strength increased as a function of alginate concentration under ambient conditions, and decreased as the pH and/or the ionic strength were changed. High molecular weight alginate gave the most pronounced effects, probably due to the accessibility of the alginate for protein binding. The chemical composition of the alginate had negligible effect on the mechanical properties of the gels. PRACTICAL APPLICATIONS: As both proteins and polysaccharides are widely used in the food industry, it is important to understand the interactions between these two biopolymers in order to envisage final product properties. The present article gives an overview of several important parameters when mixing ß-lactoglobulin and sodium alginate. ß-Lactoglobulin is the main protein in whey and one of the major food protein ingredients. Alginate is a polysaccharide that is often used in the food industry because of its functional properties. This study shows that if the conditions and the alginate type are adequately chosen, the textural properties of food products can be controlled and tailored.

Ionic and acid gel formation of epimerised alginates; the effect of AlgE4.

AlgE4 is a mannuronan C5 epimerase converting homopolymeric sequences of mannuronate residues in alginates into mannuronate/guluronate alternating sequences. Treating alginates of different biological origin with AlgE4 resulted in different amounts of alternating sequences. Both ionically cross-linked alginate gels as well as alginic acid gels were prepared from the epimerised alginates. Gelling kinetics and gel equilibrium properties were recorded and compared to results obtained with the original non-epimerised alginates. An observed reduced elasticity of the alginic acid gels following epimerisation by AlgE4 seems to be explained by the generally increased acid solubility of the alternating sequences. Ionically (Ca(2+)) cross-linked gels made from epimerised alginates expressed a higher degree of syneresis compared to the native samples. An increase in the modulus of elasticity was observed in calcium saturated (diffusion set) gels whereas calcium limited, internally set alginate gels showed no change in elasticity. An increase in the sol-gel transitional rate of gels made from epimerised alginates was also observed. These results suggest an increased possibility of creating new junction zones in the epimerised alginate gel due to the increased mobility in the alginate chain segments caused by the less extended alternating sequences.

Alginate based new materials.

Present and future applications of alginates are mainly linked to the most striking feature of the alginate molecule; i.e. a sol/gel transition in the presence of multivalent cations, e.g. Ca2+, almost independent on temperature. These very mild conditions, combined with the fact that alginates are highly characterised and understood both in the liquid and in the gel phase, makes this biopolymer unique compared to other gelling polysaccharides. Only pectins resemble alginate in the sol/gel transition behaviour, but this system can hardly be said to be as well characterised and understood as the alginates. The properties of alginate solutions and gels suggest biomedical and pharmaceutical uses. In this paper, the question of the specifications required by a polymer for applications in some biomedical areas will be discussed.

Chitosan cross-linked with Mo(VI) polyoxyanions: a new gelling system.

A procedure for preparing homogeneous chitosan gels by in situ molybdate cross-linking is described. The gels are obtained by dispersing solid MoO3 in a buffered chitosan solution and the polymer is cross-linked by formation of heavily negatively charged molybdate polyoxyanions. The resulting ionic gels are very transparent, thermoirreversible and can be made at low polymer concentrations. Depending on the ionic strength, these gels are able to swell several times their original size in aqueous solutions. Estimates of the degree of cross-linking reveal a very open pore structure which is confirmed by electron micrographs of the gel.

Plant protoplasts immobilized in calcium alginate: a simple method of preparing fragile cells for transmission electron microscopy.

A simple method for electron microscopic preparation of plant protoplasts is described. The main problems in preparing these fragile protoplasts for electron microscopy have been cell collapse due to steep gradients between protoplasts and fixatives and unacceptable loss of material during the many steps of the procedure. These problems may be solved by immobilization of the protoplasts in calcium alginate beads. The free diffusion properties of this gel prevent steep gradients. The beads also simplify handling and prevent loss of material. Protoplasts isolated from hypocotyls of rape, Brassica napus (var. Niklas), have been used as a model system. Transmission electron microscopy of the immobilized protoplasts osmotically stabilized with glucose demonstrated adequate structural and ultrastructural preservation.