ADDITIVE EFFECTS ON THE RHEOLOGICAL BEHAVIOR OF ALGINATE GELS

Abstract

ABSTRACT The effects of dextran and glycerol on the rheological properties of 1.25% alginate gels were studied. Although the dextran and glycerol dramatically changed the viscosity of the alginate solution, the gelation kinetics was not affected. This observation may be attributed to the fact that the gelling process was controlled by the combination of carboxylic groups in alginate chains with Ca 2 + , and not by the diffusion process of alginate molecules and Ca 2 + through the viscous medium. The small‐strain shear modulus of alginate gels with either low molecular‐weight dextran (MW: 140,000 Da) or glycerol remained nearly constant, as did the large deformation and fracture properties. The addition of high molecular‐weight dextran (MW: 4–5 million Da) altered the small‐strain shear modulus and lowered the gel fracture stress of the alginate gels, while the fracture strain remained the same. The change in small‐strain shear modulus and large deformation and fracture properties for alginate gels with high MW dextran cannot simply be explained by the change in viscosity of the gel liquid phase. A plausible explanation for this behavior is that, in some manner, large dextran molecules influenced the alginate gel network. PRACTICAL APPLICATIONS A common characteristic of food gels is a three‐dimensional network formed by primary gel‐forming materials, such as proteins and polysaccharides. Alongside the gelling material(s), additives are frequently included to attain desirable functionality. The gel network stabilizes the system, and the physiochemical properties of gels are dominated by structural organization at the molecular level. The inclusion of additives may affect physical and chemical properties of the gels, and subsequently, the rheological properties. Rational optimization of product formulations and processing conditions of food gels depends on a better understanding of the impact of additives on processing and rheological properties.