Kappa carrageenan fluid gel material properties. Part 1: Rheology

With the potential use of kappa carrageenan (kappa C) fluid gels in reduced fat foods, an understanding of their rheological properties was explored. Isotropic fluid gel particles were produced via sheared gelation of kappa C with potassium chloride. Bulk fluid gel rheological properties were tested for their dependence on particle elasticity and volume fraction (controlled through biopolymer concentration and dilution, respectively). To achieve this, a method for determining fluid gel particle volume fractions (Phi(FG)) was devised using a novel centrifugation technique whereby the dependence of particle compressibility on centrifugation force is accounted for. The kappa C fluid gels prepared here are suggested to behave as soft microgel particles with penetrable hairy chains allowing for particle overlap, and aggregation at low volume fractions. The 'hairy' structures are proposed to arise from incomplete helix formation during gelation (which we previously confirmed using calorimetry) as a result of the applied shear disrupting the molecular ordering process which, for kappa C, is slow relative to that of biopolymers that do not form 'hairy' fluid gel structures. (C) 2013 Elsevier Ltd. All rights reserved.