Mixtures of pregelatinised maize starch and kappa-carrageenan: Compatibility, rheology and gelation
Résumé
Compatibility, flow and visco-elastic properties of a pregelatinised maize starch mixed with K-carrageenan were investigated. After cooking of the pregelatinised starch, some undissolved granules remained in solution. Aqueous mixtures of kappa-carrageenan and starch were studied at 60 degrees C and 20 degrees C by combining rheological measurements and microscopic observations under conditions allowing gelation of carrageenan and non-gelation of starch. The viscometric study of mixed dilute solutions of amylose from pregelatinised starch and carrageenan showed that the components are slightly incompatible. Mixture viscosity and elastic modulus were studied at 60 degrees C in details as a function of mixture composition for a total polymer concentration of 3%; both were found to be significantly higher than the corresponding theoretical additive values. This finding was interpreted by starch granules excluded volume effect. At 20 degrees C, no noticeable increase of mixture elastic modulus was found as compared with the additive value. The absence of the synergistic effect is supposed to be due to the formation of highly inhomogeneous gels with agglomerates of undissolved granules.