Rheology of kappa-carrageenan and beta-lactoglobulin mixed gels

Gel formation and the melting of K-carrageenan in the presence of P-lactogl obulin were investigated using dynamic theological techniques as well as a sequence of experimental sweeps of time-temperature, frequency, and strain. The blends, initially prepared at 45 degrees C, show homogeneous mixtures, which then lead to the formation of a gelled K-carrageenan network contain ing inclusions of native beta-lactoglobulin during the controlled cooling p hase from 45 to 20 degrees C. In its native state, the protein seems to wea ken the polysaccharide network, particularly when present in high concentra tion. Upon subsequent heating to 90 degrees C, mixed gels presented a bipha sic profile: the first phase, characterized by a decrease in the storage mo dulus, involves a heat-induced meltdown of the K-carrageenan network, where as the second phase, exhibiting an increase in the storage modulus, corresp onds to the build up of a protein network. The DSC analysis showed that eac h biopolymer undergoes specific conformational changes. These results are h ighly indicative of the lack of association between the biopolymers and sug gest a phase separation and gelation in P-lactoglobulin and K-carrageenan m ixtures. The final cooling phase of the mixed gels, from 90 to 20 degrees C , induces a consolidation of the protein network and a gelation of K-carrag eenan This theological behaviour suggests that gelation of K-carrageenan in the presence of a gelled protein network would lead to the formation of a phase-separated bicontinuous network. The strain sweep results for mixed ge ls obtained at the end of the experiments support that hypothesis. (C) 2000 Elsevier Science Ltd. All rights reserved.