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Modelling of phase separation of alginate-carrageenan gels based on rheology

Wurm, Florian, Pham, Tung, Bechtold, Thomas
Food hydrocolloids 2019 v.89 pp. 765-772
alginates, biopolymers, calcium, carrageenan, gels, hydrocolloids, models, potassium, rheological properties, rheology, separation, sulfates
Application of alginates and carrageenans in food usually include one or the other biopolymer. The combination of the two polymers in gel applications is focus of the present study. Findings not only enhance gel structural understanding, but also enhance biopolymers' fields of application. Structural and rheological properties of mixed alginate/κ-carrageenan, alginate/ι-carrageenan and alginate/furcellaran gels were investigated. Ionic concentration in the gels was set to 50mM K+ and 15mM Ca2+. Based on rheological characterisation, models were utilised to draw conclusions about the gel structure. Mixed gels show phase separation behaviour. The speed of phase separation is dependent on the polysaccharide's sulphate ester content. The fewer sulphate groups present in the carrageenans, the slower phase separation is observed. Alginate/furcellaran gels can be described by an interpenetrating biphasic model, having lower than isostress stability. Alginate/κ-carrageenan gels show phase separation behaviour with counter dilution of the phases and can best be described by a quadratic model. For alginate/ι-carrageenan, a biphasic gel with discrete phase borders, a new model is presented. It is based on a sigmoid function and models the transition from an isostress to an isostrain description.