Rheological behavior of ulvan-based networks: Influence of cations, pH and chemical composition

The rheological behavior of ulvan/kappa-carrageenan, ulvan/funoran and ulvan/gelatin mixtures is investigated using dynamic rheology to provide insights into the phase aggregation behavior of each ulvan-based network. The average molecular weight of extracted ulvan was between 436 and 573 kDa, and contained varying amounts of sulfate (10.3-28.7%), rhamnose (35.3-48.1 mol%), iduronic acid (13.8-36.0 mol%) and glucuronic acid (21.1-34.3 mol%). The complex viscosity of ulvan in the presence of cations and boric acid was highly dependent on the sulfate content and sugar residues. The addition of Ca²⁺ and H₃BO₃ increases the viscosity in ulvan of reduced sulfate, rhamnose and glucuronic acid content, and vice versa for Ba²⁺ ions. The Ba²⁺ ions also increase the gel strength in ulvan/funoran, attributed to their specific gelling effect on funoran. In ulvan/gelatin, the storage modulus and solution-to-gelation temperatures are influenced by the pH of gelatin. The results based on the rheological measurements of ulvan mixed with kappa-carrageenan or porcine gelatin or funoran, suggest an interpenetrative network in ulvan-based mixtures, such that the behavior of ulvan-based networks is predominantly influenced by the added polymer, whilst ulvan interacts as the weaker phase.