Mechanisms and key factors influencing ulvan gelation

Ulvan, a sulfated polysaccharide extracted from the green seaweed Ulva, is composed primarily of rhamnose, xylose, glucuronic acid, iduronic acid, sulfate, with minor sugars such as mannose, galactose, and arabinose. Its linear structure features L-rhamnose-3-sulfate, D-glucuronic acid, L-iduronic acid, and D-xylose. Ulvan exhibits distinctive rheological properties, including shear-thinning and shear-thickening behaviors, which are crucial for its applications in biomedicine (e.g., drug delivery systems) and food science (e.g., gelling agents, functional ingredients). However, challenges persist, such as variability in mechanical stability, biocompatibility, and batch-to-batch inconsistencies resulting from extraction methods. This review comprehensively examines the gelation mechanisms of ulvan, focusing on cross-linking interactions (ionic bonding with multivalent cations) and non-cross-linking interactions (electrostatic forces and hydrogen bonding). It further reviews how both extrinsic factors (e.g., pH, concentration) and intrinsic factors (e.g., molecular weight, sulfation) influence gelation, thus advancing the potential of ulvan-based materials in biomedical and industrial applications.