Regulation of molecular structure and functional performance of Porphyra haitanensis soluble dietary fiber via temperature-controlled steam explosion

Temperature-controlled SE was applied to modulate SDF from P. haitanensis . • Moderate SE increased SDF yield and elevated acidic sugar contents. • SE at 140 °C–160 °C generated porous networks and exposed functional groups. • Functional properties improved under moderate SE and gradually declined at 180 °C. Steam explosion (SE) at different temperatures was applied to modify the structural and functional properties of soluble dietary fiber (SDF) from Porphyra haitanensis . SE treatment at 140 °C promoted partial depolymerization, reduced molecular weight, and increased the SDF yield (by 123.75%), together with significant increases in galactose (by 56.95%), galacturonic (by 66.86%), and glucuronic acids (by 73.84%) ( p  < 0.05). Meanwhile, SE-treated P. haitanensis SDF showed a looser and more porous-like microstructure, accompanied by changes in hydration-related behavior. These structural changes were associated with increases in water-holding, swelling, and oil-holding capacities, as well as glucose and cholesterol adsorption capacities and inhibitory activities against α-amylase, α-glucosidase, and pancreatic lipase. In contrast, SE treatment at 180 °C was associated with partial structural reorganization and less pronounced functional improvements. Overall, controlled SE temperature can provide a green and efficient strategy for enhancing the physicochemical and biological functionalities of seaweed-derived SDF.