Temperature-controlled steam explosion modulates structural and functional characteristics of Porphyra haitanensis dietary fiber

Developing efficient modification methods for seaweed dietary fiber (DF) is hindered by its sulfated galactan backbone, which differs fundamentally from terrestrial lignocellulosic matrices. In this study, temperature-controlled steam explosion (SE) was employed to modulate the structural and functional characteristics of Porphyra haitanensis TDF. Moderate SE (140 °C) promoted an effective IDF-to-SDF conversion, evidenced by pronounced increases in SDF (127.67 %), galactose (37.71 %), and uronic acids (22.73 %–25.65 %), accompanied by reductions in IDF (17.95 %), acid-insoluble residue (28.54 %), and sulfate groups (47.40 %) ( p  < 0.05). Multiscale characterization revealed the formation of a honeycomb-like porous network, strengthened hydroxyl/carboxyl signals, elevated crystallinity, and enhanced thermal stability. Correspondingly, hydration capacity, lipid adsorption, cholesterol binding, and inhibition of α-amylase, α-glucosidase, and pancreatic lipase increased significantly. Excessive SE (180 °C) led to structural densification and diminished functionality. These findings suggest that controlled SE may restructure sulfated seaweed DF, offering a green strategy for its functional utilization.