Effect of Different Freeze-Thaw Cycles and Fucoidan on Structural and Functional Properties of Lotus Seed Starch Gels: Insights from Structural Characterization and In Vitro Gastrointestinal Digestion.

The influence of freeze-thaw (FT) cycling and fucoidan incorporation on the structural and digestive characteristics of lotus seed starch (LS) gels was systematically examined. Fucoidan-lotus seed starch (F-LS) gels were exposed to 0, 1, 3, and 5 FT cycles. Repeated FT treatments were found to disrupt the gel matrix and decrease thermal stability, whereas the addition of 1-2% fucoidan effectively alleviated these degradations. Crystallinity was significantly reduced from 37.62% to 26.38% (p < 0.05), indicating suppressed retrogradation. Thermal gravimetric and low-field NMR analyses revealed reinforced matrix cohesion. In vitro digestion assays demonstrated that fucoidan significantly retarded starch hydrolysis and promoted resistant starch (RS) formation. After five FT cycles, the RS content of 2% F-LS gels reached 29.03%, a 30.24% increase compared to the control. These findings suggest that fucoidan could serve as a natural and effective cryoprotectant and digestibility modulator in starch-based functional foods, offering both technological and nutritional benefits.