Effects of Dried Pumpkin Powder on the Gel Properties and Protein Structural Characteristics of Trichiurus haumela Surimi

The poor gel-forming ability of myofibrillar proteins in hairtail (Trichiurus haumela) surimi limits its application in high-quality surimi products. This study investigated the effects of dried pumpkin powder (DPP) addition (0, 0.4%, 0.75%, 1.1%, 1.5%, and 1.85%, w/w) on the gel properties, protein conformation, and microstructure of frozen hairtail surimi gels. The results revealed a nonlinear, dose-dependent effect on gel quality. At 1.1% addition, gel hardness and springiness reached maximum values of 313.69 ± 2.54 g and 0.86 ± 0.004, respectively, while water-holding capacity (WHC) significantly increased by 11.21% compared with the control (p < 0.05). Fourier-transform infrared spectroscopy demonstrated a marked reduction in α-helix content with a concomitant increase in random coil content, indicating changes in protein secondary structure that may favor interactions within the protein network. Scanning electron microscopy further revealed that moderate supplementation filled network voids and produced a denser, more homogeneous microstructure, whereas excessive addition (≥1.5%) led to fiber aggregation and structural deterioration. Collectively, moderate pumpkin powder addition—specifically at 1.1%—improves hairtail surimi gel quality, and these improvements may be associated with changes in protein secondary structure and microstructural organization, offering a practical strategy for developing fiber-enriched surimi products.