Upcycling Goatskin By-Products Into Collagen Gel: Influence of Hydrothermal Intensity on Molecular Structure and Gel Performance

Goatskin by-products are generated in large quantities annually from slaughterhouses, resulting in resource waste and environmental pollution. Despite the considerable application potential of collagen, the primary component of goatskin, its extraction, and its utilization remain limited, particularly in gel-based food products. This study aims to extract goatskin collagen using a hydrothermal technique and elucidate how the hydrothermal intensity (60°C–100°C, 3–9 h) affects gel properties through structural changes. The results showed that gel properties were markedly affected by the extraction intensity. Mild conditions (3 h-60°C) produced collagen with the greatest gel strength (1569 g), along with the highest melting (35.1°C) and gelling (34.2°C) temperatures and the brightest color. In contrast, harsher conditions significantly reduced gel strength, lowered transition temperatures, and darkened gel appearance. Rheological analysis also confirmed weakened viscoelasticity and earlier structural breakdown under intensive treatments. Structural analysis further demonstrated that increasing hydrothermal intensity caused pronounced collagen degradation, increased small fragments, disordering of secondary structures with reduced α-helix and β-sheet content, and increased random coils. Meanwhile, the dominant intramolecular forces stabilizing gel network shifted from hydrogen bonds to hydrophobic and disulfide interactions. These structural changes ultimately resulted in a loose, porous, and uneven gel network accompanied by a significant decline in gel performance. Overall, mild hydrothermal treatments best preserved collagen structural integrity and yielded gels with superior functional properties, providing a theoretical basis for optimizing goatskin collagen extraction for food applications.