Structural and rheological design of fish and mammalian gelatin hydrogels by addition of κ-carrageenan.

Thanks to its natural origin, biocompatibility, and relatively simple manufacturing process, gelatin is a widely used gelling agent in the pharmaceutical, cosmetic, and food industries. Traditionally, the main sources of gelatin have been mammalian bones and skin. In recent years, there has been considerable interest in fish-derived raw materials as an alternative source of gelatin. However, the use of fish gelatin is limited by its insufficient viscoelastic properties and mechanical strength, as well as its low thermal stability. In the present work, the enhancement of the viscoelastic behavior of gelatin hydrogels in the presence of the natural polysaccharide κ-carrageenan was examined. We studied the mechanical properties, supramolecular structure, and selected physicochemical characteristics of fish and mammalian gelatin hydrogels combined with κ-carrageenan using rheological measurements, scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and contact angle analysis. Our rheological studies revealed substantial changes in the viscoelastic and stress-strain properties of hydrogels based on fish gelatin. The gel melting point of the combined system based on fish gelatin and κ-carrageenan increased from 18 to 44 °C, becoming slightly higher than that of the mammalian gelatin/κ-carrageenan system (42 °C). A much weaker effect of κ-carrageenan was observed on almost all properties of mammalian gelatin than on those of its fish analogue. Thus, κ-carrageenan significantly alters the structure and properties of fish gelatin hydrogels, increasing their gel-sol transition temperature. These results could provide new insights into protein-polysaccharide supramolecular complexes and broaden the technological applications of fish gelatin as an underused protein source.