Effect of Extraction Temperature on the Functional and Structural Properties of Mullet Scale Gelatin

The functional property is an important factor to measure the quality of fish gelatin, which directly relates to the practical application range and value of fish gelatin. In order to explore the effect of extraction temperature on the functional properties of mullet scale gelatin, this study used a hot water extraction method. Different temperatures (60, 70, 80, 90, 100 ℃) were examined to assess their impact on the surface morphology of fish scales, fish scale gelatin yield, and functional properties (foaming capacity, emulsifying activity, gel strength, gel temperature, and melting temperature). Furthermore, the structural characteristics of fish scale gelatin were investigated using SDS-PAGE, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results showed that as the extraction temperature increased from 60 ℃ to 100 ℃, the damage to the surface of mullet scales became increasingly severe. The fish scale gelatin yield increased from 31.72% to 50.97%, foaming capacity improved from 23.33% to 73.33%, and emulsifying activity increased from 15.13 m²/g to 17.27 m²/g. However, gel strength, gel temperature, and melting temperature decreased from 677.82 g, 20.80 ℃, and 28.70 ℃ to 372.91 g, 15.80 ℃, and 23.90 ℃, respectively. Additionally, with the increase in extraction temperature, the characteristic bands of mullet scale gelatin α₁, α₂, and β chains on the electrophoresis pattern became increasingly blurred. The infrared spectroscopy results showed that the fish scale gelatin had characteristic absorption peaks (amide A, amide Ⅰ, amide Ⅱ, and amide Ⅲ), with the wavenumber of amide A first increasing and then decreasing. The scanning electron microscopy results showed that the tightness of the porous grid structure of the fish scale gelatin decreased. These findings provide a theoretical basis for the industrialization of mullet scale gelatin.