Effects of concentration on nanostructural images and physical properties of gelatin from channel catfish skins

Physical properties are crucial to gelatin utilization and the physical properties are determined by structure. Therefore, it is important to investigate the nanostructure and physical properties of gelatin over the full range of concentrations which are widely applied in research and industry. Nanostructure of gelatin can be investigated by atomic force microscopy (AFM). However, it is hard to obtain reliable AFM images of gelatin with high concentrations (1–6.67%). In this study, methods for imaging gelatin with high concentration were explored and developed, which mainly included six steps. Then the relationships among concentration, nanostructure and physical property of gelatin extracted from channel catfish skins (Ictalurus punctatus) were studied. The high-resolution AFM images show fibril structure in gelatins with concentrations from 1% to 6.67%. However, in low concentrations (<1%), most nanostructures of gelatin were spherical aggregates and fibril structure only existed occasionally. Correspondingly, there were no significant differences of gel strength, texture profile and viscosity among several groups of gelatin when the concentration was lower than 1%, in contrast, these properties changed dramatically when the concentration was greater than 1%. It indicates that there must be some close relationships among concentration, nanostructure and physical property of gelatin. The illustration of nanoscale transition would help us understand the macroscale changes of physical properties.