Effects of salt content on secondary structure of protein in sodium alginate/antarctic krill protein composite system and characterization of fiber properties

Abstract

The sodium alginate (SA)/antarctic krill protein (AKP) composite fibers were prepared by wet spinning in 5% (w/w) CaCl2 coagulation bath. In this work, salt regulated protein secondary structure to prepare high performance fiber, and the relative content of secondary structure in the composite system was calculated by fourier transform infrared spectroscopy (FT-IR). The surface morphology, crystallinity, thermal stability, mechanical properties, thermal conductivity and conductivity of the composite fibers were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD), differential scanning calorimeter (DSC), orientation tester, thermal conductivity meter and resistivity test bench. The results revealed that the salt changed the secondary structure of protein by affecting the intermolecular interaction and cross-linking degree of the SA/AKP composite system. After the fine partitioning of the salt content range, with the NaCl mass fraction of 0.7–1.0%, the controllable range of α-helix content, β-sheet content and random coil content are 8.14–25.15%, 52.58–60.87%, 21.53–30.99% for the SA/AKP composite solution, respectively. And the controllable range of α-helix content, β-sheet content and random coil content are 5.62–10.32%, 50.31–57.69%, 33.71–44.07% for the SA/AKP composite fiber, respectively. With the increase of salt content, the crystallinity showed an increasing-decreasing-increasing trend, the thermal conductivity, mechanical properties and orientation degree exhibited a trend of increase-to-decrease, and the thermal stability changed little. Besides, the conductivity of the composite fibers is affected more by the crystallinity of the material, and the surface morphology is also related to the salt content.