Research On Modification Of Recombinant Ferritin By Chitosan And Influence On Physico-chemical Properties

Ferritin is a multimeric protein complex composed of 24 copies of homologous or heterologous subunits with a small cavity of 8 nm in diameter and 4500 iron ions is stored within the protein shell, which is found widely in animals, plants, bacteria and fungi.However, as a protein component, its physico-chemical properties are vulnerable to the external environment. Polysaccharide modification of protein can improve the functional properties of protein, which can be used as functional ingredients in food and pharmaceutical fields. It has been more and more attention. The main forms of polysaccharides interacting with proteins are covalent interactions and electrostatic interactions. In this paper, the surface modification of ferritin by chitosan was studied in two ways: electrostatic interaction and covalent interaction. Then the molecular structure and functional properties of ferritin after processing were studied.Firstly, chitosan was positively charged at low pH (pH6.0, below its pKa), which could interact with the acidic amino acid residues on the outer surface of the ferritin and generate ferritin-chitosan polyelectrolyte polymers. The best pH value of electrostatic interaction between ferritin and chitosan was found to be 6.0 by turbidimetric analysis and zeta-potential analysis. It was further confirmed by fluorescence spectrum that the electrostatic interaction plays an important role in the binding of ferritin to chitosan and approximately ten chitosan molecule binds to a single ferritin. Through the simulated digestion experiments in vitro, it was found that the electrostatic modification of ferritin by chitosan can improve the stability of ferritin.Secondly, the ferritin-chitosan grafts were prepared by Maillard reaction between free amino groups in the amino acid side chains of ferritin and the carbonyl groups of the chitosan. It was confirmed that it was successfully synthesized the ferritin-chitosan grafted product by SDS-PAGE and Fourier transform infrared spectroscopy (FT-IR). As measured by grafting rate, 1: 100 (The grafting ratio of ferritin: chitosan), 55? and 75% (elative humidity) and 24 h (response time) are the best conditions. Through the browning index analysis, in a certain range, the higher the grafting rate, the greater the browning degree.The antioxidation experiment showed that chitosan could improve the oxidation resistance of ferritin, and it was found that the ferritin-chitosan graft retained the hollow spherical structure of ferritin by iron reductive release experiment. It was also found by the simulated digestion experiments in vitro that ferritin-chitosan grafts were more stable than ferritin alone.