Interaction Between Oligochitosan Phycoerythrin And Its Effect On Physicochemical Properties Of Phycoerythrin

China has a vast territory,and is especially rich in algae resources.The annual production of Porphyra haitanensis is considerable.It is rich in Phycoerythrin（PE）and is a good natural raw material for the extraction of Phycoerythrin at a low price.As a physiologically active substance,phycoerythrin has great potential in the biomedical and food industries.However,the output of phycoerythrin is low,and its pigment is easy to be destroyed in the process of food application,which makes its stability weak and its application is limited.The purpose of this paper is to explore ways to improve the stability of phycoerythrin by using the non covalent and covalent interaction between oligochitosan（OCOS）and phycoerythrin.In this study,phycoerythrin was extracted from Porphyra in a yield of 0.17%（w/w）.Phycoerythrin oligochitosan complexes（POC）with molar ratios of 6.7/1,13.3/1 and20.0/1（OCOS/PE）at p H of 6.8 were prepared by self-assembly at 25℃in the dark.The effects of non covalent binding of OCOS and phycoerythrin on the structure and physicochemical properties of the products were studied.Fluorescence analysis showed that the stoichiometric number N was 21.67±2.65（OCOS/PE）and the binding constant K was（6.47±0.48）×10⁵M^-1.Oligochitosan can interact with phycoerythrin by electrostatic interaction,and increasedα-Helix content.In addition,high concentrations of oligochitosan lead to the phycoerythrin polymerization.When the reaction ratio was20.0/1（OCOS/PE）,the thermal stability（40-80℃）,natural light stability and UV irradiation（254 nm）stability of the complex were improved.Under the conditions of reaction temperature（37℃）and reaction time for 3 h,transglutaminase(10 ug^-1protein)was used to catalyze the glycosylation reaction between phycoerythrin and oligochitosan to obtain oligochitosan-modified phycoerythrin complex（OMPC）（OCOS/PE=1/1-4/1）.The results of polyacrylamide gel electrophoresis showed that the cross-linking reaction was successful.The glucosamine content and free amino content of glycosylated products were determined.When the molar ratio of oligochitosan to phycoerythrin was 3:1（OCOS/PE）,the glucosamine content of OMPC was the highest,which was 29.356±0.003 mg/g protein.The OMPC was studied by infrared spectrum,fluorescence spectrum and scanning electron microscope.The results showed that the secondary structure and the tertiary structure of glycosylated products changed,and a compact polymer formed.In addition,compared with untreated phycoerythrin,the surface hydrophobicity and emulsifying activity of OMPC decreased,while the solubility,emulsifying stability,thermal stability,photostability and p H stability were significantly improved.This work studies the functional properties of phycoerythrin through covalent and non-covalent interactions,and provides a new idea for the modification and application of phycoerythrin.This study is of great benefit to the wide application of phycoerythrin in the fields of food,cosmetics and dyeing.