Study On The Mechanism Of Interaction Between Chitosan And Bovine Serum Albumin And Its Emulsification

Proteins and polysaccharides belong to the polyelectrolyte,and have been widely used in pharmaceutical,biological engineering and food industry.The objective of this study is to explore the influence factors of the interaction mechanisms between bovine serum albumin(BSA)and water soluble chitosan(WCS),and to be used as emulsifier of sunflower oil under different pH conditions,thus affording the theoretical guide for the application of protein and polysaccharide in the field of food emulsions.The results are as follows:(1)The effects of different concentrations of polysaccharides on protein structure and their interaction mechanisms were investigated simply and quickly by UV-vis absorption spectra and fluorescence emission spectra.Results showed that the interaction between polysaccharide and protein changed with variation of pH and BSA/WCS ratio,indicating that the UV-vis absorption peak shifted with the different pH and chitosan concentration,meanwhile,WCS exhibited a quenching effect on the fluorescence of BSA.(2)Results of the determination of turbidity,zeta potential,mean particle size and rheological behavior further indicated that the complex formation between BSA and WCS mainly through electrostatic interaction and/or hydrophobic interaction and the aggregation morphology,size and rheological behavior of the complex depended on pH and biopolymer ratio.At pH 3.0 and 4.0,both BSA and WCS had positive charges,resulting in lower turbidity and smaller particle size of the mixed solutions;In addition,the soluble complexes were formed through hydrophobic interactions and the average particle sizes increased at the high chitosan concentrations.At pH 5.0,6.0 and 7.0,electrostatic interactions were the main interaction force between BSA and WCS.Moreover,the BSA-WCS mixtures exhibited Newton fluid behavior with the addition of chitosan,and the rheological behavior almost unaffected by the change of pH when the concentration of chitosan higher.(3)Study on the emulsifying properties of BSA showed that the average particle sizes of the emulsions decreased with the increasing of BSA concentrations,and there existed"emulsifier-limited zone" and "emulsifier-rich zone".The critical emulsifier concentration(optimum emulsion concentration)was 0.15%w/v,which was used as the concentration of BSA for further experiments.(4)The storage stability,zeta potential,particle size and microstructure of the emulsions stabilized by BSA-WCS mixtures were observed.The results showed that most emulsions appeared phase separation,and there were two forms of syneresis and gradient creaming.In addition,the optimum conditions of emulsion stability were pH 3.0 and 4.0,BSA/WCS ratio 8:1-1:1 and 4 ?,forming the good storage stability and small droplet size emulsions;The depletion flocculation of the emulsions was observed with the increasing of chitosan concentrations.At pH 5.0,6.0,7.0 and BSA/WCS ratio 8:1-1:8,the emulsions occurred phase separation due to charge neutralization,bridging flocculation and other mechanisms,resulting in a large range of coalescence or flocculation of droplets.The final results showed that a finer emulsion was formed at an acidic pH rather than near isoelectric point and neutral pH.