Ultrasound And Glycation Treatment On Bovine Serum Albumin Fibril

Protein fibril aggregation is a ?-sheet-based assembly that widely exists in nature.It can be used as immobilization of enzymes in biological materials,and also has important applicaitons in emulsification,foaming and gelling in food processing.However,there are problems in current preparation,including slower rate and limited selections,which restricted the application in food industry.In this study,bovine serum albumin(BSA)which was lack of ?-sheets in nature,was modified by ultrasound and glycation pretreatment to induce the production of ?-sheets,in order to promote the formation of fibril.By studying the changes of primary,secondary structure and aggregation state structure of BSA under the action of ultrasound and glycation,investigating the dynamic process of the formation of fibril and establishing the dynamic model to finally reveal the influence mechanism of ultrasound and glycation on the BSA fibrils.The study provides a useful reference for breaking through the selection limitations of fibrotic aggregates,enriching the influence of fibril aggregation process and improving the preparation efficiency of fibrils.The main research content and results were as follows:(1)Formation mechanism of BSA fibrils under acid-heated condition:Under acid-heated condition,BSA was hydrolyzed and assembled to form fibrils.The growth curve was in line with the exponential model,and the increase of antiparallel-folding content was an important reason for fibril formation.When BSA was heated at pH 3.0,content of anti-parallel sheets increased from 2.17% to 10.51%.In the process,hydrolysis occurred and disulfide bonds was firstly formed.With proper static electricity and hydrophobicity,BSA was gradually assembled and finally formed long fibrils,with better emulsification and foaming properties.However,heating under more acid conditions led to the cleavage of disulfide bond;heating closer to the isoelectric point led to agglomeration,both of which were detrimental to the formation of anti-parallel sheets and were not conducive to fibril formation.(2)Effect of ultrasound treatment on the formation of BSA fibrils:Ultrasounic pretreatment for 2~15 min could promote the formation of anti-parallel sheets and disulfide bonds.Moreover,it could promote the exposure of hydrophobic groups and increase the apparent rate constant k value,and fasterly form fibrils,which had good emulsifying activity.However,the longer time of ultrasound was not conducive to the final amount of anti-parallel sheets,inhibiting the final formation of BSA fibrils.(3)Effect of glycation on the formation of BSA fibrils:Early stage of glycation promoted the formation of anti-parallel sheets and disulfide bonds to promote aggregation.However,inhibition effect was showed in the later stage of glycation due to the decrease of anti-parallel sheets and broken of disulfide bonds.Then the fibril behavior of mildly glycated proteins was further studyed.Results showed that moderate glycation increased the anti-parallel sheets from 2.04% to 10.25%,and continuely increased to 14.81% after further heating.It also formed a disulfide bond faster,resulting in an increase in the kinetic parameters of A and k value.The "balance" time of the reaction was shortened and the number of fibrils is increased,indicating that proper glycation was an advantageous means of regulating fibril formaiton.Moreover,the products had good emulsifying actibity.(4)Effect of ultrasonication and glycation on the formation of BSA fibrils:Compared with the BSA group,the formation of anti-parallel sheets and disulfide bonds were promoted after the doubled treatments.Moreover,after the doubled pretreatments,hydrophobic interaciton was enhanced,resulting in an increase in the k value,a shortening of the "equilibrium" time.Eventually,more longer fibrils were formed with good emulsifying activity and foam stability.In addition,the A and k values were higher and more dispersed "worm-like" fibrils were formed in the group of glycation after ultrasound;while the longer and thicker "branched" fibrils were formed in the group of ultrasound after glycation.