The Effect Of Ultrasound Assisted Annealing Treatment Under Alkaline Condition On Multi-Scale Structural Changes And Acetylation Modification Of Starches

Starches is a natural polymer in nature,the inherent defects of natural starches limit its application.Therefore,it is necessary to modify the structure of natural starches with different physical or chemical treatments to meet different needs.In this study,corn starches with different amylose content（waxy corn starch（WCS）,normal corn starch（NCS）,high amylose corn starch（HCS））and different crystalline types（wheat starch（WS）,potato starch（Po S）,pea starch（Pe S））were treated byannealing（A,ALK-（A））,and ultrasound processing（U）assisted annealing(ALK-（U/A）under the alkaline condition（ALK,p H～8.2）and the sequence of U and A were compared:the influence of ultrasound processing-annealing（ALK-（U-A））,annealing-ultrasound processing(ALK-（A-U）treatments,to explore the influence of different treatments on the multi-scale structure of the starches.Then,the different pre-treated starches were treated by acetylation modification to explore the influence of pre-treatment on the acetylation modification.The main research contents and results are as follows:Firstly,the SEM,CLSM and other characterization methods were used to investigate the effects of the particle structure,crystal structure and molecular structure of WCS,NCS,HCS,WS,Po S and Pe S,which was treated by A（blank control）,ALK-（A）and ALK-（U/A）treatments.The results are as follows:（1）Compared with the A treatment,the ALK-（A）and ALK-（U/A）treatments had significant effects on the morphology of starches.The hydroxyl group on the surface of starch granules can be activated under alkaline conditions,U and A treatment further promoted the activation process of hydroxyl group inside the granules,promoted the swelling process of the starches and made the surface of the granules rough,at the same time,the cracks and holes were increased,and the cavity and pore in the particle become larger.Compared with ALK-（A）treatment,ALK-（U/A）treatment reduced the granule size of the starches.（2）Compared with A treatment,ALK-（A）significantly damaged the lamellar and crystalline structure of starches.And the U treatment assisted further aggravated the damage process.The D_Bragg of six starches were increased with ALK-（A）.All starch samples showed a mass fractal structure.The relative crystallinity and the short-range order degree of starches were decreased.（3）The gelatinization onset temperature and enthalpy of starches were increased with ALK-（A）treatment.While ALK-（U/A）treatment promoted the alkaline to enter the starch granules,the double helix structure was destroyed,and promoted the formation of unstable microcrystalline structure,which led to the starch gelatinization onset temperature decreased.（4）ALK-（A）and ALK-（U/A）treatments had no significant effect on the amylose content of the starches,but increased the water absorption and transparency of starches.Then,on the basis of the above eaperiments,the SEM,CLSM and other characterization methods were used to investigate the effects of the particle structure,crystal structure and molecular structure of six starches,which was treated by different U and A treatment sequences under the alkaline conditions（ALK-（U-A）,ALK-（A-U））.The results are as follows:（1）The morphology of corn starches with different amylose content was more significant under ALK-（U-A）treatment,and the damage degree of ALK-（U-A）treatment decreases with the increase of amylose content.The morphology of WS and Pe S was more affected by the treatment of ALK-（A-U）,while the porphology of Po S was not affected by the different U and A treatment sequences under the alkaline conditions,which was mainly due to the different arrangement of double helix in the three starches.The partial peeling off of starch granule shell and particle breakage,and enlargement of the central cavity,cracks and pores in starch granules.In addition,the re-dispersion of the agglomerated starches induced by post-U treatment under alkaline condition,resulting in the monodisperse state of starch granules,thus narrowed the particle size distribution of the starches.（2）ALK-（A-U）treatment caused more damage to the starch crystals because the surface of starch granules was rough,cracks and pores were increased after A treatment under the alkaline condition,and then U treatment promoted the alkaline into the starch granules,which intensifies the crystal structure of starch and the double helix damage process of starch molecules.（3）The different treatment sequences of U and A treatment under alkaline condition had no effect on the gelatinization characteristics and amylose content of starches.In addition,the ALK-（U-A）and ALK-（A-U）treatment can significantly improve the water absorption and transparency of starches,The ALK-（U-A）treatment had a greater effect on the water absorption of starches.Finally,the starches treated with A,ALK-（A）,ALK-（U/A）,ALK-（U-A）and ALK-（A-U）were acetylated with acetic anhydride（AWCS,ANCS,AHCS,AWS,APoS,APe S）to clarify the influence of different pretreatment on acetylation modification.The results are as follows:（1）FTIR results shouwd the characteristic peaks of acetylated starch appeared at 1730 cm^-1 and 1245 cm^-1,indicating that acetyl groups were successfully introduced into starch granules.SEM showed that the surface of acetylated starch particles became rougher after acetylation modification.XRD results showed that the crystal type of starches was unchanged,but the relative crystallinity was decreased after acetylation.（2）Compared with A treatment starches,the degree of substitution（DS）and reaction efficiency（RE）of the above pretreatment starches increased after acetylation modification.The DS_max of ANCS and APe S treated with ALK-（U-A）was 0.071 and 0.0575,and RE was increased by 74.1%and 37.7%,respectively.The DS_max of AWCS,AHCS,AWS and APoS treated with ALK-（A-U）was 0.0632,0.0621,0.0626 and 0.0534,and RE was increased by 14.1%,54.1%,116.7%and 33.8%,respectively.It can be seen that there was no synergistic effect between U and A treatment,and the sequential treatment showed greater superiority.（3）The water absorption capacity of AWCS,AWS and APoS treated with ALK-（A-U）increased the most,while the transparency of AWCS,ANCS and AHCS treated with ALK-（U-A）increased the least.（4）The acetylation reaction mainly occurred the surface and amorphous region of starch granules,while the ALK-（U-A）and ALK-（A-U）pretreatment promoted the acetylation reaction in the crystalline region of starch granules,which greatly increased the RE of acetylated statches.