Study On The Effects Of Ultra-high Pressure Treatment On Oat Starch/?-glucan Compound System And Mechanism Of Inhibiting Retrogradation Of Starch

The interaction between oat starch and ?-glucan plays a major role in the formation of oat dough.The deficiencies of starch,such as easy to retrogradation and poor shear resistance,limit its application.Ultra-high pressure treatment disrupt the structure of macromolecules by breaking non-covalent bonding and causes the modification of macromolecules.In order to investigate the effect of UHP treatment on oat starch/?-glucan mixture and its mechanism of inhibiting the retrogradation of starch.Starch extracted from oats was used as raw material,and ?-glucan was added to form an oat starch/?-glucan compound system.The effect of UHP treatment on the properties of oat starch and inhibition of retrogradation were studied by using scanning electron microscopy,fourier transform infrared spectroscopy,X-ray diffraction and nuclear magnetic resonance.Es Tablelish a model for the modification of starch microstructure by ultrahigh pressure,and explore the mechanism of the effect of different treatments on the retrogradation of oat starch.Results showed that:(1)The optimal conditions for oat starch extraction are as follows: material-to-liquid ratio of 1:10(g/ml),pH 10,extraction time 2h,and extraction temperature 35 ?.Under these conditions,the extraction rate of oat starch was 72.37%.The oat starch granules was irregular,which belonged to small granular starch and A-type starch.Oat starch has higher thermal s Tableility and shear resistance,higher pasting temperature,and easier to recrystallize.The light transmittance of oat starch lower,in the process of repeated freezing and thawing,the syneresis rate is higher,which is not sui Table for application in frozen food.(2)The alteration of oat starch microstructure by UHP goes through three stages:crystallization perfection stage,crystallization destruction stage and crystallization disintegration and gelatinization stage.When the treatment pressure is low(100?300 MPa for 15 min),the surface change of oat starch granule is not obvious,the particle size decreases.The crystal structure is still A-type,the short-range ordered structure,double helix structure and the relative crystallinity increases,the changes of proportion of amorphous area is not significantly,which is the crystallization perfection stage.When the treatment pressure is moderate(400 MPa for 15 min)and the treatment time is short(500MPa for 5 min),the granule swell,the surface becomes cohesive,particle size becomes larger,the crystal structure is still A-type,but the relative crystallinity decreases,and the proportion of amorphous area increases,which is the stage of crystal disintegration.With the increase of pressure(500?600 MPa treatment for 15 min),the treatment time(500 MPa treatment for 15?30 min)and the different concentrations of oat starch(5%?30%)treated after 500 MPa for 15 min,the oat starch granules absorbed water and swelled,the surface collapsed,adhered to form a gelatinous joint area,the particle size increased significantly.The short-range ordered structure,double helix structure and relative crystallinity decreased significantly,the crystal structure became V-type,and the proportion of amorphous area increased,which was the crystallization disintegration and gelatinization stage.(3)The relationship between the structure and properties of oat starch after UHP treatment is as follows: when the treatment pressure is low,the interaction between oat starch molecular chains is enhanced,and the crystal structure is improved due to the compressive toughening effect,which causes the paste temperature,gelatinization enthalpy,phase transition temperature,G',G',shear stress,SDS and RS content increased,the ability of shear resistance increased,the retrogradation,syneresis,breakdown value and hydrolysis rate decreased.With the increase of pressure and treatment time,the starch intermolecular association state is destroyed,light transmittance,pasting temperature,viscosity,gelatinization enthalpy,phase transition temperature,G',G' and shear stress decreased,the retrogradation,syneresis,breakdown value,hydrolysis rate,RDS content increased,and the s Tableility of starch weakened.(4)?-glucan formed a uniform,dense and cross-linked network structure with oat starch through hydrogen bonding,and had a certain protective effect on the crystallization area of oat starch.After the addition of the ?-glucan,the compound system has better thermal s Tableility and retrogradation resistance.The compound system shows weak gel dynamic rheological properties.With ?-glucan addition of 5%?10%,the viscoelasticity of compound system enhanced,consistency coefficient increased,the shear thinning phenomenon was more obvious.(5)Effect of UHP treatment on the structure of oat starch/?-glucan complex systems goes through crystallization perfection and crystallization disintegration stage.When the compound system was treated after 300?400 MPa,the change of granule surface was not obvious,and the particle size decreased.The short-range ordered structure,double helix structure and the relative crystallinity increased,the proportion of amorphous area decreased,this is the stage of crystallization perfection.Which leads to phase transition temperature,gelatinization enthalpy,pasting temperature increased,while the viscosity and breakdown value decreased.After treated at 500?600 MPa,most of the granules swelled and deformed,the granule surface became rough and sticky,and the particle size increased significantly.The short-range ordered structure,double helix structure and the relative crystallinity decreased,while and the proportion of amorphous region increased,this is the stage of crystallization destruction.Which leads to phase transition temperature,gelatinization enthalpy and pasting temperature decreased,while the viscosity and breakdown value increased.(6)The ultra-high pressure treatment and the addition of ?-glucan can inhibit the retrogradation of oat starch.Compared with oat starch,after ultra-high pressure treatment and ?-glucan addition,the hardness of the gel system decreases,the short-range order structure,double helix structure,and relative crystallinity decrease during retrogradation.In the early stage of retrogradation,the degree of freedom of amylose increases.The retrogradation kinetic model shows that after ultra-high pressure treatment and ?-glucan addition,the n value of the gel system increases,and the nucleation mode changes from instant nucleation to spontaneous nucleation.The decrease of the recrystallization rate indicates that the process of amylose interaction to form crystal nuclei is delayed.The results of water molecule migration showed that after ultra-high pressure treatment and?-glucan addition,the T2 value of the gel system decreased,the bound water in the system increased,the free water decreased,and the fluidity of water molecules decreased.(7)The ultra-high pressure treatment and the addition of ?-glucan inhibit the retrogradation of oat starch by delaying the formation of nuclei from amylose interactions at the beginning of retrogradation and reducing the mobility of water molecules.The mechanism of inhibiting retrogradation is: ultra-high pressure treatment enhances the interaction of amylose molecules in oat starch granules and reduces the dissolution of amylose during gelatinization.After ?-glucan is added,it interacts with amylose through hydrogen bonds.Which inhibits the process of amylose interaction to form crystal nuclei in the early stage of retrogradation,thereby delaying the process of forming a crystal structure of amylopectin with the crystal nucleus as the center.In addition,ultra-high pressure treatment and the addition of ?-glucan strengthen the water binding effect of starch gel system,resulting in the reduced mobility of water molecules in the system,which slows down the migration and recrystallization of starch molecules,thereby inhibiting the retrogradation of starch.