Effects Of Ultrasound On Physicochemical Properties And Emulsifying Propertiesof Dioscorin,the Yam Storage Protein

As one of the important origins of yam（Dioscorea spp.）,China has a long history of yam cultivation,a wide range of cultivation and rich resources.Yam is not only an important food crop in many countries,but also used in traditional Chinese medicine as a top-grade medicinal material in my country.The protein content of yam is about 6-9%of the dry weight of yam.Dioscorin,as the main yam storage protein,accounts for more than 80%of the total protein of yam.With the rapid development of China’s food industry,some proteins with good functional properties are added to food,which not only improves the nutritional value of food,but also improves the flavor and taste of food.It is reported that Dioscorin not only has a variety of biological activities,but also has many functional properties.However,some functional properties of Dioscorin have not been fully developed,leading to limitations in the actual application of food industry.In this paper,the effects of different ultrasonic conditions on the physicochemical properties and emulsifying properties of Dioscorin were study.The results of the study are as follows:1.Under suitable ultrasonic conditions,the non-covalent bonds of Dioscorin are destroyed by ultrasonic cavitation,the thermal stability is reduced,the large aggregates of Dioscorin are converted into small particles,and free SH and the absolute value of Zeta-potential decreases.The structure of Dioscorin changed,the content ofα-helix andβ-sheet decreased,the molecule unfolded,and the internal hydrophobic amino acids and positively charged amino acid groups were exposed on the surface of protein molecules,resulting in inccreased the H_o and fluorescence Fmax.However,when the ultrasonic power was increased to more than 200 W or the treatment time was extended to more than 30 min,the thermal effect of the ultrasonic wave increased,and the temperature of the system increased,resulting in the Dioscorin particles tending to agglomerate,the particle size increased,and other physicochemical properties developed in the opposite direction.With the increase of ultrasonic frequency,the cavitation threshold increased,and the cavitation destroyed less non-covalent bonds,which has less influence on the physicochemical properties and structure of Dioscorin.Under different ultrasonic conditions,the physicochemical properties and structure of Dioscorin changed significantly.The results of SDS-PAGE showed that the bands did not change significantly after ultrasonic treatment,indicating that the primary structure of Dioscorin was not destroyed.2.After ultrasonic treatment,the free SH of Dioscorin was slightly reduced,which was not conducive to the formation of cross-links between proteins at the interface or between proteins and oil droplets.However,the smaller D_h and higher H_o enabled Dioscorin to be better adsorbed to the oil-water interface,resulting in a significant increase in AP%and the absolute value of Zeta-potential,and stronger electrostatic interactions between droplets.Thus,the emulsifying activity and stability were significantly improved.After suitable ultrasonic treatment,the reduction of D_h and the increase of H_o of Dioscorin had a stronger positive effect on Dioscorin-stabilized emulsion than the negative effect of free SH reduction,resulting in higher FI,EAI and ESI.The study found that with the change of ultrasonic conditions,the change of the emulsification properties of Dioscorin was basically the same as the change of the physicochemical properties.3.Molecular dynamics simulation studies found that at low square wave frequency and square wave pressure,the non-covalent interactions（such as hydrogen bonds）of Dioscorin were disrupted,resulting in a decrease in the content ofα-helix andβ-sheet structures,and the unfolding of Dioscorin molecules,resulting in an increase in the average size and exposure of more hydrophobic groups.So RMSD,RMSF,Rg and SASA were relatively high and the conformational changed larger.As the frequency of the square wave increases,the structure of Dioscorin changes less,which is basically consistent with the results in Chapter 1.With increasing square wave pressure,the mobility of Dioscorin decreases,resulting in reduced flexibility of many residues and less molecular structural changes.