Study On The Combined Modification Of Glutinous Rice Protein By Freezing Ball Milling And Enzymatic Hydrolysis

Glutinous rice protein is a high-quality plant protein with reasonable amino acid composition and low allergenicity,but its application in food processing is limited due to its poor solubility,so it needs to be modified to improve its functional properties and expand its application.This thesis aims to optimize the extraction process of glutinous rice protein by alkaline solution and acid precipitation using glutinous rice flour as raw material.To improve the functional properties of glutinous rice proteins,freezing ball milling was carried out to investigate the effects of freezing ball milling on the physicochemical and functional properties of glutinous rice proteins.Based on this,the glutinous rice protein was modified by enzymatic digestion after ball milling to investigate the effects of combined freezing ball milling and enzymatic digestion on the physicochemical properties,functional characteristics,and antioxidant properties of glutinous rice protein,providing a certain theoretical basis for the modification and application of glutinous rice protein.The main findings are as follows:(1)The optimum conditions for the preparation of glutinous rice protein by alkali solubilization and acid precipitation were studied using glutinous rice powder as raw material.The extraction process of glutinous rice protein was optimized by orthogonal tests based on single-factor experiments of p H,extraction time,and solid-to-liquid ratio.The results showed that the best extraction conditions for glutinous rice protein were p H 12.0,120 min of extraction time,and a 1:7 solid-liquid ratio,and the glutinous rice protein was precipitated at p H 4.7.(2)The effect of freezing ball milling on the physicochemical properties and functional characteristics of glutinous rice proteins was investigated,and the glutinous rice proteins were subjected to ball milling for 0 min,10 min,20 min,30 min,and 40 min.The results showed that the particle size of glutinous rice proteins decreased significantly with the increase of ball milling time,the free sulfhydryl content increased and then decreased,the surface hydrophobicity increased,the α-helix content decreased and then increased,the β-fold content decreased and the secondary structure was transformed,but there was no significant change in the electrophoretic bands before and after freezing ball milling,which indicated that freezing ball milling did not affect the subunit composition of glutinous rice proteins.This indicates that freezing ball milling did not affect the subunit composition of the glutelin.The solubility of glutelin increased from 0.92 % to 1.95 % after ball milling,and the foaming and emulsification properties improved significantly,but the foam stability and emulsification stability decreased.(3)Based on freezing ball milling,enzymatic modification of glutinous rice protein was carried out to investigate the effects of combined freezing ball milling and enzymatic modification on the physicochemical properties and functional characteristics of glutinous rice protein.The proteins were enzymatically modified by freezing ball milling for 10 min and 40 min,and their hydrolysis,particle size,free sulfhydryl groups,surface hydrophobicity,and solubility,foaming,and emulsification were measured.The results showed that the freeze-ball milling treatment facilitated the enzymatic digestion and significantly increased the degree of hydrolysis from 7.83 % to 10.72 %,and the combined modification by freezeball milling and enzymatic digestion significantly reduced the particle size of the hydrolysate,the free sulfhydryl content and the surface hydrophobicity of the glutinous rice protein.The combined modification of freezing ball milling and enzymatic digestion significantly increased the solubility of glutelin from 0.92 % to 78.74 % but reduced its foaming and emulsification properties.The DPPH and ABTS radical scavenging ability of glutinous rice proteins were significantly improved by the combined modification of freezing ball milling and enzymatic digestion,but the OH· radical scavenging ability and reduction ability were not significantly improved.