Research On Modification、Properties And Application Of Peanut Protein By Ultrasonic Grafting Of Isomaltooligosacchraide

As a kind of high quality plant protein,peanut protein isolate has widely developmental prospect of the protein following soybean protein,which is widely used in food industry.However,it is difficult to compound with other nutrients because of low solubility under the condition of weak acid.Protein modification is one of the main manners to improve the structure and functional properties of protein.So peanut protein modification may broaden its application scope,providing a new method for deep processing of peanut protein product.So the peanut protein isolate extracted from the hot pressed peanut dregs was grafted with isomaltooligosaccharide by ultrasound-assisted method in this thesis.Grafting modification and the effect of physical treatments were analyzed through the structure characterization;the functional properties of peanut protein grafts under the two ways of ultrasonic assisted and magnetic stirring were studied.Finally,apply ultrasonic-assisted peanut protein glycosylation product was applied into surimi product in order to improve its texture features,which provide theory basis for peanut protein modification and application.The results of this research are mainly as follows:1.Research on the modification of ultrasonic-assisted peanut protein isolateisomaltooligosaccharide grafts.As the raw material,peanut protein was gained from high temperature peanut meal by alkaline extraction and acid deposition.Effects of main factors,including p H,Isomalto-oligosaccharide-peanut protein mass ratio,ultrasonic power,ultrasonic temperature and time on the modification of peanut protein were investigated.Response surface experiments were used to optimize the glycosylation of peanut protein based on the results of single factor experiments.And the superiority of glycosylation of peanut protein by ultrasonic treatment was illuminated.Under ultrasonic waves,the number of free amino is reduced after the reaction,so peanut protein interact with isomaltooligosaccharide and the graft modification of protein peanut is successful.Results showed that a maximum graft degree of 21.30% was achieved at ratio of Isomalto-oligosaccharide to peanut protein 3/1,ultrasonic power160 w,ultrasonic temperature 70 ℃,ultrasonic time 90 min and p H 9.0.In corresponding conditions,the degree of graft by traditional heating methods was up to 20.19%.2.Research on the structural characteristics of peanut protein isolate grafts.Determination of amino acids,infrared spectrum and SDS-PAGE electrophoresis analysis showed that peanut proteins concentration covalently bound at isomaltooligosaccharide,especially lysine and arginine.The secondary structure and three-dimensional structure of peanut protein grafts were investigated by circular dichroism and fluorescence spectroscopy.Compared with magnetically-agitated peanut protein isolateIsomaltooligosaccharide grafts,the structure change from order to disorder state was bigger through ultrasonic method of glycosylation,the degree of structure was much looser;average particle size analysis results showed that the peanut protein grafts particle size increased,and ultrasonic-assisted peanut protein grafts particle size had a great change.3.Study on the functional properties of peanut protein grafts.Through comparing the functional properties of magnetically-agitated peanut potein isolate、ultrasonic-assisted peanut protein isolate 、 magnetically-agitated peanut potein isolate-Isomaltooligosaccharide grafts and ultrasonic-assisted peanut potein isolate-Isomaltooligosaccharide grafts,Results showed that the solubility 、 oil absorbency 、 foamimg ability and foam stability of peanut potein isolate grafts are increased,the denaturation temperatures increase and surface hydrophobicities were lower compared with peanut potein isolate.Using a laser scattering method to determine the emulsifying properties of peanut protein grafts,the effect of protein concentration,p H,ion strength and heat treatment on the emulsification and stability of peanut protein grafts were discussed.The results showed that in peanut protein isolate of 15 mg/m L,the emulsion particle size normally distributed,and the average particle size were the smallest;the emulsifying activity and stability of peanut protein grafts were increased,and presented different trends as the increase of the p H,ion concentration and temperature.4.Study on the effect of ultrasonic-assisted peanut protein isolate grafts on the textural properties of surimi product.Surimi cooking loss rate and water retention shwed that peanut protein isolate and grafts possessed water retention and oil binding capacity,when their addition levels were 1.5%,the yield of the surimi product was the biggest and the water-holding capacity was also the biggest,the water and oil holding capacity of peanut protein grafts were better than peanut protein;aberration analysis showed that the whiteness decreased with the increasing addition levels and that of surimi product added peanut protein grafts were less than that added peanut protein.Texture property analysis indicated that surimi product presented the same change trends in hardness,cohesiveness and chewiness when it was added to peanut proteins and grafts.while the addition level was 2.0% of surimi,the masticatory force and taste increased,textural characteristics were improved significantly.The results of gel strength researches showed that both of the them firstly increased and then decreased with the protein and grafts addition increase,and reached the maximum when the protein content increased to 1.5%,the gel strength of surimi product added peanut protein grafts was greater than that added peanut protein.