Effect Of Freezing Induced Aggregation Behavior Of Soy Protein Isolate

Frozen foods have developed rapidly in recent years,and soy protein isolates are widely used as food additives in food ingredients.Therefore,based on the structure of frozen soy protein isolate,the mechanism of freeze-denaturation of soy protein isolate was discussed.In-depth study of the frozen aggregation behavior of soy protein isolate.The effect of freezing on the structure and emulsification properties of soy protein isolate was studied.This paper selected several freezing temperatures commonly used in food production,storage and life-5??-20??-40? and-80? to study the different degrees of aggregation state changes.This paper indicated the type of aggregation state of soy protein isolate by solubility and turbidity.Stability and microstructure changes of protein frozen aggregates in aqueous phase were observed by stability kinetic index and scanning electron microscopy.The results showed that under the freezing condition of-5?,the solubility of soy protein isolate was the lowest,only 62.3%.The turbidity of the protein has been increasing with the decrease of temperature,and the absorbance of the maximum turbidity has reached about 1.6.The microstructure suggested that freezing caused the protein microstructure to undergo a tight-loose-tight process.It is indicated that the binding between protein aggregates has undergone a process from compact to loose to tight.Proteins formed soluble aggregates to produce insoluble aggregates.The sulfhydryl and disulfide bond content and surface hydrophobicity analysis were used to study the changes of disulfide bond and hydrophobic interaction in the aggregate;the structural changes of frozen soy protein isolates were characterized by SDS-PAGE gel electrophoresis,UV absorption spectroscopy,endogenous fluorescence spectroscopy and Fourier transform infrared spectroscopy.The results showed that the freeze-treated soy protein isolate formed a reversible protein.Only when ultra-low temperature(-80?)conditions,the protein structure is seriously damaged,will produce a small amount of irreversible.Freezing promoted the formation of disulfide bonds in the free sulfhydryl groups of the protein,increasing the disulfide bond content.And under the freezing condition of-20?,the content of diterpene bond was 22.18 ?mol/g,which was 64.17%higher than the content of disulfide bond in natural protein.The surface hydrophobicity of soy protein isolates treated at different freezing temperatures was much greater than the surface hydrophobicity of native proteins.The freezing treatment increased the content of ?-sheet and random coil of the protein,decreased the ?-turn content,and deepened the disorder of the protein structure.The emulsion properties of frozen soy protein isolate were investigated by droplet distribution,microscopic morphology and stability of the emulsion.The results showed that the freeze-induced protein aggregates were not destroyed by the high shear action during emulsification.The freezing caused the droplet size of the emulsion to increase,the emulsifying ability is deteriorated,and the stability is deteriorated.