Study Of The Effects Of Lipoxygenase-induced Oxidation On The Structure And Digestibility Of Soybean Protein Isolate

Soy protein is an important element in many food systems,the oxidation of protein will impact the food quality,which depends on the structure of the protein oxidation process changes.In food system,lipid and protein are often coexistent,studies have shown that lipid oxidation and protein oxidation are closely related,but the mechanism of lipid and protein oxidation is not studied thoroughly.In this paper,soybean protein isolate was used as the research object,and the free radicals produced by the oxidation of linoleic acid were catalyzed by lipoxygenase,and induce soybean protein isolate to an oxidation.The changes of soybean protein structure and its digestion were studied.First,soy protein isolates were extracted from soybean and defatted soybean flour with different storage times,and their structures was evaluated.The results showed that soybean protein isolate obtained from soybean have a lower degree of oxidation,which indicated that the protein was oxidized during the processing of defatted soybean flour.The soybean protein isolate obtained from defatted soybean flour had an increasing degree of oxidation with longer storage time.Then,we established the oxidation system with linoleic acid,lipoxygenase and soybean protein isolate.The soybean protein isolate was induced by different concentrations of linoleic acid,and the structure of soybean protein was analyzed,to explore the mechanism of lipid oxidation on soybean protein isolation.The results showed that with the increase of substrate linoleic acid concentration,the carbonyl content of protein increased and the content of sulphydryl decreased,indicating that the protein had been oxidized.With the increaseof soybean protein oxidation,the surface hydrophobicity increased first and then decreased,and the endogenous fluorescence first occurred inred shift and then blue shift,The protein particle size decreased first and then increased,it can be seen that the protein oxidation first occurred in unfolding and then gathering.In addition,the solubility of isolated soybean protein in different solvents and gel electrophoresis showed that the molecular structure of the protein changed,and formated the covalent aggregates of non-disulfide bond.Finally,isolated soybean proteins with different oxidation degree were digested in vitro,it was found that oxidation was not conducive to the hydrolysis of isolated soybean protein.With the increase of oxidation degree of isolated soybean protein,the antioxidant activity and free radical scavenging ability of digestive solution decreased and the amino acid content decreased gradually.Oxidation had destroyed the amino structure of soybean protein isolate,reducing the quality of soy protein isolate.