| Soybean protein has more than 19 kinds of amino acids,and contains all the essential amino acids for human body.It is a high quality protein.Soybean protein isolate(SPI)was obtained from fresh soybean by extraction and centrifugation.The protein content of SPI was greatly increased.In the modern food industry,the freezing and thawing of proteins directly affect the storage and transportation conditions of frozen food.The functional properties of proteins are determined by their composition and preparation conditions,and are also influenced by external factors.Catechin(EGCG),a flavane derivative,is a polyphenolic active substance mainly extracted from tea.It can precipitate protein and heavy metals,and also has very important functional properties for human health.Therefore,the combination of catechin and soy protein for freezing and thawing treatment,and studying its changes,is of great significance to the development of the food industry.This paper mainly studies the regulation mechanism of catechin on the frozen and thawed structure and functional properties of soy protein.In the experiment,soybean protein isolate and catechin were used as the main raw materials,and 0,1,3,and 5 freeze-thaw cycles were carried out respectively.Under these conditions,the regulation of the structure and functional properties of soy protein by catechin was studied.mechanism.The three-stage structure,secondary structure and microstructure change of soybean protein were analyzed by fluorescence quenching mechanism analysis,surface hydrophobicity measurement,circular dichroism,particle size measurement,potentiometry and thiol content determination.It is concluded through experiments that the catechin and soy protein are statically quenched,and the interaction between the two is tightly combined to form a soy protein-catechin complex with a binding site of 1.It was found by hydrophobic interaction experiments that catechins altered the tertiary structure of soy protein and increased the hydrophobic interaction of soy protein.The interaction between catechin and soy protein was studied by circular dichroism.The results showed that catechin increased the α-helix content in the secondary structure of the protein and decreased the β-sheet content,which changed the secondary structure of the protein..In the determination of sulfhydryl content,the free sulfhydryl content in the soy protein solution decreased,and the catechin changed the microscopic structure of the soy protein.The addition of catechin can increase the absolute value of the potential of the soy protein solution and decrease the volume average diameter,thereby enhancing the stability of the system.The functional properties of the soy protein solution mainly studied solubility,foaming and foaming stability,emulsifying activity and emulsion stability,layering coefficient and oxidation resistance.The solubility of soy protein decreased after the addition of EGCG.The foaming property and foaming stability are enhanced,the emulsification and emulsion stability are enhanced,the milk layering coefficient is lowered and the oxidation resistance is improved.The above experimental results show that the EGCG interact with soy protein after the addition,so that the protein structure is unfolded,the hydrophobicity is enhanced,and the EGCG is more tightly bound,and the EGCG also provides an appropriate amount of activated hydroxyl groups for the soy protein.The complex effectively improves the functional properties of the soy protein under freezing and thawing conditions.Taking full account of the various characteristics of soy protein,starting from the various structures of soy protein,and then analyzing the functional properties,it is concluded that the addition of EGCG can change the structure of soy protein under freezing and thawing conditions,and enhance the soy protein.The functional properties have a positive regulatory effect on the frozen thawed structure and functional properties of soy protein. |
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