Interaction Between Catechins And Soybean Protein Isolate And The Application Of Their Complexes In Meat Batters

Soy protein isolate is a high-quality plant protein with rich nutritional value.It is widely used in food processing because of its emulsifying and gelling properties.In order to use it better,how to improve the functional properties of soy protein isolate become a hot research issue.Catechin is a kind of polyphenolic active substance.The hydroxyl component contained in its structure are used to interact with macromoleculares.The functional properties of soy protein isolate can be altered because the addition of catechins alters its structure.This article took catechins and soybean protein isolate as the research object,analyzed the influence of different compound conditions on the interaction between them,and studied the application of the compound in meat batters.The effect of different amounts of catechins on the binding affinity of catechin/soy protein isolate and the physicochemical functional properties of the composite system was studied.When the amount of catechins added was 10%,binding affinity and emulsibility of the complexes reached the maximum.When the catechins added was 4%,the gel hardness is the largest.Structure analysis results shows that the structure of SPI was stretched due to the addition of catechins.The internal chromophoric groups and hydrophobic groups were exposed to promote the formation of stable complexes through hydrophobic interactions.The effect of different pH on the binding affinity of catechin/soy protein isolate and the physical and chemical properties of the composite system was studied.Under acidic conditions,catechins were difficult to be bound with SPI,and the emulsification and stability of the composite system were poor.They cannot form a gel near the isoelectric point.When the pH value is 3.5,5.5,6.5,the electrostatic force is the dominant force,and when the pH value is 4.5,the hydrogen bond and van der Waals force are the dominant force.However,alkaline conditions were conducive to the interaction between catechins and SPI.The binding affinity and gel hardness of them were improved.With the gradual increase of pH,complex structure had been changed,which lead to the improvement of its functional properties.The effect of different preheating temperatures on the binding affinity of catechin/soy protein isolate and the physical and chemical functional properties of the composite system was studied.It was found that when the preheating temperature is mild,the free sulfhydryl content and α-helical structure in the solution gradually increased,the random coil structure and the surface hydrophobicity decreased,indicating that proper heating can promote the unfolding of the soybean protein isolate structure.The structure of soy protein isolate was easy to expand,under the condition of proper heating,it is helpful for catechins and soy protein isolate to form a more stable complex through hydrophobic interaction,and increase the emulsification of the solution.When the temperature is too high,the content of free sulfhydryl groups in the solution will decrease and the hydrophobicity of the surface will increase.Macromolecular polymers with a molecular weight greater than 180 kDa were found in solution.It showed that the hydrophobic interaction between the two may be weakened and covalent bonds appeared.The emergence of macromolecular soluble polymers limits the rapid deployment of the compound at the oil-water interface.Resulting in decreased emulsification.Through response surface experiments obtained the preparation conditions of the complexes with different functional properties.The composite conditions of the gel type were 4.4%added catechin,temperature 49.0℃,pH 9.6 and the emulsifying type were 10.1%catechin addition,temperature 59.3℃,and pH value 7.7.Through measured the peroxide value,thiobarbituric acid value,the total number of colonies,the content of volatile base nitrogen and the color change of the meat batters in 0,1,3,5 and 7 days,which separately added soy protein isolate,emulsified complex,gel complex,different content of catechins and without adding.The results showed that both the complexes and catechins have the effects of inhibiting the oxidation of meat batters and antibacterial,and the gel-type compound is better than the other groups in improving the quality of meat batters.Through measured the changes in sensory quality,texture characteristics,moisture content,water retention,and color of tin foil sausages during storage made from different groups of meats batters.The results showed that the complexes can significantly improve the organoleptic quality of the meat sausage,and protect its color.The gel-type complex has stronger water retention,compared with other groups.