Study On Tenderness Specificity And Mechanism Of Myofibrillar Protein Structure Change Of Beef With High Degree Of Doneness

In modern society,meat usually needs to be heated before consumption.Compared with the consumption of beef in the West,the cooking mode of beef in China is mainly stewing.In this paper,the changes of beef tenderness and myofibrillar protein structure during beef cooking were studied with reference to the Chinese beef stewing process and the western steak cooking method,and the changes of myofibrillar protein conformation in beef cooking were revealed at the molecular level.The evaluation method of beef tenderness with high degree of doneness was established,and the relationship between the structural characteristics of myofibrillar protein and beef tenderness was studied,and the correlation between myofibrillar protein conformation change and beef tenderness was revealed.The results were as follows:1.As the degree of doneness increased,the tenderness of meat decreased,the average particle size,turbidity,surface hydrophobicity,sulfhydryl content and dityrosine content of myofibrillar protein particles increased first and then decreased,and the carbonyl content increased gradually.Intrinsic fluorescence intensity showed a trend of U font change.Medium was the turning point of the relative content change of myofibrillar protein secondary structure.Correlation analysis showed that the content of β-sheet structure,random coil and the carbonyl group of myofibrillar protein were significantly correlated with the shear force values of beef.2.During the cooking process of beef,the protein amide Ⅰ and Ⅱ bands were the main regions of protein structure change caused by degree of doneness.With the increase of degree of doneness,the peak intensity of myofibrillar protein decreased in the wave number range of 1700～1500 cm-1.According to the results of two-dimensional correlation spectrum analysis,the Medium was the turning point of the change of protein temperature sensitive region.With the increase of doneness,the temperature sensitive key region of myofibrillar protein was transferred from the amide Ⅱ band to theα-helix structure of the amide Ⅰ band.3.The effects of different heating temperature(70～100℃)and time(0～180 min)combination conditions on the shear force values and texture characteristics of different parts of beef were studied.Using principal component analysis,three principal components were effectively extracted,which representing the chewing,compressive and shear characteristics of beef,respectively.A comprehensive evaluation equation of beef tenderness based on principal component analysis was established.4.During heating process in the condition of different heating temperature(70～100℃)and time(0～180 min)combinations,heating temperature and time had a significant effect on the structural characteristics of beef myofibrillar protein.The state of myofibrillar protein in the solution was gradually transformed from aggregation to cleavage.The intrinsic fluorescence intensity decreased gradually,and the content of dityrosine increased gradually.The surface hydrophobicity,carbonyl content,sulfhydryl content and secondary structure of myofibrillar protein were significantly affected by heating temperature.The results of correlation analysis showed that the carbonyl content and dityrosine content of myofibrillar protein were significantly correlated with the tenderness of beef with high degree of doneness.In conclusion,after cooking,beef had been completed the transition from raw to well done,and then from well done to over cooked.During the first process,beef tenderness was mainly related to the carbonyl content and the content of β-sheet structure,random coil of myofibrillar protein.And during the secondary process,beef tenderness was mainly related to carbonyl content and dityrosine content of myofibrillar protein.This study will provide theoretical basis for Chinese beef cooking process optimization and quality control.