Construction Of Grading Model Of Wooden Breast And Degradation Mechanism Of Myofibrillar Protein Oxidized By Hydrogen Peroxide In Vitro And Improvement Of Functional Characteristics

Chicken is widely loved by consumers worldwide due to its high nutritional value and low price.With the increasing demand for chicken,the modern aquaculture industry has limited its industrial objectives to the rapid growth of broilers and the increase in breast meat production,but this has also led to many chicken anomalies.Wooden breast（WB）is a highly abnormal meat found in the white feather broiler industry in recent years,with a global incidence of about60%.According to the evaluation of appearance and touch,it can be divided into three levels:mild,moderate,and severe.Among them,moderate and severe wooden breast exhibit undesirable characteristics such as ridges,bleeding,and sticky,as well as poor edible quality characteristics（water holding capacity,texture characteristics）that make them unable to be recognized by consumers and are on the verge of being discarded,resulting in serious economic losses.However,due to the limitations of efficiency and accuracy,manual classification and instrument classification are difficult to be widely used in the classification of wooden breast,which hinders its further processing and utilization.There have been many assertions about the quality deterioration of wooden breast,but the reasons for the decline in its protein properties have not been studied.Myofibrillar protein（MP）is closely related to the edible quality of meat,and it carries the adverse effects caused by the decline in meat quality.For this reason,wooden breast may have a profound impact on the molecular structure and functional characteristics of its myofibrillar protein.However,the mechanism of functional degradation of wooden breast myofibrillar protein（WBMP）remains unclear.In addition,the resulting reduction in the quality of protein gel and emulsion products also needs to be improved through a series of technologies.Therefore,this article mainly explores the deterioration mechanism of the selected WBMP functional properties.And then uses physical or chemical methods to improve its functional properties,aiming to improve the utilization value of wooden breast and WBMP.This study is divided into three parts.Firstly,by comparing the differences in the quality and functional characteristics of mild,moderate,and severe wooden breast and WBMP,to characterize the degree of negative impact on the functional characteristics of different grades of WBMP.At the same time,establish a relationship between the functional characteristics of different grades of wooden breast and WBMP to build a quality evaluation model for different grades of wooden breast.Subsequently,this model was used to screen and extract myofibrillar proteins from moderate wooden breast,and compare and analyze the molecular structure of myofibrillar proteins from normal chicken breast meat oxidized by free radicals（H₂O₂）,clarifying the mechanism of free radical oxidation attacking WBMP.Finally,in view of the damage to the physicochemical properties and functional properties of WBMP.The glycosylation method,preheating cooperate with high-intensity ultrasound（HIU）method,（-）-epigallocatechin-3-gallate（EGCG）composite emulsion regulation method were used to treat the natural structure of WBMP and its gel and emulsion to improve the physicochemical properties,gel properties and emulsifying properties of WBMP.The main research results are as follows:（1）According to the comparison of quality characteristics between wooden breast and normal chicken breast,it can be seen that the drip loss,cooking loss,shear strength,p H value,and other indicators of wooden breast are significantly higher than those of normal meat.And with the deepening of the severity,the water holding capacity of wooden breast significantly decreased,especially in severe wooden breast,the water drip loss and cooking loss significantly increased.The L*and a*of wooden breast is significantly lower than that of normal chicken breast,and the overall meat color is darker.The increased hardness,chewability,and decreased elasticity and cohesion of severe wooden breast indicate that the severity of wooden breast enhances muscle stiffness,and its muscle fibers become thicker and more resilient again.In terms of functional characteristics of different grades of WBMP.As the degree of wooden breast increases,the solubility of severe WBMP decreases,while the emulsifying activity and emulsifying stability decrease.The quality of the gel formed by WBMP also decreased correspondingly,its water holding capacity and texture properties were far less than those of normal myofibrillar protein,and its emulsification also decreased seriously.In summary,it has been confirmed that the deterioration of wooden breast and its myofibrillar proteins becomes more severe with the increase of grade.（2）Collect different grades of wooden breast with mild,moderate,and severe degrees,and use correlation analysis method to analyze its quality and WBMP functional characteristics indicators.After removing the b*,cohesion,and chewing ability with small correlation coefficient and correlation.According to the principal component analysis method,the indicators were further classified and simplified into two principal components.The contribution rate of the first principal component was 76.76%,and the representative indicators were p H value,cooking loss,and a*.The contribution rate of the second principal component is 22.01%,and the representative indicators are cooking loss,b*and p H value.Based on correlation and coefficient of variation,two main indicators representing the quality grade of lignified chicken breast meat（redness:a*and p H value:P）were selected.The weights of the two indicators were determined to be 0.353 and 0.219 using the independent weight coefficient method,respectively.Therefore,the formula for calculating the comprehensive evaluation score of wooden breast meat quality of different grades was obtained:Y=0.353a*+0.219P.Regression analysis and model validation combined with sensory evaluation data obtained a fitting formula:y=2.4071x+0.0343（R²=0.9883）,with a fitting coefficient greater than 0.8.That can accurately predict sensory evaluation scores,better reflect the quality differences of different grades of lignified chicken breast meat,and can be used for accurate and rapid grading.（3）The zeta potential,particle size,solubility,and sulfhydryl and carbonyl content of OBMP-3（3m M,low dose free radical oxidation MP）and WBMP are similar.Low dose free radical oxidation leads to a significant increase in surface hydrophobicity and endogenous tryptophan fluorescence intensity.Changes in sulfhydryl and carbonyl content caused by oxidation and the formation of disulfide bonds are the main reasons for WBMP aggregation.In addition,WBMPα-helix content significantly decreased.The significant increase inβ-fold and irregular curl content indicates that free radical attacks causeα-helix conversion intoβ-fold leads to the destruction of the structure of proteins.A large number of transformations with irregular curls promote the disorder of protein structures.Therefore,low dose free radical oxidation attacks the proteome,inducing secondary and tertiary structural changes,leading to deterioration in the functional properties of WBMP.（4）In terms of the molecular structure and physicochemical properties of WBMP,the glycosylation reaction in the presence of D-ribose（RI）makes WBMP more uniformly dispersed in solution,with a significant reduction in particle size.Therefore,WBMP-RI solubility andα-helix content increased.Compared with WBMP-ribose,WBMP-sodium alginate and WBMP-glucosamine have poor particle distribution,solubility,and emulsifying properties.That indicating that the aldehyde group in aldose is more suitable for glycosylation modification of WBMP than the ketone group in ketose.And this can effectively change the conformation of the initial WBMP to form a normal protein structure with more complete functional characteristics.In terms of improving the gel performance,compared with the preheating groups of 30,40 and 60℃,the collaborative HIU（450W,20k Hz）treatment during preheating to 50℃（PT50）makes the G’value of WBMP solution in temperature scanning higher than that of other groups,and has excellent rheological properties.PT50 gel has better hardness,elasticity and water holding capacity,so the relative content of water that is not easy to flow is also the largest.Higherβ-fold content makes the microstructure of PT50 gel uniform and compact.All these indicate that preheating to 50℃can significantly enhance the effect of HIU on protein structure,thus producing improved WBMP gel.In terms of improving emulsification performance,compared to low dose（0.01%,0.02%）and high dose（0.04%）EGCG,medium dose EGCG（0.03%）can significantly improve the emulsification activity and stability of emulsion,and reduce the particle size of WBMP emulsion.From the perspective of microstructure and coagulation index,0.03%EGCG delayed phase separation by preventing the aggregation of droplets and proteins,thus significantly improving the stability of WBMP emulsion.During the storage experiment at 50℃for 96h,0.03%EGCG inhibited lipid oxidation（formation of lipid hydrogen peroxide and 2-thiobarbituric acid reactive substances）and protein oxidation（carbonyl formation and sulfhydryl loss）.In contrast,lower and higher EGCG concentrations（0.01%,0.02%,and 0.04%）have drawbacks in improving the quality and oxidative stability of emulsions（such as weak antioxidant capacity or excessive protein aggregation）.Therefore,the medium dose of EGCG（0.03%）can improve the quality and shelf life of WBMP emulsion.