Mechanical Property Of Wooden Breast In Chicken Broiler And Its Development Mechanism

Wooden breast is breast muscle with wooden breast myopathy or abnormality,which has low protein content,high water and fat contents.These breast fillets are pale and hard in lesion areas,which are covered with a layer of viscous fluid as well as petechial hemorrhagic lesions in a part of wooden breast fillets.Severe wooden breast fillets show diffuse,pale and hardened areas in whole fillet as well as ridge-like bulges at the caudal end.The incidence of moderate and severe wooden breast fillets is more than 30%,which leads to economic loss for poultry industry.Many studies have focused on the quality of normal chicken breast and its products for a long time,but there are a few studies on the mechanism of quality formation of wooden breast meat.In this paper,a 3D classification model was established from the perspectives of stress in order to solve the quality heterogeneity of chicken breast fillets.The effects of wooden breast myopathy on meat quality of chicken breast were investigated by histology and oral processing.The development mechanisms of wooden breast meat quality was revealed by studying the changes of connective tissue and using TMT（Tandem Mass Tag）proteomics technology.The main research contents and results were as follow:1.Classification of wooden breast myopathy in chicken pectoralis major based on stress distribution characteristics and meat quality under this classification methodWooden breast fillets were mainly distributed in the heavier and thicker breast fillets,and the degree of wooden breast myopathy was highly correlated with hardness（R²=0.80）,weight（R²=0.74）and thickness（R²=0.83）.A 3D model based on highly correlated characteristic parameters can distinguish between normal breast and wooden breast.The stress of chicken breast increased from caudal part to cranial part,and it also increased with an increase in the severity of wooden breast myopathy.The 3D model based on the stress distribution can effectively distinguish chicken breast fillets with different degrees of wooden breast myopathy,and it also digitally shows lesion position and myopathy severity.The surface fitting equation is z=-2.071+0.1999x+0.5579y–0.01188xy（R²=0.84）through 3D scatter surface fitting,where x is stress in cranial part,y is stress in middle part,and z is stress in caudal part.Histologically,wooden breast myopathy caused muscle fiber degeneration,fibrosis,necrosis,nucleation,fatty tissue deposition,inflammatory cell infiltration and connective tissue proliferation in muscle tissue.With an increase in the severity of wooden breast myopathy,the relaxation time T_2bincreased and T₂₂decreased,and P_2band P₂₁decreased and P₂₂increased.As the severity of this myopathy increased,the contents of water,fat,collagen and soluble collagen increased（P<0.05）,and the contents of protein and ash decreased（P<0.05）,and the ultimate p H,drip loss,cooking loss,thawing loss and purge loss increased（P<0.05）when the severity of this myopathy increased,and shear force of moderate wooden breast meat was the highest（P<0.05）among all breast meat with the severity of this myopathy.The hardness of fresh normal chicken breast（36.17 N）was significantly lower than those of mild wooden breast（56.13N）,moderate wooden breast（58.72 N）and severe wooden breast（75.49 N）,and the hardness,gumminess and chewiness of cooked wooden breast were significantly higher than those of cooked normal chicken breast（P<0.05）.There was no difference in mastication time and mastication frequency between normal chicken breast and mild,moderate and severe wooden breast fillets（P>0.05）,but moderate wooden breast showed longer chewing time and smaller chewing frequency when compared to those in the other groups.Wooden breast showed poor oral processing property,high masseter muscle activity and big particles in the bolus.The stress,Dx50,Dx90 and D[4,3]of chicken breast were significantly different from each other.2.Influence of heat temperature on oral processing and in vitro digestion of wooden breast meat of chicken broilerAs cooking temperature increased,cooking loss of chicken breast significantly increased（P<0.05）,and cooking loss of wooden breast was higher than that of normal chicken breast（P<0.05）.The relaxation time T_2bvalues of normal chicken breast and mild wooden breast reached the minimum at 90℃,and those of moderate and severe wooden breast reached the minimum at 80℃.The relaxation time T₂₁of chicken breast meat was prolonged,and the relaxation time T₂₂of chicken breast meat was shortened.The relative water content P₂₁and P₂₂of chicken breast meat increased with the increase of temperature,and the water content P_2bof chicken breast meat increased at first and then decreased.The chewing time and masseter activity of chicken breast meat increased with the increase of cooking temperature,and decreased at 100℃.With the increase of cooking temperature,the water content of chicken breast meat significantly decreased（P<0.05）,and the water content of chicken breast meat bolus decreased.The Dx50,Dx90,D[3,2]and D[4,3]of chicken breast bolus were decreased,but the SSA of bolus was increased.The microstructure showed that the amount of muscle fiber bundle and muscle fiber filament decreased gradually,the length and width of muscle fiber decreased,and the tissue of the bolus tended to be uniform,however,there were some big particles in moderate and severe wooden breast fillets.With the extension of enzymatic hydrolysis time,the degree of proteolysis of chicken breast bolus increased gradually,and the degree of proteolysis of chicken breast bolus increased at first and then decreased with the increase of cooking temperature.3.Physiochemical,gelling and oral processing properties of ground meat of wooden breast filletsWith the increase of the severity of wooden breastmyopathy,the contents ofβsheet andβturn of ground meat decreased significantly（P<0.05）.Compared with ground normal meat,cooking loss and thawing of wooden breast meat significantly increased（P<0.05）,and the water holding capacity of chicken breast meat decreased with the increase of the severity of wooden breast myopathy.The viscosity of all ground chicken breast meat showed a similar decreasing trend,and the storage modulus and loss modulus of ground meat decreased.The L*of meat gels decreased when the severity of this myopathy increased.Considering water distribution of meat gels,the T_2b1,T_2b2and T₂₁gradually increased and T₂₂decreased,and P_2b1,P_2b2and P₂₁gradually decreased and P₂₂increased.The hardness,gumminess and Chewiness of meat gels graduallydecreased,and the cohesiveness of meat gels slightlydecreased.The structure of meat gels became very loose and the number of large carves increased.The chewing time and masseter activity of groundmeat gels significantlydecreased,and the chewing frequencysignificantly increased（P<0.05）.The water content of mild and moderatewooden breast meat gels was significantly lower than those of normal chicken breast meat and severewooden breast meat gels,and the water content of the bolus formed by oral processing of chicken breast meat gels obviously increased,and the distribution curve of the bolus size moved to the direction of the big size.Wooden breast myopathy causes large muscle fiber fragments in the bolus of chicken breast meat gels.At the end point of in vitro digestion,moderate and severe groups had the highest degree of protein hydrolysis,followed by mild groups,and normal groups had the lowest degree of hydrolysis.4.Physicochemical properties of intramuscular connective tissue and collagen in wooden breast of chicken broilerThe mechanical strength of intramuscular connective tissue increased with an increase of the severity of wooden breast Myopathy,and the mechanical strength of intramuscular connective tissue decreaseddue to heating treatment.The temperature of thermal denaturation of intramuscular connective tissue was increased by wooden breast myopathy.Histologically,the arrangement,cross-linking and fiber diameter of collagen fibers are obviously different.The contents ofα-Helix andβ-sheet of collagen decreased due to the severity of wooden breast myopathy,and the contents of random coil increased.Zeta potential and particle size of collagen increased,and the viscosity,surface hydrophobicity and sulfhydryl group content of collagen increased.The largest fluorescence emission peak of collagen was at 338,and the fluorescence intensity of connective tissue protein graduallydecreased from normal meat to severe wooden breast meat.SDS-PAGE showed that the bands of connective tissue proteins in wooden breast were similar to those in normal breast,and the aggregation or molecular weight of connective tissue proteins was up to 499.22 k Da.5.Development mechanism of meat quality of wooden breast of chicken broiler based on TMT whole muscle proteomicsThrough TMT proteomics,2536 proteins were identified in three groups of chicken breast meat.In Mod vs.Nor group,160 differentially expressed proteins were identified,including 124 up-regulated proteins and 36 down-regulated proteins.In Sev vs.Nor group,500 differentially expressed proteins were identified,including 414 up-regulated proteins and 86 down-regulated proteins.In Sev vs.Mod group,153 differentially expressed proteins were identified,including 117 up-regulated proteins and 36 down-regulated proteins.Among differentially expressed proteins,the hydrophilic proteins（Gravy<0）in Mod vs.Nor group,Sev vs.Nor group and Sev vs.Mod group were 151,474 and 142,respectively,and hydrophobic differentially expressed proteins in Mod vs.Nor group,Sev vs.Nor group and Sev vs.Mod groupwere 9,26,11.Bioinformatic analysis showed that the differentially expressed proteins were mainly involved in muscle contraction,muscle system development,muscle structure development and stress fiber assembly and others.By KEGG analysis,the differentially expressed proteins were mainly involved in glycolysis and gluconeogenesis,amino acid biosynthesis,cardiac muscle contraction,ribosome and other important pathways.The protein interaction network showed that two major functional modules are enriched in Mod vs.Nor group,ten major functional modules is enriched in Sev vs.Nor group,and three main functional modulesis enriched in Sev vs.Mod group.These functional modules are mainly related to muscle contraction,muscle structure development,skeletal muscle organization development,tight junction,adherens junction and so on.Therefore,it is concluded that mechanical properties of wooden breasts of chicken broilers are affected by water in muscle（myowater properties）,connective tissue,muscle structure and state,constitution and structure of muscle fiber,fibrosis and fiber necrosis,etc.