Study On Quality Characteristics And Mechanisms Of White Striping And Wooden Breast In Broilers

In recent years,the sharp increase in global demand for chicken meat has led to a shift in the main breeding standards for modern broilers towards rapid growth and increased breast yield.However,the remarkable increase in broiler production efficiency was accompanied by the occurrence of several myopathies.Among them,white striping(WS)and wooden breast(WB)have gradually attracted the attention of meat researchers and practitioners due to their high incidence and wide influence.Both WS and WB cause appearance defects of chicken breasts,reduce consumers’ desire to buy,and have serious impacts on meat quality,nutritional value and processing characteristics of chicken meat.In addition,the causes of WS and WB are very complex,involving many metabolic pathways.The formation mechanism is still unclear,which needs further exploration.This study first analyzes the differences in meat quality,nutritional composition and microstructure between WS,WB and normal breast meat,and clarifies the quality characteristics of the myopathies.Furthermore,we explored the redox status and changes in energy metabolism in WB-affected and unaffected chickens,combined with muscle tissue damages and meat quality changes,revealed the underlying mechanism of the myopathies.1.Study on the quality characteristics of white striping and wooden breastAccording to the criteria of WS and WB(appearance and palpation),fillets were classified into normal meat(NOR),WS and WB(n=12),samples were selected from a large broiler slaughterhouse.The quality characteristics of the breast meat were analyzed.The results showed as follows:compared with normal meat,the acceptability of WS and WB was poor,the weight and thickness of WS and WB were significantly increased(P<0.05);histological morphology of WS and WB showed degeneration of muscle fiber,the muscle fiber diameter was significantly increased(P<0.05),and the muscle fiber density was significantly decreased(P<0.05).In terms of meat quality,pH24h value of WS and WB was significantly increased(P<0.05),T23 peak area ratio and water holding capacity were significantly decreased(P<0.05),L*and b*of WB were significantly increased(P<0.05),while cohesiveness and resilience were significantly decreased(P<0.05),b*and gumminess of WS were significantly increased(P<0.05).In addition,the fat content of WS and WB was significantly increased(P<0.05),the protein and ash content were significantly decreased(P<0.05),and the moisture content of WB was significantly increased(P<0.05).These results implied that,the sensory characteristics of WS and WB are poor,muscle tissue shows fibrotic necrosis and other pathological symptoms,accompanied by the decrease in quality characteristics such as meat quality,texture characteristics,and nutritional value.2.A comparative study on the redox status of WB-affected and unaffected chickensBased on the previous research,42-day-old WB-affected and unaffected chickens(n=12)under commercial breeding conditions were collected to explore the differences in redox status.The results showed as follows:the activities of plasma creatine kinase(CK)in the WB group was increased(P<0.05).Histologically,WB showed serious structural damage and accumulation of connective tissue.The activities of T-SOD and GSH-Px in the plasma of the WB group were increased(P<0.05),and the activities of T-AOC,GSH-Px,and T-SOD in breast muscle and liver were increased in the WB group(P<0.05).In addition,compared with the NOR group,the levels of ROS,protein carbonyl,MDA,LPO and 8-OHdG in the breast muscle were significantly increased in the WB group(P<0.05),and the levels of MDA,LPO and 8-OHdG in the liver were also significantly increased(P<0.05).Moreover,some swelled mitochondria were observed in the breast muscle in the WB group,and the mitochondrial membrane potential was significantly lower than that of the NOR group(P<0.05).Furthermore,the mRNA expression levels of Nrf2 and its downstream target genes HMOX-1,NQO1,SOD,GPX,GCLC and GCLM in the WB group were significantly increased(P<0.05).These results suggested that the change of redox state can cause irreversible damage to skeletal muscle and mitochondria,and seriously damages the muscle tissue structure,which further induce the formation of WB.3.A comparative study on the energy metabolism of wooden breast and normal breastWe used the breast muscle samples collected in Chapter 2 to analysis the energy metabolism of WB and normal breast.The results showed as follows:compared with the NOR group,the glycogen contents,lactic acid contents and the glycolytic potential in the WB group were significantly decreased(P<0.05).Moreover,the ATP content was significantly decreased in the WB group(P<0.05),while the AMP content was significantly increased(P<0.05),and the AMP/ATP was significantly increased(P<0.05).In addition,the key enzymes of glucose metabolism in the WB group,such as the activities of CS and MDH were significantly increased(P<0.05),while the activities of HK,PK,PFK,LDH,PEPCK,PC,G6P and GCS were significantly decreased(P<0.05).The mRNA expression levels of LKB1,AMPKal,GLUT3,OGDH,SUCLA2,SUCLG1 and SUCLG2 in the WB group were significantly increased(P<0.05),and the expression level of PDK4 was significantly decreased(P<0.05).These results implied that:the energy metabolism disorder of WB was characterized by the decrease of glycolysis,gluconeogenesis and glycogen anabolism,on the other hand,the increase of AMP/ATP activates AMPK,which promotes energy production by up-regulating tricarboxylic acid cycle metabolism.In conclusion,the quality characteristics such as meat quality,nutritional value and texture characteristics of white striping and wooden breast are reduced;the changes in the redox state and energy metabolism played important role in the development of wooden breast.