Abstract: 【OBJECTIVE】This study was conducted to determine the effects of heat stress on pH, lipid peroxidation, protein oxidation and protein functionality in broiler breast meat. 【METHOD】Two hundred of AA broilers were randomly divided into 5 groups ,40 broilers for each group. After 30 days adaptive feeding under the normal temperature, broilers were suddenly stressed for 0h, 1h, 2h, 3h and 5h by increasing environmental temperature from(25士1)℃ to (40士1)℃. The pH, lipid or protein oxidative status and protein functionality of 10 broiler breast muscles in every group were investigated. 【RESULTS】As compared with the control group, the pH30min and pH24h of muscle decreased significantly (p＜0.05), oxidative extent of intramuscular fat increased significantly at 3h and 5h(P＜0.01), oxidative extent of sarcoplasmic and myofibrillar protein also increased significantly at 2h, 3h and 5h(P＜0.01). A decreasing tendency was found in muscle protein solubility and water holding capacity from 1 h to 5 h. Lower hardness and springness was observed in myofibrillar protein gels of breast musles in heat stress groups (P＜0.01), also lower water holding capacity was scrutinized in 2h, 3h and 5h treatmeats(P＜0.01). 【CONCLUSION】The results indicated that preslaughter exposure of broiler chickens to heat stress could induce breast muscle lower pH and oxidative damage, increase intramuscular fat and protein oxidation, also decrease solubility of muscle protein and water holding capacity, have greatly negative influence on myofibrillar protein gels.

Key words: oxidation, protein, functionality, heat stress, broiler breast muscle