| The consciousness of PSE-like muscle issue, which has a higher L* value combined with the lower processing properties, has extensively grown over the world. It has been currently suggested that lightness (L*) values could be used as an indicator of poultry breast meat quality for further processing and for evaluating the incidence of PSE-like condition in poultry. However, limited research on the chilled broiler meat could be found in China and details on characteristics of PSE-like muscle in broiler Pectoralis muscle need to be further investigated. This work was supported by’China Agriculture Research System (CARS-42)’, and also by’Joint Training Ph. D Student Program from China Scholarship Council’. Starting with the investigation on the distribution and variation of color (L*, a*, b*) of poultry breast muscles processed in a Chinese major commercial plant, we found out the changes of the color under different seasons and evaluated the characteristics of breast muscles classified by L*. With the help of modern biological technology, we investigated the effects of postmortem temperature on the development of poultry PSE muscle in order to find the interrelationship of meat biological changes and development of meat quality. The possible measures to improve the processing properties of PSE-like breast meat with compound phosphate were also studies. The aim of the results of the thesis is to provide a theory basis and technique for the control of quality during slaughter and processing of chilled poultry meat.The contents and results are as follows:1、Study on the changes of commercially processed poultry Pectoralis muscle color. The aim of this study is to investigate the changes of broiler pectoralis muscle color commercially produced in China under different season and incidence of PSE-like meat. The birds were randomly chosen in a Chinese major commercial slaughter house. A total of 1274 Pectoralis muscles of Arbor Acre broiler were randomly obtained from the processing line at 2 h postmortem to determine the changes of color of the broiler muslces in summer and A total of 1284 Pectoralis muscles of Arbor Acre broiler were randomly obtained from the processing line at 2 h postmortem to determine the changes of color of the broiler muscles in winter. It is determined that significant differences were found in L*, a* and b* values between summer and winter (P<0.05), the means of L* and a* values of broiler Pectoralis muscles investigated in summer were higher compared with those in winter, however, lower means of b* in summer than in winter were found. Values of L* values in summer somehow showed a normal distribution, Wheares a* values and b* values in winter showed a distribution with positive kurtosis and skewness indicating a relatively flatter peak and asymmetric tail extending toward more positive values than a normal distribution. According to the results of different classification using different L* cutoff, it was established that the occurrence of PSE-like meat is greater during summer compared with winter. By applying the L* cutoff value (L*=53), the ratio of PSE-like meat would be 23.39% and 20.95% in summer and winter, respectively. The incidence could somehow represent the whole industry indicate that part of commercially processed broiler Pectoralis in China exhibited pale and exudative characteristics. It is necessary to investigate the main characteristics of broiler PSE-like Pectoralis muscles in the next.2、The main characteristics of poultry PSE-like Pectoralis musclesThe aim of the study was to characterize broiler PSE-like breast meat, compare it with normal breast meat. Characteristics of normal (L*≤53, n=33) and PSE-like broiler breasts (L*≥53, n=33) obtained at a commercial slaughter plant were evaluated. It is determined that there is no significant differences in pH, a* and b* values between PSE-like and normal muscles. Nevertheless, significant differences in L*, water-holding capacity (WHC) and protein solubility between PSE-like and normal muscles were found (P>0.05). Compared with normal meat, PSE-like muscles showed the higher L* value, drip loss, cook loss, thaw loss (P<0.05), lower sarcoplasmic and total protein solubility (P< 0.05). Correlation analysis showed that L* values have significant correlation with WHC and protein solubility (P< 0.05). SDS-PAGE profile also showed that bands of approximate 96 kDa and 24 kDa in sarcoplasmic protein and myofibrillar protein varied between these two groups, suggesting partial denaturation of sarcoplasmic proteins and precipitation on myofillarments. The SEM results also showed that myfibrilars contracted transversely, resulting in larger space among myfibrilars, which supported that the PSE-like muscles had poor water-holding capacity. These results clearly suggested L* values to classify the occurrence of PSE-like meat in broiler Pectoralis muscles using a cutoff point. Further research is needed to determine the possible causes of the sarcoplasmic protein denaturation during early postmortem thus resulting in the pale, exudative characteristics.3. The effect of post-mortem temperature on meat quality of poultry Pectoralis major musclesThis study investigated the effect of early postmortem temperature on poultry (broiler and turkey) protein characteristics and meat quality. Muscles were kept at different temperatures (0,20 and 40℃) until 4 h post-mortem and then stored at 4℃. Rapid degradation of ATP and glycogen (P<0.05), thus inducing a high rate of lactate formation and pH drop (P<0.05), were found in the 40℃group during incubation. The results also suggest that activation of AMPK could be partial molecular target for controlling glycolysis during the early postmortem in the present experimental model. When extracting proteins, a lower protein content of the sarcoplasmic fraction (P<0.05) and a higher protein content of the myofibrillar fraction (P<0.05) were found in the 40℃group at 24 h post-mortem; SDS-PAGE and western-blotting results revealed that phosphorylase was associated with the myofibrillar fraction. Furthermore, the 40℃group had paler surfaces (P<0.05), higher drip loss (P< 0.05) and lower processing properties (P<0.05). These data suggest that elevated temperature during early post-mortem period, resulting in rapid glycolysis, induced phosphorylase denaturation and association with myofibrillar proteins thus generating pale and exudative characteristics. It is necessary to investigate the possible measure of the improving the processing properties of poultry PSE-like Pectoralis muscles in the next.4. The effect of phosphates on the processing characteristics of the poultry PSE-like Pectoralis major muscles The aim of this study is to investigate the marination of muscles with commercial phosphates (CP,58% P2O5) to determine the effects on PSE-like and normal meat, also to study the possible measure to improve the processing properties of PSE-like meat. A total of 15 kg normal (L*≤53) and a total of 15 kg PSE-like broiler breasts (L*≥53) were randomly obtained from a Finnish commercial slaughter plant, then the muscles were minced in order to process cooked ham with three receipt:(1) 2%(w/w) NaCl+0.2% (P2O5 w/w) pH 9 CP; (2) 2%(w/w) NaCl+0.2%(P2O5 w/w) pH 7 CP; (3) 2%(w/w) NaCl +0%(P2O5 w/w) CP as controls. The pH, water-holding capacity of meat batters, hardness and sensory evaluation of cooked hams were studied. Results showed that significant differences in pH of either PSE-like or normal could be found among different three receipts group (P<0.05). However, no significant differences in pH could be found between PSE-like and normal meat batters using one of the same receipt (P>0.05). Furthermore, marination both with CP (pH 9) and with CP (pH 7) improved WHC of significantly (P<0.05) compared with control. However, no significant differences in WHC could be found between the receipt group with CP (pH9) and the receipt group with CP (pH9) of either normal meat batters or PSE-like meat (P>0.05). Sensory evaluation results showed that marinated with CP resulted in better slice interity, spriness and lower watery of all meat compared with control. Whereas no significant differences could be found between PSE-like meat and normal meat. These results suggest that marinating PSE meat with the high-pH phosphate marinade used in this study could improve PSE processing properties. However, similar results in WHC and texture would be achieved by using different high-pH phosphate. |
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