Study On Effects And Mechanism Of Lairage Condition On The Pig Stress And Meat Quality Of Chilled Pork

With the improvement of people’s life, chilled pork become the main products in raw meat market of China for its safety and health. However, the quality of chilled pork in our country was still lower compared with developed countries. The quality of chilled pork is influenced by multiple factors, such as varieties, genetic, breeding conditions, lairage conditions, stunning method, cooling way and storage conditions. Lairage conditions is one of the important factors. Moreover, lairage conditions is currently the hot topic of meat science. This paper investigated the effect of seasons and lairage time on meat quality, analysed blood constituents and energy metabolism as an indicator of stress and welfare to explain the change of meat quality, and studied water distribution and mobility with LF-NMR-MRI to explored the mechanism of water holding capacity of meat. This work provided theoretical basis on the industrial production of chilled pork. This study mainly focused on the following aspects:The meat pH, temperature, color, shear force and drip loss were determined in different seasons and lairage times. The results showed that the pork quality was significantly influenced by season and lairage time. Pigs transported in summer increased muscle temperature, L*value, drip loss and cooking loss, reduced pH value, a*value, and shear force, while pigs transported in cold winter presented lower pH24value, a*value and shear force, but had lower drip loss; Pigs resting for3h presented lower drip loss and higher a*value compared with, while overlong lairage might increase carcass yield and shear force, but had no good to water holding capacity of meat. Therefore, the proper lairage time for the tested pig breed is3h from the viewpoint of meat quality.To investigate the effect of lairage condition on pig stress and energy metabolism in muscle, blood constituents, lactate and glycogen contents were determined. Transporting in hot summer and cold winter could induce stress of pigs, which showed higher RBC, WBC, HGB.HCT, ACTH, cortisol and glucose in blood, pigs transported in winter increased carcass skin blemish and presented poor animal welfare; Proper lairage time could relieve stress of pigs, pigs resting for3h decreased RBC, ACTH and cortisol, and no more skin blemishes than pigs slaughtered without rest, while overlong lairage increased cortisol and skin blemish;3h lairage decreased gh/coh/sis in early stage postmortem muscle, a More lactate accumulation in muscle of pigs without rest confirmed that more glycolysis occurred compared with pigs rested for3h before slaughter. Therefore,3h lairage alleviate stress effectively, no lairage or excessive lairage time might increase stress of pigs and compromise animal welfare, furthermore reduce meat quality.The effect of lairage time on stress and meat quality in pigs was studied by our experiment. The results showed that, under the most frequent commercial conditions in Beijing, the proper lairage time for the tested pig breed is3h after four hours of travel in winter, both from the viewpoint of animal welfare and meat quality. No lairage or excessive lairage time might compromise animal welfare and meat quality. Pigs resting for3h showed decreased RBC and cortisol, and no more skin blemishes than pigs slaughtered without rest. Three hours of lairage did not reduce carcass yield or increase shear force of muscles, compared with the8h or24h lairage groups. Lairage with8h or24h increased skin blemish and carcass weight, this might compromise animal welfare. Moreover, overlong lairage time would increase meat hardness, but had no good to water holding capacity of meat.Multi-exponential fitting of the bulk NMR T2relaxation time data demonstrated three distinct water populations followed by T21(1～10ms), T22(25～80ms) and T23(150～700ms), which was supposed to reflect water closely associated with macromolecules, immobilized water and free water. The change of the proportion of the three fractions in postmortem muscle showed that, pork with higher drip loss had lower proportion of T22and higher T23. Moreover, the peak tended to moved back as times increased after slaughter, this also presented increased moisture degree of freedom. The MRI images showed more moisture on the surface of all pork samples at postmortem24h, which could reflect the moisture transfer rate in meat, so MRI could be used to predict the water holding capacity of pork.