【作者】 甄少波；

【导师】 任发政；

【作者基本信息】 中国农业大学 ， 农产品加工及贮藏工程， 2013， 博士

【摘要】 随着人们生活水平的提高,安全卫生、滋味鲜美的冷却肉逐渐成为我国生肉消费市场的主要产品,尽管如此,我国冷却肉与发达国家相比仍然品质较低。冷却肉品质的影响因素很多,如品种、基因、饲养条件、待宰环节、击晕方式、屠宰方法、冷却工艺和贮藏条件等,其中待宰是影响冷却肉品质的重要因素之一,也是目前肉品科学的研究热点。本文通过研究季节和待宰时间对宰后猪肉品质的影响,确定了猪宰前合理待宰时间,通过分析不同待宰条件下猪血液学指标及宰后能量代谢的变化,从动物应激反应和肌肉能量代谢角度解释冷却猪肉肉质变化,并利用LF-NMR-MRI技术研究宰后猪肉水分分布状态及迁移规律,探究冷却猪肉保水机理。本研究为指导冷却肉生产提供了理论基础。论文主要研究结果如下：本文研究了不同季节和待宰时间下冷却肉pH值和温度、色泽、剪切力和滴水损失等指标的变化,结果发现,季节和待宰时间能显著影响宰后猪肉品质。夏季高温运输导致宰后猪肉温度.上升,pH值显著降低,滴水损失和蒸煮损失显著增加,保水性下降,肉品a*下降,L值增加,剪切力变小；猪在冬季运输时,宰后24h的pH值显著上升,a*值增加,肉色变暗；与未休息组相比,3h待宰处理使得猪肉滴水损失显著下降,a*值升高,待宰时间延长至8h或24h时,胴体重量损失增加,猪肉剪切力变大,肉质变老,但保水性无明显改善。因此,宰前进行3h左右的待宰处理能有效提高宰后猪肉品质。通过测定不同待宰条件下猪血细胞成分、生化指标及宰后肌肉中乳酸和糖原含量的变化,评价了待宰对猪应激反应及肌肉能量代谢的影响。结果表明,夏季高温和冬季低温运输都会造成猪应激,使得猪血液中白细胞数、血红蛋白及红细胞压积上升,ACTH和皮质醇浓度显著升高,血糖浓度增加；猪在冬季运输时胴体损伤程度明显增加,福利水平降低；待宰处理能够降低猪宰前应激反应,3h待宰明显降低了猪血液中红细胞数、ACTH和皮质醇浓度,缓解了动物宰前应激；过长时间的待宰反而使得皮质醇浓度升高,胴体皮肤损伤程度显著增加；3h待宰能降低宰后猪体肌糖原的消耗速率,减少乳酸积累。因此,3h待宰能有效降低猪宰前应激,8h及更长时间的待宰处理反而会增加动物应激,降低猪福利,也不利于肉质的改善。利用LF-NMR-MRI技术研究了不同滴水损失肉样水分分布状态与保水性的关系,发现T2弛豫图显示出三个弛豫峰,横向弛豫时间分别为T21(1～10ms),T22(25～80ms),T23(156～700ms),分别代表了肉中三种状态的水——结合水、不易流动水和自由水；宰后不同时间下三个保水性组的T21、T22和T23峰面积比例的变化表明,肉品滴水损失越大,T22峰面积比例越小,而T23的峰面积比例也越大,且随着宰后时间的延长,各个峰向后移动,水分自由度增加；MRI成像技术可以直观地反映出猪肉内部的水分分布情况,能用于判断冷却猪肉保水性大小。更多还原

【Abstract】 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.更多还原