Title: Extended insight in effects of exogenous factors before and at slaughter on pork quality
Other Titles: Invloed van exogene factoren voor en tijdens slachten op de kwaliteit van varkensvlees
Authors: Vermeulen, Liesbeth
Issue Date: 29-Oct-2015
Abstract: Nowadays the pork industry is facing an intensified export competition, pushing the industry to look for procedures which improve the production efficiency as well as the product quality. Furthermore, consumers’ choices are more often driven by the pork quality and the way food is produced, taking into account sustainability aspects, such as animal welfare, health and the ecological footprint. This manuscript conducts analyses of certain aspects of the pork production, aiming to propose procedures to achieve higher pork quality, which is the common interest of industry and consumers.
This study presents that almost 20% of the pork produced in Belgium, has an inferior pork quality resulting in significant production losses. The most prevalent defect in pork that strikes the pork industry in Belgium, is Pale, Soft and Exudative meat (PSE meat). This pork quality condition is known to be caused by acute stress prior to slaughter. Piétrain-sired pigs, the most popular pig breed in Belgium for its high lean meat percentage, are genetically susceptible to stress due to a gene mutation and thus have a higher likelihood of developing PSE meat. Acute stress accelerates the glycolysis in the muscles. This metabolism operates anaerobically whereby more H+ protons and heat, originating from ATP hydrolysis, are produced, which in turn results in a faster drop of the meat pH leading to PSE meat. This defect can be detected by measuring the meat pH 30 minutes post-mortem. The recommended muscle to detect PSE meat, is the Musculus Longissimus thoracis, a glycolytic muscle, which is more sensitive to develop a fast pH drop 30 minutes after sticking (pH30LT).
In this dissertation, it was investigated whether a sound level above 85 dB(A), determined in scientific literature as the critical sound level inducing stress in pigs, has also an effect on the prevalence of PSE meat. Sound levels were recorded during four pre-slaughter phases: firstly after arrival of the truck at the slaughterhouse, just before unloading, secondly during unloading, thirdly in lairage and finally while moving to the stunner. The pH30LT of the observed carcasses was measured. The results determine that maintaining the mean sound level below the cut-off value of 85 dB(A) during the pre-slaughter phases, not only controls the pigs’ stress level, as indicated in literature, but can be associated with a slower drop of the pH30LT. Furthermore, a sound level model indicates that sound levels during lairage and prior to stunning have statistically a higher impact on pH30LT of pork compared to sound levels during the other phases.
Along with sound levels, various pre-slaughter environmental and handling variables were recorded during each pre-slaughter phase. Based on statistical analysis of the collected data, variables which significantly influence the pH30LT could be determined. The results were used to infer a checklist with critical control points to represent and predict PSE traits of pork for all kind of pre-slaughter situations. The checklist presents that the pork quality is influenced by factors of each pre-slaughter phase, but the impact is more decisive for variables measured closer to the stunning phase.
In a later stage of this research, the scope was extended to investigate handling procedures during loading prior to transport to the slaughterhouse. The environmental and handling variables, as in the study of previous phases, were monitored. Likewise, the pH30LT was measured from the examined pigs. The data from the loading phase was used to complete the sound level model and the checklist for the entire pre-slaughter process. This research determines that sound level fluctuations during loading, the difference in environmental temperature during loading and lairage, and the feed withdrawal period also influence the risk of developing PSE meat.
The efficiency of high quality pork production could benefit from a methodology prior to stunning that assesses the risk of developing pork with PSE characteristics. Therefore, a new methodology which can give an indication about the pork quality prior to slaughter, is proposed in this thesis. Since body temperature is related to the stress status of the pigs, it was investigated if rectal temperature of pigs before stunning (TempRLairage) and the core temperature of the ham, measured 30 minutes after slaughter (Temp30Ham), were correlated with the pH30LT. The results present a significant positive linear correlation between TempRLairage and Temp30Ham. Furthermore, pH30LT was negatively related to Temp30Ham and TempRLairage. Based on the conducted analysis, it can be concluded that the risk to develop PSE meat can be estimated by the pig’s rectal temperature just before stunning. This research is a very important first step towards the development of an online non-invasive method, e.g. an infrared camera, as measuring rectal temperature may also induce stress.
The cooked ham production struggles with the presence of destructured zones, resulting in high slicing losses. Scientific literature describes that these destructured zones are strongly associated with PSE meat. As this research established a negative linear correlation between Temp30Ham and pH30LT, it was further investigated whether it was possible to select fresh ham based on Temp30Ham, to produce cooked ham with a minimum percentage of slicing losses. Results present that hams, suitable for the production of cooked hams, can be selected by measuring Temp30Ham.
In summary, this thesis provides slaughterhouses and stakeholders with essential information and practical guidelines on minimizing the incidence of PSE traits and thus on working towards high pork quality.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division Animal and Human Health Engineering
Division of Livestock-Nutrition-Quality (-)

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