Date Full Report Received02/20/2020
Date Abstract Report Received02/20/2020
Funded ByIowa Pork Producers Association
The production of high-quality pork is important to the success and sustainability of food and agriculture industries. This is true for competition in domestic and international markets. Even more important is a quality differentiation with trendy plant-based products that are on the market today. Tenderness and water binding capacity of fresh meat are among the most critical attributes determining consumer satisfaction of fresh pork. While there is no question that the quality of fresh pork impacts the profitably of value-added pork industries, most of the successful innovations to measure pork value determine the quantity of pork, rather than quality. This is primarily because it is far easier to measure and control carcass weight and lean percentage/yield than it is to measure quality. Controlling and predicting fresh pork quality is extremely challenging because despite years of research, we still do not fully understand the biology of early postmortem muscle that governs major quality features, including tenderness and water-holding capacity The only way the research community and the food industry can develop reliable pork quality indicators is to understand factors that really determine quality. Our experience is that the primary factors that influence the fresh pork loin quality are protein factors and these are influenced by postmortem metabolism (pH decline) and handling (postmortem aging). In order to learn more about these processes and to apply them in a meaningful way, we proposed the following objectives:
Objective 1: Determine the contribution of key proteins in the postmortem aging process to the development of fresh pork tenderness.
Objective 2: Define the protein profile of early postmortem pork loin chops that is associated with a beneficial postmortem aging process and improved pork loin tenderness.
To address the objectives, we used fresh pork loin selected from a commercial processing facility one day post-harvest. Fresh pork quality (tenderness, color, water holding capacity) was determined on pork loin aged 1, 8, 14, and 21 days. Importantly, we evaluated product fresh at those days of aging and frozen at the end of each of those aging periods. We also measured the protein features (degradation of meat proteins troponin-T and desmin, length of protein structure in muscle called the sarcomere).
The most extreme examples of tough and tender pork loin in the experiment were chosen to investigate the protein profile (at day 1 postmortem) of the most tough and tender pork loin chops (observed after aging 14 days).The method used (2D -DIGE) provides a direct comparison of proteins in samples that represent the tough (High star probe (HSP)) and tender groups (Low star probe (LSP)).
Aging fresh pork loin for 8 d showed a 22% and 32% improvement in SP and WBS values, respectively. The current results suggest that aging 14 or 21 d did not result in improved SP or WBS values compared 8 d aging. Degradation of troponin-T and Desmin both showed that as degradation progressed with aging, so did improvement in star probe. Sarcomere length did not change during the postmortem aging process. Protein degradation data were numerically more highly correlated with instrumental tenderness measurements later postmortem when compared with sarcomere length, suggesting protein degradation may have a greater impact on tenderness values later postmortem. Importantly, freezing pork at 1 d postmortem will not allow products to improve in SP or WBS values so a recommended best practice is aging pork prior to freezing.
The immediate application of this research is that fresh pork loin should be allowed to age before freezing in order to improve fresh pork quality. This might have immediate considerations for smaller processors. In addition, it is clear that pork aging must be considered as a source of variation in fresh pork loin quality. This must be clarified, especially in local markets or “farmers’ markets” where product might be frozen very early postmortem. Further, these results may have implications for merchandizing pork in home delivered meal kits that might have a frozen fresh pork product.
Variations in star probe values were attributed to differences in pH, marbling, water holding capacity, proteolysis, and sarcoplasmic protein profile at 1 d aging. The HSP (less tender) had a lower pH, less marbling, and poorer water holding capacity. In addition, the HSP group showed less degradation of key proteins desmin and troponin. In the protein profile experiment, (comparing protein profile at day 1 postmortem to fresh pork tenderness at day 14), the HSP group had greater abundance of metabolic, regulatory, and mitochondrial associated proteins whereas the LSP group had greater abundance of stress response proteins. The sarcoplasmic proteome analysis results confirm a difference in glycolytic metabolism capabilities between star probe groups, thus demonstrating the need to investigate more deeply the role of metabolic and regulatory proteins in the development of pork tenderness. Identification of many mitochondrial proteins in the sarcoplasmic proteome may suggest solubilization of by-products of the mitochondrial electron transport chain due to rupture of mitochondria. The rupture of mitochondria in muscle may increase the need for stress related proteins or need for antioxidant proteins. Once the status of these proteins is defined, robust protein biomarkers can identify products of differing tenderness.
Immediate researchable questions surround the topic of the heretofore un-reported observation that mitochondrial disruption in post mortem or post rigor pork can be an indication of the progression of proteolysis and improvement in tenderness. The rupture of mitochondria in muscle may increase the need for stress related proteins or need for antioxidant proteins. Once the status of these proteins is defined, robust protein biomarkers can identify products of differing tenderness.
Steven Lonergan, Professor, Animal Science Department. Iowa State University. 515-460-0895. firstname.lastname@example.org
• Protein degradation was confirmed to be a key component of fresh pork loin quality
• Abundance of antioxidant proteins (peroxiredoxin-2) in aged pork was linked to pork tenderness
• Abundance of mitochondrial proteins in sarcoplasmic fraction from tough pork loins suggests that fiber type and mitochondrial disruption may be linked to processes that interrupt normal aging of pork.
• Fresh pork tenderness was affected by pH, marbling score, protein degradation and sarcomere length