Dr Chunyan Zhang, Geneticist, Genesus Inc.
Meat is a major source of proteins that are necessary for human health. Consumers commonly freeze meat after purchasing it to manage household meat supply. Freezing meat also plays an essential role in prolonging the shelf-life and ensuring meat safety during transport. The global value of pork exports has increased by 29.9% since 2015 and reached US$32.9 billion in 2019 (http://www.worldstopexports.com/pork-exports-by-country/). Frozen pork products represent the major proportion of pork exports. Currently, the industry mainly evaluates quality using fresh pork samples and assumes these quality measures relate to differences the consumer experiences when they prepare and consume the product after freezing and thawing. Therefore, it is very important to understand the potential changes that freezing and thawing have on pork quality.
In pig breeding programs, pork quality traits such as pH, Minolta L* (lightness) and drip loss are usually measured on fresh loin muscle samples (at approximately 24 hours post-slaughter) and selection using this data will result in genetic improvement in fresh pork quality. How much of this genetic progress is reflected in the improvement of frozen-thawed pork quality is not well known. We have collected fresh and frozen-thawed pork quality measurements from the same loin sample for many Genesus commercial pigs. These data enable us to investigate potential changes in pork quality before and after freezing, which will allow us to better focus our breeding program on consumer level pork products.
We (Lei et al., 2018 . Can. J. Anim. Sci. 98: 453-462) found that measurements of pH and Minolta L* from fresh and frozen-thawed samples were significantly different (P < 0.0001). Frozen-thawed pork was darker (decreased L*), with lower pH. Higher heritability for these two traits were found from measurements on fresh meat (0.07 for pH and 0.33 for L*) than on frozen-thawed meat (0.02 for pH and 0.17 for L*), which means better selection response is expected when using the data acquired from the fresh samples. Further, high genetic correlations (> 0.6) were found between fresh and frozen-thawed samples for pH and L*, indicating that for these traits, selection based on fresh sample measurements would result in favourable genetic progress in frozen-thawed pork quality.
These results indicate that using pork quality measurements acquired from fresh samples is an efficient and effective way to genetically improve quality of both fresh and frozen-thawed pork. Genesus has conducted a weekly carcass and pork quality program since 1998 and continues to conduct a substantial pork quality research program. These programs continue to improve quality of both fresh and frozen-thawed pork which ultimately benefits our consumers around the world.