What is Meat Quality?

Factors such as juiciness, tenderness, taste, appearance, price, package appearance, colour, size, brand name and food safety all influence consumer decisions to purchase meat in the retail store. Consumers’ behaviour is influenced by several questions: When I cook this product, is it going to taste good? What about the tenderness and juiciness? Is the product free from contamination? Does the product look good?

Research shows that the top five attributes that influence consumer decisions are taste, tenderness, food safety, appearance, and juiciness. Taste, tenderness, and juiciness are attributes that are influenced by past experiences. Was this product tender the last time I purchased it? Was it juicy? Another important attribute is appearance. It includes packaging, cut size, meat-case lighting and amount of juice released, but mostly colour of the meat. It is considered one of the most important properties that consumers use to judge meat quality.

According to meat scientists, factors such as ultimate pH, colour, water-holding capacity, and intramuscular fat, are the main technical attributes that drive consumer purchasing decisions.

What is Ultimate pH and how does it influence Meat Quality?

The pH of muscle/meat is a measurement of acidity. In a normal living muscle the pH is approximately 7.2. Glycogen is broken down to lactic acid when muscle turns into meat. The pH of meat can range from 5.2 to 7.0. The highest quality products tend to fall in the pH range of 5.7 to 6.0. Both the rate and extent of post-mortem pH fall will influence pork quality characteristics. Pale, Soft, and Exudative (PSE) pork commonly results from a rapid breakdown of glycogen into lactic acid after slaughter. This rapid pH fall can be seen in pigs carrying the halothane gene (stress gene).

The ultimate pH is determined by the extent of the pH decline at 24 hours after slaughter. The variation in ultimate pH influences factors such as colour and the ability of the meat to retain water. A low ultimate pH results in meat proteins having decreased water-holding capacity and a lighter colour. Conversely, a higher ultimate pH will give a darker colour and less drip loss. Figure 1 (opposite) shows the relationship between ultimate pH and the amount of drip loss in a halothane-gene-free pig population.

For slaughterhouses and further processors, a lower ultimate pH will lead to less saleable product, due to increased drip losses during the production processes of fresh meat and/or cooked pork products. Drip loss in a consumer package will negatively affect the appearance and thereby the purchase intent. Ultimate pH also impacts eating quality characteristics such as juiciness, tenderness, and taste. Pork with a higher ultimate pH, which retains more water during storage, will also keep more juice after preparation of the meat. More juice in the prepared meat will give a juicier, more succulent and tender eating experience (see Table 1 above).

How can Genetics and Gene Markers influence ultimate pH and Pork Quality?

Environment, genetics and the interactions between both factors will influence the extent of pH fall. Longer times of feed withdrawal, before transport for instance, will decrease the amount of glycogen present in the muscle at slaughter; thereby resulting in a higher ultimate pH. There are differences in ultimate pH between and within different pig breeds. An extreme breed, like the Berkshire, is known to have a higher ultimate pH than other more commercial breeds. It is possible, however, to genetically increase the ultimate pH of modern pig breeds by using this trait in the selection procedure for commercial parent boars and gilts e.g. in PIC’s terminal 280 sire, a pure red Duroc line - lean and efficient with high meat quality.

The use of gene marker technology is a powerful tool to increase ultimate pH (and other meat quality traits) in a pig population. The RN gene is an example of a major gene which influences ultimate pH. Two copies of the negative allele (22) cause an extreme low ultimate pH ("acid meat") and most of the breeding companies have erased the negative allele from the breeding herds.

Researchers are constantly searching for DNA variation that is associated with variation in meat quality traits. Once these associations are identified, young animals can be tested for their potential to deliver better quality meat, before they are tested for traditional traits such as growth rate. Sygen has developed a series of DNA markers that can be used to improve meat quality attributes, such as pH, colour and tenderness, to increase the accuracy and speed of genetic improvement. Selection of the right genotypes, based on multiple DNA markers, can shift a pig population from a low to high ultimate pH and thereby decrease drip losses.

Selection for greater meat quality characteristics does not necessarily result in a higher cost of production. Extremes do exist within the rare breeds, such as Gloucester Old Spot, Tamworth or Berkshire, that provide exceptional meat quality, but at a cost of poor efficiency and low overall lean. But by using a tailored selection index, DNA marker technology and good on-farm nutrition, meat quality can be greatly enhanced within efficient, fast-growing and lean commercial lines. Ultimate pH is an important meat quality characteristic and the aim is to optimize pork quality whilst continuing to improve the cost of production for different market requirements.