Using pre-rigor meat to improve sausage yield and texture

By Joseph Sebranek Ph.D on 2/1/2009
MeatingPlace.com

In this article:
What is pre-rigor meat?
Handling and preparation
Advantages of pre-rigor meat in sausage

One of the most fragile and variable properties of meat as a raw material for sausage products is the ability of meat to bind and retain water during and after processing and packaging. Drip losses, low product yields and package purge are all common problems that result from poor water-binding.

Because the retention of water is critical to texture, mouthfeel and juiciness, water-binding problems during processing carry over to consumer-perceived product quality. Further, because water-binding is a meat property that is sensitive to changes in processing procedures, it often serves as a warning indicator for other product changes. For example, in emulsified products such as frankfurters, water-binding ability is one of the first changes to occur when the emulsion is becoming less stable. This means that a decrease in yields may be a warning that the emulsion is close to breaking down with release of fat as well as water if corrective action is not taken.

Lean meat has an inherent water content of about 70 percent, and water is often added during formulation. Consequently, retaining both inherent and added water in sausage is a significant challenge. One of the most effective ways to meet this challenge is with the use of pre-rigor meat. Pre-rigor meat offers some tremendous advantages over post-rigor meat for sausage and processed products, but must be handled correctly to realize those advantages.


What is pre-rigor meat?
Simply stated, pre-rigor meat is meat that has been "hot-boned," or removed from the carcass prior to chilling and before development of rigor mortis. Pre-rigor meat is characterized by a pH well over 6.0 — usually in the range of 6.4 to 7.0 — and a high degree of protein solubility.

The muscles of live animals have a normal pH of just over 7.0, but biochemical changes in muscles that begin immediately postmortem will generate lactic acid, which in turn will change the meat pH to about 5.2 to 5.6 over a period of several hours. The reduced pH is typical of post-rigor meat and means that the proteins in the meat now have a weaker molecular attraction for water molecules.

At the same time, the reduced pH stimulates irreversible muscle contraction. Contraction or rigor mortis results in less structural space between muscle protein filaments as the muscle attempts to shorten. This physical effect reduces the space within the muscle that is available for water.

The combined effect of a weaker molecular attraction for water as well as less space for water means that post-rigor meat has considerably less ability to hold water than does pre-rigor meat. The key to retaining the advantages of pre-rigor meat is to minimize the pH change and the muscle shortening that normally occur as postmortem muscle develops rigor mortis.


Handling and preparation
To fully realize the advantages of pre-rigor meat, it is critical to remove the meat from the carcass as soon as possible following slaughter. However, this process introduces three potential problems.

First, intact muscles removed from the carcass will contract and shorten excessively if allowed to go into rigor, greatly reducing the space available within the muscle structure for water binding. This problem is easily overcome by coarse-grinding the meat immediately to break up the muscle contractile structure.

Grinding introduces a second potential problem in that the biochemical changes in muscle that produce lactic acid are accelerated by grinding. It is critical at this point to blend the meat mixture with salt, because salt disrupts the acid-producing enzymes and virtually stops the production of acid to prevent further decline in meat pH. It is important to add salt as soon as possible in order to retain the meat pH at the highest possible value.

Salting pre-rigor meat has additional advantages of solubilizing salt-soluble proteins to a greater extent than in post-rigor meat. This results in a firmer texture in cooked products and more effective stabilization of fat in emulsified products.

The salt concentration used may be in the range of 1.5 percent to 4 percent, depending on the salt concentration desired in the product in which the pre-rigor meat is to be used. The salting step is also the appropriate time to add nitrite if the pre-rigor meat is intended for use in a cured product, making the mixture similar to a pre-blend but with the advantages of pre-rigor meat. Typically, one-half of the final product nitrite concentration is used in pre-blends.

The third potential problem that can arise in handling pre-rigor meat is rapid bacterial growth in the warm, coarsely ground mixture. Rapid chilling such as with carbon dioxide snow in a mixer/blender becomes an important step. Rapid chilling also helps to slow the production of lactic acid, and when combined with salting will virtually stop the change in pH. If the pre-rigor meat is to be used for an uncured product such as pork sausage, it may be of value to chill prior to or with the addition of salt to minimize the effects of salt on fresh meat color.

Thus, to maximize the advantages of pre-rigor meat, deboning must be done as quickly as possible, followed immediately by coarse-grinding, blending with salt (and nitrite if appropriate) and chilling as rapidly as possible to 28 degrees F to 30 degrees F.


Advantages of pre-rigor meat in sausage
With proper preparation, use of pre-rigor meat brings several advantages to sausage products. Cooked product yields can be dramatically improved, with increases of 4 percent to 10 percent reported in research literature. Both fat and moisture retention are improved, resulting in improved palatability. Product texture also is modified due to greater protein extraction, with firmer texture resulting from pre-rigor meat.

In the case of cured products, the pre-cured, pre-blended mixture provides superior binding for emulsions and improved cured color. In the case of fresh uncured sausage, pre-rigor meat provides a brighter fresh meat color and longer color life in a product that is typically very color-sensitive.

Finally, the rapid chilling and early addition of salt keeps bacterial numbers low and results in longer product shelf life in terms of bacterial spoilage. Consequently, there is little not to like about using pre-rigor meat for sausage products.