Identifying quality defects in poultry processing

It is important to identify and track thetypes and causes of quality defects in processed poultry for corrective actionto be taken.

Poultry processing can be divided into several unit operations including preslaughter activities, stunning, slaughter, scalding and picking, evisceration and chilling. During processing operations, issues will arise with the quality of or defects in poultry products. Several of these defects can be observed, and some are associated with various steps in the process in terms of the time that they are first identified and/or the time at which they occur. These flaws can result in products being discarded in their entirety, or in parts or products having decreased meat quality/functionality and/or consumer acceptance. With over 8.5 billion broilers produced in the U.S. poultry industry in 2013 (USDA-NASS, 2014), sold at market weights from nearly 2 to 10 pounds depending on the desired market (such as Cornish hen or heavy debone chickens), these downgrades and quality issues can cost the industry millions of dollars each year.

COMMON QUALITY DEFECTS

Commonly occurring quality defects in poultry meat include bruising, over-stunning, over-scalding, Green Muscle Disease (GMD), and Pale, soft and exudative (PSE) meat.

Bruising

Bruising occurs in the live animal when there is trauma to a vessel causing it to rupture. Bruising mostly occurs on the appendages of the broiler and can occur at any point prior to exsanguination during slaughter.

The color of the bruise can give some indication on the time at which the bruise occurred. According to study by Hamdy et al. (1960), bruises will be red in the beginning within the first couple minutes of the associated trauma. This redness will then change to a darker red-purple color within the first 12 hours. Within 24 hours, the bruise will change to a light shade of green-purple and then a yellow-green shade at 48 hours. Between 48 and 72 hours, the color will change to a yellow-orange shade and then back to normal coloring by 96 hours. This is important to know when trying to identify root causes of bruising.

The legs and wings are most susceptible during catching, transport (i.e., issues with transport modules) and unloading at the processing plant. Monitoring bruising at the plant can help to identify possible trends that can help, in turn, to correct problems that may be causing it. Residual blood in meat or parts can reduce shelf life and cause other quality issues in processed meats. If blood is present in meat used for deli loaves, it can cause decreased consumer acceptance of that product.

Overstunning

In the U.S., electrical stunning is the primary method of stunning broilers. Broilers are stunned in order to humanely render birds unconscious prior to slaughter, or exsanguination. Stunning also results in a better bleed-out and cutting efficiency (cut all birds properly).

Low voltage/amperage systems are predominant in the U.S., and these systems typically provide good product with limited quality defects. However, stun settings can be too high at times resulting in an “overstun.” This results in some quality issues such as broken bones, ruptured arteries and other hemorrhaging.

Stunning causes a surge of blood pressure, so when the settings are too high, the pressure can be so great that they rupture. This leads to the ruptured arteries primarily in the thigh and the ruptured capillaries in the breast, which results in “blood splash."

Additionally, the high stun settings can cause a more-forceful muscle contraction of the breast, which can lead to breaking the clavicle, or wishbone. A classic sign of over-stunning is the broken clavicle with associated hemorrhaging around the break. These quality issues can occur at a greater frequency when higher stunning amperages are used, as in the case of processors in Europe where higher amperages are legally required.

Overscalding

Overscalding can occur when the scalder water is too hot and/or birds are in the scalder too long at higher temperatures. The heat of the scalders can begin to denature, or cook, the proteins on the surface of the breast fillets.

Generally, two white-colored bands with one "pinkish" band in the middle will be apparent when the carcass is overscalded. The pinkish band is located just beneath the breast feather tract. The feather tract helps protect this area of the breast meat from the extreme temperature and prevents the denaturation of proteins.

In cases of severe overscalding, the appearance of the fillet and the functionality/water-holding capacity could be negatively affected. 

Green Muscle Disease

Green Muscle Disease (GMD), or Deep Pectoral Myopathy, is a condition that occurs primarily in the pectoralis minor, or breast tender. This occurs as a result of a physical stress on the bird in the antemortem state which causes necrosis in the tender. It is generally observed when the birds are cut into parts, or breast deboned, or at more problematic times when the consumer is first to observe it as they cut into their whole bird.

As birds have been bred for larger breast muscle, or pectoralis major, this muscle can cause trauma to the pectoralis minor with major muscle contractions that can happen when birds flap. The movement of the wings is a function of the pectoralis muscles. When the pectoralis minor contracts, it also expands in volume (~25 percent); but because of its location under the pectoralis major, there is little room for expansion (Bilgili and Hess, 2002). This results in increased pressure on the blood vessels, which in turn causes decreased blood supply to the muscle until the muscle begins to die, where necrosis begins.

The “green muscle” takes several days to develop after the trauma. Two to three days post trauma (i.e., wing flapping), the tenders will have signs of hemorrhaging with red color associated. Much like with bruising, the red color will begin to turn to a green color with time. This can occur four to five days post trauma, and continue one to eight days or longer. Additionally, the pectoralis minor will begin to atrophy over time (e.g., day eight-plus) and the fibers will readily separate.

Due to the amount of deboning and further processing, plants will identify most cases of GMD and remove it. However, GMD is particularly an issue when it is found by consumers in whole birds, including prepared rotisserie birds, or in some parts. Though it does not present a food safety issue, it is considered a quality defect. Minimizing stress on birds in the antemortem period can help to reduce this defect.

Pale, soft and exudative meat

Pale, soft and exudative (PSE) meat became more apparent in the poultry industry about 20 years ago. PSE meat is characterized by a pale color, softer gels upon cooking and poor water-holding capacity (i.e., exudative).

PSE meat is associated with antemortem and postmortem stressors, including heat stress, preslaughter handling practices (i.e., short term stress), and carcass chilling regimes (e.g, poor chilling rates). However, heat stress is a primary trigger of this condition, and the incidence of PSE meat rises in the summer months as a result.

It has been estimated that PSE-type meat represents 5 percent to 40 percent of meat that is produced in the poultry industry (Barbut, 1996; Owens et al., 2000) and can cost the industry millions of dollars each year. The degree of severity can vary and, in the more extreme cases, may cause problems with water-holding capacity, product binding, etc., resulting in defective products, especially further processed products such as a deli loaf. In more mild cases, yields will be primarily affected.

Remediation practices using functional ingredients (e.g., starch, gum, phosphate) can help to improve water holding capacity of PSE meat. More recent issues that can arise include dealing with PSE-type meat while producing a product with clean labels, i.e., limited functional ingredients, no phosphates, etc. Because pale meat is highly correlated to low water-holding capacity, sorting of meat is possible in plants to divert PSE meat away from products that require highly functional proteins such as whole muscle deli loaves.

EMERGING QUALITY DEFECTS

White striping in breast meat and “woody,” or hard, breast meat are emerging quality defects in processed poultry. These two conditions may sometimes occur together in chicken breast meat.

White striping

One issue that has become more apparent in recent years in the U.S. and other major global poultry markets is the appearance of white striations, or white striping, in the breast muscle, typically in larger broilers (Owens and Kuttappan, 2013). The condition is characterized by white striations, or “stripes,” that run parallel to the muscle fibers on the ventral surface (skin side), often beginning at the cranial portion of the fillet near the wing attachment where it is most concentrated. The striped areas of the fillet show areas of muscle fiber degeneration along with an increase in fat cells (lipidosis) and connective tissue (fibrosis).

The striping is readily visible even in moderate cases across the fillet, but it can be distracting in severe cases where the lines are very prominent. As the condition worsens (as in severe cases), the stripes, or striations, are visible throughout the fillet and can become wider in appearance and cover more area of the fillet. In fact, Kuttappan et al., (2012) showed reduced consumer acceptance of the visual appearance of the fillets as the severity of white striping increased.

Not only is the breast appearance affected, but composition is also affected. Proximate analysis has shown increased fat percentage and decreased protein content. This condition results in decreased meat quality, characterized by decreased water-holding capacity, poor product binding, changed nutritional content (fat, protein), and continued reduced consumer acceptance, all which can have negative economic impacts.

Woody breast

Another emerging problem is a condition referred to as “Woody” or “Wooden” breast. At this time, little is really known about the condition. However, it is an issue that is observed worldwide especially in fast-growing, high-breast-yielding broilers.

The condition can be characterized by breast tissue that is hard to the touch, much like a muscle would be tense or contracted. This hardness can be present in the live bird prior to processing and even in the grow-out period as early as a few weeks old (detected by palpation) in addition to the postmortem period. The degree of hardness can be subjectively identified and a scoring system can be used to categorize fillets.

Some fillets can be hardened throughout with limited flexibility while others can be hardened but with some flexibility toward the mid-part of the fillet. Often times, a ridge or out-bulge is described on the tail end of the fillet. This ridge is likely an artifact of the hardening and the architecture of the muscle where the muscle fiber is shorter in this region.

There is no reported incidence, but anecdotal accounts suggest up to 50 percent in flocks at times. However, it is likely that the percentage of the most severe woody (hard) fillets would be much lower, likely less than 10 percent.

Often times, the woody condition is also observed with the presence of white striping, especially in the heavy-market birds. Sihvo et al. (2013) reported that hard, or woody, fillets accompanied by presence of white striping had histological signs of myofiber degeneration and connective tissue accumulation (i.e., fibrosis). These are the same characteristics observed with white striping alone.

Therefore, more research is needed to fully characterize this condition taking care to separate it from fillets with white striping. It is not clear if these conditions are related to each other, or if they are both just related to rapid growth in conjunction with genetics, nutrition or other sources. Regardless, this condition can cause potential problems with processing methods such as deboning, portioning and even problems with marination in terms of pickup along with sensory qualities.

Monitoring of defects

All of these defects discussed are some of the major quality defects that the poultry industry faces, but it is certainly not all. Broken bones and dislocations, cellulitis (inflammatory process), mis-cuts on parts, bones in boneless products and reduced tenderness of broiler meat, etc., are also common quality defects. These defects will likely occur at some level year-round, but it is important to know if and when these defects increase in incidence. Monitoring the incidence of these defects can help to determine if there larger issue at hand where corrective actions need to occur.

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