White striping in broiler breast meat

White striations, or white striping, in the breast muscle isan emerging problem in the U.S. and other major global poultry markets, including Brazil and Europe.

The major reasons for consumers disliking the meat with striations were the appearance of lines or fatty tissue.
The major reasons for consumers disliking the meat with striations were the appearance of lines or fatty tissue.

Boneless broiler breast meat is a popular product in the global poultry industry. It is a basic form of adding value, resulting in high-value cuts used in a variety of markets, including retail, further processing and foodservice. Due to the popularity of boneless breast meat, processors have been using large, high breast yielding broilers as their source in recent years. The high yielding birds in the big bird market allows for increased yields and pounds per man hour in processing.

In the U.S., the average live weight of birds in this segment is now approximately 7.5 pounds, but can range from 6 to 9 pounds or more. The big bird market segment (greater than 6 lbs) makes up over 50 percent of the overall market in the U.S. This segment (greater than 6 lbs) has grown from only 23 percent in 2000 to over 50 percent in 2013. Furthermore, approximately 20 percent of the overall market consists of birds 7.5 lbs or more. This trend for increased bird size and the increased percentage of the market will likely continue.

Developing product issue  

One issue that has become more apparent in recent years in the poultry market is the appearance of white striations, or white striping, in the breast muscle, typically in larger broilers. It can also be observed in thighs and tenders. This condition is an emerging problem in the U.S. and other major global poultry markets, including Brazil and Europe.

White striping described  

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 striping is readily visible even in moderate cases across the fillet, but 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 (length of muscle fibers and from the cranial to caudal portion of fillet) and can become wider in appearance. Other reports from the industry show that in extreme cases, the white portion can cover a much greater area (i.e., not only a striation).

Upon histological examination, the striped areas of the fillet are characterized by an increase in fat cells (lipidosis) and connective tissue (fibrosis) along with areas of muscle fiber degeneration. It is likely that fat and connective tissue infiltrate the areas where fiber degeneration occurs. There are elevated levels of enzymes related to muscle damage, such as creatine kinase, in those fillets exhibiting more pronounced white striping. Proximate analysis has shown increased fat percentage and decreased protein content. Another study, based on the evaluation of hematologic profiles of normal and severely striped birds, suggested that white striping was not a result of any infection, inflammation or stress condition.  

Incidence variable but increasing  

In the past several years, we have observed varying frequencies of fillets with white striping. Personal observations suggest that the problem is worsening over a period of years, indicated by a greater proportion of moderate and severely striped fillets. Approximately five years ago, over 50 percent of fillets from 60-day-old high breast yielding broilers exhibited some degree of white striping (moderate or severe). Yet in a recent study with big broilers, approximately 75 percent exhibited moderate or severe degrees of striping.

While the moderate classification of white striping is most predominant, approximately 10 percent to 15 percent of fillets in our research studies have been categorized as severe. A recent study in Italy reported approximately 12 percent of commercial 45- to 54-day-old broilers surveyed (n=28,000) exhibited white striping. Differences in incidences across studies are likely due to the age of broiler and/or growth rate.  

Body size and growth rate  

Previous studies and communication with the industry indicate that the condition is associated with fast growth rates and heavy birds (high breast yielding broilers). It is usually more predominant in males and in high breast yielding broilers compared to standard yielding broilers. Though the condition is associated with heavier broilers, it is observed in the major commercial broiler strains. Differences that may exist among strains are likely to occur due to different growth rates/breast yields associated with the various strains.

Growth rate has also been specifically evaluated, and a faster growth rate has been associated with a higher incidence of birds exhibiting white striping. Trends in the industry over the past few decades have been to improve broiler performance and produce a high breast yielding broiler with a typical market weight in a shorter period of time (i.e., faster growth rate). Since 1925, the average market weight has more than doubled (2.4 to 5.7 lbs) in less than half the grow-out time (112 days to 47 days).

Breast meat yield has also increased significantly during that period. More recent trends in the poultry meat industry are to produce birds to heavier weights (thus, older birds) in order to gain more breast meat per bird for portioning and further processing. Therefore, it is likely that a high percentage of today's birds will be affected by moderate or severe white striping now and in the future. Also, a percentage of birds may exhibit severe or extreme cases of this condition more frequently as well.  

Meat quality

Initial studies in our lab suggested that general meat quality attributes (drip loss, cook loss, color, shear properties) were not majorly affected by the white striping condition. However, another report indicated that cook loss increased and shear force decreased with increasing severity of striping (Petracci et al., 2013). The differences between these studies may be related to other processing factors such as debone time or cooking parameters.

Marination properties of white striped fillets have also been evaluated, and results indicated that water-holding capacity was negatively affected in the severe fillets. Due to the limited research available, further research is still warranted in this area of meat quality especially to evaluate the most extreme cases of severity.

Flavor, oxidation and texture (mouthfeel) of these fillets with striping has yet to be evaluated, but with increased fat associated with it, it is possible that these attributes would be affected. The white striping condition could potentially lead to issues with product quality in the future.  

Appearance has impact on product acceptance  

Because white striping is visually apparent on raw breast fillets, consumers evaluated the visual appearance of raw breast fillets and determined acceptability in a consumer sensory study. Results showed that consumer acceptance of raw fillets significantly decreased as severity increased. The major reason for the consumer dislike, indicated by consumer comments, was the "fatty" or "marbled" look of the product.

These findings are important because consumer acceptance of products can have a major impact on their purchasing choices. Consumers have traditionally viewed poultry meat as lean, making it a healthy food choice. Increasing the intramuscular fat content, especially visual fat, would lead to decreased consumer acceptance in the marketplace.

In the U.S., fresh, raw breast fillets are common in the retail market (i.e., grocery store) and size of fillets can vary between specific products and brands, coming from birds from a wide variety of sizes. Fillets from larger broilers can be portioned to a more acceptable piece size. Therefore, the large fillets affected by striping can still easily end up in the retail fresh market, seen by consumers.

Sorting strategies to deal with striping  

Regardless of the cause, processors have to deal with the problem now. For product going into the raw retail market, it would be advantageous for processors to sort the product based on striping severity.

Generally, fillets categorized as severe have stripes that are very prominent and distracting to the eye. Additionally, using image analysis for detecting white portions could potentially be a tool for sorting fillets though the methods would have to be optimized. Regardless, fillets exhibiting the most severe striping should be diverted away from products that are sold as raw where consumers are able to choose product based on appearance.

In addition to appearance, the white striping condition may cause issues in marinated, cooked fillets based on water-holding capacity and texture. However, it is possible that fillets with severe striping may be used for other products such as further processed, pre-cooked fillets or breaded products (whole muscle or comminuted) if issues of water-holding capacity could be overcome with use of functional ingredients.  

Research needed for causes, nutritional strategies

Research is needed even in the area of further processing and the incorporation of striped fillets into products and the potential effect striping could have on binding in whole-muscle products. It is very possible that in the severe/extreme cases, product quality may be more greatly affected than what has been observed to date. Furthermore, proximates (fat/protein content) of final products could be affected, thereby causing issues with nutritional labeling.

Nutritional strategies to improve the condition without sacrificing broiler performance, if that's possible, need to be investigated. Growth rate and market endpoint weights have a great deal of influence on the severity of white striping. In the short-term, finding a balance between growth performance/yield and end-product quality may be necessary to decrease the severity of white striping in broilers.  

White striping's increasing importance

Striping of breast meat is commonly observed in the industry especially in big bird markets, and it's unfortunate that this is becoming more common due to the negative attributes associated with it. While the moderate classification is the most predominant, severe and extreme cases also are observed, especially in the largest, fastest growing broilers. Furthermore, the industry could potentially see these severe/extreme cases more frequently in the future as the industry continues to make advancements in broiler performance.   This would lead to much greater economic loss through decreased quality and consumer acceptance.
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