IMPLICATIONS OF DEFECTS AND EMERGENT MYOPATHIES ON BROILER MEAT QUALITY
Giuseppe Maiorano* and Siria Tavaniello
Professor Giuseppe Maiorano
University of Molise, Department of Agricultural, Environmental and Food Sciences, University of Molise, Via F. De Sanctis, snc, 86100 Campobasso, Italy, +39 0874 404819;
*Giuseppe Maiorano:
ABSTRACT
Due to intensive selection, broiler chickens became the most efficient meat producing animals because of their fast growth. Modern birds undergo a 50-fold multiplication in body mass in just six weeks. Stimulating birds, within a short period of time, to improvements in growth rate, body size, breast yield and feed conversion by intense genetic selection, has determined various muscle defects or myopathies which adversely affect the poultry meat industry. In particular, over the last decades has increased the incidence of breast meat abnormalities such as deep pectoral myopathy (DPM) and pale-soft-and-exudative (PSE)-like meat, and more recently white-striping (WS), wooden-breast (WB) and intramuscular connective tissue defects (poor cohesiveness). The prevalence of these conditions indicates that further improvements in industry-efficiencies and meat production may be constrained by the physiological capabilities of broilers because internal organs, vascular system and skeleton appear to be close to their functional limit. DPM or green muscle disease, is a degenerative disease of the pectoralis minor muscles characterized by atrophy and necrosis. The resultant necrotic muscle varies in color, progressing from a pink hemorrhages to a gray-greenish discoloration. This lesion can be both unilateral or bilateral and it is found only during cut-up and deboning. The occurrence of this defect in broilers is estimated to be about 0 to 1.88%. The (PSE)-like condition is the major defect affecting color (paler than normal), texture (softer than normal) and water holding capacity (lower than normal) of meat. The causes of this condition in chicken may be related to pre-slaughter stress, environmental factors (i.e. heat stress) and genetic selection. Usually, it is attributed to the rapid pH decline, in the post mortem period, while the temperature of meat is still high (fast-acidifying meat and acid meat). It has been reported that genetic selection for increased growth rate and muscle size altered intracellular calcium homeostasis and consequent changes in sarcolemma integrity with deep implication for meat quality. Moreover, it has been shown that modern chicken hybrids are more susceptible to heat stress and to stress-induced myopathies which may have a great implication on meat quality. PSE-like meat has a poor processing ability due to a lower water holding capacity (exudative) and too soft texture compared to normal fillets. The occurrence of this defect is estimated to be about 5 to 40% of the meat in poultry industry, with significant economic losses. Recently, fillets from broiler birds of market age were identified with varying degrees of white striations, seen parallel to muscle fibers. This is causing concern among broiler chicken producers because of reduced consumer appeal, in fact the presence of white striations gives a “fatty look” to fillets which are perceived by consumers as “unhealthy”. The condition, mainly associated with rapid growth rate, large size, and high breast yield of modern broilers, is referred to as WS. Based on the visual scoring of the severity of condition, fillets can be classified as: normal or no striping, moderate, or severe fillets. The etiology of WS is currently unknown, nevertheless several are the factors which can affect the occurrence of WS in breast meat: genotype, sex, growth rate, diet and slaughter weight. Histopathological data has demonstrated that WS usually is associated with muscle degeneration and myopathic changes beneath the striation area, consisted of loss of cross striations, abnormal fiber increase, floccular/vacuolar degeneration and lysis of fibers, mild mineralization, occasional regeneration, lipidosis, interstitial inflammation and fibrosis. Various studies have also shown that fillets with severe WS have an increase in fat content, with modification of fatty acid composition, a decrease in protein quantity and functionality, and an increase in total collagen compared with normal fillets. Furthermore, negative impact of WS on technological quality traits of poultry meat has been observed. Recently, it has also been observed that WS can be accompanied by another type of muscle abnormality called ‘wooden breast’, which shows pale expansive areas, in the caudal part of the fillet, of substantial hardness; in some cases, a clear viscous fluid and small hemorrhages (petechial lesions) on the fillet surface is observed. Various studies observed that WS and WB muscles have similar histopathological changes and thus they may have a common etiology, even if it remains yet obscure. It has been found that fillets with WB showed changes in proximate composition similar to WS. Also the WB is negatively impacting the poultry processing industry, and the industry is facing great economic losses due to customer complaints about fillets affected by these myopathies. A newer emerging quality issue in poultry is the poor cohesiveness of meat related to immaturity of intramuscular connective tissue (tendency toward separation of muscle fiber bundles). It was found that endomysium and perimysium thickness of breast muscles was larger and much smaller, respectively, in fast-growing broilers compared with slow-growing ones; this suggests that the growth of endomysium and perimysium can occur separately causing poor slicing and fragmentation of cooked products. In conclusion, a great deal of research have shown that the intense genetic selection is connected with the increased incidences of different types of myopathies, which adversely affect the poultry meat industry. Hence, it is questionable whether it is better to continue to have new goals in performance or to consider a step back in the selection process and try to reduce the extend of these new emergent quality issues.
Keywords: broiler, Deep pectoral muscle, PSE-like, White striping, Wooden breast, Poor cohesiveness