Samer Mudalal

Meat quality in fast-growing broiler chickens

During the past few decades there has been a notable increase in the demand for poultry meat due to its low cost, good nutritional profile and suitability for further processing. Moreover, current forecasts and projection studies have predicted that the expansion of the poultry market will continue in the future. This growing demand has led to progressive improvements in genetic selection to produce fast-growing broilers, inducing the appearance of several spontaneous, idiopathic muscle abnormalities along with an increased susceptibility to stress-induced myopathy. Such muscle abnormalities have several implications for the quality of fresh and processed products, as breast meat that is affected by deep pectoral myopathy is usually rejected due to its unacceptable appearance. In addition, pale, soft and exudative like meat has a low processing ability due to its reduced water holding capacity, soft texture and pale colour. Finally, the high incidence of abnormalities observed in chicken breast muscles such as white striping (characterised by superficial white striations) and wooden breast (characterised by pale and bulging areas of substantial hardness) impair both the appearance and technological traits of breast meat. This review evaluates the consequences of genetic selection on muscle traits and describes the relevance of major breast abnormalities on nutritional, technological, sensorial and microbial characteristics of raw and processed meat.

Implications of white striping and wooden breast abnormalities on quality traits of raw and marinated chicken meat

One of the consequences of intense genetic selection for growth of poultry is the recent appearance of abnormalities in chicken breast muscles, such as white striping (characterised by superficial white striations) and wooden breast (characterised by pale and bulged areas with substantial hardness). The aim of this study was to evaluate the quality traits of chicken fillets affected by white striping and wooden breast abnormalities. In two replications, 192 fillets were divided into the following four classes: normal (n=48; absence of any visual defects), white striping (n=48, presence of white striations), wooden breast (n=48; diffusely presence of hardened areas) and white striping/wooden breast (n=48; fillets affected by both abnormalities). Morphology, raw meat texture and technological properties were assessed in both unprocessed (pH, colour, drip loss, cooking loss and cooked meat shear force) and marinated meat (marinade uptake, purge loss, cooking loss and cooked meat shear force). Fillets affected by white striping, wooden breast or both abnormalities exhibited higher breast weights compared with normal fillets (305.5, 298.7, 318.3 and 244.7 g, respectively; P<0.001). Wooden breast, either alone or in combination with white striping, was associated with a significant (P<0.001) increase of fillet thickness in the caudal area and raw meat hardness compared with both normal and the white striping abnormality, for which there was no difference. Overall, the occurrence of the individual and combined white striping and wooden breast abnormalities resulted in substantial reduction in the quality of breast meat, although these abnormalities are associated with distinct characteristics. Wooden breast fillets showed lower marinade uptake and higher cooking losses than white-striped fillets for both unprocessed and marinated meats. On the other hand, white-striped fillets showed a moderate decline in marinade and cooking yield. Fillets affected by both abnormalities had the highest (P<0.001) ultimate pH values. In contrast, the effects on colour of raw and cooked meat, drip loss, purge loss and cooked meat shear force were negligible or relatively low and of little practical importance. Thus, the presence of white striping and wooden breast abnormalities impair not only breast meat appearance but also the quality of both raw and marinated meats mainly by reducing water holding/binding abilities.

Occurrence of white striping under commercial conditions and its impact on breast meat quality in broiler chickens

The aims of this study were to evaluate the incidence of white striping (WS) under commercial conditions and assess its effect on some quality traits in broiler breast fillets. In the first experiment, occurrence of WS (absence = normal; presence classified in 2 levels as moderate or severe) was assessed in a major commercial processing plant on 28,000 breast fillets (pectoralis major muscles) chosen at random from 56 flocks of broilers processed at 45 to 54 d of age. In the second experiment, 153 fillets were selected based on WS degree (normal, moderate, or severe) and used to assess ultimate pH, color, drip loss, cook loss, and Allo-Kramer-shear force on raw meat as well to determine marinade uptake, purge loss, cook loss, total yield, and Allo-Kramer-shear force after tumbling with a 15% (wt/wt) solution containing sodium tripolyphosphate (2.3%) and sodium chloride (7.6%). The total incidence of white striped breast fillets was 12.0% (8.9 and 3.1% in moderate and severe degree, respectively). Considering the effect of genotype, high-breast yield hybrids exhibited a higher overall incidence of WS compared with standard breast yield birds (15.2 vs. 10.0%; P ≤ 0.001). Severe fillets showed higher pH than moderate and normal groups (5.95 vs. 5.88 and 5.86; P ≤ 0.05). Fillets with severe and moderate WS also exhibited lower marinade uptake compared with normal fillets (7.92 vs. 10.97 vs. 12.67%; P ≤ 0.05). Moreover, cook losses increased as the degree of WS increased from normal to severe groups in both raw (21.27 vs. 23.20 vs. 26.74%; P ≤ 0.05) and marinated meat (14.59 and 14.84 vs. 15.93%; P ≤ 0.05). Finally, nonmarinated fillets with severe striping had lower Allo-Kramer-shear force compared with moderate and normal ones (3.69 vs. 4.41 and 4.91 kg/g; P ≤ 0.05). In conclusion, this study revealed the importance achieved by WS defects in the production of broiler meat as well as its very negative impact on water holding and binding capacity of breast meat.

Quantity and functionality of protein fractions in chicken breast fillets affected by white striping

Recently, white striations parallel to muscle fibers direction have been observed on the surface of chicken breast, which could be ascribed to intensive growth selection. The aim of this study was to evaluate the effect of white striping on chemical composition with special emphasis on myofibrillar and sarcoplasmic protein fractions that are relevant to the processing features of chicken breast meat. During this study, a total of 12 pectoralis major muscles from both normal and white striped fillets were used to evaluate chemical composition, protein solubility (sarcoplasmic, myofibrillar, and total protein solubility), protein quantity (sarcoplasmic, myofibrillar, and stromal proteins), water holding capacity, and protein profile by SDS-PAGE analysis. White-striped fillets exhibited a higher percentage of moisture (75.4 vs. 73.8%; P < 0.01), intramuscular fat (2.15 vs. 0.98%; P < 0.01), and collagen (1.36 vs. 1.22%; P < 0.01), and lower content of protein (18.7 vs. 22.8%; P < 0.01) and ash (1.14 vs. 1.34%; P < 0.01), in comparison with normal fillets. There was a great decline in myofibrillar (14.0 vs. 8.7%; P < 0.01) and sarcoplasmic (3.2 vs. 2.6%; P < 0.01) content and solubility as well as an increase in cooking loss (33.7 vs. 27.4%; P < 0.05) due to white striping defects. Moreover, gel electrophoresis showed that the concentration of 3 myofibrillar proteins corresponding to actin (42 kDa); LC1, slow-twitch light chain myosin (27.5 kDa); and LC3, fast-twitch light chain myosin (16 kDa), and almost all sarcoplasmic proteins were lower than normal. In conclusion, the findings of this study revealed that chicken breast meat with white striping defect had different chemical composition (more fat and less protein) and protein quality and quantity (low content of myofibrillar proteins and high content of stromal proteins) with respect to normal meat. Furthermore, white striped fillets had lower protein functionality (higher cooking loss). All the former changes indicate that white striping has great impact on quality characteristics of chicken breast meat.

Effect of White Striping on Chemical Composition and Nutritional Value of Chicken Breast Meat

White striping defect (appearance of white striations parallel to muscle fiber on surface of breast) is considered an emerging issue in chicken breast meat which is related to increasing growth rate of modern hybrid birds. This study was aimed at evaluating the effect of white striping on chemical composition and nutritional value of chicken breast meat. During three replications, a total of 108 Pectoralis major muscles representing three degrees of white striping (absence=normal; presence classified in 2 levels as moderate or severe) were selected to determine proximate composition (moisture, protein, lipid and collagen) as well as sarcoplasmic and myofibrillar protein profile by sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis. The results showed that both severe and moderate white-striped fillets had higher fat content (2.53 vs 1.46 vs 0.78%; P<0.001), lower protein level (20.9 vs 22.2 vs 22.9%; P<0.001), decreased quality of protein as proven by higher collagen content (1.30 vs 1.37 vs 1.43%; P<0.001), and different pattern on myofibrillar and sarcoplasmic fractions when compared to normal fillets. Moreover, severe white-striped fillets exhibited higher energy content (450.7 vs 421.1 kJ/100g; P<0.01) with respect to normal meat. In conclusion, there was a large worsening of nutritional value of chicken breast meat following occurrence of white striping and this might impair consumer attitude towards poultry meat.