Effect of spaghetti-meat abnormality on quality and histological traits of broiler breast fillets

During the last few years, the increasing growth rate and meat yield of modern broiler hybrids caused the appearance of several breast muscle abnormalities, such as white striping and wooden breast. Recently, a new myopathy termed spaghetti-meat (SM) characterized by extremely soft and friable pectoralis major when palpated after chilling has emerged. Since the occurrence of SM is often associated with white striping (WS), this study aimed at evaluating the effects of SM and/or WS conditions on meat quality and histological traits in broilers. For this purpose, 96 pectoralis major muscles were selected from homogeneous flocks (47 d of age and 2.8 kg of live weight at slaughter) into two independent trials and classified as follows: 24 Normal (N), 24 WS, 24 SM and 24 WS/SM. Each fillet was cut in order to separate the superficial layer from the deep one and both used to assess proximate composition, histological features, colour, pH and protein profile. Data were analyses by two-way ANOVA using abnormality and sampling position as the main variables. Proximate composition was found to be significantly modified according the type of abnormality, especially in the superficial layer of the fillets. The SM and WS/SM groups had a remarkable decrease in total protein content coupled with an increased moisture level (p<.001), while WS group was associated with higher lipid content. Histological evaluations of abnormal samples evidenced several degenerative aspects that almost completely concern the superficial layer of the fillets. The SM samples showed poor fibres uniformity and a progressive rarefaction of the endo- and peri-mysial connective tissue. The WS fillets exhibited necrosis and lysis of fibres, fibrosis, lipidosis, loss of cross striation and vacuolar degeneration, while WS/SM fillets exhibited intermediate histological features. No relevant effect on meat colour has been detected, however abnormal fillets showed increased yellowness (b) and ultimate pH values (p<.001). Moreover, both WS and SM abnormalities were associated with a more intense proteolytic degradation of muscle tissue (p<.001), which led to the formation of high molecular-weight protein fragments. In conclusion, both muscle myopathies mainly affect the superficial layer of pectoralis major muscle, while deep section is poorly involved. Furthermore, if compared with WS, SM abnormality is associated with a more remarkable alteration of the proximate composition and quality traits of the meat.