Meat Quality for Further Processing

In the past few decades, the genetic selection programs carried out to increase the production traits of broilers and obtain high-growth rate and breast yield hybrids led to profound changes in muscle structure and metabolism resulting in an increased incidence of abnormalities mainly affecting the Pectoralis major muscle. White-striping (WS), wooden breast (WB) and poor cohesion (PC) defects are of relevant importance. Within this scenario, this PhD thesis aimed at deepening the current knowledge concerning histological features, quality traits and technological properties of broiler pectoral muscles affected by abnormalities, clarifying their peculiarities and similarities as well as investigating the underlying mechanisms involved in their occurrence. Irrespective of the type of abnormality, similar histological alterations including profound degenerative myopathic changes, variable fibers cross-sectional area as well as proliferation of loose connective tissue and fat deposition were observed within the endomysial and perimysial spaces of the Pectoralis major muscles affected by abnormalities. As for quality traits, the abnormal muscles exhibited severely impaired technological properties (reduced water-holding/-binding capacity and altered texture) with the alterations being more pronounced within the superficial layer of the cranial portion of the muscle when more than one abnormality coexist. With regard to chemical composition, an overall higher moisture, fat and collagen content to the detriment of protein and total heme pigments levels were found in abnormal muscles which exhibited altered sodium and calcium homeostasis as well as 204 differentially expressed genes related to several functional categories. In addition, the hardened consistency of the WB cases is only partially counteracted by the endogenous proteolytic processes taking place during the post-mortem period. In conclusion, it is reasonable to hypothesise the existence of a complex network of biological changes responsible for the phenotypic features and the consistent impairment of muscular metabolism of the abnormal muscles.