The objective of this work was to investigate the occurrence of pale, soft, exudative meat (PSE) in chicken by submitting birds to physical stress. Dietary supplementation of vitamin E was undertaken to overcome this syndrome. Postmortem muscle biochemical events and their consequence on meat properties were evaluated in samples with and without supplemented vitamin E. Our studies showed chickens were susceptible to heat stress which promoted changes in the glycolytic parameters causing the development of chicken PSE. Dietary vitamin E was capable of inhibiting the development of the syndrome hence improving meat functional properties.

The change in the amounts of the three major reducible cross-links was followed throughout the bovine-life span. The major reducible cross-link in embryonic skin is 6,7-dehydro-N(epsilon) -(2-hydroxy-5-amino-5-carboxypentyl)hydroxylysine, but this is gradually replaced in the latter stages of gestation or early postnatal growth period by two other Schiff bases, 6,7-dehydro-N(epsilon)-(5-amino-5-carboxypentyl)hydroxylysine and a component not yet identified, designated Fraction C. These latter two Schiff bases increase in amount during the rapid growth period to a maximum, after which they then slowly decrease until at maturity they are virtually absent. The proportion of these Schiff bases closely reflects the rate of growth, i.e. the amount of newly synthesized collagen present at any one time. Similarly, the three Schiff bases present in tendon and the one in cartilage slowly decrease during maturation. No evidence for the possible stabilization of these aldimine bonds during maturation by reduction in vivo was found by three different analytical techniques. Concurrently with the decrease in the proportion of the Schiff bases some new reducible components increased during maturation, but their characterization as N(epsilon)-glycosylamines demonstrated that they were not related to the lysine-derived aldehyde components. The significance of these components in the aging process cannot at present be assessed. As no evidence was obtained for any new reducible cross-links replacing the Schiff bases, it is probable that the latter are intermediate cross-links and that during maturation they are stabilized to some as yet unknown non-reducible cross-link as previously proposed (Bailey, 1968).

a b s t r a c tThe biological cause of broiler PSE meat seems to be an excessive release of Ca 2+ , promoted by a genetic mutation of ryanodine receptors located in the sarcoplasmic reticulum of skeletal muscle cells. Excessive Ca 2+ , associated with protein denaturation in meat, enhances protease activity and influences the functional properties of PSE meat. Twenty-four-hour post-mortem Pectoralis major m. samples exhibited lower values for pH, water-holding capacity, and shear force than did control samples, in contrast to colour (L * ) and cooking loss values. Protease activity, measured as myofibril fragmentation index, presented higher values in PSE meat than in control samples. Ultrastructural examination revealed shrinking and depolymerisation of myofilaments and Z-lines disorganisation within the sarcomere in PSE meat. Intense calpain activity was also observed, indicating that the process may initiate at the filaments, because of protein denaturation, and spread through Z-lines, resulting in the collapse of the sarcomere structure.

The connections between the redox imbalance in post-mortem muscle, early protein oxidation and the onset of pale, soft and exudative (PSE) condition in chicken breast are studied. PSE was induced by incubation of post-mortem chicken carcasses at 37°C for 200min. PSE-induced muscle consistently had faster pH decline and lower pH at 200min (5.84 vs. 6.59) and 24h (5.69 vs. 5.96), higher L(∗) (54.4 vs. 57.3), and lower texture and water holding capacity (WHC) than normal meat. The activities of catalase, glutathione peroxidase and superoxide dismutase were significantly lower in PSE-induced samples than in the normal counterparts. PSE was more susceptible to proteolysis and protein oxidation than normal meat during succeeding chilled storage with more intense tryptophan and thiols depletion, higher protein carbonylation and more intense formation of protein cross-links. We provide plausible explanations to support the role of protein oxidation in the impaired quality PSE chicken.

The objective of this work was to investigate the influence of water spray treatment before broiler slaughtering on the quality of breast meat (Pectoralis major) and to observe ultrastructural changes promoted by the biochemical/physiological events during rigor mortis onset. Commercial Ross chickens were divided into two groups: Untreated Group (UG) (n = 608) and Treated Group (TG) (n = 611), without and with water shower treatment, respectively. Drip and cook losses, pH and color measured after 24 h postmortem demonstrated that antemortem water shower treatment inhibited PSE development in chicken breast meat. Histological studies of the PSE samples from UG birds after 72 h postmortem revealed under light microscopy a shrinking of muscle cell diameter by approximately 10% in relation to TG samples and an extracellular enlargement of endomysium and perimysium sheaths. By electron microscopy of PSE meat, Z‐lines appeared fragmented, A‐bands including the M‐line disappeared and a super‐contraction of sarcomeres was observed, indicating that proteins were adversely affected by heat stress.

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