The objective of this work will be to investigate the effect of castration, feedlot period, muscular fiber type and aging on the beef protein and lipid oxidation, and quality attributes. For this, it will be used 40 Nellore breed male (20 intact and 20 castrated) bovines, with approximate age of 24 months. The animals will be confined for 56, 84, 112, and 140 days and, in the end of each period, it will slaughtered 10 animals (5 intact and 5 castrated). The Longissimus Lumborum (red) and Semitendinosus (white) muscles will be collected from the carcasses 24 h after the slaughter and aged for 1, 7 and 14 days postmortem. The laboratoral analyses that will be performed are: muscular composition (fatty acids composition, protein and fiber type), protein oxidation (carbonil and thiol group contents), lipid oxidation (thiobarbituric acid-reactive substances and peroxide value), pH value, instrumental color, metmyoglobin, calpastatina activity, protein fragmentation index (two-dimensional electrophoresis), Warner-Bratzler shear force and cooking losses. The experimental design will be completely randomized with 2 (sex condition) x 4 (feedlot period) x 2 (muscle types) x 3 (times of aging) factorial arrangement, and the program used for the statistical analysis will be the SAS (2000). It will be expected with the results from this project to propose a relationship between castration and feedlot period with muscular fiber type, quality and aging time of beef.
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