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This Article Full Text (PDF) All Versions of this Article: jas.2008-1469v1 87/5/1764    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gonzalez, J. M. Articles by Johnson, D. D. Search for Related Content PubMed PubMed Citation Articles by Gonzalez, J. M. Articles by Johnson, D. D.

Effect of ractopamine-HCl on the fiber type distribution and shelf-life of six muscles of steers

Department of Animal Sciences, University of Florida, Gainesville, FL 32611

dwainj{at}ufl.edu

Abstract

The goal of this study was to evaluate the effects of ractopamine-HCl (RAC) supplementation on the myosin heavy chain (MyHC) isoform distribution and shelf-life properties of muscles from beef top round, knuckle and loin. Thirty-four steer carcasses were selected from four separate slaughter groups. Within each harvest group (3 groups n = 8; 1 group n = 10), steers were separated into pens (n = 8) and fed 0 or 200 mg•hd^-1•d^-1 of RAC for the final 28 days of feeding. Seventy-two hours postmortem, the longissimus lumborum (LL), semimembranosus (SM), adductor (ADD), gracilis (GRA), vastus lateralis (VL), and rectus femoris (RF) were removed from each carcass. A subsample of each muscle was collected for immunohistochemical analysis. Whole muscles were vacuum packaged and wet aged at 1 ± 2°C for 13 days prior to processing into steaks for a five-day simulated retail display study. Daily, steaks were analyzed for reduction of nitric oxide metmyoglobin (NOM), lean color, fat color, and surface discoloration. Objective measures of metmyoglobin, oxymyoglobin, L*, a*, and b* values were recorded daily. Ractopamine significantly (P < 0.05) changed the fiber type isoform distribution in all muscles except the SM. The VL and GRA presented the greatest fiber type switch with approximately 21% of type I fibers switching to type IIA fibers. However, the fiber type shifts induced by RAC supplementation had little to no effect on subjective and objective color measurements during the five-day retail display period. Metmyoglobin and oxymyoglobin accumulation, L*, a*, and b*-values were not affected (P > 0.05) by RAC supplementation. Percent NOM reduced data indicate that reducing ability of RAC treated steaks from the ADD and LL were significantly affected (P < 0.05). Visual panel data suggests that RAC tended (P < 0.10) to have the most detrimental effect on the lean color and surface discoloration scores of steaks from the VL during the last three days of display. Ractopamine significantly (P < 0.05) increased the surface discoloration of the RF and SM on day 5. While RAC supplementation had no effect on objective color measurements, subjective measurements indicate that it may have some effect surface discoloration of some muscles.

Key Words: ractopamine • skeletal muscle • myosin heavy chain • shelf-life • muscle fiber