title: Effect of ractopamine-hydrochloride on the fiber type distribution and shelf-life of six muscles of steers.
abstract: The goal of this study was to evaluate the effects of ractopamine-hydrochloride (RAC) supplementation on the myosin heavy chain isoform distribution and shelf-life properties of muscles from beef top round, knuckle, and loin. Thirty-four steer carcasses were selected from 4 separate slaughter groups. Within each slaughter group (3 groups, n = 8; 1 group, n = 10), steers were separated into pens (n = 8) and fed 0 or 200 mg x animal(-1) x d(-1) of RAC for the final 28 d of feeding. Seventy-two hours postmortem, the longissimus lumborum, semimembranosus (SM), adductor, gracilis, vastus lateralis (VL), and rectus femoris 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 degrees C for 13 d before processing into steaks for a 5-d simulated retail display study. Daily, steaks were analyzed for reduction of nitric oxide metmyoglobin, 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 gracilis 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 5-d retail display period. Metmyoglobin and oxymyoglobin accumulation, L*, a*, and b*-values were not affected (P > 0.05) by RAC supplementation. Percent nitric oxide metmyoglobin reduction data indicate that reducing ability of RAC-treated steaks from the adductor and longissimus lumborum were significantly affected (P < 0.05). Visual panel data suggest 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 3 d of display. Ractopamine significantly (P < 0.05) increased the surface discoloration of the rectus femoris and SM on d 5. Although RAC supplementation had no effect on objective color measurements, subjective measurements indicate that it may have some effect on surface discoloration of some muscles.
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Gonzalez
authors.forename: S E
authors.initials: SE
authors.lastname: Johnson
authors.forename: T A
authors.initials: TA
authors.lastname: Thrift
authors.forename: J D
authors.initials: JD
authors.lastname: Savell
authors.forename: S E
authors.initials: SE
authors.lastname: Ouellette
authors.forename: D D
authors.initials: DD
authors.lastname: Johnson
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D003116:Color; D005511:Food Handling / Q000592:standards*; D006801:Humans; D008297:Male; D008460:Meat / Q000592:standards*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects*; D010627:Phenethylamines / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D000318:Adrenergic beta-Agonists; D010627:Phenethylamines; C060897:ractopamine