Gonzalez J M, Johnson S E, Thrift T A, Savell J D, Ouellette S E, Johnson D D
Department of Animal Sciences, University of Florida, Gainesville 32611, USA.
J Anim Sci. 2009 May;87(5):1764-71. doi: 10.2527/jas.2008-1469. Epub 2009 Jan 30.
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.
本研究的目的是评估补充盐酸莱克多巴胺（RAC）对牛上腰部、膝关节和腰部肌肉中肌球蛋白重链亚型分布及货架期特性的影响。从4个独立的屠宰组中选取了34头阉牛胴体。在每个屠宰组内（3组，每组n = 8；1组，n = 10），将阉牛分到栏中（n = 8），并在饲养的最后28天内给每头阉牛饲喂0或200 mg·头⁻¹·天⁻¹的RAC。宰后72小时，从每头胴体上取下腰大肌、半膜肌（SM）、内收肌、股薄肌、股外侧肌（VL）和股直肌。采集每块肌肉的一个子样本用于免疫组织化学分析。将整块肌肉真空包装，在1±2℃下湿腌13天，然后加工成牛排进行为期5天的模拟零售展示研究。每天对牛排进行分析，测定一氧化氮高铁肌红蛋白的减少量、瘦肉颜色、脂肪颜色和表面变色情况。每天记录高铁肌红蛋白、氧合肌红蛋白、L*、a和b值的客观测量数据。RAC显著（P < 0.05）改变了除SM外所有肌肉中的纤维类型亚型分布。VL和股薄肌的纤维类型转换最大，约21%的I型纤维转换为IIA型纤维。然而，在为期5天的零售展示期内，补充RAC引起的纤维类型变化对主观和客观颜色测量几乎没有影响。高铁肌红蛋白和氧合肌红蛋白的积累、L*、a*和b*值不受补充RAC的影响（P > 0.05）。一氧化氮高铁肌红蛋白减少百分比数据表明，RAC处理的内收肌和腰大肌牛排的还原能力受到显著影响（P < 0.05）。视觉评定小组数据表明，在展示的最后3天，RAC对VL牛排的瘦肉颜色和表面变色评分往往有最不利的影响（P < 0.10）。RAC显著（P < 0.05）增加了第5天股直肌和SM的表面变色。虽然补充RAC对客观颜色测量没有影响，但主观测量表明它可能对某些肌肉的表面变色有一定影响。
