Conclusion: These data indicate that nuclei, β-1AR, and β-2ARdensities are not affected by feeding encapsulated amino acids incombination with zilpaterol HCl during the finishing period.

Keywords: Beta-1 adrenergic receptor, Beta-2 adrenergic receptor,Zilpaterol hydrochloride

doi:10.1016/j.meatsci.2013.07.154

117 Effects of supplemental lysine and methionine incombination with zilpaterol hydrochloride on musclefiber type and size in finishing feedlot cattleA.D. Hosforda,⁎, J.E. Hergenredera,W. Roundsb, B.J. Johnsona, aAnimal andFood Sciences, Texas Tech University, Lubbock, United States, bKeminIndustries, Inc., North America, Des Moines, IA 50317, United States

Objectives: Feeding β-adrenergic agonists, like zilpaterol hydro-chloride (ZH), have been shown to increase muscle accretion bycausing hypertrophy of the muscle fiber. Additionally, a shift fromsmaller oxidative muscle fibers to larger glycolytic fibers has beenreported with ZH feeding. Little is known about the limiting aminoacid requirements during this phase of rapid muscle growth. Ourobjective was to evaluate the effects of feeding encapsulated aminoacids in combination with ZH on muscle fiber type and muscle fibersize in continental crossbred steers.

Materials and methods: Steers (n = 180; initial BW= 366 kg)were blocked by weight and randomly assigned to pens (n = 45pens; 9 pens/treatment) and to 1 of 5 treatments including: 1) noamino acids and no zilpaterol HCl (Cont−); 2) no amino acids andzilpaterol HCl (Cont+); 3) encapsulated lysine supplement (Lys;LysiPEARL™) and zilpaterol HCl; 4) encapsulated methionine (Met;MetiPEARL™) and zilpaterol HCl; and 5) encapsulated lysine andmethionine (Lys +Met) and zilpaterol HCl. Zilpaterol HCl (8.3 mg/kgDM) was fed for the last 20 d of the finishing period with a 3 dwithdrawal. Lysine and Met were top dressed daily for 134 d toprovide 12 or 4 g·h d−1·d−1, respectively to the small intestine. Atthe end of the trial, steers were harvested at a commercial abattoir,and one steer per pen was selected for longissimus muscle histologyanalysis. Longissimus muscle samples were cryosectioned (10 μm)and immunoflourescence stained. Myosin heavy chain (MHC) typesI, IIA, and IIX were identified and area was measured.

Results: Myosin heavy chain (MHC) type I muscle fiber area wasincreased for Lys + Met treated cattle when compared to Lys andMet (P= 0.03). There was no difference in MHCI fiber abundance forany treatment. Myosin heavy chain IIX muscle fiber size wasincreased for Lys + Met when compared to Cont− (P = 0.05). TheMHCIIA fiber area tended to be increased for Lys +Met treatment ascompared to Met and Cont− (P = 0.10). The proportion of MHC IIAfibers were increased with Cont+ as compared to Cont− and Met(P= 0.05 and 0.03, respectively).

Conclusion: These data indicate that muscle hypertrophy isoccurring with ZH administration, and that this hypertrophic effect isincreased with the addition encapsulated lysine and methionine.

Keywords: Fiber area, Lysine, Methionine, Zilpaterol hydrochloride

doi:10.1016/j.meatsci.2013.07.155

118 Investigating the usefulness of cyclic voltammetry todetermine myoglobin reduction potential and oxygenationR. Ramanathana,⁎, R. Nerimetlab, S. Krishnanb, D.L. VanOverbekea, G.G.Mafia, aAnimal Science, Oklahoma State University, Stillwater, UnitedStates, bChemistry, Oklahoma State University, Stillwater, United States

Objectives: Myoglobin is the protein primarily responsible for meatcolor and can exist in three different forms; namely deoxy-, oxy-, ormetmyoglobin. Although various pre- and post-harvest factors canincrease myoglobin oxidation, meat has an inherent capacity to delaymetmyoglobin accumulation by a process called metmyoglobinreduction. To date, research has been focused on the role of enzymes,mitochondria, and NADH levels in metmyoglobin reducing capacity.However, it is possible that reduction potential of myoglobin also caninfluence metmyoglobin reduction. The term reduction potential refersto the ability of iron in myoglobin to accept an electron (or to undergoreduction). Nevertheless, no reports have as yet characterized the roleof myoglobin reduction potential in beef color. The objectives of thecurrent study were to investigate the usefulness of cyclic voltammetry(1) to determine beef myoglobin reduction potential and (2) toevaluate myoglobin oxygenation at pH 5.6 or 7.4.

Materials and methods: Myoglobin was isolated from bovinecardiac muscle by gel filtration technique. Briefly, myoglobin solution(0.15 mM) was passed through chromatography columns pre-calibrated with either pH 5.6 or 7.4 buffer to alter myoglobin pH.Approximately 10 μL of metmyoglobin was placed on a high puritygraphite electrode, and adsorbed for 10 min. A CH electrochemicalanalyzer was used to perform voltammetry. The myoglobin reduc-tion potential responses were recorded in millivolt (mV) units. Forthe second objective, a controlled amount of oxygen was allowed tobind with deoxymyoglobin at pH 5.6 or 7.4 using an oxygen massflow controller. The experimental design was completely random-ized and the data were analyzed using Proc Mixed of SAS (n = 3replications). Least-squares means were separated with a protectedpairwise t-test and were considered significant at P b 0.05.

Results: There was a significant effect of pH on myoglobinreduction potential. At pH 5.6, myoglobin reduction potential was−290 mV compared with −330 mV at pH 7.4 (P b 0.05). Thereduction potential value provides information about the ability ofheme within myoglobin to accept electron. A lower number indicatesthat the myoglobin has greater capacity for reduction. For the secondobjective, 0–1600 μM of oxygen was allowed to bind with myoglobinat pH 5.6 or 7.4. The oxygen binding to myoglobin produced electriccurrent and this response was recorded in micro ampere. The greaterthe oxygen binding, the larger is the resulting current. Thisrelationship was used to determine the myoglobin oxygen affinity.

Conclusion: The results from the current study suggest that cyclicvoltammetry is a useful tool to determine myoglobin reductionpotentials and to quantify myoglobin oxygenation capacity. Theapplication of electrochemical methods will help to probe themyoglobin reduction potential changes in the microenvironment ofheme cofactor. Thus, characterizing the interrelationship betweenmyoglobin reduction potential (related to color stability) andmyoglobin oxygenation (related to bloom) will increase the bodyof knowledge related to beef color.

Keywords: Meat color, Metmyoglobin reduction, Myoglobin

doi:10.1016/j.meatsci.2013.07.156

119 Effects of oxygen on beef myoglobin reduction potentialin vitroR. Nerimetlaa, S. Krishnana, G.G. Mafib, D.L. VanOverbekeb, R.Ramanathanb,⁎, aChemistry, Oklahoma State University, Stillwater,United States, bAnimal Science, Oklahoma State University, Stillwater,United States

Objectives: Metmyoglobin reducing capacity is an importantintrinsic property that can influence color stability of beef. Thisinvolves addition of an electron to metmyoglobin via enzymatic or

Abstracts494