Fresh meat slowly changes from a bright red to a brown color due to the oxidatio

Question

Fresh meat slowly changes from a bright red to a brown color due to the oxidation of oxy-myoglobin to met-myoglobin upon aging. The concentrations of both of these proteins can be measured in ground meat (after extraction, purification, and separation) using a spectrophotometer. The oxy-myoglobin is measured at 417 nm with a molar absorbtivity of 12,800 M-1 cm-1 . The met-myoglobin is measured at 409 nm with a molar absorbtivity of 17,900 M-1 cm-1 . In an extract of 10.0 g of ground meat (in 3.0 mL total solution) the absorbance of the oxy-myoglobin sample was found to be 0.769 using a 1 cm cell and the met-myoglobin was 0.346. Determine the moles of oxy-myoglobin and met-myoglobin per gram of ground meat.

Explanation / Answer

We can use the Beer´s law where: A=aLc

A=absorbance

a= absorbtivity

L=pathlength

c=concentration

A met-myoglobin= 17900 x 1x C= 0.346 -----> C= 1.93 x 10-5M

Molarity= mol/Volume(L) ---> mol met-myoglobin= 1.93 x 10-5M x 3 x 10-3L= 5.79 x 10-8mol

A oxy-myoglobin= 12800 x 1 x C= 0.769 ---->C= 6.01 x 10-5M ---->mol= 6.01 x 10-5M x 3 x 10-3L= 1.8 x 10-7mol

5.79x10-8 mol ---------- 10 g

x= 5.79 x 10-9mol -------- 1g -----------> 5.79x10-9 mol of met-myoglobin/gram of ground meat

1.8 x 10-7 mol ----------- 10g

x= 1.8 x 10-8 mol  --------- 1g ------------> 1.8 x 10-8 mol of oxy-myoglobin/gram of ground meat

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