Biomedical Engineering Reference
In-Depth Information
thickness of material, steam pressure and temperature, and roll speed of the drum. Drum
dryers have been successfully used to dry a variety of protein extracts.
Although drum dryers are easy to operate and have high energy efficiency, they have
relatively low throughput compared to spray dryers. Materials may also be unevenly dried
and become scorched, resulting in the generation of unacceptable colors or flavors, or the
loss of functionality. Thus, drum dryers may be better suited for the drying of lower cost
protein extracts (e.g., food and feed applications) than for pharmaceutical or nutraceutical
Protein extraction efficiency is an important measure of the effectiveness of protein
separation. Calculating the amount of protein recovered is, therefore, important to assess the
efficiency of the technique used. Protein recovery may be defined as the ratio of the total
mass of protein recovered in the dried extract divided by the total mass of protein present in
the starting material as shown in Equation 3.1 below:
Mass of protein extracted (g)
Protein recovery (%)
Total mass of protein in starting material (g)
Thus, the closer the mass of the protein extracted to the original amount present in the
starting material, the more efficient is the protein recovery.
Protein extraction efficiency is sometimes simply reported as protein yield defined as the
ratio of the total mass of protein recovered in the dried extract divided by the total mass of
the starting material (Equation 3.2):
Mass of protein extracted (g)
Protein yield (%)
Total mass of starting material (g)
Another frequently used measure of protein extraction efficiency is protein purity, defined
as the concentration of protein in the final extract as measured by the Kjedhal or Dumas
methods or a method analyzing for true protein (e.g., Lowry, Bradford or BCA methods).
Protein purity may, therefore, be defined as the ratio of the mass of protein in the dried
recovered extract divided by the total mass of the dried extract as shown in Equation 3.3:
Mass of protein in extract extracted (g)
Protein purity (%)
Total mass of recovered extract (g)
Protein purity, yield and quality are easily affected by processing conditions (e.g. tempera-
ture, time, flour to solvent ratio, condition and protein solubility of the starting material,
type of equipment and process used, g forces used for centrifugation, laboratory vs. pilot
scale extraction, batch vs. continuous extraction, etc.).
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