How can I remove the caseins from milk to produce whey, and how can I separate the various proteins that are left in the whey?

BIOL 1406

PreLab 8a.2

How can I remove the caseins from milk to produce whey, and how can I separate the various proteins that are left in the whey?

Major Milk Proteins	Molecular Weight (daltons)
α-lactalbumin β-lactoglobulin various caseins blood serum albumin lactoferrin various immunoglobulins	14,437 18,000 ~19,000-30,000 68,000 87,000 ~160,000-1,000,000

Casein molecules coagulate (stick together) when the pH of milk drops below 4.8, while α-lactalbumin and the other non-casein milk proteins do not coagulate until the pH drops below 4.5. Therefore, you can selectively coagulate only the caseins by using acid to adjust the pH of milk between 4.8 and 4.5. This process is enhanced by heating the acid-milk mixture.

Once the caseins have coagulated, the resulting “curdled” mixture will be centrifuged to force the coagulated caseins into a firm pellet at the bottom of the centrifuge tube. Milk minus the caseins is called whey.

Your Turn
After centrifugation, how can you obtain a sample of milk whey?	Hint	Check your answer.
Based on your understanding of the purification process for α-lactalbumin, list the major milk proteins that should be present in each of the following milk fractions:
Nonfat milk:	Hint	Check your answer.
Pellet:	Hint	Check your answer.
Whey:	Hint	Check your answer.

After filtering the whey to remove any remaining particles, you will use size exclusion chromatography (also called gel filtration chromatography) to separate the proteins in the whey based on their size. During size exclusion chromatography the stationary and mobile phases are packed in a narrow column, so this technique is also referred to as column chromatography.

Use the interactive exercise below to learn more about size exclusion chromatography.

Your Turn
Based on your understanding of how size exclusion chromatography works, list the whey proteins in the order in which they will emerge from the bottom of the column:
First:	Hint	Check your answer.
Second:	Hint	Check your answer.
Third:	Hint	Check your answer.
Fourth:	Hint	Check your answer.
Last:	Hint	Check your answer.

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