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  Home > JCE Print > Journal of Chemical Education > Issues > 1996  > September  >
In The Laboratory
The Use of a "Qual" Centrifuge for Greatly Simplifying and Speeding the Study of Milk
Quentin R. Petersen
Central Michigan University, Mt. Pleasant, MI 48858
Cover
September 1996
Vol. 73 No. 9
p. 848
Abstract
Laboratory study of the constituents of milk is almost always slowed by difficult separation of relatively large amounts of curd and whey by filtration. In the two-and-one-half hour experiment described, only 5 mL of skim milk is used and the curd is separated from the whey by using a simple "qual" centrifuge. Casein and serum proteins are quickly isolated as solids in essentially-quantitative yields in a procedure utilizing only two 13 x 100 mm test tubes and a 50 mL beaker along with the centrifuge and a hotplate. Protein solutions are prepared in the test tubes in which they were isolated and subjected to a variety of classical tests, the most dramatic of which is the Hopkins-Cole test which shows the presence of tryptophan in casein and its absence in serum protein. An essentially-quantitative yield of solid lactose is obtained by evaporation of the supernatant liquid obtained from the serum protein centrifugation. A lactose solution is subjected to Benedict's and Barfoed's tests, identifying it as a disaccharide. Sufficient time is available to compare the fat and enzyme contents of raw milk and skim milk.
More Information
*  Citation
 J. Chem. Educ. 1996 73 848.
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Last Updated:		 September 21, 1999
February 21, 2006
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