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
J. Chem. Educ., 1996, 73 (9), p 848
DOI: 10.1021/ed073p848
Publication Date (Web): September 1, 1996

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.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Biochemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Proteins / Peptides
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  • Received: August 03, 2009

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