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Purification of Rennin from Commercial Rennin Extract: Properties of Purified Product

C. L. Hankinson and L. S. Palmer

Division of Agricultural Biochemistry, University of Minnesota, St. Paul

ABSTRACT

A stable purified rennin sol was prepared from a commercial rennet extract by means of an isoelectric precipitation procedure. One part of dry rennin coagulated 72,300,000 parts of fresh raw skim milk at pH 5.75-5.80 (obtained by added CaCl₂) in 10 minutes at 40° C, which was 4.55 times that of the dry organic matter of the original extract. The peptic activity, measured by a method which estimates quantitatively 10 µg. crystalline pepsin, was only 6.25 per cent of the original dry organic mixture. The rennin was therefore 99.77 per cent "pure" from the standpoint of peptic activity. The purified rennin exhibited the properties of a globulin. Its isoelectric point in 16.7 per cent NaCl solution was pH 4.5. The rennin sol, freed from NaCl by dialysis, showed a progressive increase in negative zeta potential from pH 6.0 to 7.5, and at pH 6.5 showed about the same negative zeta potential as calcium caseinate particles. Rennin and calcium casemate, therefore, do not exhibit opposite electropotentials at the pH of milk.

^* Paper No. 1871, Scientific Journal Series, Minnesota Agricultural Experiment Station. Presented at 35th Annual Meeting, American Dairy Science Association, Purdue University, June 27, 1940.

Carnation Company Research Laboratory, Milwaukee, Wisconsin.