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Journal of Dairy Science Vol. 18 No. 6 401-414
© 1935 by American Dairy Science Association ®
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Behavior of Caseinate Sols in a Study of a Hysteresis-Like Phenomenon in the Rennet Coagulation of Heated Milk*

Milton E. Powell and L. S. Palmer

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

ABSTRACT

It is commonly known that heated milk does not react normally with rennet. That heat treatment is not always detrimental was first observed by Stassano and Talarico (1), who noticed that milk heated to 65° C. coagulates more rapidly than raw milk. Similar observations were made by Rupp (2), and Mattick and Hallett (3), the latter investigators also observing an apparent hysteresis-like phenomenon.1 They found that when milk is heated for 30 minutes at 105° F. to 141° F. and rapidly cooled to 84° F. the first effect is increased coagulability, but the milk gradually loses coagulability as the interval between heating and addition of rennet lengthens. When the milk is heated above 145° F. the loss of coagulability is immediate and continues to increase as rennet addition is delayed, reaching a maximum after 5 hours. Moir (4) made a similar observation with flash pasteurized milk.

As Hammarsten (5) early demonstrated that only the calcium casemate and calcium phosphate systems in milk are involved in the clotting by rennet, it appeared feasible to employ these two components as an artificial "milk" in the study of the hyteresis-like phenomenon of heated milks.

FOOTNOTES

* Condensed from the thesis of Milton E. Powell submitted in partial fulfillment of the requirements for the degree of Ph.D., University of Minnesota. All pertinent data are available in the Division of Agricultural Biochemistry, University of Minnesota. Paper No. 1338, Journal Series, Minnesota Agricultural Experiment Station.

1 Hysteresis is a term applied to colloidal systems that react according to the past treatment which they have received.






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Copyright © 1935 by the American Dairy Science Association ®.