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Milk Lipase Activity: A Method for its Determination, and its Relationship to the Estrual Cycle^*

University of Arkansas

ABSTRACT

1. A new method for lipase analysis has been reported.
   
2. Tributyrin appeared to be a more sensitive indicator of milk which developed rancidity than did tricaproin, triacetin, tripalmitin, or sterilized butter oil.
   
3. The method was developed primarily for the study of milk lipase activity with pure substrate. Enough data have not been taken under different conditions to set absolute limits to indicate rancidity by organoleptic test. Most of the data obtained were from milk which had a high total solids content. One series of samples from a cow producing milk with a low butterfat content was slightly higher in activity per gram of dried, defatted milk powder than some others which had shown rancidity on organoleptic test and yet they produced milk in which the defect could not be detected. It is possible that these border-line cases could have been eliminated had total solids as well as the titration per gram of dried, defatted milk been considered.
   
4. The milk lipase appeared to show some selectivity in its hydrolysis, acting more rapidly on the volatile than on the non-volatile substrates.
   
5. When the milk was kept for an additional 24 hours before drying, there was a marked increase in tributyrinase activity.
   
6. Cream which was obtained by gravity separation contained much higher lipase activity than did the skim milk from the same sample.
   
7. There appeared to be no relationship between the lipolytic action which causes hydrolytic rancidity and that which attacks the substrates diacetin and ethyl-oleate.
   
8. When samples of milk were collected at frequent intervals from open cows, the data showed a definite relationship between the estrus cycle and the lipase activity.
   

^* Research paper No. 801, Journal Series, University of Arkansas. Published with the approval of the Director of the Agricultural Experiment Station.

¹ Now at South Dakota State College