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Effects of in Vivo and in Vitro Acid Environments on Activity of Pregastric Esterase¹

Department of Animal Science, University of Minnesota, St. Paul 55101

ABSTRACT

Abomasal samples were collected at 0, 30, 60, 120, and 180 minutes post-feeding from a rumen-fistulated calf fed nonfat milk. Abomasal pH decreased progressively with time after feeding. Lipolytic activity, presumably due to pregastric esterase, was apparent in all samples; however, activity was considerably less in samples taken 180 minutes post-feeding.

In another trial, nonfat sham-fed milk, collected by way of an esophageal fistula, was subjected in vitro to acid conditions of pH 4.0, 3.5, 3.0, 2.5, and 2.0 for intervals of 15, 30, 60, 120, and 180 minutes. The pH of each preparation was then adjusted to 6.1 and incubated at 37 C with evaporated milk. Lipolytic activity of samples subjected to pH 4.0, 3.5, and 3.0 was about 65% of the control, irrespective of time held at these levels of acidity. Samples subjected to pH 2.5 and 2.0 lost nearly all of their lipolytic activity irrespective of time interval.

¹ Paper no. 7025, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul.

² NDEA Fellow, Title IV.

³ Data in this paper are from a thesis submitted by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy.