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Assay and Characterization of Pregastric Esterase

Dairyland Food Laboratories, Inc., Waukesha, Wisconsin

ABSTRACT

A recording pH stat has been adapted to the assay of pregastric esterase preparations. Assay substrate containing 5 ml n-tributyrin, 0.5 ml 10% soy lecithin in mineral oil, 0.6 g acid casein, and 95 ml water is emulsified in a blender. Enzyme inoculum is prepared via rehydration of 0.2 to 1.0 g powder in 75–80 ml 0.5 M NaCl solution for 20 min at ambient temperatures. The suspension is made up to 100 ml and 1 ml is inoculated into 5 ml of substrate on a pH stat, set to control at pH 6.20 and 40 C. The resultant slope is a function of enzyme activity. This assay is more precise than currently used colorimetric tests.

Calf pregastric esterase was found most stable at pH 5.5, using the pH stat. The enzyme was most active at 45 C. Kid and lamb enzymes also had maximum activity at 42–45 C. pH optima occurred at 5.3 to 5.5 on both tributyrin and milk fat substrates. Minor peaks occurred at pH 8.5 and 8.7 for calf and kid, respectively.

Pregastric esterase has esterase characteristics when evaluated on solutions and emulsions of triacetin. The enzyme is not as active upon 1-mono- and dibutyrin as pancreatic, milk, or Aspergillus niger lipases.

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