Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Committee Chair(s)

Rodney J. Brown


Rodney J. Brown


C. A. Ernstrom


Daren Cornforth


F. J. Post


D. V. Sisson


Protein recovery and coagulation properties of five commercial and fractionated milk clotting enzymes were studied. The fractionated enzymes were Sephadex G-100 fractions of the commercial enzymes. Milk clotting activity of each fraction was tested using Berridge substrate. All fractions from each preparation which had milk clotting activity as measured with the Formagraph were collected and pooled. These samples and the original enzyme preparations were used to coagulate milk. Percent of protein lost in whey was determined by Kjeldahl. Coagulation was followed using a spectrophotometer monitoring changes in apparent absorbance at 600 nm. Curd protein yields using the five original enzyme preparations were compared with each other. Also, protein lost in whey from the five original preparations were compared with those using the isolated fraction. There was a significant difference among the original enzymes in protein lost in whey. There were also significant differences between some of the commercial enzyme preparations and their fractionated preparations. Gel filtration through Sephadex G-100 improved bovine rennet and calf rennet/porcine pepsin mixture more than the other three enzyme preparations. Calf rennet, Mucor miehei protease and modified M. miehei protease showed no significant reduction in protein lost to whey after fractionation. Protein loss using original calf rennet, bovine rennet and modified M. miehei protease were not significantly different from each other. M. miehei protease and calf rennet/porcine pepsin mixture were not significantly different from each other, but, the two groups were significantly different from each other.

There were noticeable differences in coagulation curves of the five original enzymes. Coagulation properties of commercial and fractionated enzyme were different in all five pairs.