Date of Award:

5-1983

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Committee Chair(s)

Rodney J. Brown

Committee

Rodney J. Brown

Committee

Gary Richardson

Committee

Art Mahoney

Committee

Betty Boeker

Abstract

Enzymic milk coagulation was monitored by measuring changes in curd firmness and apparent absorbance of undiluted milk. Detection of coagulation, visually or rheologically, occurred after the milk changes from a system of aggregating particles to an extended space network. This change was observed as a shoulder in apparent absorbance plots and coagulation time was defined as the critical point in the aggregation process analogously to non-linear condensation polymerization reactions. It corresponds to the inflexion point during the period when apparent absorbance was rapidly increasing and can be calculated by fitting curd firmness data to an exponential equation.

Addition of calcium chloride to milk reduced coagulation time with a minimum occurring at .05M calcium. Also, curd firmness increased with a maximum at .02M calcium. It appears that calcium affects all stages of coagulation: proteolysis, micelle aggregation, and gelation. When bulk culture media was added to milk, the pH of the media had a greater effect on coagulation time than did presence of phosphate in the media.

Non-specific proteolytic activity of milk coagulants affects the initial rate of curd firming but not the maximum firmness. The more proteolytic the enzyme the slower the curd firming rate. This can be used to rapidly assay for pepsin content of bovine rennets.

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