Date of Award:

5-2004

Document Type:

Thesis

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Committee Chair(s)

Donald J. McMahon

Committee

Donald J. McMahon

Committee

Jeffery R. Broadbent

Committee

Marie K. Walsh

Committee

Timothy A. Taylor

Committee

Conley L. Hansen

Committee

Ross E. Robson

Abstract

The changes in quaternary structure of casein supramolecules with various physical and chemical treatments were studied using transmission electron microscopy, and a model to account for the changes is put forth. The effects of casein structure on coagulation properties were also studied. The sample preparation for transmission electron microscopy involved physical methods of fixation and flash freeing to preserve the structure of caseins in the sample.

The structure of caseins in sodium and calcium caseinate varied with sodium caseinate not exhibiting any spherical structure as opposed to the spherical structure seen in calcium caseinate, non-fat dried milk and native milk. This difference in structure was carried over to rennet coagulum made from those sources of casein. Addition of calcium and phosphate to sodium and calcium caseinate, respectively, improved their coagulation properties. Hydration parameters such as time and shear of hydration affected the extent of hydration. High shear (733 s-1) or approximately 10 hr of hydration was required to disperse and hydrate the dried milk protein powders.

Acidification and treatment with excess EDTA resulted in dissociation of casein supramolecules into various sizes and shapes. Heat treatment of milk in the presence of ethanol also resulted in its dissociation. High heat treatment of milk at various pH levels induced different types of whey protein casein interactions.

All these changes can be explained using an irregular supramolecular structure of caseins based on a node and strand network of proteins and calcium phosphate nanoclusters. Such a filigreed sponge-like appearance is seen in native bovine milk and in milk of other species.

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