Submitted to: Protein Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/16/2006
Publication Date: 9/1/2006
Citation: Sood, S.M., Lekic, T., Harbir, J., Farrell, H.J., Slattery, C.W. 2006. Reconstituted micelle formation using reduced, carboxymethylated bovine k-casein and human b-casein. Protein Journal. 25(352-360). Interpretive Summary: For young children, milk represents a major source of calcium in their diet. Human milk formulas are currently based upon cows’ milk and use limited amounts of bovine proteins. There are however major differences between human and cows’ milk proteins, particularly in the caseins the major class of milk proteins which carry calcium. No one has studied whether or not mixtures of human and cows’ milk proteins will work together to carry calcium in a nutritionally usable form. The caseins can be divided into two classes; one which directly carries casein (Ca-carrier) and another which helps the digestion of the calcium (Ca-helper). In this work the (Ca-helper) from cows’ milk was mixed with the Ca-carriers of human milk to test the viability of the mixed system to effectively carry calcium. The mixtures appeared to work well at first, but the complexes were larger than those in normal human milk. To limit the size of the complexes, we chemically modified the cows’ milk protein to appear more like its human counterpart. Surprisingly the proteins still carried calcium, but also formed long regular strands. It appears as though the normal cows’ milk protein is better as a Ca-helper than the modified protein as the nutritional value of the long strands is unknown. The regularity of these aggregates however suggests that the mixtures have the potential to form unusual films or coatings never before seen for caseins. This information can be used to design new products for the food ingredient market or possibly for non-food applications.
Technical Abstract: In milk, K-casein, a mixture of disulfide-bonded polymers, stabilizes and regulates the size of the unique colloidal complex of protein, Ca+2 and inorganic phosphate (Pi) termed the casein (CN) micelle. However, reduced, carboxymethylated bovine K-CN (RCM-K) forms fibrils at 37 degrees C and its micelle-forming ability is in question. Here, the doubly- and quadruply-phosphorylated human B-CN forms and 1:1 (wt:wt) mixtures were combined with RCM-K at different B/K weight ratios. Turbidity (OD 400 nm) and a lack of precipitation up to 37 degrees C were used as an index of micelle formation. Studies were with 0, 5 and 10 mM Ca+2 and 4 and 8 mM Pi. The RCM-K does form concentration-dependent micelles. Also, B-CN phosphorylation level influences micelle formation. Complexes were low-temperature reversible and RCM-K fibrils were seen. There appears to be equilibrium between fibrillar and soluble forms since the solution still stabilized after fibril removal. The RCM-K stabilized better than native bovine K-CN, but fibrillar forms were always present.