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Journal of Dairy Science Vol. 65 No. 7 1074-1083
© 1982 by American Dairy Science Association ®
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Resin-Contact-Time Method for Determination of Protein-Bound Calcium in Milk and Model Systems1

H. O. Jaynes2 and R. McL. Whitney

Department of Food Science, University of Illinois, Urbana 61801

ABSTRACT

A theory for exchange of calcium between milk or model milk-protein system and an appropriately buffered weak cation-exchange resin was developed which could be used for determination of protein-bound or colloidal calcium. With suitable preconditioning of the resin, the resin-contact-time method yielded results for ionic and protein-bound calcium in a model ß-casein system which not only conformed to the proposed theory but also agreed with those by the murexide method of Sundararajan and Whitney. ß-Casein dispersions (3%) in calcium-potassium chloride solutions at pH 7.0, 172 .14, and 2°C bound calcium as if there were 11.20 binding sites per molecule, each with an intrinsic association constant of 76.62 liters per mole. Data from skim milk samples at 23°C and 2°C by the resin-contact-time method also were consistent with the proposed theory and yielded protein-bound or colloidal calcium in reasonable agreement with reported results.

FOOTNOTES

1 Taken in part from the thesis of H.O. Jaynes presented to the University of Illinois in partial fulfillment of the requirements for the degree of Doctor of Philosophy. This study was a part of Project No. 50—0343 of the Agricultural Experiment Station, College of Agriculture, University of Illinois at Urbana-Champaign and was supported in part by Public Health Service Training Grant No. 5TO1FD0O004 from the National Center for Urban and Industrial Health.

2 Department of Food Technology and Food Science, University of Tennessee, Knoxville TN 37901.






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Copyright © 1982 by the American Dairy Science Association ®.