HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Marier, J. R. Articles by Rose, D. Search for Related Content PubMed Articles by Marier, J. R. Articles by Rose, D.

Incomplete Release of Citrate During Acid Precipitation of Casein

Division of Applied Biology, National Research Council, Ottawa, Canada

ABSTRACT

In previous publications (2, 4) it was shown that less citric acid was found in acid sera than in skimmilk, and that this was probably caused by a loss of citrate adsorbed on the precipitated casein, and not attributable to an artificially high result with skimmilk. However, the similar citrate content of HCl and TCA acid filtrates (2) indicated a similar degree of citrate adsorption, despite the radically different surface charges of the two caseins (pH 4.5 and <1.0, respectively). This suggested that (i) citrate was bound externally at specific sites, or that (ii) the adsorption was not a peripheral surface phenomenon. The general nature of the adsorption was therefore studied by comparing the effect of trichloroacetic acid (12% final concentration) on removal of citrate adsorbed by a suspended casein, and by solubilized casein subjected to reprecipitation.

In the study with suspended casein, Van Slyke and Baker (6) casein was freed of other milk components by seven washings in 0.1 M acetate buffer at pH 4.5 (4) and 3.0-g. portions were then suspended in 100 ml. of solution containing: (a) citrate at pH 4.5, (b) citrate + TCA at pH <1.0, (c) citrate + phosphate + lactate + calcium + TCA at pH <1.0, and (d) same as (c), but at pH 4.5.