Calcium-induced precipitation of αs1-casein: effect of inclusion of citrate or phosphate

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Abstract
SUMMARY: The calcium-induced aggregation of αs1-casein at pH 7·0 has been studied in the presence of citrate and phosphate anions. The effects of the citrate can be reconciled with the suggestion that the citrate, acting as a Ca chelator, reduces the Ca available for the aggregation reaction, but in no other way interferes with the mechanism of that process. In the presence of phosphate, precipitation is induced below the normal critical Ca concentration. This reaction proceeds to completion at low and high concentrations of phosphate. There is, however, an intermediate range of phosphate concentrations, whose limits depend on the protein concentration, where a colloidally stable precipitate is produced. The significance of these observations is discussed in terms of the currently held theories of micellar structure and formation.