17B-13 |
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A. C. TEZCUCANO-MOLINA, I. Alli, S. Kermasha, and S. Karboune. Dept. of Food Science & Agricultural Chemistry, McGill Univeristy, Macdonald Campus, 21,111 Lakeshore Road, Ste-Anne de Bellevue, QC H9X 3V9, Canada Whole casein fractions account for more than 80% of the total protein of cow's milk. Phosphorylation occurs in the b-, as1- and as2-casein fractions. The phosphate groups play an important role in the stability of the milk micelle. However, phosphate groups can influence the bioavailability of divalent metal ions (Zn+2, Mg+2 and Fe+2) by binding to these ions. In addition, the phosphate groups of caseins have been reported to induce immunoglobulin E (IgE) response in humans. Functional properties of caseins can also be influenced by the presence of phosphate groups. The objectives of this work were to study the enzymatic dephosphorylation of bovine casein and to characterize the dephosphorylated casein fractions. Bovine casein was precipitated at pH 4.3 from reconstituted, commercial skim milk powder. Potato acid phosphatase (EC 3.1.3.2) was used to dephosphorylate the casein at pH 5.8 and 37 °C. Protein determination was performed. The phosphorus was measured colorimetrically as molybdenum blue. The dephosphorylated casein was freeze-dried and subjected to SDS- and urea-PAGE. The inorganic phosphate content of the precipitated casein was 0.81%. More than 70% of this phosphate was removed by the enzymatic dephosphorylation. SDS-PAGE demonstrated that both the a- and b-casein fractions were dephosphorylated. Urea-PAGE suggested that dephosphorylation of a-casein was accompanied by protein hydrolysis. The apparent Km and Vmax values for the enzymatic dephosphorylation were 9.95 mg/ml and 0.283 mmol P/mg enzyme min, respectively. Enzymatic dephosphorylation of a- and b-casein has been shown to affect the molecular structure of the proteins. Further work will be undertaken to investigate the effects of dephosphorylation on the biological and functional properties of the caseins.
Session 17B, Dairy Foods: General
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