Two-dimensional gel electrophoresis of proteins and peptides in bovine milk

Proteins and peptides in bovine milk and colostrum were separated by two-dimensional gel electrophoresis (2-DE). The proteins were separated in the first dimension by isoelectric focusing in the pH ranges 4-7 and 6-11, and in the second dimension by sodium dodecyl sulphate polyacrylamide gel electrophoresis on 12.5% T homogeneous gels. The peptides were separated in the pH range 3-10 in the first dimension, while 15% T homogeneous gels were used in the second dimension. 2-DE evaluation of samples with various somatic cell counts showed an increased number of peptides with increased cell count. 2-DE analysis of samples heated at 65 and 85 °C for 30 min showed a decrease in the number of proteins and peptides with increased temperature. Colostrum exhibited a peptide pattern in which the intensity and number of spots decreased with time postpartum. These results show that 2-DE is a useful tool to detect variations of proteins and peptides in milk.