Abstract: The activities of four enzyme (γ-glutamyl transpeptidase, γ-GT; alkaline phosphatase, AKP; peroxidase, LP; amylase, AMY) in Henan dairy goat milk (a local variety of dairy goat in the west part of Henan province) was measured and the milk protein composition was determined by SDS-PAGE in this study. The results showed that the activities of r-GT, AKP, LP and AMY in colostrum and common milk of Henan dairy goat were 322.46 U/100 mL and 247.71 U/100 mL, 248.62 U/100 mL and 200.14 U/100 mL, 281.76 U/mL and 205.07 U/mL, and 71.20 U/100 mL and 22.15 U/100 mL, respectively. The activity of AKP was significantly higher in colostrums milk compared to common milk (0.01 < P < 0.05), and the activities of γ- GT, LP, and AMY presented a highly significant increase (P < 0.01). The major proteins in Henan dairy goat milk were showed in the SDS-PAGE from top to bottom as follows: α-La, β-LG, IgG-L (light chain), CN, IgG-H (heavy chain) and SA, of which the contents were 4.52%, 18.78%, 7.52%, 11.29%, 6.95% and 5.48% in colostrums milk and 4.51%, 9.59%, 3.95%, 11.49%, 4.07% and 5.39% in common milk, respectively. Therefore, β-LG was the most predominant protein in Henan dairy goat milk, of which the content could reach up to 20.96%, whereas the content of α-La was the lowest among the identified protein constituents. Moreover, IgG (IgG-L, IgG-H) and β-LG were significantly more abundant in colostrum than in common goat milk (P < 0.01 or 0.01 < P < 0.05), and the content of β-LG was extremely significantly higher in colostrum compared with common milk (P < 0.01). The lactglobulin and immune globulin in goat milk presented a pronounced upward trend with increasing number of secretion days, but no significant changes in other proteins were observed. Furthermore, the contents of the major milk proteins differed among individual goats.

Key words: dairy goat, milk, enzyme, protein composition