Abstract

The nutrient composition, enzyme activities, the profile of free amino acids (FAAs) and protein compositions in Tibetan sheep milk were assayed and compared with those in Chengdu Ma goat. The results showed that the total solids, milk fat andactivity of alkaline phosphatase (AKP) in Tibetan sheep milk were significantly higher than that in Chengdu Ma goat. Conversely, the activities of γ-glutamyltransferase (γ-GT) and lactoperoxidase (LP) were significantly lower than that in Chengdu Ma goat. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the concentration of casein (CN) in Tibetan sheep milk (accounting for more than 50% of total milk protein) was significantly lower than that in Chengdu Ma goat, but the concentration of β-lactoglobulin (β-Lg) and serum albumin (SA) were significantly higher than that in Chengdu Ma goat. Seventeen different FAAs were identified from the Tibetan sheep milk by reversed phase high performance liquid chromatography (RP-HPLC). Arg was the most abundant FAA (192.15 ± 119.78 mg/L), while Ala was the poorest one (4.34 ± 1.12 mg/L). Interestingly, the concentrations of the following amino acids: Asp, Gly, Lys, Glu, Thr, Ala and Val in Tibetan sheep milk were significantly lower than those of Chengdu Ma goat. On the contrary, the Met concentration of Tibetan sheep was significantly higher than that of Chengdu Ma goat. The distinct nutritional characteristics of Tibetan sheep milk indicated their adaption to the harsh environment in Tibetan area.

Key words: Tibetan sheep, milk composition, free amino acids (FAAs).

Abbreviation

 FAAs, Free amino acids; AKP, alkaline phosphatase; γ-GT, γ-glutamyltransferase; LP, lactoperoxidase; AMY, amylase; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; RP-HPLC, reversed phase high performance liquid chromatography; CN, casein; β-Lg, β-lactoglobulin; SA, serum albumin; α-La, α-lactalbumin.