Study on Nutrition, Flavor Characteristics and Antioxidant Activity of Yak Milk Dregs at Different Elevations in Tibet

The physical, nutritional, flavor and antioxidant characteristics of yak milk dregs (N_A, N_B, and N_C) obtained from three different elevations (2500~2800 m; 3500~4000 m; above 4300 m) in Tibet were analyzed in this study. The results showed that the elevation had obvious effects on the physical, nutritional, flavor characteristics and antioxidant activity of yak milk dregs. Among the three yak milk dregs, N_C had the highest contents of proteins (71.00 g/100 g), vitamin A (3.52 μg/100 g), vitamin E (0.33 mg/100 g), vitamin D₃ (0.66 μg/100 g), iron element (55.51 g/kg), total amino acid (79.32 g/100 g) and essential amino acid (36.40 g/100 g). The extreme temperature of N_B (129.68 ℃) was significantly lower than those of N_A and N_C; its tan δ was higher than those of N_A and N_C, which indicated that N_B had the strongest liquidity. The volatile components of yak milk residue were mainly aldehydes (V_min > 30%). The main volatile component of both N_A and N_B was nonanal, which gave the scent of rose flowers of milk dregs; while the main volatile component of milk dregs N_C was hexanal, which led to the scent of grass of milk dregs. Other ingredients in Yak milk dregs include acids, olefins, alcohols, etc. Yak milk dregs had good antioxidant activity. Among the three yak milk dregs, N_C had the strongest DPPH free radical scavenging ability, and N_A had the strongest peroxide scavenging ability.