Contents Of The Bioactive Minor Proteins In Yak Milk And The Thermaldynamic Properties Of Lactoperoxidase

Yak milk is characterized as naturally concentrated milk for its richness nutrients such as proteins, fat and lactose, etc. The compositions and contents of minor proteins in the milk are affected by genetic and other internal factors. This paper focuses on the contents of several bioactive minor proteins and the thermodynamic properties of lactoperoxidase in Maiwa yak milk. It will benefit to the understanding the characteristics of minor proteins and the future research and utilization of yak milk.The contents of minor proteins original from 46 Maiwa Yak milk, like lactoferrin (Lf), immunoglobulins (IgG, IgM, IgA), transforming growth factor beta-2 (TGF-β2) and insulin-like growth factor-I (IGF-I), were analyzed using ELISA methods. The average content of lactoferrin was 3.53±2.74μg/mL which was lower than that reported of cow, goat and porcine milk. IgG was the main component of immunoglobulins, and it had an average content of 0.201±0.012 mg/mL which was similar to that of cow milk. However, the average contents of IgM and IgA were 56.87±40.03 and 12.57±2.98 ng/mL, respectively which were far lower than that of cow milk and other varieties milks. TGF-β2 was rich in Maiwa yak milk, with the average content of 76.41±43.66 ng/mL, which was much higher than that of human and cow milk.Based on the correlation analysis, the positive correlations were found between the content of TGF-β2 and the contents of IgM and IgA, as well as Lf and IgG, and IgM and IgA.The paper also studied the properties of enzymatic system of lactoperoxidase in Maiwa yak milk. The average content of SCN– was 1.72±0.79μg/mL, and the content of OSCN- was 2.54±1.21μg/mL; The activity of LPO was much higher than that of goat, sheep and cow milk, with the average content of 2.95±1.24 U/mL. The results demonstrated that lactoperoxidase was more thermal stable at 63℃, but the denaturation process was accelerated with the increase of heating temperature. Thermaldynamic analysis showed that D-Values for denaturation of lactoperoxidase was 207.43 (63℃), 33.41 (65℃) and 13.42 min (67℃), respectively. The corresponding Z-value and Ea-value were 3.36℃and 557.20 kJ/mol, respectively.Therefore, except Lf and Igs, higher content of TGF-β2 was detected in Maiwa yak milk. The Yak lactoperoxidase had higher thermal stability at 63℃.