Browsing by Author "Cui, Jie"
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Item Thermal Properties of Yak α-Lactalbumin and β-Lactoglobulin: a DSC Study(Springer, 2017-09-18) Wang, Lifeng; Ma, Ying; Cui, Jie; Oyeyinka, Samson; He, S; Li, HeA differential scanning calorimetry (DSC) method was used to investigate the denaturation temperature of yak α-lactalbumin (α-La), β-lactoglobulin (β-Lg), and a mixture of two proteins and the thermal properties of α-La and β-Lg in the presence of glucose, lactose, sucrose, NaCl, CaCl2, and at various pH (4.0–10.0). The denaturation temperature (T d) of α-La increased from 52.1 °C in the absence of β-Lg to 53.9 °C in the presence of β-Lg, while the T d of β-Lg decreased from 81.4 °C in the absence of α-La to 79.9 °C in the presence of α-La. α-La was thermal stable in the range of pH 4.0–10.0, while β-Lg was more thermal stable in acidic pH than in alkaline pH. Sugars, Na+, and Ca2+ influenced the stabilization of the two proteins against thermal denaturation with greatly influenced for β-Lg. α-La kept reversibility in the presence of sugars, NaCl, CaCl2, and over a wide pH range (4.0–10.0), with most of the reversibility values being greater than 90%. In contrast, β-Lg was completely irreversible whether in its native state or in the presence of the additives.Item Yak milk whey protein denaturation and casein micelle disaggregation/aggregation at different pH and temperature(Elsevier, 2017-04-04) Wang, Lifeng; Ma, Ying; Cui, Jie; Oyeyinka, Samson; Cheng, Jinju; He, ShenghuaAt the natural pH of yak milk (pH 6.6), a low level (<30%) of k-casein (k-CN) was found in the serum phase after heating at 95 oC for 30 min, indicating that as much as 70% of the b-lactoglobulin (b-Lg) and k-CN complexes is associated with the micelle colloidal particles. The b-Lg and k-CN levels increased from 13.2% and 2.6% at pH 6.0 to 35.2% and 60.1% at pH 7.0, respectively, when yak milk was heated at 95 oC for 30 min. At pH 6.0-6.4, the denatured whey proteins were associated with the caseins in the colloidal phase, resulting in milk gelation upon heating. The distribution of b-Lg and k-CN complexes increased in the serum phase, demonstrated by the increasing levels of both b-Lg and k-CN with increasing pH; at high pH (6.6-7.0), large proportions of b-Lg and a-lactalbumin were lost, presumably forming complexes in the colloidal phase.Item Yak milk whey protein denaturation and casein micelle disaggregation/aggregation at different pH and temperature(Springer for International Dairy Journal, 2017-03-22) Wang, Lifeng; Ma, Ying; Cui, Jie; Oyeyinka, Samson; Cheng, J; He, SAt the natural pH of yak milk (pH 6.6), a low level (<30%) of κ-casein (κ-CN) was found in the serum phase after heating at 95 °C for 30 min, indicating that as much as 70% of the β-lactoglobulin (β-Lg) and κ-CN complexes is associated with the micelle colloidal particles. The β-Lg and κ-CN levels increased from 13.2% and 2.6% at pH 6.0 to 35.2% and 60.1% at pH 7.0, respectively, when yak milk was heated at 95 °C for 30 min. At pH 6.0–6.4, the denatured whey proteins were associated with the caseins in the colloidal phase, resulting in milk gelation upon heating. The distribution of β-Lg and κ-CN complexes increased in the serum phase, demonstrated by the increasing levels of both β-Lg and κ-CN with increasing pH; at high pH (6.6–7.0), large proportions of β-Lg and α-lactalbumin were lost, presumably forming complexes in the colloidal phase.