Browsing by Author "Ma, Ying"

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    In vitro bioaccessibility and physicochemical properties of phytosterol linoleic ester synthesized from soybean sterol and linoleic acid.
    (Published by Elsevier for Journal of the Swiss Society of Food Science and Technology, 2018-06) Yang, Fuming; Oyeyinka, Samson; Xu, Weili; Ma, Ying; Zhou, Shaobo
    Phytosterols are bioactive components capable of reducing cholesterol level in serum and reducing risk of arteriosclerosis. In this study, conditions for the synthesis of maximum yield of phytosterol linoleic ester (PLE) was optimized and the physicochemical properties and in vitro bioaccessibility of the PLE were assessed. Under the optimized condition of 1:1.1 mol ratio of phytosterol and linoleoyl chloride at 80 °C for 1.5 h, the conversion rate of phytosterol reached 96.1%. Its solubility in oil increased 20 times, up to 33.8%. Also, peroxide value of PLE was much lower than linoleic acid (32.9 and 47.0 mmol/kg), which means better oxidative stability. Bioaccessibility of PLE was affected by time, concentration of bile extract, and dissolved medium. It was 4.93% alone, increased by 2.5 times compare to phytosterol; or 53.46% in oil, under the condition of 40 mg/mL bile extract for 120 min. In conclusion, under the tested condition, phytosterol conversion rate, its solubility in oil and bioaccessibility were improved significantly. The method showed great potential in manufacture high quality and quantity of PLE.
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    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, He
    A 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.
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    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, S
    At 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.
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    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, Shenghua
    At 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.