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He S.-H.,Harbin Institute of Technology | Ma Y.,Harbin Institute of Technology | Li Q.-M.,Harbin Institute of Technology | Li D.-H.,Northeast Forestry University | And 2 more authors.
International Journal of Dairy Technology | Year: 2013

The fatty acid profiles of Chinese Maiwa yak milk samples were evaluated at different seasons (n = 96) and parities (n = 32). Saturated fatty acid content and monounsaturated fatty acid content showed no significant difference (P > 0.05) between warm season and cold season; however, polyunsaturated fatty acid (PUFA) content in warm season was higher (P < 0.05) than in cold season. Monounsaturated fatty acid and PUFA contents were higher (P < 0.05) in multiparous Maiwa yak milk than in primiparous Maiwa yak milk. Trans-11C18:1, cis-9, cis-12C18:2, CLA and C18:3 contents were higher (P < 0.05) in multiparous Maiwa yak than in primiparous Maiwa yak milk. © 2012 Society of Dairy Technology.


Xu W.,Harbin Institute of Technology | He S.,Harbin Institute of Technology | Ma Y.,Harbin Institute of Technology | Zhang Y.,Harbin Institute of Technology | And 3 more authors.
International Journal of Dairy Technology | Year: 2015

Serum heat-induced protein aggregates at various pH levels were isolated from heated yak milk by size-exclusion fast protein liquid chromatography. Analysis by reversed-phase high-performance liquid chromatography showed that β-lactoglobulin and κ-casein were the two main proteins in these aggregates. The amount of serum heat-induced protein aggregates increased from pH 6.6 to 7.4, whereas the content of β-lactoglobulin in aggregates decreased from 61.9% at pH 6.6 to 50.4% at pH 7.2, and then increased to 51.3% at pH 7.4. The content of κ-casein, αs1-casein and β-casein increased from pH 6.6 to pH 7.4. These results show that serum heat-induced protein aggregates are pH dependent. © 2015 Society of Dairy Technology.


He S.-H.,Harbin Institute of Technology | Ma Y.,Harbin Institute of Technology | Wang J.-Q.,New Hope Dairy Holding Ltd Company | Li Q.-M.,New Hope Dairy Holding Ltd Company | And 2 more authors.
International Journal of Dairy Technology | Year: 2012

The lipoprotein lipase (LPL) was purified almost 3800-fold from yak skimmilk by Heparin-Sepharose CL-6B column chromatography; nonhydrophobic fraction of proteose-peptone (NHFPP) and hydrophobic fraction of proteose-peptone (HFPP) from yak milk whey were separated by Phenyl-Sepharose-6FF column chromatography. The HFPP was subjected to hydroxyapatite chromatography, and two fractions were collected: one fraction did not absorb onto the calcium phosphate matrix (HA1); the other fraction contained all the protein components of HFPP (HA2). The effects of the proteose-peptone fractions on lipoprotein lipase lipolysis were studied. The results of experiments showed that NHFPP and HA1 enhanced the LPL lipolysis; in contrast, the HFPP and HA2 inhibited LPL lipolysis. © 2011 Society of Dairy Technology.


He S.,Harbin Institute of Technology | Ma Y.,Harbin Institute of Technology | Wang J.,New Hope Dairy Holding Ltd Company | Li Q.,New Hope Dairy Holding Ltd Company | And 4 more authors.
Dairy Science and Technology | Year: 2010

The objective of this work was to characterize the fat globule and milk fat globule membrane (MFGM) proteins in Maiwa (n = 6), Gannan (n = 4) and Zhongdian yak whole milks (n = 4). Fat globule size distribution and specific fat surface area of whole yak milk were determined using a laser diffraction particle size analyzer. The average specific fat surface area of Gannan yak milk (2.05 m 2·mg-1) and Zhongdian yak milk (2.01 m 2·mg-1) was higher (P < 0.05) than that of Maiwa yak milk (1.92 m2·mg-1). The total protein content of MFGM and surface protein coverage of fat globule in Maiwa yak milk (11.12 mg·g-1 fat and 5.67 mg·m-2, respectively) and Gannan yak milk (12.24 mg·g-1 fat and 5.97 mg·m-2, respectively) were higher (P < 0.05) than that of Zhongdian yak milk (9.72 mg·g-1 fat and 4.81 mg·m -2, respectively). Protein components in the MFGM of yak milk were analyzed using an Ultrascan XL laser densitometer and an LKB 2400 GelScanXL software program. No major differences (P > 0.05%) in the protein patterns on the SDS gel were observed among the MFGM of Maiwa yak, Gannan yak and Zhongdian yak, with the exception of mucin 1 and butyrophilin which were significantly lower (P < 0.05) in the MFGM of Zhongdian yak milk. © INRA, EDP Sciences, 2010.


Li Q.,Harbin Institute of Technology | Ma Y.,Harbin Institute of Technology | He S.,Harbin Institute of Technology | Elfalleh W.,Harbin Institute of Technology | And 3 more authors.
International Dairy Journal | Year: 2014

Heat stability of yak milk protein reached a maximum at approximately pH 6.8 and was low at pH<6.4 and pH>7.0. At pH 6.4, the particle size of yak milk increased by approximately 20 and 25nm when heated at 140°C for 2min and 120°C for 10min, respectively. The particle size of heated yak milk decreased markedly with increasing pH. The content of κ-casein dissociated from the casein micelles increased from 5.7% to 9.5% at pH 6.4-76.3% and 81.5% at pH 7.2 when yak milk was heated at 140°C for 2min and 120°C for 10min, respectively. The proteins αS1-casein and β-casein showed a much lesser extent of dissociation from the micelles than did κ-casein. The levels of α-lactalbumin and β-lactoglobulin in ultracentrifugal supernatants increased from pH 6.4 to pH 7.2 and decreased above pH 7.2. © 2013 .

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