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Wang X.Y.,Key Laboratory of Functional Dairy | Guo H.Y.,Key Laboratory of Functional Dairy | Zhang W.,China Agricultural University | Wen P.C.,Gansu Agricultural University | And 3 more authors.
Journal of Dairy Science | Year: 2013

We studied the effect of iron saturation level on the osteogenic activity of lactoferrin (LF) in vitro and in vivo. Different iron saturation levels of LF (1.0, 9.0, 38, 58, and 96%) were prepared as the following samples: apo-LF, LF-9, LF-38, LF-58, and holo-LF. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, we observed that the stimulating osteoblast proliferation activity of LF in vitro decreased with increasing iron saturation level at 100 and 1,000. μg/mL. In vivo, 4-wk-old ICR Swiss male mice were randomly divided into 4 groups: blank control (physiological saline), negative control (BSA), apo-LF, and holo-LF. Four groups of mice were injected subcutaneously with physiological saline, BSA, apo-LF, or holo-LF over the calvarial surface twice a day for 5 consecutive days at a dose of 4. mg/kg per day. Bone histomorphometry showed that new bone formation (assessed using tetracycline-HCl labels) tended to be stronger with apo-LF than with holo-LF. Using fluorescence spectroscopy and circular dichroism measurements, we found that exposure of tryptophan increased, α-helix content increased, but β-structure content decreased with increasing iron saturation level. These findings indicated that the osteogenic activity of LF decreases with increasing iron saturation level in vitro and in vivo, which may be related to conformational changes in LF. © 2013 American Dairy Science Association. Source

Luo J.,China Agricultural University | Guo H.Y.,Beijing Key Laboratory of Nutrition | Ren F.Z.,China Agricultural University
Journal of Dairy Science | Year: 2013

A soft, pasty, high-moisture surface defect occurs with progressive brining of Mozzarella cheese. Addition of calcium is traditionally used to prevent this defect but the underlying mechanism is not clear. Mozzarella cheese was formed into a cylinder inside brine on its plane surface to ensure semi-infinite, unidirectional mass transfer and placed into brine containing 0, 0.1, or 0.25% (wt/wt) calcium chloride. To monitor the effect on cheese composition of calcium in brine, we measured calcium and water contents of the cheese during brining. The extent of calcium loss from the cheese decreased significantly with the addition of calcium. Addition of calcium to a final concentration of 0.25% decreased the loss of calcium from 94.13 to 18.22% from the outside region of the cheese after 30. d, and the water content of the cheese was decreased from 67.8 to 48.8%. To further elucidate the effect of calcium in brine, the Boltzmann method was used to determine the effective diffusion coefficient value, and low-field nuclear magnetic resonance was used to measure the cheese transversal relaxation time. The migration of calcium interfered with salt diffusion. At the end of brining, the amount of water bound to the protein of the cheese significantly increased. Addition of calcium to a final concentration of 0.25% diminished the proportion of bound water by 20.96%. In conclusion, addition of calcium hinders the diffusion of sodium and modifies the distribution of water in Mozzarella cheese during brining. © 2013 American Dairy Science Association. Source

Cui N.,Gansu Agricultural University | Wen P.C.,Gansu Agricultural University | Liang Q.,Gansu Agricultural University | Liu H.N.,Northwest University for Nationalities | And 6 more authors.
Journal of Animal Physiology and Animal Nutrition | Year: 2015

The objective of this study was to assess the changes in the chemical composition of yak colostrum and transient milk. Samples were collected from 12 yaks on days 1, 2, 3, 4, 5, 6 and 7 post-partum (PP). The gross composition, nitrogen fraction distribution, amino acid (AA) profile and fatty acid (FA) profile were analysed. All the components decreased rapidly during the first 3 days except lactose which increased. The ratio of whey protein to casein protein decreased from 46:54 to 17:83 during the first 7 days PP. The content of all the AAs decreased, while the percentages of eight essential AAs in protein of samples increased during the study period. Monounsaturated FAs and polyunsaturated FAs decreased in the first 7 days PP, whereas saturated FAs increased. In conclusion, the changes in chemical composition were remarkable during the first 3 days. The slight variations, happened during the transient period, are not negligible, which also should be taken into account in the development of yak colostrum supplements. © 2015 Blackwell Verlag GmbH. Source

Tian M.,China Agricultural University | Fang B.,Academy of State Administration of Grain | Jiang L.,China Agricultural University | Guo H.,Beijing Key Laboratory of Nutrition | Ren F.,China Agricultural University
Dairy Science and Technology | Year: 2015

Antioxidative peptides derived from food proteins have been screened and characterized in in vitro assays, and several quantitative structure–activity relationship (QSAR) models have been established to understand the structure–activity relationship of the selected antioxidant peptides. However, a systematic evaluation of each fragment that could be produced by a certain protein is still lacking. In this study, all the tripeptides that could possibly derive from bovine beta-lactoglobulin based on its amino acid sequence have been synthesized, and their antioxidant activities were measured using a ferric-reducing antioxidant power assay. Three of the peptides (i.e., LTC, CQC, and GTW) exhibited higher activities than that of glutathione. A QSAR model was also computed using multiple linear regression with divided physicochemical property scores descriptors, and the validity of the model was confirmed by cross-validation and Y-scrambling. The result of the QSAR modeling indicated that the electronic and hydrogen-bonding properties of the amino acids in the tripeptide sequences, as well as the steric properties of the amino acid residues at the C- and N-termini, played an important role in the antioxidant activities of the tripeptides. The antioxidant activities of the tripeptides were generally higher with Cys and Trp amino acid residues in the sequence. The structural characteristics we found may contribute to the further research of antioxidative mechanism. © 2015, INRA and Springer-Verlag France. Source

Liu H.N.,Gansu Agricultural University | Zhang C.,Gansu Agricultural University | Zhang H.,China Agricultural University | Guo H.Y.,China Agricultural University | And 4 more authors.
Journal of Dairy Science | Year: 2013

Qula is made from yak milk after defatting, acidifying, and drying. Yak milk caseins are purified from Qula by dissolving in alkali solution. The effects of different pH treatments on the functional and structural properties of yak milk caseins were investigated. Over a broad range of pH (from 6.0 to 12.0), functional properties of yak milk caseins, including solubility, emulsifying activities, and thermal characteristics, and the structural properties, including 1-anilino-8-naphthalene-sulfonate fluorescence, turbidity and particle diameter, were evaluated. The results showed that the yak milk casein yield increased as the pH increased from 6.0 to 12.0. The solubility dramatically increased as the pH increased from 6.0 to 8.0, and decreased as the pH increased from 9.0 to 12.0. The changes in emulsifying activity were not significant. Caseins were remarkably heat stable at pH 9.0. The turbidity of the casein solution decreased rapidly as the pH increased from 6.0 to 12.0, and the results suggested that reassembled casein micelles were more compact at low pH than high pH. At pH values higher than 8.0, the yield of yak milk caseins reached more than 80%. The highest solubility was at pH 8.0, the best emulsification was at pH 10.0 and the greatest thermal stability was at pH 9.0. According to the functional characteristics of yak milk caseins, alkali conditions (pH 8.0-10.0) should be selected for optimum production. These results suggested that pH-dependent treatment could be used to modify the properties of yak milk caseins by appropriate selection of the pH level. © 2013 American Dairy Science Association. Source

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