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Li C.,Northeast Agricultural University | Liu L.,Northeast Agricultural University | Xie H.,Northeast Agricultural University | Liu N.,Northeast Agricultural University | Liu N.,National Dairy Engineering and Technical Research Center
International Journal of Dairy Technology

The aim of this work was to measure N-acetylneuraminic acid (Neu5Ac) in milk-based infant formulas. The analysis was performed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The total Neu5Ac were released using trichloroacetic acid and hydrochloric acid and purified using a HLB column. The linearity from 0.05 to 5.0 μg/mg Neu5Ac was adequate. Sialic acid recoveries ranged from 91.8% to 112.4%. The detection and quantification limits (limit of detection, 0.01 μg Neu5Ac/mg; limit of quantitation, 1.08 μg Neu5Ac/mg) were low enough to determine the sialic acid in infant formulas. The validated method is highly reproducible and sensitive, and it is easy to perform. © 2015 Society of Dairy Technology. Source

Wang Y.,Northeast Agricultural University | Guo W.,Northeast Agricultural University | Chi T.,National Dairy Engineering and Technical Research Center | Cheng T.,Northeast Agricultural University | Cheng T.,National Dairy Engineering and Technical Research Center
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering

In recent years, yogurt products are usually developed and designed by using different raw materials and food additives, less by innovations of production processes. For the development of new technology for producing yogurt, considering the technical feasibility of nanofiltration concentration's application in yogurt production process, the paper put forward an idea for developing new yogurt products by improving the workmanship. In this study, the raw milk was concentrated by nanofiltration membrane when producing yogurt with transmembrane pressure of 1.0, 1.6, 2.0, 2.4 MPa and the milk temperature of 10, 15, 55, 65℃, respectively, in order to investigate the change of milk composition during concentration and its influence on yogurt texture and rheological parameters, as while as the influence of raw milk on nanofiltration membrane performance at different temperatures and pressures. The results indicate that, under the conditions of 65℃ and 2.0 MPa, the concentration was feasible and it can be applied in yogurt production when the membrane flux is 7.5 L/(m2·h) and concentration time is about 85 min. The retention rates of monovalent ions of sodium, potassium, chlorine are 40.8%, 46.5% and 17.8%, respectively, while the divalent ions of calcium and magnesium are 94.2%, 95.7%, respectively, and the other milk contents, the lactose and protein, are 92.4% and 95.7%, respectively. The non-fat dry matter increases by 1.24 times, the fat increases by 1.3 times and the milk acidity increases by 1 degree. The viscosity of yogurt producing through concentration is 27.8 Pa·s, and which of yogurt without concentration is 16 Pa·s. With the texture profile analysis (TPA) on yogurt texture, the hardness, adhesiveness, gumminess and chewiness of yogurt with concentration is 0.4605 N, -0.6492 N·s, 0.3253 N·s and 0.2987 N·s, respectively, while the indexes of yogurt without concentration is -0.1102 N, -0.4787 N·s, 0.0680 N·s and -0.0586 N·s, respectively. These texture and rheological parameters of the yogurt with concentration are all superior to those of the yogurt without concentration technology. Source

Lu Y.,Northeast Agricultural University | Lu Y.,National Dairy Engineering and Technical Research Center | Chen Y.,Chinese Academy of Inspection and Quarantine | Lu X.A.,Chinese Academy of Inspection and Quarantine | And 5 more authors.
Journal of Dairy Science

Cronobacter species represent an emerging opportunistic foodborne pathogen associated with meningitis and necrotizing enterocolitis in infants. Current evidence indicates that powdered infant formula (PIF) is the main source of Cronobacter contamination. A total of 75 strains of Cronobacter spp. from different geographic regions, as well as from PIF processing environments, were identified and typed with different methods, including biochemical profiling by the API 20E system (bioMérieux, Marcy l'Etoile, France), protein profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and genotypic profiling by ribotype. Analysis by MALDI-TOF MS and biochemical identification was more accurate compared with ribotype analysis. However, MALDI-TOF MS typing and ribotype analysis showed more discriminatory ability compared with biochemical phenotyping. In conclusion, MALDI-TOF MS is a rapid and reliable tool to identify Cronobacter spp. in PIF and has the potential to trace dissemination of Chronobacter along the production chain. © 2014 American Dairy Science Association. Source

Huang Y.,National Dairy Engineering and Technical Research Center | Huang Y.,Northeast Agricultural University | Ren H.,National Dairy Engineering and Technical Research Center | Ren H.,Northeast Agricultural University | And 6 more authors.
Chinese Journal of Chromatography (Se Pu)

The selective precipitation of whole casein from skimmed milk was achieved by the addition of calcium salt under acidic pH. The effects of pH, centrifugal force and final concentration of CaCl2 on the separation of casein were studied by measuring the purity of final products using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that casein with the highest purity could be obtained with the pH of 4. 3, the centrifugal force of 10 400 g and the final concentration of CaCl2 of 60 mmol/L. The casein was processed with DEAE anion exchange chromatography and three peaks were obtained. Then the third peak (peak II) was identified with Western-Blot method and matrix-assisted laser desorption/ ionization time of flight/time of flight mass spectrometry (MALDI-TOF/TOF MS). The identification of Western-Blot showed that peak III can combine with the specificity of human milk β-casein antibody, and it is proved to be human milk β-casein. The fingerprints of peak M were analyzed by Mascot searching, and the sequence coverage was 50%, further supporting it is human milk β-casein. In conclusion, an effective method to obtain human milk β-casein from milk samples through DEAE anion exchange chromatography was established, and it is suitable for the proteomics research requirements of the β-casein from human milk. Source

Li X.-Y.,National Dairy Engineering and Technical Research Center | Li X.-Y.,Northeast Agricultural University | Fang X.,Northeast Agricultural University | Ren H.-W.,National Dairy Engineering and Technical Research Center | And 5 more authors.
Fenxi Huaxue/ Chinese Journal of Analytical Chemistry

Human milk β-casein was digested in vitro by simulated neonatal digestive model to explore the peptidome of human β-casein digested in neonate by matrix-assisted laser desorption/ionization-time-of-flight tandem mass spectrometry (MALDI-TOF/TOF). The accelerating voltage was 20 kV. The laser wavelength was 337 nm and the frequency was 200 Hz. Ion extraction delay was 330 ns. Final mass spectra were produced by averaging 2000 laser shots taken at five different positions within each spot. The peptides scanning range is from m/z 500 to m/z 5000. A total of 26 peptides were identified in the molecular weight range of 1000-4000 Da, and no bioactive peptides were found. Instead, we found nine bioactive peptide precursors which include four ACE (Angiotensin converting enzyme) inhibitory peptide precursors, two CPP (Caseinophosphopeptide) precursors, two antioxidant peptide precursor and one immune active peptide precursor. Most of the bioactive peptide precursors might be further digested into biologically active peptides by proteases according to the present cleavage sites. Copyright © 2015, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Source

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