Natural variation of bovine milk fat globule size within a herd

Native milk fat globule (MFG) size, pH, total fat, protein, and lactose composition in milk from individual cows was examined in autumn and spring 2012 and autumn 2013. Mean MFG diameters ranged between 2.5 and 5.7 µm. Some cows were observed to consistently produce small or large MFG throughout the sampling period, though trends were not consistent across all cows. Small-MFG milk contained more total polar lipids; however, the relative proportion of individual polar lipids did not differ with MFG size, with the exception of phosphatidylcholine, which was greater in small-MFG milk. No significant correlation between MFG size and proximate composition, including calculated fat yield or pH, was found. This work revealed a natural cow-to-cow variation in MFG size exists, which could potentially be exploited to improve the functionality of milk for manufacturing and some products.     

Bacterial Community of Koumiss from Mongolia Investigated by Culture and Culture-Independent Methods

The bacterial community of fermented horse milk (koumiss) from Mongolia was studied using three methods: cultivation, direct identification by 16S rRNA clone library and denaturing gradient gel electrophoresis (DGGE). Ninety-eight strains were isolated by traditional cultivation and 61 of those were randomly selected for further identification by 16S rRNA gene sequencing. The strains were dominated by lactic acid bacteria (LAB; six different lactobacilli), Acinetobacter, Bacillus and Psychrobacter. Construction of the clone library analysis revealed that 16S sequences of 220 clones, genus Lactobacillus was dominant, but Streptococcus thermophilus, Acetobacter pasteurianus and uncultured clones were also detected. Ten unique bands were sequenced from the DGGE and revealed: Lactococcus lactis, Lactococcus lactis subsp. lactis, Clostridium acidurici, Acinetobacter johnsonii, Dickeya sp., Enterobacter sp., Pseudomonas sp., Raoultella sp., and Ruminococcus sp.. In vitro growth inhibition of three human pathogens, Escherichia coli, Enterobacter sakazakii and Staphylococcus aureus by 14 culturable bacteria displayed that only three of the isolates tested inhibit growth of E. sakazakii while most of the other bacteria delayed growth of the target bacteria.     

高效液相色谱法测定母乳及牛乳中总核苷酸含量

建立高效液相色谱测定母乳和牛乳中总核苷酸含量和组成的分析方法。总核苷酸包括游离核苷酸、游离核苷、核苷聚合物及加合物等不同来源的可利用核苷总量。利用酶解法释放出母乳中的核苷,以硼化聚丙烯酰胺凝胶（Affi-Gel 601）作为固相萃取介质进行样品净化,用反相高效液相色谱仪检测,内标法定量,检测结果以核苷酸计。且针对母乳样品的特性,增加高温灭活步骤进行样品前处理,以检测母乳中核苷酸的天然含量及组成。对所建方法进行全面验证,结果表明其具有良好的线性,相关系数（r2）均在0.999以上;母乳中各核苷酸的检出限和定量限分别在0.18～0.45 mg/L和0.60～1.51 mg/L之间;母乳基质中3 种不同加标水平下总核苷酸的回收率均在99%～108%之间,连续3 d 6 次检测结果的相对标准偏差在0.8%～7.8%之间,显示了良好的准确性及精密度。然后进一步利用所建检测方法,评估母乳及5 种市面常见的牛乳中的核苷酸总量及组成用以验证该方法的适用性。该方法的灵敏度、准确性及精密度均可满足对母乳和牛乳样品中天然的核苷酸含量及组成的测定要求。本研究为今后大样本量调查母乳及牛乳样品中核苷酸的含量和组成提供了更加科学准确的方法。     

大豆蛋白用作啤酒泡沫稳定剂的研究

本研究以脱脂大豆蛋白粉为原料,碱溶酸沉法制备大豆分离蛋白(SPI)和大豆乳清蛋白(WSP),根据大豆分离蛋白酶解过程中溶解性及泡沫稳定性的变化情况,确定大豆分离蛋白的酶解程度。再通过对酶解大豆分离蛋白(ESPI)及大豆乳清蛋白(WSP)的性能实验及应用实验进一步考察大豆蛋白用作啤酒泡沫稳定剂的可行性。结果表明,酶解30min后,ESPI溶解性和泡沫稳定性均有所增强;ESPI和WSP不仅能改善低度熟啤酒的泡持性,而且可以明显改善纯生啤酒货架期内的泡持性;大豆蛋白的添加不会影响啤酒的非生物稳定性。     

Modeling extended lactations of Holsteins

Modeling extended lactations for the US Holsteins is useful because a majority (>55%) of the cows in the present population produce lactations longer than 305 d. In this study, 9 empirical and mechanistic models were compared for their suitability for modeling 305-d and 999-d lactations of US Holsteins. A pooled data set of 4,266,597 test-day yields from 427,657 (305-d complete) lactation records from the AIPL-USDA database was used for model fitting. The empirical models included Wood (WD), Wilmink (WIL), Rook (RK), monophasic (MONO), diphasic (DIPH), and lactation persistency (LPM) functions; Dijkstra (DJ), Pollott (POL), and new-multiphasic (MULT) models comprised the mechanistic counterparts. Each model was separately tested on 305-d (>280 days in milk) and 999-d (>800 days in milk) lactations for cows in first parity and those in third and greater parities. All models were found to produce a significant fit for all 4 scenarios (2 parity groups and 2 lactation lengths). However, the resulting parameter estimates for the 4 scenarios were different. All models except MONO, DIPH, and LPM yielded residuals with absolute values smaller than 2 kg for the entire period of the 305-d lactations. For the extended lactations, the prediction errors were larger. However, the RK, DJ, POL, and MULT models were able to predict daily yield within a ± 3 kg range for the entire 999-d period. The POL and MULT models (having 6 and 12 parameters, respectively) produced the lowest mean square error and Bayesian information criteria values, although the differences from the other models were small. Conversely, POL and MULT were often associated with poor convergence and highly correlated, unreliable, or biologically atypical parameter estimates. Considering the computational problems of large mechanistic models and the relative predictive ability of the other models, smaller models such as RK, DJ, and WD were recommended as sufficient for modeling extended lactations unless mechanistic details on the extended curves are needed. The recommended models were also satisfactory in describing fat and protein yields of 305-d and 999-d lactations of all parities.     

饲喂大豆类代乳料对犊牛生长发育和日粮养分消化率的影响

研究饲喂含常规大豆蛋白代乳料对犊牛生长增重、小肠发育和日粮养分消化率的影响.结果表明:A、B组日粮的养分表观消化率和氮沉积率明显低于C组,其中粗蛋白质表观消化率和氮沉积率差异显著(P＜0.05);A、B组犊牛小肠发育不良,小肠绒毛高度差异极显著(P＜0.01),平均日增重仅为C组的48.28%和70.96%,说明去皮豆粕和全脂大豆不宜作为36日龄前的犊牛代乳料的蛋白质来源.     

三种不同酵母对啤酒发酵及风味的影响

本实验采用Y1110、安琪、模式三种不同的啤酒酵母,在同种工艺条件下测定发酵过程中α-氨基氮(α-AN)、pH、双乙酰、高级醇等指标,并比较三种不同啤酒的风味物质含量。结果表明:Y1110增殖最快,α-AN和pH值下降最快,双乙酰还原较快,后酵结束双乙酰含量最低,啤酒样品含醇量较高,适于醇厚型啤酒酿造;安琪酵母增殖最慢,α-AN和pH值下降最慢,啤酒样品含酯量较高,适于淡爽型啤酒酿造;模式酵母酯类与醇类含量都很高,不适于实际生产。     

高效液相色谱测定广西生鲜乳中的维生素A

为了建立生鲜乳中维生素A的一种快速、准确、灵敏度高的检测方法,样品经皂化后,经石油醚提取,浓缩后采用高效液相色谱法,以Shim-pack VP-ODS柱(4.6 mm×150 mm,5μm),柱温35℃,检测波长325 nm,流动相为甲醇∶水(98∶2,体积比),流速1.0 mL/min的条件进行实验。结果维生素A在0.174～87.2μg/mL范围内线性关系良好,相关系数r=0.9999,平均回收率为98.17%,RSD=1.90%。建立的方法准确、可靠,可以用于生鲜乳中维生素A的含量检测。     

啤酒中挥发性含硫化合物的检测方法及在啤酒硫化味品尝的相关性研究

在国内首次建立啤酒中挥发性含硫化合物的HS—SPME—GC—FPD色谱检测方法,该方法可同时检测啤酒中8种挥发性含硫化合物,方法重复性、回收率满足痕量检测要求。根据检测结果,结合啤酒感官品尝,找出了检测和品尝量级的对应关系,确定了影响啤酒硫化味的含硫化合物主要是甲硫醇、乙硫醇、二甲基二硫及二甲基三硫,为提高啤酒风味纯净性提供了有益的指导。