Differently sized native milk fat globules separated by microfiltration: fatty acid composition of the milk fat globule membrane and triglyceride core

The aim of this study was to characterize the fatty acid composition of the core and membrane of differently sized milk fat globules separated by microfiltration, which can now be used to manufacture dairy products. Native milk fat globules of various mean diameters, ranging from d₄₃ = 2.3 µm to 8.0 µm, were obtained using microfiltration of raw whole milk. After milk fat globule washing, the milk fat globule membrane (MFGM) and the triglyceride core (TC) were separated by manual churning. After total lipid extraction from each fraction, their fatty acid composition was characterized using methyl ester analysis by gas chromatography. Regardless of season, no significant differences were observed in the fatty acid composition of the MFGM phospholipids. Conversely, significant differences were found in the fatty acid composition of TC; particularly, small fat globule TC contained more medium‐chain fatty acids and less stearic acid than large fat globule TC. These results show that the previously observed differences in total fatty acid composition among differently sized milk fat globules are due to their triglyceride composition and MFGM amount rather than to the composition of the MFGM.     

Effect of DAG on milk fat TAG crystallization

The effect of milk fat and standard DAG on the crystallization behavior of milk fat TAG (MF-TAG) was investigated. When milk fat DAG were added to MF-TAG at the 0.1 wt% level, crystallization was delayed. Racemic purity was shown to be an important factor in the ability of DAG to influence TAG crystallization. Only sn-1,2 isomers of blends of MF-TAG with 0.1 wt% of the racemic mixtures of dipalmitin and diolein increased the activation free energy barrier to MF-TAG nucleation (ΔG _c ) and delayed the subsequent crystallization process by increasing the crystallization induction time (τ_SFC) determined from solid fat content-time measurements. Although crystallization kinetics were affected, the properties of the resulting network structures remained unchanged upon addition of milk fat minor components at the 0.1 wt% level     

4—（2—吡啶偶氮）间苯二酚分光光度法测定奶粉中微量锌的含量的研究

研究了在溴化十六烷基三甲基铵（ＣＴＭＡＢ）存在下，４－（２－吡啶偶氮）间苯二酚（ＰＡＲ）与Ｚｎ（Ⅱ）显色反应的适宜条件，结果表明，在ｐＨ值为８．０～１０．５的范围内，锌与ＰＡＲ形成稳定的１：２的橙红色络合物，其最大吸收波长为５０５ｎｍ试剂的最大吸收波长为４２５ｎｍ配合物的摩尔吸光系数在５０５ｎｍ，处为８６２×１０＾４ｌ．ｍｏｌ＾－１．ｃｍ＾－１。Ｚｎ（Ⅱ）浓度在０～２５μｇ／２５ｍｌ范围内符合比耳     

Characterization of the TAG of peanut oil by electrospray LC-MS-MS

A study of processed peanut oil was undertaken to assess the utility of HPLC combined with tandem MS to obtain data easily regarding the number of TAG of fats and oils and their FA composition. Mass chromatograms and spectra corresponding to only TAG of a single M.W. were obtained for the full range of TAG in the sample. Analysis of the mass spectra allowed the identification of more than 160 TAG in the sample by their FA composition. In addition, it was possible to estimate relative abundances of the TAG and suggest the position of the FA on glycerol for a limited number of cases. This technique greatly simplifies the task of assigning FA to coeluting TAG and facilitates identification of TAG present in trace quantities in mixtures, with possible application in circumstances where such trace TAG could be significant markers. Results are quickly obtained without extensive sample preparation or prefractionation of the sample.     

β-乳球蛋白IgG抗原决定簇的识别

以β-乳球蛋白氨基酸序列为模板,错位合成β-乳球蛋白多肽,以收集到的牛乳过敏患者血清为抗体,鉴定β-乳球蛋白IgG抗原决定簇,探讨牛乳过敏机理．结果表明,β-乳球蛋白IgG抗原决定簇有2条,它们在β-乳球蛋白中的氨基酸序列定位分别为aa22—36和aa127—141．结果表明通过特异性水解抗原决定簇实现牛奶脱敏的方法是可行的．     

蜂胶对牛乳保鲜作用的研究

以蜂胶对牛乳的保鲜作用为基础,探讨了蜂胶的添加方式和浓度对牛乳的酸度和细菌总数的作用效果．将0．2％的蜂胶添加到经巴氏灭菌（65℃,30min）后的牛乳中,牛乳酸度变化最慢,在保质期内可控制到17．5。T,细菌总数可以控制在8．5×10^8个cfu／mL．该研究为蜂胶保鲜剂在牛乳中的应用提供了理论参考．     

米曲霉在牛乳中最适生长条件的研究

利用米曲霉对牛乳进行发酵,通过单因子及正交试验以菌丝体干重为指标对其在牛乳中的生长进行了研究．结果表明：接种量为4％,装液量为30mL,摇床转速为180r／min时菌丝体干重可达到最大．此外测得最大菌丝体干重时的蛋白质分解率可达35．6％．     

固相萃取与高效液相色谱联用快速测定鲜奶中的三聚氰胺

采用固相萃取—高效液相色谱法测定鲜奶样品中的三聚氰胺。固相萃取柱为Strata-X-C,液相色谱柱Thermo BDS HYPERSIL C8（4.6 mm×250 mm,5μm）;流动相为乙腈：0.01 mol/L辛烷磺酸钠—柠檬酸缓冲溶液（10：90,V：V）,检测波长为238 nm。三聚氰胺峰的保留时间为8.25 min。三聚氰胺在1.0-50μg/mL范围内具有良好的线性关系（R=0.997）,在添加量为30,60,90 mg/kg时,三聚氰胺标准加入回收率为90.40%-91.10%,RSD为1.14%-1.88%。方法检出限为0.1 mg/kg。     

生态葛根奶中铜、锌、铁、钙、镁含量测定

测定生态葛根奶中矿物质的含量,探讨其营养价值.硝酸-高氯酸消解样品,用火焰原子吸收光谱法测定生态葛根奶(饲喂葛根4周)及未饲喂葛根的对照组奶样中铜、锌、铁、钙、镁的含量,应用F检验、SNK法和LSD-t检验对结果进行统计分析.测定方法的精密度介于0.04％～0.7％,平均回收率介于93.70％～106.20％.试验组和对照组比较:铜的含量差异没有统计学意义(F=2.702,P＞0.05);锌的含量差异没有统计学意义(F=1.684,P＞0.05);钙的含量差异没有统计学意义(F=2.253,P＞0.05);铁的含量试验组(饲喂葛根1周、2周、3周)高于对照组且差异有统计学意义(F=9.369,P＜0.05);镁的含量试验组(饲喂葛根1周、2周、4周)高于对照组且差异有统计学意义(F=4.142,P＜0.05).生态葛根奶中铜、锌、钙含量与普通奶中含量无显著差异,铁、镁的含量较普通奶含量丰富.     

三聚氰胺分子印迹聚合物的合成与光谱学特性

采用非共价印迹法,以三聚氰胺为模板分子,甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,合成了三聚氰胺分子印迹聚合物．实验表明该印迹聚合物对甲醇溶液中三聚氰胺具有良好的选择性结合能力,对液态奶中的三聚氰胺的富集率可达98％以上．并结合紫外光谱及红外光谱对分子印迹聚合物的合成及结合机理进行了初步解析．