A canonical discriminant analysis to study the association between milk fatty acids of ruminal origin and milk fat depression in dairy cows

Although milk fat depression (MFD) has been observed and described since the beginning of the last century, all the molecular and biochemical mechanisms involved are still not completely understood. Some fatty acids (FA) originating during rumen biohydrogenation have been proposed as causative elements of MFD. However, contradictory results were obtained when studying the effect of single FA on MFD. An alternative could be the simultaneous evaluation of the effect of many FA using a multivariate approach. The aim of this study was to evaluate the relationship between individual milk FA of ruminal origin and MFD using canonical discriminant analysis, a multivariate technique able to distinguish 2 or more groups on the basis of a pool of variables. In a commercial dairy herd, a diet containing 26% starch on a DM basis induced an unintentional MFD syndrome in 14 cows out of 40. Milk yielded by these 14 animals showed a fat content lower than 50% of the ordinary value, whereas milk production and protein content were normal. The remaining 26 cows secreted typical milk fat content and therefore were considered the control group, even though they ate the same diet. The stepwise discriminant analysis selected 14 milk FA of ruminal origin most able to distinguish the 2 groups. This restricted pool of FA was used, as variables, in a run of the canonical discriminant analysis that was able to significantly discriminate between the 2 groups. Out of the 14 FA, 5 conjugated linoleic acid isomers (C18:2 trans-10,trans-12, C18:2 trans-8,trans-10, C18:2 trans-11,cis-13, C18:2 cis-9,cis-11, C18:2 cis-10,cis-12) and C15:0 iso were more related to the control group, whereas C18:2 trans-10,cis-12, C16:1 trans-6–7, C16:1 trans-9, C18:1 trans-6–8, C18:1 trans-9, C18:1 trans-10, C18:1 cis-11, and C18:3n-3 were positively associated with the MFD group, allowing a complete discrimination. On the basis of these results, we can conclude that (1) the shift of ruminal biohydrogenation from C18:1 trans-11 to C18:1 trans-10 seemed to be strongly associated with MFD; (2) at the same time, other C18:1 trans isomers showed a similar association; (3) on the contrary, conjugated linoleic acid isomers other than C18:2 trans-10,cis-12 seemed to be associated with a normal fat secretion. Results confirmed that MFD is the consequence of a combined effect of the outflow of many ruminal FA, which collectively affect mammary fat synthesis. Because the animals of the 2 groups were fed the same diet, these results suggested that factors other than diet are involved in the MFD syndrome. Feeding behavior (i.e., ability to select dietary ingredients in a total mixed ration), rumen environment and the composition of ruminal bacteria are additional factors able to modify the products of rumen biohydrogenation. Results of the present work confirmed that the multivariate approach can be a useful tool to evaluate a metabolic pathway that involves several parameters, providing interesting suggestions about the role of some FA involved in MFD. However, results about the MFD syndrome obtained in the present research require a deep molecular investigation to be confirmed.     

气相色谱法测定婴幼儿配方奶粉和母乳中的碘

目的建立气相色谱法测定婴幼儿配方奶粉和母乳中碘的方法。方法在GB 5413.23-2010食品安全国家标准《婴幼儿食品和乳品中碘的测定》的基础上,对碘的气相色谱(gas chromatography,GC)检测方法进行改进,应用改进后的方法对62种婴幼儿配方奶粉和124份母乳样品进行检测。结果碘在1.00~2000.00μg/L范围内线性关系良好,线性相关系数(r~2)为0.9999;检出限、定量限分别为0.30、1.00μg/L;利用不同品牌婴幼儿配方奶粉中碘检测结果的相对标准偏差(relative standard deviation,RSD)考察方法精密度,相对标准偏差值在1.39%~1.61%之间;在5、25、100μg/100 g的加标浓度下,回收率在97.46%~98.98%之间,对应的RSD值在2.52%~2.73%之间。婴幼儿配方奶粉中的碘含量在33.14~132.94μg/100 g之间,母乳样品中的碘含量在31.25~1690.00μg/L之间。结论本方法减少了样品和试剂的使用量,节约了实验成本,简化了实验步骤,提高了检测效率,对于碘的准确测定、保障婴幼儿的健康成长具有重要意义。     

固相萃取净化-气相色谱法检测人乳中 持久性有机氯农药

目的 建立母乳中有机氯农药六六六和滴滴涕的检测方法, 并对北京、兰州和杭州三个地区的蓄积水平现状进行分析。方法 母乳样品用乙腈提取, 经过酸化的硅胶固相萃取柱净化, 浓缩后, 采用气相色谱仪检测。结果 8种农药的线性范围在5~200 ng/mL, 相关系数0.9955~0.9994, 定量限均小于2.6 μg/kg, 平均回收率在70%~122%, 相对标准偏差在3.91%~10.77%。结论 本方法结合磺化法和固相萃取法, 能有效去除基质中的杂质。通过方法学验证证明, 本方法操作简单、精确、快速, 适用于母乳中有机氯的检测。随着六六六、滴滴涕等持久性有机氯农药的禁用或严格限用, 母乳中持久性有机氯农药的蓄积水平明显降低。     

石家庄地区牛乳脂肪中脂肪酸成分的分析

选取石家庄地区的牛乳样品，采用OP乳化剂提取出样品中的脂肪，对其进行甲酯化，用填充柱气相色谱法测定了其中的脂肪酸成分；采用面积归一法确定了主要的脂肪酸组成为月桂酸1．415％，豆蔻酸6．735％．十五烷酸0.646％，棕榈酸27．71％，棕榈油酸0．874％，十七烷酸0.46％，硬脂酸17．91％，油酸34．29％．亚油酸4．608％．亚麻酸1．013％，花生酸0．102％(均为质量分数)。     

气相色谱结合化学计量在核桃油、菜籽油掺伪混合物含量判别分析中的应用

目的：识别核桃油中同时掺入多种其他植物油的多元掺伪。方法：采用气相色谱技术分析核桃油、菜籽油掺伪混合物中脂肪酸含量,结合化学计量方法对气相色谱数据进行建模,并对不同比例核桃油、菜籽油混合物进行判别分析。结果：主成分分析法（PCA）能快速鉴别出纯核桃油和掺伪核桃油,并在一定程度上反映样本的掺伪比例;Bayes判别分析将83.33%的样品归入正确的分类;偏最小二乘判别分析法（PLS-DA）的判别准确率达87.50%;基于BP神经网络模型的判别分析,其训练集的正确率为84.21%,测试集的正确率为80.00%;基于遗传算法优化支持向量机（SVM-ga）的判别分析,其训练集和测试集的正确率均为100%。结论：多种分析模型均能不同程度地识别核桃油、菜籽油掺伪比例,其中SVM-ga模型的预测精度最佳。     

LDA优化电子鼻传感器阵列的研究

利用PEN3电子鼻系统对6个糖酸比不同的乳饮料样品进行检测,采用线性判别分析(LDA)对传感器响应值进行分析,确定优化传感器阵列方法,并将各优化结果进行对比,最终确定阵列优化结果,使电子鼻可以用更少的传感器达到更好的分类效果,为电子鼻传感器阵列优化提供了新的思路和方法。     

人乳脂中甘油三酯分析方法及组成的研究进展

人乳脂对于婴儿的生长发育有举足轻重的作用。人乳脂是甘油三酯组成最复杂的脂类,详细分析人乳脂中甘油三酯的组成是油脂领域的一大难题。介绍了人乳脂中甘油三酯的分析方法,并比较了国内外人乳脂中甘油三酯的组成。总结了泌乳时期、母亲饮食等因素对人乳脂中甘油三酯组成的影响。对于了解人乳脂的生理功能和人乳替代脂的开发具有重要意义。     

Comparison of gas chromatographic methods for analysis of butyric acid in milk fat and fats containing milk fat

 The analysis of butyric acid (C4) is of importance for the determination of the proportion of milk fat in mixed fats. Three gas chromatographic methods were compared with regard to their precision for the measurement of C4, i.e. analysis of butyric acid methyl ester after trans-esterification of fat by sodium methylate (method A) or trimethyl sulphonium hydroxide (method B), as well as analysis of free butyric acid (method C), using an internal standard with each method. The examination of 30 milk fats which varied greatly in terms of their C4 content, using methods A, B and C, resulted in mean values of C4 of 3.42 g/100 g fat, 3.71 g/100 g fat and 3.06 g/100 g fat, respectively. The value determined using method B seemed too high, and this may have been due to the presence of co-eluting artefacts, whereas the value determined using method C was clearly too low, and can probably be attributed to losses during sample preparation. The standard deviation (SD) of 0.015 obtained from repeated analyses using method A was quite good. Results obtained using methods B and C had SDs of 0.029 and 0.074, respectively. Different levels of free fatty acids did not affect the results obtained using method A. When method A was checked by analysis of the reference fat, CRM 164, the C4 level determined was found to deviate from the certified C4 content of 3.49 (± 0.06) g/100 g fat by only 0.05 g C4/fat 100 g. Thus method A proved the most suitable for the determination of the proportion of milk fat in mixed fats by analysis of butyric acid. Received: 1 October 1997     

Comparison of gas chromatographic methods for analysis of butyric acid in milk fat and fats containing milk fat

 The analysis of butyric acid (C4) is of importance for the determination of the proportion of milk fat in mixed fats. Three gas chromatographic methods were compared with regard to their precision for the measurement of C4, i.e. analysis of butyric acid methyl ester after trans-esterification of fat by sodium methylate (method A) or trimethyl sulphonium hydroxide (method B), as well as analysis of free butyric acid (method C), using an internal standard with each method. The examination of 30 milk fats which varied greatly in terms of their C4 content, using methods A, B and C, resulted in mean values of C4 of 3.42 g/100 g fat, 3.71 g/100 g fat and 3.06 g/100 g fat, respectively. The value determined using method B seemed too high, and this may have been due to the presence of co-eluting artefacts, whereas the value determined using method C was clearly too low, and can probably be attributed to losses during sample preparation. The standard deviation (SD) of 0.015 obtained from repeated analyses using method A was quite good. Results obtained using methods B and C had SDs of 0.029 and 0.074, respectively. Different levels of free fatty acids did not affect the results obtained using method A. When method A was checked by analysis of the reference fat, CRM 164, the C4 level determined was found to deviate from the certified C4 content of 3.49 (± 0.06) g/100 g fat by only 0.05 g C4/fat 100 g. Thus method A proved the most suitable for the determination of the proportion of milk fat in mixed fats by analysis of butyric acid. Received: 1 October 1997     

气相色谱法测定婴幼儿乳粉中肌醇含量的不确定度评定

目的分析气相色谱法测定婴幼儿乳粉中肌醇含量的不确定度。方法通过分析与量化气相色谱法测定肌醇含量的实验过程,对标准物质、样品处理过程、测量重复性及分析仪器4个方面进行不确定度分析,建立不确定度的数学模型,计算合成不确定度,得到扩展不确定度和置信水平。结果气相色谱法测定婴幼儿乳粉中肌醇含量的合成不确定度为0.94 mg/100 g,扩展不确定度为1.88 mg/100 g,乳粉中肌醇含量的测定结果为(65.5±1.88)mg/100 g。结论本方法适用于婴幼儿乳粉中肌醇的不确定度分析,通过揭示实际检测过程中不确定度的来源,有效把握实验过程的质量控制,提高检测结果的可靠性,增强测量结果之间的可比性。     

气相色谱法测定牛奶中c9,t11-共轭亚油酸的含量

为建立简单高效的分析方法测定牛奶中c9,t11-共轭亚油酸的含量,应用GC-FID法,采用CP-Sil88(60m×0.25mmi.d×0.20μm)气相色谱柱,以程序升温方法,应用带校正因子的面积归一法进行定量分析。结果表明,c9,t11-共轭亚油酸得到很好的分离,平均回收率为97.7%,RSD为1.08%。     

Validation of a rapid milk fat separation method to determine the fatty acid profile by gas chromatography

An improved rapid method for separating lipids from milk to determine the fatty acid composition using 2 centrifugations at room temperature (20°C) was compared with the ISO-IDF reference procedure based on solvent extraction. The new method is useful for research and routine quality control and has a number of advantages over the reference procedure—mainly no solvents are required and it saves time. Applicability of the rapid separation method was confirmed in fats with different physical characteristics from ewe and goat milk samples. Minor differences were found in the proportions of some fatty acids in the reference and centrifugation methods. Milk fat separated by centrifugation at room temperature did not differ in fatty acid composition from milk centrifuged at 4°C.     

Transfer of dietary zinc and fat to milk--evaluation of milk fat quality, milk fat precursors, and mastitis indicators

The present study demonstrated that the zinc concentration in bovine milk and blood plasma is significantly affected by the intake of saturated fat supplements. Sixteen Holstein cows were used in a 4 × 4 Latin square design with 4 periods of 12 d, and 4 dietary treatments were conducted. A total mixed ration based on corn silage, grass-clover silages, and pelleted sugar beet pulp was used on all treatments. A high de novo milk fat diet was formulated by adding rapeseed meal and molasses in the total mixed ration [39 mg of Zn/kg of dry matter (DM)], and a low de novo diet by adding saturated fat, fat-rich rapeseed cake, and corn (34 mg of Zn/kg of DM). Dietary Zn levels were increased by addition of ZnO to 83 and 80 mg of Zn/kg of DM. Treatments did not affect daily DM intake, or yield of energy-corrected milk, milk fat, or milk protein. The high de novo diet significantly increased milk fat percentage and milk content of fatty acids with chain length from C6 to C16, and decreased content of C18 and C18:1. Treatments did not influence milk free fatty acids at 4°C at 0 or 28 h after milking. The average diameter of milk fat globules was significantly greater in milk from cows offered low de novo diets. Furthermore, the low de novo diet significantly increased the concentration of nonesterified fatty acids and d-β-hydroxybutyrate in blood plasma, the latter was also increased in milk. Treatments did not affect the enzyme activity of lactate dehydrogenase and N-acetyl-β-d-glucosaminidase in milk or the activity of isocitrate dehydrogenase and malate dehydrogenase in blood plasma. The low de novo diet significantly increased plasma Zn and milk Zn content, whereas dietary Zn level did not in itself influence these parameters. This indicates that the transfer of fat from diet to milk might facilitate transfer of Zn from diet to milk.     

牛奶中三种糖醇类甜味剂的气相色谱测定及前处理方法研究

利用冷冻干燥处理与毛细管气相色谱外标法测定牛奶中的糖醇类甜味剂。牛奶用乙酸锌和氢氧化钡除去蛋白质后,经冷冻干燥,样品中的糖醇与吡啶-乙酸酐（1∶1,v/v）于90℃反应30min,生成的糖醇乙酰酯衍生物经HP-5毛细管柱色谱分离,氢火焰离子化检测器检测。结果表明:与旋转蒸发相比,冷冻干燥处理样品的回收率更高。在优化的色谱条件下,本方法在10⁹0μg/m L范围内线性关系良好（r=0.9974⁰.9999）,重复性好（RSD=1.37%².04%）,平均加标回收率在91.17%⁹2.06%之间。该方法简单、快速、灵敏,适用于牛奶中糖醇类甜味剂含量的测定。      

Principal component and multivariate analysis of milk long-chain fatty acid composition during diet-induced milk fat depression

The objective of this study was to assess the relationship between individual milk fatty acids (FA) and diet-induced milk fat depression (MFD) using principal component analysis (PCA) and multivariate analysis (MA). Cow treatment observations (n = 63) from 3 published feeding experiments with lactating dairy cows were used in the analyses. In the PCA, principal component loading plots 1 (PC1) and 2 (PC2) described 55.9% of the total variation in milk FA and fat concentrations. Saturated FA (14:0, 16:0, and 17:0) and milk fat percentage showed negative loading for PC1. Trans-18:1 isomers (trans-6+7+8 to trans-15), trans-7, cis-9 conjugated linoleic acid (CLA), and trans-10, cis-12 CLA showed positive (opposite) loading, suggesting a negative relationship between these isomers and milk fat percentage. Cis-11, trans-13 CLA and cis-9, trans-11 CLA were associated with the PC2 axes (neutral), indicating that they were not associated with MFD. Multivariate analysis with milk fat percentage as the dependent variable and individual PC1 positive loading variables showed a breakpoint relationship for trans-6+7+8-, trans-9-, trans-10-, and trans-13+14-18:1 and a linear relationship for trans-11-, trans-12-, trans-15-18:1, trans-10, cis-12 CLA, and trans-7, cis-9 CLA. Subsequent MA was conducted on 41 treatment means from 12 independent experiments from the literature, in which concentrations of trans-6+7+8-, trans-9-, trans-10-, and trans-11-18:1, and cis-9 trans;-11, and trans-10, cis-12 CLA were reported. Significant negative effects of trans-9-18:1, trans-10-18:1, and trans-10, cis-12 CLA on milk fat percentage were observed. In this study, the PCA and MA showed that among trans-18:1 isomers, trans-10-18:1 was the most negatively correlated to milk fat percentage. However, the threshold concentration related to maximum MFD indicated that the relative potency was greatest for trans-6+7+8- and lowest for trans-10-18:1. These results suggested that trans-6+7+8-18:1 might be more important than trans-10-18:1 in MFD. Principal component analysis also showed that trans-10, cis-12 and trans-7, cis-9 CLA were the isomers most negatively correlated to milk fat percentage, implying a possible role of trans-7, cis-9 CLA in MFD. Additional experiments are needed to establish whether trans-7-18:1 is involved in MFD or that its effects are mediated via the endogenously synthesized trans-7, cis-9 CLA.     

Short communication: Regulation of milk fat yield and fatty acid composition by insulin

Diet-induced milk fat depression in dairy cows has been known for many years and several theories have been proposed. One that continues to receive support is the glucogenic-insulin theory. Previous studies testing this theory using a hyperinsulinemic-euglycemic clamp have had variable results attributable to variability in the use of body fat reserves as a source of milk fatty acids. Our objective was to test the glucogenic-insulin theory using cows immediately postpartum, a period when the use of body fat for milk fat synthesis is greatest. During wk 2 postpartum, 5 cows were given a 2-d baseline period and then clamped for 4 d. Insulin was increased more than 2-fold during the clamp while the blood glucose concentration was maintained. Milk yield was not altered by administration of the clamp (38.7 vs. 39.0 ± 1.4 kg/d); however, the milk fat percentage and yield were reduced by 27% and plasma nonesterified fatty acids were reduced by 68%. Analysis of the milk fatty acid composition revealed that the decrease in milk fat yield during use of the clamp was almost exclusively due to reductions in preformed fatty acids; this is the exact opposite of what is observed with diet-induced milk fat depression. Therefore, our results do not support the glucogenic-insulin theory of diet-induced milk fat depression. The results further indicated that reductions in milk fat observed previously with hyperinsulinemic-euglycemic clamps or with glucose or propionate infusions were most likely consequences of the ability of insulin to inhibit lipolysis, thereby limiting the mammary availability of preformed fatty acids mobilized from body reserves.     

羊乳脂肪中脂肪酸成分的气相色谱分析

选取广州花都地区的羊乳样品,采用OP乳化剂提取出样品中的脂肪,对其进行甲醋化,用填充柱气相色谱法测定了其中的脂肪酸成分;采用面积归-法确定了主要的脂肪酸组成为乙酸9.48%,丁酸2.08%,已酸1.67%,辛酸3.62%,癸酸4.26%,月桂酸2.34%,豆蔻酸7.42%,十五烷酸0.65%,棕榈酸22.32%,棕榈油酸0.87%,硬脂酸10.04%,油酸23.78%,亚油酸6.54%,亚麻酸2.53%,其他脂肪酸2.30%（均为质量分数）,饱和脂肪酸和不饱和脂肪酸之比为1.39：1.     

气相色谱法快速测定食品中的过氧化苯甲酰

目的建立毛细管柱气相色谱法检测食品中过氧化苯甲酰的分析方法。方法考察不同提取时间和不同提取方法对过氧化苯甲酰测定的影响。试样在酸性石油醚中还原成苯甲酸,经DB-1701毛细管气相色谱柱分离,用气相色谱仪氢火焰离子化检测器检测,外标法定量。结果过氧化苯甲酰在质量浓度0~20μg/m L范围内,峰面积与其浓度线性范围良好,相关系数为0.9994,方法检出限为3 mg/kg。在0.5、1、1.5、2和3 g/kg5个添加水平下,平均加标回收率为94.0%~104.0%,相对标准偏差为2.38%~6.20%(n=5)。结论与国标方法相比,本法不仅缩短了检测时间,而且提高了检测灵敏度,可适用于食品中过氧化苯甲酰的检测。     

高效液相色谱法测定乳制品中三聚氰胺含量

采用高效液相色谱仪,通过对样品前处理进行优化,测定乳制品中的三聚氰胺含量,方法检出限为0.05mg/kg,相对标准偏差RSD为1.406%,添加标准回收率为100%～104%。