杜马斯燃烧法测定牛奶中的蛋白质含量

目的通过对杜马斯燃烧法和凯氏定氮法测定牛奶中的蛋白质含量的比较,建立杜马斯燃烧法测定牛奶中蛋白质的方法。方法杜马斯燃烧法检测条件:称样量100 mg,通氧量80 m L/min,通氧时间80 s;结果选用合适的燃烧条件用杜马斯燃烧法可以准确测定牛奶中的蛋白质含量。结论此方法具有结果准确、精密度高、易于操作的优点,适用于大批量牛奶样品的检测。     

Comparison of analytical methods and the influence of milk components on milk urea nitrogen recovery

The objectives of this study were to compare analytical instruments used in independent laboratories to measure milk urea nitrogen (MUN) and determine whether any components in milk affect the recovery of MUN. Milk samples were collected from 100 Holstein cows fed one ration in a commercial dairy herd with a rolling herd average of 9500 kg. Half of each sample was spiked with 4 mg/dL of urea N, while the other half was not, to determine recovery. Both milk samples (spiked and not spiked) were sent to 14 independent laboratories involved in the MUN Quality Control Program through National Dairy Herd Improvement Association and analyzed for MUN, fat, protein, lactose, somatic cell count (SCC), and total solids. The laboratories analyzed MUN using CL-10 (n = 3), Skalar (n = 2), Bentley (n = 3), Foss 4000 (n = 3) or Foss 6000 (n = 3) systems. When recovery of MUN was evaluated among the 5 analytical methods, the mean recoveries for the Bentley, Foss 6000, and Skalar systems were 92.1 (SE = 2.76%), 95.4 (SE = 10.1%), and 95.1% (SE = 7.61%), respectively, and did not differ from each other. However, MUN recovery was 85.0% (SE = 2.8%) for the CL-10 system and 47.1% (SE = 9.9%) for the Foss 4000 system, both of which differed from the other 3 systems. Recoveries from Foss 4000, Foss 6000, and Skalar varied among laboratories using the same instrument. As initial MUN concentration increased, recovery decreased using the Bentley and CL-10 systems. Increasing milk fat resulted in a decrease in recovery using the Foss 6000 system. For 4 of the 5 methods, recovery of MUN was not associated with specific milk components. Recovery of MUN was inconsistent for laboratories using the Foss 4000 and the Foss 6000 method and using these systems may result in an overestimation or underestimation of MUN.     

乳品中蛋白质检测方法的研究进展

对乳品中蛋白质质量分数的各种检测方法进行了评述。蛋白质的质量分数是评价乳品质量的重要指标。近年来,围绕着乳品蛋白质的食品安全事件接连发生,对人们的生命和健康造成了极大的危害。目前,传统的评价乳品蛋白质的检测方法均存在着一定的缺陷,并给不法分子带来可乘之机,而现代的仪器分析方法尚不成熟。因此,开发出更加合理的蛋白质测定方法成为研究的焦点课题。     

Comparison and characterisation of fat and protein composition for camel milk from eight Jordanian locations

Camel milk was collected from eight locations in Jordan followed by studying molecular characteristics and fatty acids contents. Lactoferrin content ranged between non-detectable amount (Al Hamra and Al Jweideh) and 0.43% of total protein (Al Hazeem). Serum albumin ranged between non-detectable amount (Al Hazeem) and 0.34% of total protein (Wadi Araba). Lactophorin variants A and B were in non-detectable amount in milk collected from Al Khalidyah and Al Hazeem, whereas the highest content of lactophorin was in milk collected from Al Qatrana. Saturated fatty acids content ranged between 50.15% (Al Umari) and 64.12% (Al Qatrana) of total fatty acids. Unsaturated fatty acids content ranged between 35.89% (Al Qatrana) and 49.85% (Al Umari) of total fatty acids. unsaturated fatty acids (C 18:1–C 18:3) varied significantly and ranged between 17.13% (Al Qatrana) and 38.85% (Al Umari) of total fatty acids.     

山羊奶与牛奶和人奶营养成分的比较

对山羊奶、牛奶和人奶中蛋白质、脂肪、维生素、矿物质等主要营养成分进行了比较,分析了3种奶中主要营养成分的差别。通过比较发现,山羊奶在总体营养成分方面优于牛奶,更接近人奶。但山羊奶存在铁、叶酸和维生素B12含量较低以及羊奶膻味的问题,应在营养上对这方面加以重视。     

Heritabilities of measured and mid-infrared predicted milk fat globule size,milk fat and protein percentages,and their genetic correlations

The objective of this study was to estimate the heritability of milk fat globule (MFG) size and mid-infrared (MIR) predicted MFG size in Holstein cattle. The genetic correlations between measured and predicted MFG size with milk fat and protein percentage were also investigated. Average MFG size was measured in 1,583 milk samples taken from 254 Holstein cows from 29 herds across Canada. Size was expressed as volume moment mean (D[4,3]) and surface moment mean (D[3,2]). Analyzed milk samples also had average MFG size predicted from their MIR spectral records. Fat and protein percentages were obtained for all test-day milk samples in the cow's lactation. Univariate and bivariate repeatability animal models were used to estimate heritability and genetic correlations. Moderate heritabilities of 0.364 and 0.466 were found for D[4,3] and D[3,2], respectively, and a strong genetic correlation was found between the 2 traits (0.98). The heritabilities for the MIR-predicted MFG size were lower than those estimated for the measured MFG size at 0.300 for predicted D[4,3] and 0.239 for predicted D[3,2]. The genetic correlation between measured and predicted D[4,3] was 0.685; the correlation was slightly higher between measured and predicted D[3,2] at 0.764, likely due to the better prediction accuracy of D[3,2]. Milk fat percentage had moderate genetic correlations with both D[4,3] and D[3,2] (0.538 and 0.681, respectively). The genetic correlation between predicted MFG size and fat percentage was much stronger (greater than 0.97 for both predicted D[4,3] and D[3,2]). The stronger correlation suggests a limitation for the use of the predicted values of MFG size as indicator traits for true average MFG size in milk in selection programs. Larger samples sizes are required to provide better evidence of the estimated genetic parameters. A genetic component appears to exist for the average MFG size in bovine milk, and the variation could be exploited in selection programs.     

Annual rhythms of milk and milk fat and protein production in dairy cattle in the United States

An annual pattern of milk composition has been well recognized in dairy cattle, with the highest milk fat and protein concentration observed during the winter and lowest occurring in the summer; however, rhythms of milk yield and composition have not been well quantified. Cosinor rhythmometry is commonly used to model repeating daily and annual rhythms and allows determination of the amplitude (peak to mean), acrophase (time at peak), and period (time between peaks) of the rhythm. The objective of this study was to use cosinor rhythmometry to characterize the annual rhythms of milk yield and milk fat and protein concentration and yield using both national milk market and cow-level data. First, 10 yr of monthly average milk butterfat and protein concentration for each Federal Milk Marketing Order were obtained from the US Department of Agriculture Agricultural Marketing Service database. Fat and protein concentration fit a cosine function with a 12-mo period in all milk markets. We noted an interaction between milk marketing order and milk fat and protein concentration. The acrophase (time at peak) of the fat concentration rhythm ranged from December 4 to January 19 in all regions, whereas the rhythm of protein concentration peaked between December 27 and January 6. The amplitude (peak to mean) of the annual rhythm ranged from 0.07 to 0.14 percentage points for milk fat and from 0.08 to 0.12 percentage points for milk protein. The amplitude of the milk fat rhythm generally was lower in southern markets and higher in northern markets. Second, the annual rhythm of milk yield and milk fat and protein yield and concentration were analyzed in monthly test day data from 1,684 cows from 11 tiestall herds in Pennsylvania. Fat and protein concentration fit an annual rhythm in all herds, whereas milk and milk fat and protein yield only fit rhythms in 8 of the 11 herds. On average, milk yield peaked in April, fat and protein yield peaked in February, fat concentration peaked in January, and protein concentration peaked in December. Amplitudes of milk, fat, and protein yield averaged 0.82 kg, 55.3 g, and 30.4 g, respectively. Milk fat and protein concentration had average amplitudes of 0.12 and 0.07, respectively, similar to the results of the milk market data. Generally, milk yield and milk components fit annual rhythm regardless of parity or diacylglycerol O-acyltransferase 1 (DGAT1) K232A polymorphism, with only cows of the low-frequency AA genotype (5.2% of total cows) failing to fit rhythm of milk yield. In conclusion, the yearly rhythms of milk yield and fat and protein concentration and yield consistently occur regardless of region, herd, parity, or DGAT1 genotype and supports generation by a conserved endogenous annual rhythm.     

Effects of calcareous marine algae on milk production,feed intake,energy balance,mineral status,and inflammatory markers in transition dairy cows

The objective of this experiment was to compare the effects of calcareous marine algae (CMA; Acid Buf, Celtic Sea Minerals) with a limestone-based control on feed intake, milk production, energy balance, serum mineral metabolites, and inflammatory markers in transition dairy cows. Twenty-two multiparous and 10 primiparous cows were assigned to 2 treatments from 25 d before expected parturition until 42 d postpartum. Cows were assigned to treatment according to a randomized complete block design based on parity, pre-experimental body condition score, previous 305-d milk yield, and either fat + protein yield (for multiparous cows) or predicted transmitting ability for milk yield and fat + protein yield (for primiparous cows). Cows were fed a negative dietary cation-anion difference [?50 mEq/kg] total mixed ration (TMR) based on corn silage, grass silage, and straw during the prepartum period and a 50:50 forage:concentrate TMR based on grass silage, corn silage, and concentrate during the postpartum period. The 2 dietary treatments consisted of a control (CON), which contained limestone as the primary calcium source, and CMA, in which limestone was replaced by CMA at 0.42% and 0.47% of dry matter for the pre- and postpartum periods, respectively. The dietary treatments were fed as 2 different concentrate pellets added to the TMR. Cows fed the CMA diet had higher dry matter intake in both the prepartum (+1.08 kg) and postpartum (+0.94 kg) periods compared with cows fed the CON diet. Fat yield (+0.11 kg), fat concentration (+0.43%), and 4% fat-corrected milk (+1.56 kg) were higher in cows fed CMA than in cows fed CON. The concentration of plasma serum amyloid A was reduced and that of serum P was increased on the CMA treatment compared with the CON treatment. These findings demonstrate the benefits of supplementing CMA to dairy cows during the transition period compared with a CON treatment containing limestone as the primary Ca source.     

牛奶中无乳链球菌DNA提取方法的比较

目的以牛奶中的致病性无乳链球菌作为研究对象,对9种常用的细菌核酸提取方法进行比较。方法选用紫外分光光度计法和实时荧光PCR法对各方法进行系统评估。结果超声波处理结合天根吸附柱的方法能提取到得率较高、纯度较好的DNA,结合实时荧光PCR法后对牛奶中无乳链球菌的检测灵敏度能达到90 cfu;天根吸附柱法提取所得DNA得率稍低,结合实时荧光PCR法后对牛奶中无乳链球菌的检测灵敏度也能达到90 cfu;溶菌酶法和超声波破碎提取法用于实时荧光PCR后对牛奶中无乳链球菌的检测灵敏度能达到350 cfu;Chelex-100法更适于纯菌的检测,该法结合实时荧光PCR法对无乳链球菌的检测灵敏度能达到350 cfu的灵敏度。结论应根据样品类型、方法要求和检测成本来选择适合的核酸提取方法。     

Early lactation ratio of fat and protein percentage in milk is associated with health, milk production, and survival

An observational study was conducted on 1,498 cows in 3 large Italian dairy farms. The objective of the study was to evaluate the prognostic value of early lactation fat-to-protein ratio in milk. In all 3 herds, an intensive herd health monitoring program was being practiced that included weekly visits and extensive data collection on health, reproduction, production, and culling. A milk sample was collected from all cows at approximately 7 d postpartum and the ratio of fat-to-protein percentage in this milk sample was measured. Animals with a fat-to-protein ratio in early lactation greater than 2.0 showed an increase in postpartum diseases such as retained placenta, left-displaced abomasums, metritis and clinical endometritis. We also observed a decrease in early lactation milk production but this was limited to cows in lactation 2 and higher when the fat-to-protein ratio was greater than 2.0 in the early postpartum milk sample. Finally, an increased risk of being culled from the herd was observed, with the risk of culling increasing with increasing fat-to-protein ratio in the early lactation milk sample. No effect of fat-to-protein ratio was found on the incidence of clinical mastitis in the 3 herds. From this study, we conclude that analyses of milk components in early postpartum (6-9 days in milk), particularly the ratio of fat-to-protein percentage, is a valuable indicator of lipo-mobilization and the negative energy balance status in postpartum cows. Because a single milk sample is sufficient to provide valuable information, we suggest that this is a valuable addition to herd health programs on dairy farms.     

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     

原料乳中药物残留和掺假物质检测方法的研究进展

原料乳中药物残留或掺假物质的存在造成的安全事件屡屡发生,这使我国乳品行业面临着巨大的挑战。本文主要综述了常规检测法、免疫分析法、仪器检测分析法、生物传感器和蛋白质芯片技术等对原料乳中常见聚醚类抗生素、类固醇激素、苯二氮卓类药物、苯基脲类除草剂、四环素类抗生素和青霉素类抗生素等药物残留、物理性质与原料乳相近的物质、常见电解质、非电解质、防腐剂等掺假物质的检测方法,以及对单一成分掺假物和多种成分掺假物的检测方法,并比较了不同检测方法的准确度、灵敏度、成本等优缺点,以期为相关检测部门进行质量监测或生产厂家牛乳收购提供技术参考。     

Effect of the sampling device on fat and protein variation in cow milk samples obtained for official milk recording

The paper was designed to assess the effect of the type of milk meter used by dairy farms for official milk testing to obtain individual milk samples for fat and protein determination. This study was performed in 2006 in Galicia, which is Spain's main dairy cattle region; data were collected from 2,149 Holstein cow farms enrolled for official milk recording. Findings indicate that the milk sampling system used has a substantial effect on the fat contents recorded for individual milk samples. Such variation could arise from poor functioning of the equipment, inadequate mixing of the milk portion from which the sample is obtained, or from the nonproportionality of the sample. Samples obtained from only one point in the milk line may not be representative of all the milk produced. The most significant differences are observed in the percentage of fat, whereas differences in percentage of protein are smaller. The sampling method used should, but does not always, provide a representative sample of the milk from a single milking.     

2种微生物法测定婴幼儿乳粉中维生素B5 含量的比较

目的比较国家标准GB 5009.210-2016《食品安全国家标准食品中泛酸的测定》和试剂盒法定量检测婴幼儿乳粉中维生素B_5含量的差异。方法采用微孔试剂盒法和国标法测定婴幼儿配方奶粉的维生素B_5含量,通过相对标准偏差(relative standard deviation, RSD)来比对两种方法的重现性、精密度,通过加标回收实验对比方法准确度。结果由精密度与准确度实验结果可知,国标法与试剂盒法的相对标准偏差分别为6.92%和3.18%,回收率分别为87.60%和97.61%。结论相对于国标GB 5009.210-2016的传统微生物法,试剂盒法操作简单,检验周期短,可以快速有效的测定婴幼儿乳粉中维生素B_5的含量。     

Comparison of calcium salts and formaldehyde-protected conjugated linoleic Acid in inducing milk fat depression

Abomasal infusion studies have shown that trans-10, cis-12 conjugated linoleic acid (CLA) decreases milk fat synthesis. However, supplements of CLA must avoid rumen biohydrogenation for this technology to be applied to ruminants. Rumen protection methods would reduce CLA metabolism in the rumen and increase its supply to the small intestine. Our objective was to compare the efficacy of 2 forms of rumen-protected CLA at inducing milk fat depression. Three mid to late lactation Holstein cows each fitted with a rumen fistula were used in a 3 x 3 Latin square design. Treatments were: 1) control, 2) calcium salts of CLA (Ca-CLA), and 3) formaldehyde-protected CLA (FP-CLA). Supplements were designed to provide 10 g/d of trans-10, cis-12 CLA and were administered intraruminally once per day to ensure exact delivery of amount. Both CLA treatments substantially reduced milk fat yield and content compared with control, with the reductions in milk fat yield averaging 34% for the Ca-CLA treatment and 44% for the FP-CLA treatment. In contrast, milk yield, milk protein yield, and dry matter intake were unaltered by CLA treatment. Efficiency of transfer of trans-10, cis-12 CLA from the supplement into milk fat was 3.2 and 7.0% for Ca-CLA and FP-CLA, respectively. These values are much lower than transfer efficiencies reported for abomasally infused CLA, suggesting that much of the trans-10, cis-12 CLA present in the 2 formulations was biohydrogenated in the rumen. Overall, the extent of the reduction in milk fat yield indicates that both protection formulations are acceptable methods for the formulation of CLA supplements to induce milk fat depression in lactating dairy cows.     

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。     

Genomic prediction of lactation curves for milk,fat, protein,and somatic cell score in Holstein cattle

Application of random regression models (RRM) in a 2-step genomic prediction might be a feasible way to select young animals based on the complete pattern of the lactation curve. In this context, the prediction reliability and bias of genomic estimated breeding value (GEBV) for milk, fat, and protein yields and somatic cell score over days in milk (DIM) using a 2-step genomic approach were investigated. In addition, the effect of including cows in the training and validation populations was investigated. Estimated breeding values for each DIM (from 5 to 305 d) from the first 3 lactations of Holstein animals were deregressed and used as pseudophenotypes in the second step. Individual additive genomic random regression coefficients for each trait were predicted using RRM and genomic best linear unbiased prediction and further used to derive GEBV for each DIM. Theoretical reliabilities of GEBV obtained by the RRM were slightly higher than theoretical reliabilities obtained by the accumulated yield up to 305 d (P305). However, validation reliabilities estimated for GEBV using P305 were higher than for GEBV using RRM. For all traits, higher theoretical and validation reliabilities were estimated when incorporating genomic information. Less biased GEBV estimates were found when using RRM compared with P305, and different validation reliability and bias patterns for GEBV over time were observed across traits and lactations. Including cows in the training population increased the theoretical reliabilities and bias of GEBV; nonetheless, the inclusion of cows in the validation population does not seem to affect the regression coefficients and the theoretical reliabilities. In summary, the use of RRM in 2-step genomic prediction produced fairly accurate GEBV over the entire lactation curve for all analyzed traits. Thus, selecting young animals based on the pattern of lactation curves seems to be a feasible alternative in genomic selection of Holstein cattle for milk production traits.     

利用不确定度比对乳粉中叶酸含量的快速检测方法

目的 利用不确定度比对乳粉中叶酸含量的快速检测方法。方法 分别用进口和国产的微生物法和酶联免疫法的试剂盒对代表性乳粉样品进行3 d 3平行检测, 对检测数据做正态分布分析及不确定度计算。结果 各方法检测结果正态分布检验值(anderson-darling, AD)均小于临界值0.725(95%置信区间), 服从正态分布; 微生物快速检测方法不确定度范围为13.3%~27.4%; 酶联免疫方法不确定度范围为9.6%~ 31.3%。结论 微生物试剂盒快速检测方法, 具有稳定性较好, 品牌差异较小的特点, 适合质控品的长期监测, 质控图的建立。酶联免疫检测方法, 具有简单、快速的特点, 适合样品中叶酸的快速检测。     

不同基质奶粉中泛酸检测方法对比

目前,市面上水解蛋白奶粉的需求与日俱增,但是针对这类奶粉HPLC法分离效果较差,目标峰与杂峰不易分离,为解决这一问题,实验室从优化色谱条件、更换色谱柱、沉淀蛋白PH值调整等几个方面进行优化,同时采用微生物法与仪器法进行比对验证,为进一步解决部分水解蛋白奶粉泛酸不易检测的问题提供实验数据和研究材料。实验结果表明：微生物法和HPLC法检测一致性较好,精密度、准确性等均符合要求。微生物法检测范围广,市面上常见的婴幼儿配方奶粉均可检测;HPLC法适用于检测不含水解蛋白奶粉;调整流动相比例可以实现目标锋和杂峰的分离,但是耗时长、无规律、重复性低。