原料乳体细胞数对乳酪品质影响的研究进展

体细胞数是评估原料乳质量的重要指标,不同国家对原料乳体细胞数的限量值建立了不同的标准.乳酪的品质主要与其加工过程中所用原料乳的质量相关,因此,原料乳体细胞数可能是反映乳酪品质的重要因素.从乳酪的成分、凝乳、产量、感官特性和生物胺等方面综述不同体细胞数牛乳、绵羊乳和山羊乳对乳酪品质的影响,发现原料乳体细胞数对乳酪品质影响...     

毛细管电泳法测定不同体细胞数的原料乳的蛋白组成及含量

为明确不同体细胞数(Somatic Cell Count,SCC)数量的原料乳蛋白质组成的变化规律。本研究首先建立了乳蛋白的毛细管电泳分析方法,并采集了不同SCC数量原料乳,分析其乳蛋白成分及含量的差异。结果表明,随着SCC数量的增加,原料乳中酪蛋白的占比显著降低(p<0.05),乳清蛋白比率相对增加;酪蛋白中β-酪蛋白B和β A1-酪蛋白的含量显著下降(p<0.05),水解为新的小片段。毛细管电泳技术能够更准确的分析原料乳蛋白质的组成及变化规律,有利于乳品企业在原料乳收购时进行更深一层的品质分析。     

体细胞数对乳的影响及其控制措施

分析了乳中体细胞升高的原因，阐述了高体细胞数对乳的组成和乳制品加工的影响，并简要的说明了降低体细胞数的控制措施。     

原料乳中体细胞检测方法

本实验通使用亚甲基蓝作为染色剂,对原料乳中体细胞核进行染色,详细的规范了操作细节,通过公式进行计算,得到原料乳中体细胞数目,该方法实用有效。     

不同体细胞数原料乳对UHT贮存期间蛋白和脂肪水解的影响

不同体细胞数(21.4×104mL-1,75.8×104mL-1,118.1×104mL-1和216.2×104mL-1)原料乳生产的4组UHT乳在37℃贮存84d,对其贮存期间的蛋白水解及脂肪水解进行研究。结果表明,4组UHT乳贮存期间的蛋白水解速率无显著性差异(P>0.05),原料乳体细胞数并未对蛋白水解造成影响;4组UHT乳贮存期间的脂肪水解速率具有显著性差异(P<0.005),原料乳体细胞数与脂肪水解速率间存在极明显的正相关(R=0.9886,P<0.05)。     

原料乳体细胞数与纤溶酶活性的相关性研究

随机检测了102个原料乳样品的体细胞数(SCC)与纤溶酶(PL)活性。结果显示,SCC与PL活性之间存在一定的正相关。以总体为样本,PL活性与SCC线性相关系数为0.7367;SCC3×105mL-1样本的相关系数达到0.7928,SCC5×105mL-1样本的相关系数达到0.8616。SCC在3×105mL-1时SCC与PL无相关性。人工调配的含不同SCC的11个原料乳样,采用荧光染色法进行SCC计数,其理论折算数和实际数配对两处理t检验,结果t=1.2787,P=0.2299,差异不显著。线性回归分析得:Y=1.0055X-3.4473(R2=0.9996)。11个人工调配SCC原料乳样品的PL活性随SCC数的增加而明显增加(R2=0.9619)。通过超声波处理模拟SCC自溶状态,原料乳中体细胞经超声波处理后,PL活性明显增加。     

原料乳中体细胞数与UHT乳中酪蛋白成分的关系研究

研究了原料乳中体细胞数与15批次UHT乳样本中酪蛋白成分之间的关系。将原料乳巴氏杀菌后进行超高温处理。分别于8,30,60,90和120 d采集贮藏于室温条件下的UHT乳样本,并使用高效液相色谱法对酪蛋白成分进行分析。体细胞数范围1.97×105～8×105 mL-1。体细胞数与原料乳或UHT乳中的κ-酪蛋白质量浓度之间没有相关性(P<0.05)。原料乳中αs2-酪蛋白和β-酪蛋白与体细胞数呈负相关(P<0.05)。UHT乳中,αs1-酪蛋白(P<0.05)和β-酪蛋白(P<0.05)与体细胞数在贮藏第8天呈负相关,αs2-(P<0.01)与体细胞数在贮藏第60天呈负相关。结果表明,原料乳中体细胞数较高与β-酪蛋白和αs-酪蛋白的大量水解有关,并且可能导致UHT乳在贮藏期内出现质量问题。     

体细胞数对半硬质山羊奶干酪品质影响的研究

山羊奶特殊的顶浆分泌机制使正常山羊奶的体细胞数要高于正常牛奶和绵羊奶.因此,有必要探讨高体细胞数对山羊奶成分及其半硬质干酪品质的影响.本研究针对三组不同体细胞数(＜5×105/ml、5×105～1×106/ml和1×106～1.5×106/ml)非乳房炎山羊奶的分析结果表明该范围内的体细胞数对山羊奶的成分,半硬质干酪的产量和成分均无显著的影响.但是,在60d和120d成熟之后,高体细胞数的干酪具有最高的水溶性氮占总氮的比率和12%三氯乙酸可溶性氮占总氮的比率;同时,高体细胞数导致成熟干酪的硬度和咀嚼性降低,弹性、内聚性和粘性都显著增高.本研究结果将为山羊奶体细胞形成机制的研究和山羊奶分级体系的建立提供有用的数据信息.     

牛乳中体细胞数与乳成分和部分理化性质的相关性研究

对呼和浩特郊区一牧场30头荷斯坦乳牛进行6个月单个采样,共得452个有效样本,检测乳样包括:体细胞数、脂肪、蛋白质、乳糖、总固形物、细菌总数、比重、黏度、电导率、氯糖数、滴定酸度和pH值。结果表明,蛋白质质量分数与牛乳中的体细胞数(Somatic CellCount,SCC)SCC呈显著正相关(P<0.05);乳糖含量与SCC呈显著负相关(P<0.001);脂肪、总固形物质量分数、电导率、氯糖数与SCC呈极显著正相关(P<0.001)。细菌总数、比重、黏度、滴定酸度、pH值与SCC的相关性不显著。从5～10月,乳中体细胞数有逐渐降低趋势,9月骤然升高,其中5月和9月样品平均体细胞数较高,分别为78×104 mL-1和96×104 mL-1。10月份样品平均体细胞数最低为28×104 mL-1。     

乳体细胞数对干酪生产的影响

论述了原料乳中体细胞数对干酪加工、成熟和产量的影响,以期为干酪生产提供理论参考.     

我国生牛乳菌落总数和体细胞数调查及其影响因素分析

目的调查我国生牛乳菌落总数和体细胞数情况,分析养殖模式与区域等因素对我国生牛乳菌落总数和体细胞数的影响。方法对17个省(市、自治区)2014—2015年连续12个月共17 527份生牛乳样品菌落总数的数据和6 633份体细胞数的数据进行研究,采用SPSS 19.0的Kruskal-Wallis秩和检验分析养殖模式和养殖区域对生牛乳菌落总数和体细胞数的影响。结果我国生牛乳中的菌落总数、体细胞数的平均值分别为3.27×10~5CFU/ml、46.0万个/ml。来自牧场、养殖小区、散户的生牛乳样品菌落总数的中位数分别为1.00×10~5、1.85×10~5、2.37×10~5CFU/ml,体细胞数的中位数分别为35.0万、73.0万、59.1万个/ml;东北内蒙古产区、华北产区、南方产区、大城市周边产区、西部产区生牛乳菌落总数的中位数分别为2.40×10~5、1.43×10~5、1.50×10~5、1.60×10~5、2.14×10~5CFU/ml,体细胞数的中位数分别为57.2万、33.0万、38.2万、56.0万、40.0万个/ml。结论生牛乳的菌落总数99%以上均可达到我国现行标准的要求,标准对菌落总数的要求有进一步提升的空间。来自大规模牧场的生牛乳菌落总数和体细胞数均较低。     

Application of a new portable microscopic somatic cell counter with disposable plastic chip for milk analysis

The somatic cell count (SCC) is one of the international standards for monitoring milk quality, and it is a useful indicator of mastitis. The current reference method for determining the SCC in raw milk is direct microscopic analysis, but this method requires well-trained staff to maintain its accuracy and reproducibility. To overcome these inconveniences, we developed a portable system (the C-reader system) that utilizes the capillary flow of a microfluidic chamber by surface modification of the hydrophilicity. The microfluidic technology of disposable microchips allows for low consumption of reagents, and a combination of ready-to-use reagents makes the daily work easier. The repeatability test of the C-reader using 10 composite bovine milk samples satisfied the recommended values for SCC equipment. In addition, an acceptable accuracy level of the natural logarithmic-transformed SCC [ln(SCC/1,000): ± 0.059 to 0.112] was achieved using composite raw milk samples and various somatic cell standard solutions from the American Eastern Laboratory and the Korean National Veterinary Research and Quarantine Service. After testing 875 composite milk samples, the C-reader showed a high correlation coefficient (R² = 0.935 to 0.964) and a low mean difference value in log-transformed SCC (−0.088 to 0.004) compared with 3 automatic commercialized somatic cell counters (Fossomatic 4000, Somacount 150, and Somascope). In conclusion, the C-reader system is a new, easy-to-use automatic on-farm method with acceptable repeatability and accuracy for measuring SCC in large dairies and smaller laboratories.     

Genetic and phenotypic correlations between milk coagulation properties, milk production traits, somatic cell count, casein content, and pH of milk

Genetic and phenotypic correlations between milk coagulation properties (MCP: coagulation time and curd firmness), milk yield, fat content, protein content, ln(somatic cell count) (SCS), casein content, and pH of milk and heritability of these traits were estimated from data consisting of milk samples of 4664 Finnish Ayrshire cows sired by 91 bulls. In addition, differences in average estimated breeding values (EBV) for the above traits between the cows with noncoagulating (NC) milk and those with milk that coagulated (CO samples) were examined. The estimations were carried out to study the possibilities of indirect genetic improvement of MCP by use of the above characteristics. The genetic and phenotypic correlations between MCP and the milk production traits were low or negligible. The genetic associations between desirable MCP and low SCS were rather strong (-0.45 to 0.29). Desirable MCP correlated both genetically and phenotypically with low pH of milk (-0.51 to 0.50). The rather high heritability estimates for curd firmness in different forms (0.22 to 0.39), and the wide variation in the proportion of daughters producing NC milk between the sires (0 to 47%) suggested that noncoagulation of milk is partly caused by additive genetic factors. Based on the genetic correlations between curd firmness and SCS and the high EBV for SCS obtained for the cows with NC-milk, it is possible that the loci causing noncoagulation of milk and increasing somatic cell count of milk are closely linked or partly the same. One means to genetically improve MCP and to reduce the occurrence of NC milk could thus be selection for low somatic cell count of milk.     

Correlation between standard plate count and somatic cell count milk quality results for Wisconsin dairy producers

The objective of this study was to determine if a correlation exists between standard plate count (SPC) and somatic cell count (SCC) monthly reported results for Wisconsin dairy producers. Such a correlation may indicate that Wisconsin producers effectively controlling sanitation and milk temperature (reflected in low SPC) also have implemented good herd health management practices (reflected in low SCC). The SPC and SCC results for all grade A and B dairy producers who submitted results to the Wisconsin Department of Agriculture, Trade, and Consumer Protection, in each month of 2012 were analyzed. Grade A producer SPC results were less dispersed than grade B producer SPC results. Regression analysis showed a highly significant correlation between SPC and SCC, but the R² value was very small (0.02–0.03), suggesting that many other factors, besides SCC, influence SPC. Average SCC (across 12 mo) for grade A and B producers decreased with an increase in the number of monthly SPC results (out of 12) that were ≤25,000 cfu/mL. A chi-squared test of independence showed that the proportion of monthly SCC results >250,000 cells/mL varied significantly depending on whether the corresponding SPC result was ≤25,000 or >25,000 cfu/mL. This significant difference occurred in all months of 2012 for grade A and B producers. The results suggest that a generally consistent level of skill exists across dairy production practices affecting SPC and SCC.     

Short communication: Comparison of bulk milk, yield-corrected, and average somatic cell counts as parameters to summarize the subclinical mastitis situation in a dairy herd

In this study, the correlation was determined between the prevalence of high cow-level somatic cell count (SCC >250,000 cells/mL), a summary of the subclinical mastitis situation in a dairy herd, and 3 average herd SCC parameters: bulk milk SCC (BMSCC), yield-corrected test-day SCC (CHSCC), and the arithmetic average test-day SCC (HSCC) of the lactating herd. The herd prevalence of cows with an SCC of >250,000 cells/mL was calculated by using Dairy Herd Improvement data. Herds were included if BMSCC was sampled within 2 d of the Dairy Herd Improvement test day and if the BMSCC did not exceed 400,000 cells/mL. The interval between sampling, 0, 1, or 2 d, did not significantly influence the correlation between BMSCC and the prevalence of high SCC. The correlations between the prevalence of high SCC and BMSCC, yield-corrected test-day SCC, and HSCC, examined by using a linear regression model, were 0.64, 0.78, and 0.89, respectively. Therefore, it can be concluded that, based on the highest correlation, HSCC is a more appropriate parameter than BMSCC to summarize the average herd subclinical mastitis situation in a dairy herd.     

生乳中体细胞数对乳品质量安全的影响研究进展

体细胞数增加会改变乳成分、影响牛乳风味及缩短乳制品货架期,并且使乳中抗生素和药物残留的风险增加。乳中体细胞数是衡量乳畜健康、乳品质量与安全的标准,也是国际判定隐形乳房炎的重要指标。为了保障乳品质量和安全,许多国家规定了生乳中体细胞数的限量。本文从体细胞数和乳品质量与安全的关系、不同国家对生乳中体细胞数的限量及影响体细胞数的因素和体细胞数的检测方法等方面作一综述。     

Importance of the sampled milk fraction for the prediction of total quarter somatic cell count

This study investigated the changes in somatic cell counts (SCC) in different fractions of milk, with special emphasis on the foremilk and cisternal milk fractions. Therefore, in Experiment 1, quarter milk samples were defined as strict foremilk (F), cisternal milk (C), first 400 g of alveolar milk (A1), and the remaining alveolar milk (A2). Experiment 2 included 6 foremilk fractions (F1 to F6), consisting of one hand-stripped milk jet each, and the remaining cisternal milk plus the entire alveolar milk (RM). In Experiment 1, changes during milking indicated the importance of the sampled milk fraction for measuring SCC because the decrease in the first 3 fractions (F, C, and A1) was enormous in milk with high total quarter SCC. The decline in SCC from F to C was 50% and was 80% from C to A1. Total quarter SCC presented a value of approximately 20% of SCC in F or 35% of SCC in C. Changes in milk with low or very low SCC were marginal during milking. Fractions F and C showed significant differences in SCC among different total SCC concentrations. These differences disappeared with the alveolar fractions A1 and A2. In Experiment 2, a more detailed investigation of foremilk fractions supported the findings of Experiment 1. A significant decline in the foremilk fractions even of F1 to F6 was observed in high-SCC milk at concentrations >350 × 10³ cells/mL. Although one of these foremilk fractions presented only 0.1 to 0.2% of the total milk, the SCC was 2- to 3-fold greater than the total quarter milk SCC. Because the trait of interest (SCC) was measured directly by using the DeLaval cell counter (DCC), the quality of measurement was tested. Statistically interesting factors (repeatability, recovery rate, and potential matrix effects of milk) proved that the DCC is a useful tool for identifying the SCC of milk samples, and thus of grading udder health status. Generally, the DCC provides reliable results, but one must consider that SCC even in strict foremilk can differ dramatically from SCC in the total cisternal fraction, and thus also from SCC in the alveolar fraction.     

Changes of protein content and its fractions in bovine milk from different breeds subject to somatic cell count

Global milk production is undeniably dominated by 2 dairy breeds recognized worldwide: Holstein-Friesian and Jersey. A third breed, Simmental, serves as a dual-purpose breed. The objective of the present research was to establish potential changes in the fractional components of bovine milk protein (mainly whey) in relation to the health status of a dairy cow's mammary glands, which is closely determined by somatic cell count (SCC). The milk of 3 breeds was studied: Polish Holstein-Friesian (Black and Red-White varieties), Simmental, and Jersey. The cows were housed in freestall barns and fed according to the total mixed ration feeding system for both winter and summer periods. Milk samples were collected individually from each cow twice a year, in the winter and summer seasons. A total of 1,822 milk samples were evaluated (946 in winter and 876 in summer). The milk was examined for SCC, crude protein, casein, and whey fraction proteins (α-lactalbumin, β-lactoglobulin, lactoferrin, BSA, and lysozyme). The research material for each breed was split into 4 groups based on SCC (group I: ≤100,000 cells/mL; group II: 101,000 to 400,000 cells/mL; group III: 401,000 to 500,000 cells/mL; and group IV: 501,000 to 1,000,000 cells/mL). It was found that an increase of SCC promulgated a progressive decline in the daily yield of milk, which was significantly true for the Polish Holstein-Friesian. The level of crude protein decreased slightly as SCC increased, and casein concentration (r = −0.591) also followed this trend of decline. Elevation of SCC produced a decrease of major albumins (i.e., α-lactalbumin and β-lactoglobulin). However, SCC increase induced an increase in the immunoactive proteins (lactoferrin and lysozyme) as well as BSA. The interactions of a breed with increased SCC, which can be measured based on the BSA content of the milk, has indicated various levels of susceptibility to the increase in different breeds. This is confirmed by different values of correlation coefficients for these relationships: 0.71 in the Holstein-Friesian, 0.58 in Simmental, and 0.47 in the Jersey cows. Holstein-Friesian cows are more sensitive to mammary gland infections causing a greater decline of their daily milk yields, which, in turn, is reflected in an increase of the negative value of the correlation coefficients between SCC and milk efficiency (−0.24). In the other 2 breeds, the correlations were also negative, but substantially lower (−0.12 and −0.15).     

牛乳体细胞数与乳中离子含量相关性的研究

对呼和浩特市郊区一牧场30头荷斯坦乳牛进行6个月跟踪采样,共得427个有效样本。根据体细胞数的高低将乳样分成五个不同的组,分别测定样本的氯、钾、钠、游离钙、总钙含量。结果表明:牛乳中氯、钠的含量与SCC呈显著的正相关(p＜0．001);游离钙含量与SCC有一定的负相关(p＜0．05);总钙、钾离子的含量与SCC的相关性不显著(p＞0．05)。乳中体细胞数和乳中氯、钾、钠、游离钙、总钙含量与月份没有相关性(p＞0．05)。氯与总钙有显著的正相关性(p＜0．001);乳中氯离子与钠离子之间;总钙与游离钙之间有一定的正相关(p＜0．05);钠离子与总钙之间有显著的正相关(p＜0．01)。其余离子之间相关性均不显著(p＞0．05)。