不同体细胞数原料乳对契达干酪成熟过程中蛋白水解的影响

为探讨原料乳中体细胞数(SCC)对契达干酪成熟过程中蛋白质水解的影响,选择SCC分别是5.6×104(LSCC)、48.8×104(MSCC)、476.1(HSCC)×104 个/mL的原料乳制作契达(cheddar)干酪,得到LSCC、MSCC、HSCC组干酪,并对各组干酪成熟过程中蛋白质水解的各项指标进行了测定.结果显示3组干酪成熟过程中蛋白的水解产物不同,LSCC组干酪品质更好.     

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.     

原料乳体细胞数对硬质干酪蛋白水解及风味与质构品质的影响

干酪成熟过程中蛋白质的水解是风味形成的重要途径。在中国自由放养和小规模奶牛养殖仍占有一定比例,这其中的手动挤奶方式会导致原料乳中含有一定数量具有蛋白酶活性的体细胞,影响干酪成熟及风味。目前关于体细胞通过蛋白水解作用对脱脂干酪挥发性风味物质的影响尚未明确。本研究选取3 种不同体细胞数的原料乳,解析体细胞的细胞组成并制作脱脂干酪,在90 d的干酪成熟期中测定干酪的蛋白酶活性、蛋白水解水平、成熟后干酪的挥发性风味物质组成及其质构特性,评价不同体细胞数、干酪的蛋白质水解程度及其对干酪风味和品质的影响。结果表明：体细胞数越高的干酪蛋白酶活性越高,αs2酪蛋白水解程度越高,对干酪风味和质构也有不同程度的影响;使用体细胞数适量增加的原料乳（10×104～30×104 个/mL）有利于干酪风味的形成;中等体细胞数组中干酪特征风味物质3-羟基-2-丁酮含量最高（34.57%）,是低体细胞数组含量（28.64%）的1.2 倍、高体细胞数组含量（20.72%）的1.6 倍;原料乳中过多体细胞（多于86×104 个/mL）则会导致干酪过度水解并产生不良风味,高体细胞数组中检测到会引起不良风味的风味物质如辛醛、壬醛、仲辛酮、己醛。     

Effects of Somatic Cell Counts and Milk Composition on the Coagulating Properties of Milk

Forty-two Holstein cows were selected to provide monthly milk samples with varying SCC for 1 yr. Coagulating properties of samples measured as rennet clotting time, rate of curd firming, and curd firmness at cutting were determined by a formagraph. Milk samples were analyzed for fat, protein, lactose, total solids, casein, individual caseins, urea, SCC, and pH. Least squares analyses of data, after adjustments were made for the effect of milk composition, indicated that elevated SCC were associated with a significant increase in rennet clotting time and slower rate of curd firming. An increase of SCC from 100,000 to 500,000 SCC/ml resulted in an increase of approximately 2.1 and 2.2% in RCT and K20, respectively. A further increase of SCC to above 1,000,000/ml resulted in an overall increase of 20.7 and 13.84% in RCT and K20, respectively. Regression analyses indicated that K20 was decreased by 5.42 min and curd firmness at cutting was increased by 12.92 mm for every percentage in milk casein. Rennet clotting time, rate of curd firming, and curd firmness at cutting were increased by 3.52, 3.41, min and decreased by 9.45 mm, respectively, for every unit increase in milk pH.     

Association Between Somatic Cell Count of Milk and Cheese-Yielding Capacity

During 1 yr, 42 Holstein cows were selected to provide monthly individual milk samples with SCC, which ranged from less than 100,000 to more than 1,000,000/ml of milk. Milk was analyzed for fat, protein, lactose, casein, and SCC and was used for laboratory-scale cheese making. Data obtained from the milk input and the cheese output were used to determine actual, moisture-adjusted, Van Slyke's theoretical yields, and efficiency of yield. Least squares analyses of data which adjusted for the effect of milk composition indicated that SCC in milk were inversely related to moisture-adjusted yield and efficiency of yield. An increase of SCC from 100,000 to 500,000/ml was associated with a decrease of approximately 5.0 and 11.0% in adjusted yield and efficiency of yield, respectively. A further increase of SCC to 1,000,000/ml resulted in an overall decrease of 8.7 and 13% in adjusted yield and efficiency of yield, respectively.     

不同体细胞原料乳对Mozzarella干酪特性的影响

以膜过滤(M)、低体细胞(LSCC)、高体细胞(HSCC)原料乳为原料加工Mozzarella 干酪,对其成分回收率及1 、15、30、45、60d 成熟期的蛋白降解、游离脂肪酸含量、油脂析出、融化性、质构及感官等特性进行分析。结果表明：体细胞数对成分回收率的影响不显著(P ＞ 0.05)。LSCC 组与HSCC 组干酪特性差异不显著,但是微滤处理对Mozzarella 干酪特性的影响显著。体细胞数＜ 600000cells/mL时该指标并不是影响Mozzarella干酪品质的重要因素。     

泌乳月份及部分乳成分与牛乳中体细胞数关系的相关性研究

本研究利用陕西省西安市草滩牛场第五奶牛场62头泌乳牛2003年8个月的DHI记录资料,对泌乳月份及部分乳成分与牛乳中体细胞数的关系进行了研究.结果表明,体细胞数与日产奶量,日产奶量与乳蛋白率、乳脂率呈极显著的负相关(P＜0.01),体细胞数与乳蛋白率与乳脂率之间无显著相关关系(P＞0.05),乳蛋白率与乳脂率呈极显著的正相关(P＜0.01).5、7和10月份样品平均体细胞数较高,分别为789×103mL-1,696×103mL-1、1031×103mL-1,3月份样品平均体细胞数最低为390×103mL-1.     

豆奶,牛奶混合型干酪的研制

以豆奶和牛奶为原料，通过干酪制作条件的优化研究，得出了生产混合型干酪的重要工艺参数和技术要点。实验表明，用含有２０％豆浆的牛奶作为混合原料奶，消毒后加入２％的发酵剂和凝乳酶，经１－２月成熟，即可得到风味与纯牛奶干酪无显著差异的优质混合型干酪。     

牛乳中体细胞数与脂肪酸含量的相关性分析

目的：研究牛乳中体细胞数（somatic cell count,SCC）对乳脂肪酸含量的影响。方法：采集474 头处于泌乳早期（30～100 d）的中国荷斯坦奶牛乳样,测定乳中SCC及各种脂肪酸单体的含量,分析乳中SCC对脂肪酸相对含量的影响及相关性。结果：SCC极显著影响乳中C4∶0、C16∶1、cis9, trans11-CLA和C18∶3 n3脂肪酸单体的含量（P＜0.01）。同时,随着乳中SCC的升高,多不饱和脂肪酸（polyunsaturated fatty acid,PUFA）的相对含量也显著增加（P＜0.05）。相关性分析显示乳中SCC与PUFA含量呈极显著正相关（P＜0.01）,与短链脂肪酸含量呈显著负相关（P＜0.05）。结论：研究结果初步揭示了乳中SCC与乳脂肪酸相对含量的关系,为进一步揭示SCC对牛乳品质的影响提供了依据。     

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。     

Cheddar Cheese from Ultrafiltered Whole Milk Retentates in Industrial Cheese Making

Transporting whole milk retentates of ultrafiltration to a distant large industrial Cheddar cheese making site resulted in 16 lots of Cheddar cheese from vats containing 2,546 to 16,360 kg of cheese milk. Whole milk retentates concentrated by ultrafiltration to 4.5:1 were added to cheese milks to give mixtures concentrated 1.2:1 and 1.3:1 with approximately 20 and 30% more protein and fat, respectively, than in unsupplemented control whole milks or unsupplemented commercial reference milks.Gross composition of Cheddar cheese made from commercial reference, control, and retentate-supplemented milk generally showed no major differences. Yield increased in cheese made from retentate-supplemented milk. Yield efficiency per kilogram total solids rose in retentate cheese over controls but not among commercial reference, control, and retentate lots based on per kilogram fat or total protein. Milk components were higher in wheys from retentate cheeses, but loss of components per kilogram cheese obtained generally showed lower values in whey from retentate cheese.General quality of retentate Cheddar cheese was equal to that of reference unsupplemented commercial cheese and higher than unsupplemented control Cheddar cheeses. It appears technically feasible to ultrafilter milk at one site, such as the farm, collecting station, or specialized center, and transport it to an industrial site for Cheddar cheese making.     

Cottage Cheese from Ultrafiltered Skim Milk Retentates in Industrial Cheese Making

Ultrafiltered skim milk retentates were transported to a large industrial cottage cheese plant for milk supplementation leading to cottage cheese. The resulting industrial products were observed for composition, yields, whey component losses, and quality.Ten lots of small curd cottage cheese were made in vats containing up to 6593 kg skim milk. Retentate supplemented skim milks, concentrated approximately 10% (1.1:1) and 20% (1.2:1) in total protein, were very similar in initial composition to the controls. Mean cheese yield values from milks supplemented to 1.2:1 total protein were significantly higher than mean unsupplemented control milk values. Cheese yield efficiencies, per kilogram total solids, were also significantly higher in the retentate cheese but not when calculated per kilogram total protein.Total solids, total protein, and ash were higher in cottage cheese wheys from retentate supplemented cheese and were directly related to retentate supplementation concentration. Mean whey component loss per kilogram cheese exhibited significant decreases from milks of higher retentate supplementation. Retentate supplemented skim milk produced industrial cottage cheese of comparable quality to cheese made from unsupplemented control skim milks.     

Transmission Electron Microscopy Study of Casein Micelle in Raw Milk with Different Somatic Cell Count Levels

The relationship between elevated raw milk somatic cell count (SCC) and casein micelle dimension was investigated by transmission electron microscopy (TEM). Milk samples collected from the dairy cattle with three different levels of SCC (<200,000, 200,000 to 800,000, and >800,000 cells/ml) were studied by TEM. The results indicated that an increase in SCC resulted in a decrease in the casein micelle size with an increase in their aggregation. The present research supported the hypothesis that elevated proteolytic activity, reduced secretary ability of the mammary glands, lower electrostatic and steric repulsion as well as different mineral contents of mastitic milk could affect casein micelle properties.     

Variation in Milk Fat,Protein, and Somatic Cell Count from Four Dairy Herd Improvement Laboratories

Information on variability in milk fat, protein, and somatic cell count among four Dairy Herd Improvement laboratories was studied. Approximately 395 individual cow samples from four herds were shipped in blind duplicate via common carrier to four Dairy Herd Improvement laboratories for analysis. One herd was sampled twice and one of the four laboratories was not equipped for protein determinations. As expected, samples differed among herds, laboratory, and interaction of herd by laboratory for the constituents analyzed. Reasons for the interactions could not be fully explained. However, delay in shipment of one set of herd samples to one laboratory probably contributed to the interaction for somatic cell count. Means from laboratories 1, 2, 3, and 4 across herds were 3.99, 3.90, 3.89, and 3.88 for percent fat, 3.45, 3.31, and 3.16 for percent protein and 364, 430, 322, and 380 for somatic cell count (× 1000). Variation among laboratories could not be explained by type of analytical instrument or time in shipment. These data indicate a need for use of uniform standards by testing laboratories to reduce variation in laboratory results.     

Whole Milk Reverse Osmosis Retentates for Cheddar Cheese Manufacture: Cheese Composition and Yield

The impact of concentrating whole milk by reverse osmosis prior to Cheddar cheese making was studied. Heat treated, standardized, whole milk was reduced in volume by 0, 5, 10, 15, and 20% prior to Cheddar cheese manufacture. Milk solids at various milk volume reductions were 11.98, 12.88, 13.27, 14.17, and 15.05%, respectively. Permeates contained only traces of organic matter and would not create a significant by-product handling problem for a cheese plant. Solids content of the whey from cheese making increased with increasing milk concentration. Proximate compositions of reverse osmosis cheeses were comparable to control cheeses. Fat losses decreased, and fat retained in the cheese increased with increasing milk solids concentration. Improved fat recovery in the cheese was related to the amount of mechanical homogenization of milk fat during the concentration process. Actual, composition adjusted, and theoretical cheese yields were determined. Increased retention of whey solids and improved fat recovery gave cheese yield increases of 2 to 3% above expected theoretical yields at 20% milk volume reduction. Water removal from whole milk prior to Cheddar cheese manufacture gave increased productivity and cheese yield without requiring different cheese-making equipment or manufacturing procedures.     

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)。     

Yield and Quality of Cheddar Cheese from High Somatic Cell Milk Supplemented with Retentate to Varying Concentrations or Directly Ultrafiltered

High somatic cell milk with a mean cell count of 2,235,000/ml was supplemented to 1.25:1 to 1.88:1 total protein with approximately 5.5:1 low somatic cell whole milk retentate of UF. Curd formation time of cheese milk decreased with increasing concentration of SCC. Supplemented milk concentrated to 1.65: 1 and 1.88:1 total protein displayed normal curd formation times: 34 and 31 min, respectively. Also, cheese made from these mixtures had normal moisture, whereas the remaining cheeses had higher than normal moisture. Supplementation to 1.65:1 and 1.88:1 total protein increased cheese yield by 9.67% and 11.38%, respectively, and produced excellent quality cheese after 2 mo at 10°C.Direct UF of high SCC milk to 1.84:1 total protein improved cheese quality and increased yield over control milk cheeses but not to the same high level attained with retentate supplementation.     

快速检测牛奶中体细胞数方法的改进

为探求1种简单、快速、准确的牛奶体细胞数测定方法,将牛奶样品经表面活性剂十二烷基硫酸钠处理后,奶样中体细胞的细胞膜和核膜被破坏,细胞核DNA大量释放,引起奶样稠度发生很大的变化,可用Lamb-lewis稠度计测量其稠度的变化。通过分析缓冲液pH、处理时间、温度等条件对奶样稠度的影响,结果表明,在一恒定温度条件下,缓冲液pH7.5、处理时间15～20min时,乳样体细胞数与SDS处理后奶样稠度之间存在显著的线性关系;通过测定SDS处理后奶样的稠度,可以快速、准确地检测出其中的体细胞数。     

凝乳工艺对功能性低脂干酪中活菌数的影响

活菌数是功能性低脂干酪的重要指标,就凝乳工艺过程对功能性低脂干酪活菌数的影响进行了研究,旨在通过控制凝乳工艺过程参数而使干酪最终活菌数达到功能性食品的标准。通过对单因素试验和正交试验研究与分析,结果表明:凝乳酶添加量0.01%,凝乳温度35℃,凝乳pH 6.2,CaCl2添加量0.03%,干酪活菌数均能达到107CFU/mL,符合功能性低脂干酪的活菌数要求,能够获得较为理想的试验效果。