The microbial content of unexpired pasteurized milk from selected supermarkets in a developing country

Objective:To determine the presence and levels of microbes in unexpired pasteurized milk from randomly selected supermarkets in Kingston,Jamaica.Methods:The quantitative study used a stratified random sampling technique in the selection of the 20 representative milk samples from six(6) supermarkets.Microbiological tests such as methylene blue reduction,standard plate count(SPC),coliform plate count(CPC),purity plate culture,gram staining and biochemical tests were performed to examine the microbes in purchased unexpired pasteurized milk.Results:One sample(BCr016) had a pH of 4.0.a rancid odour and curdled appearance.It decolourized within one hour during the methylene blue reduction test and was classified as class 4 milk.Seven of the samples were sterile with no microbe growth on the plate count agar and violet red bile salt agar(VRBA).The milk samples that appeared to be safe for consumption were all 10,11,12 and 13 days before expiration.The VRBA sample BCr016,had a colony count of 13 400 CFU/ mL.There was the presence of Escherichia coli in sample LCr021 which had a standard plate count of 1 580 SPC/mL and a coliform count of 500 CFU/mL.Enterobacter sp.was present in colonies from BCr016 and all the other milk samples.Conclusions:Unacceptable levels of Entembacter spp.and Escherichia coli were found in most of the samples.Effective measures to ensure safe milk for human consumption such as the phosphatase test and methylene blue reduction test should be routinely performed on each batch of milk processed by dairy plants.

Contents of Trace Metal Elements in Cow Milk Impacted by Different Feedstuffs

Feedstuff intake plays key role in impacting the yield and quality of milk. In this study, we discussed the contents of trace metal elements in cow milk impacted by different feedstuffs. We detected the contents of Pb, Cd, As, Cu, Mg, Ca, Fe and Zn in different feedstuffs and milk by atomic absorption spectrophotometry. The determinations of Pb, Cd and As contents were by graphite furnace A_AS and Cu, Mg, Ca, Fe and Zn was by flame atomic absorption spectrometry. The results showed that Pb, Cd, As and Cu presented in feedstuffs, but Pb, Cd and As were lowly detected in milk samples, and Cu was not detected in milk samples. The content of Mg in concentrates was lower than that in forages. However, the content of Mg in milk from concentrate feed was higher than that in forage feed. This suggested that the utilization of Mg in concentrate feed was higher than that in forage feed. The contents of Ca and Zn were opposite to Mg, and the utilization of Ca and Zn in forage feed was higher than that in concentrate feed. There was no obviously change law of Fe in different feedstuffs and milk samples. The relationship between the contents of trace metal elements in milk to feedstuffs would provide a theoretical basis for dairy farming. It would be useful for improving the milk yield and milk quality of dairy production.

The Detection of STAT1 Gene Influencing Milk Related Traits in Turkish Holstein and Jersey Cows

The main purpose of this study was to detect an association of cytoplasmic signal transducers and activators of transcription-1 （STAT1） with milk production traits in 472 Holstein and 283 Jersey cattle breeds of Turkey. This gene, located on chromosome 2, was chosen due to its role on development of mammary gland. A polymorphism of selected 314 bp allele fragment was detected by the restriction fragment length polymorphism analysis of polymerase chain reaction-amplified fragments （PCR-RFLP） method and also confirmed by DNA sequencing. The association tests were conducted between STAT1 genotypes and some economically important dairy traits. The genotypes for C/T as a single nucleotide polymorphism （SNP） were identified at interval 60 cM to 63 cM. The effects of STAT1 gene on milk production traits were not significant in Holstein cows, although animals with CT genotypes showed fairly close to significant value for the corrected 305 d milk yield. However, Jersey cows with/7＂ genotype were 2.07 kg higher for test-day milk yield （P 〈 0.05）, 0.13 kg for fat yield （P 〈 0.01） and 0.07 kg for protein yield （P 〈 0.05） compared with animals having CC and CT genotypes. Definitely, the further research should be conducted to search this gene intensively with larger samples to identify polymorphism and any association between the economically important traits and genotypic class in Holstein cows. Finally, based on the findings, it was concluded that STATI gene might be used as a potential candidate gene to improve milk yield and milk fat and protein contents in dairy cows breeding programs.

Effect of Bospro on High and Mid-to-Low Milk Yielding Chinese-Holstein Cow

A total of 90 cows from two farms (farm A 30 cows, farm B 60 cows) were used to study the effect of Bospro on milk production, milk quality and subclinical mastitis incidence. The cows in the test group were supplied with 20 g of Bospro per head per day and meanwhile, the percentage of milk fat, protein and lactose and moisture of the milk samples were analysed. The results showed that the milk yield of both high production and mid-to-low milk producting cows increased by 3.3% to 5.3% respectively compared with their control group of cows, but there was no changes on the milk content between the treated and the control cows. The treated cows also showed an increased body weight (P>0.05) and significantly reduced incidence of mastitis, as Compared with that of the control group.The experiment dcmonstrats that Bospro can increase milk yield, but not at the expense of milk quality and body weight.

Application of Colligative Properties in Quality Detection of Watering Raw Milk

[ Objective] To investigate the effects of different water amount on freezing point of raw milk. EMetbodl The freezing point of raw milk added water at different proportions was detected by SWC-LG freezing point detector. The linear regression equation was obtained. The reproduc- ibility was checked. The water content in raw milk was calculated according to the standard regression curve. E Result~ When the water content changed from 0 to 10%, the freezing point of raw milk increased linearly. As evidenced by the reproducibility test, the standard deviation and rela- tive standard deviation were less than 1%. The milk concentration obtained by detecting the freezing point of blind milk samples had an absolute er- ror of no more than 0.5%, compared with actual watering milk concentration. [ ConcluMonl Water content in raw milk can be determined by measur- ing freezing point, and this method is reliable and reproducible.

基于BP神经网络的UHT纯牛奶包装货架期预测

为探究初始蛋白质与脂肪含量、贮藏温度对UHT纯牛奶包装货架期的影响,以三种UHT纯牛奶为研究对象,试验测定23、30和37℃贮藏过程中样品褐变指数、蛋白水解度指标。将数据集整合,根据其在预测集上的表现确定具体的输入参数,开展基于BP神经网络的UHT纯牛奶包装货架期预测。结果表明,BP神经网络模型对UHT牛奶褐变指数、蛋白水解度指标的拟合度为0.9412、0.9527,相较于传统多元线性回归模型的0.8799和0.9211,经优化隐含层神经元数的BP神经网络模型对UHT纯牛奶贮藏期间的特征指标变化预测精度更高,为不同配方UHT纯牛奶货架期的快速准确预测提供技术支持。

^(60)Co-γ射线辐照对紫云英生长及利用的影响

为探究^(60)Co-γ射线对紫云英(Astragalus sinicus)种子的诱变效应,明确适合紫云英翻压利用及生长的辐照剂量,本研究以紫云英种子为试验材料,采用不同^(60)Co-γ射线辐照剂量[0(CK)、300、500、700 Gy]处理种子,观察比较紫云英的养分吸收特性、发芽率和田间生长状况。结果表明,辐射处理可提高紫云英盛花期的氮(N)含量,500 Gy处理盛花期N含量最高。在等N投入量下,与CK相比,500 Gy处理的翻压量可减少2063 kg·hm^(−2),便于机械翻压操作。与CK相比,辐照处理的出苗数、株高等多项指标均呈降低趋势,高辐照剂量700 Gy处理的鲜草产量和种子产量均显著降低(P<0.05),500 Gy处理的各项指标与CK最为接近,且相差较小。综上,用500 Gy的^(60)Co-γ射线辐照紫云英种子,提高了单位质量的氮素含量,便于盛花期轻简翻压利用。

特色乳中低聚糖组成及生物活性研究进展

我国特色乳资源丰富,不同来源特色乳营养成分组成、含量及其功能活性各有特点。低聚糖作为乳中重要的生物活性成分具有多种重要生物学功能。本文综述近年来羊乳、驴乳、水牛乳、牦牛乳、驼乳、马乳等特色乳中低聚糖种类、结构及含量研究进展,阐述乳源低聚糖益生、抗菌、抗炎、促进大脑发育等生物活性,旨在为特色乳中低聚糖的开发与利用提供理论参考。

初始脂肪含量对超高温灭菌牛奶贮存品质变化及货架期的影响

该文旨在研究初始脂肪含量、贮存温度对超高温灭菌(ultra high temperature sterilized,UHT)牛奶贮存期间的品质变化及货架期影响规律。对23、30、37℃无光照贮存过程中不同初始脂肪含量UHT纯牛奶的色泽、蛋白水解度、羰基含量进行分析,比较各指标对感官评分的Pearson系数,应用Arrhenius方程等建立货架期预测模型。随着贮存时间的延长、贮存温度的升高,样品的褐变指数、蛋白水解度、羰基含量均随之提高,而感官评分值降低;将感官评分和其他指标进行Pearson相关性分析筛选出褐变指数作为反映其品质变化的关键指标,建立基于初始脂肪含量和贮存温度影响的货架期预测模型,模型预测值与实际货架期验证比较,相对误差小于10%。所建预测模型可有效预测无光照下不同初始脂肪含量UHT牛奶货架期。

不同泌乳期山羊乳与牛乳中类固醇激素含量差异

目的:了解不同泌乳期山羊乳与牛乳中类固醇激素含量差异。方法:采用超高效液相色谱-串联质谱方法,分析不同泌乳期山羊乳和牛乳中类固醇激素含量。以0.5 mmol/L氟化铵溶液和甲醇作为流动相进行梯度洗脱,采用电喷雾离子化质谱的多反应监测模式对目标分析物进行定性和定量检测。结果:山羊乳与牛乳样品中共检出11种类固醇激素,分别为17α-羟基孕烯醇酮、17α-羟基孕酮、表睾酮、孕烯醇酮、孕酮、雄烯二酮、睾酮、雌二醇、雌激素、皮质醇和可的松,其中,泌乳初期山羊乳与牛乳相比,17α-羟基孕烯醇酮、雌激素、皮质醇含量差异显著(P<0.05),孕酮、孕烯醇酮含量差异极显著(P<0.01);泌乳盛期17α-羟基孕烯醇酮、17α-羟基孕酮、雄烯二酮、可的松含量差异显著(P<0.05),孕酮、孕烯醇酮含量差异极显著(P<0.01);泌乳末期17α-羟基孕酮、雄烯二酮、雌激素、皮质醇含量差异显著(P<0.05),17α-羟基孕烯醇酮、孕烯醇酮、孕酮含量差异极显著(P<0.01)。结论:山羊乳与牛乳中类固醇激素含量的差异可能是由于妊娠状态不同导致。

玉米籽粒乳线比例与籽粒相关性状的关系

选用3个不同粒型玉米品种马齿型郑单958(ZD958)、半马齿型先玉335(XY335)和硬粒型长单106(CD106)为试验材料,研究玉米籽粒乳线比例与粒长、粒宽、百粒鲜质量、含水率、灌浆速率、脱水速率的关系,以期为玉米最佳收获期的确定和适宜机械粒收玉米新品种的选育提供依据。结果表明,品种对玉米籽粒乳线比例的影响达到显著或极显著水平,XY335籽粒乳线比例增加速率最快,其次是CD106、ZD958。不同粒型玉米品种粒长、粒宽、百粒鲜质量对乳线比例的作用效应不同,粒宽、百粒鲜质量对乳线比例的作用效应较大。籽粒乳线比例与籽粒含水率、灌浆速率、脱水速率总体上呈显著或极显著负相关,含水率与灌浆速率、脱水速率呈显著或极显著正相关,灌浆速率与脱水速率呈极显著正相关。

全自动凯氏定氮仪测定婴幼儿奶粉中的粗蛋白含量

优化了全自动化凯氏定氮仪测定婴幼儿奶粉粗蛋白含量的前处理条件。探究了样品含量、催化剂配比、浓硫酸投加量、消化温度、消化时间等因素对粗蛋白质含量测定的影响。实验得到了最好的前处理条件:样品量1.0 g,催化剂质量配比为8∶0.5,浓硫酸加入量为12.0 mL,消化温度/时间为200℃(20 min)、300℃(20 min)、420℃(80 min)。平行测定结果的标准偏差为0.54%,加标回收率超过99%。奶粉中粗蛋白含量经优化前处理条件测定,精密度高、稳定性好,测定结果与外包装标注接近一致,达到国家乳制品蛋白含量标准。

盖勃法测定牛奶中脂肪含量的优化

[目的]为提高盖勃法测定牛奶中脂肪含量准确度和结果可靠性。[方法]本文研究《GB 5009.6—2016食品安全国家标准食品中脂肪的测定》中第四法盖勃法,分析操作过程遇到的问题。[结果]优化溶液总体积和调节时间控制等关键节点,明确硫酸浓度和静置时间等参数。[结论]实现检测步骤快速便捷、检测结果稳定准确,满足实验室日常检测,尤其适合生产企业和基层检测机构。

双峰驼乳功能蛋白及脂肪酸在泌乳期内的变化研究

为探究泌乳双峰骆驼乳功能性蛋白及脂肪酸变化规律,该研究动态追踪20峰泌乳双峰驼并采集泌乳期330 d内的驼乳,基于超高效液相色谱和气相色谱分析,检测α-乳白蛋白(α-lactalbumin,α-LA)、乳铁蛋白(lactoferrin,LF)、免疫球蛋白(immunoglobulin G,IgG)和溶菌酶4种目标功能蛋白及34种脂肪酸含量变化情况。结果表明,驼乳中共检测到4种目的功能蛋白及32种脂肪酸,色谱峰形尖锐、无杂峰干扰。驼乳4种功能蛋白含量在初乳期极显著高于常乳期(P<0.01),泌乳后期随着泌乳时间延长含量缓慢降低,功能蛋白间具有显著正相关性(P<0.05),其中α-乳白蛋白与IgG具有强正相关。脂肪酸含量在初乳期至常乳期30 d内波动明显,其余时期脂肪酸含量变化不大。长链脂肪酸、多不饱和脂肪酸和中链脂肪酸在泌乳期含量较为稳定;饱和脂肪酸和不饱和脂肪酸的比例合理,且饱和脂肪酸与不饱和脂肪酸及单不饱和脂肪酸变化趋势相反,在初乳期3~7 d内变化较为明显,在泌乳高峰期90~150 d波动极为明显,少数脂肪酸间具有较强的正相关。驼初乳功能蛋白与脂肪酸的组成及含量优于常乳,结果为深入研究双峰驼的泌乳生理特点及驼乳功能性制品的开发提供基础数据。

原料乳及乳制品中三聚氰胺含量检测研究

三聚氰胺对人体健康有一定的危害,长时间摄入会严重危害人类的健康,包括对生殖能力造成潜在损害,增加患上膀胱或肾结石的风险,甚至可能诱发膀胱癌,极端情况下甚至可能致命。本文用HPLC-MS对牛奶、巧克力进行三聚氰胺的含量测量,经比较,最终结果可靠且符合标准方法要求。

苦荞芽粉对大豆生乳腥味的影响及应用研究

目的研究苦荞芽粉对大豆生乳腥味的影响及其在大豆大樱桃酸奶中的应用。方法通过单因素实验探究苦荞芽粉的添加量、作用温度及作用时间对大豆脂肪氧合酶酶活、总醛含量和感官评分的影响,用正交实验优化工艺参数,再以感官评分、大豆总醛含量和脂肪氧合酶活性为验证指标,验证苦荞芽粉对大豆生乳脱腥效果。大豆生乳脱腥后加入大樱桃浆发酵得到大豆大樱桃酸奶,并与未脱腥处理发酵的大豆大樱桃酸奶进行对比。结果苦荞芽粉能抑制大豆脂肪氧合酶的活性,减少大豆总醛的产生,有效降低大豆生乳的腥味。苦荞芽粉用量、作用温度和时间对大豆总醛含量有显著影响(P<0.05)。最佳脱腥参数:作用温度为45℃,作用时间为2.5 h,苦荞芽粉添加量为2%,此条件下试验组比对照组总醛含量降低59%,脂肪氧合酶活性降低85%,大豆生乳豆香味浓郁,无腥味,口感细腻,无苦涩味,色泽均匀,感官评价为8.2分,显著优于对照组(P<0.05)。制成的大豆大樱桃酸奶呈粉红色、香气浓郁、口感细腻,感官评分(86.00分)显著高于对照组,蛋白质含量为3.59 g/100 g、脂肪为2.73 g/100 g、乳酸菌4.9×10^(8)CFU/mL,大肠杆菌没有检出,其余各项指标均达到国家标准要求。结论在大豆生乳中添加苦荞芽粉能抑制脂肪氧合酶酶活,降低总醛含量,有效降低了大豆腥味,经苦荞芽粉脱腥处理后的大豆生乳制成的大豆大樱桃酸奶品质更高,这可为提高大豆制品的食用品质及相关食品的开发和应用提供参考。

考马斯亮蓝法快速测定乳品中蛋白质含量

采用考马斯亮蓝G-250染料染色法对市售乳品中蛋白质进行测定,在595 nm波长处测定溶液的吸光度。实验结果表明,标准蛋白质在10～80μg/mL之间呈现良好的线性关系。该法简便快速、灵敏度高、重现性好,是测定乳品中蛋白质的有效方法。

圈养大熊猫乳汁营养成分分析及育幼营养对策初探

连续测定了１只１０ａ大熊猫产后１ｍｏ内１２个乳汁样品中水份、粗蛋白（ＣＰ）、粗脂肪（ＥＥ）、粗灰分（ＣＡ）、乳糖（Ｌａｃ）、１７种氨基酸（ＡＡ）、１０种矿物元素、６种维生素的含量．结果表明，大熊猫产后前６ｄ乳汁中多数营养素含量与６ｄ后含量差异明显．产后ｄ１乳汁中ｗ（ＣＰ）＝６．３４％，ｄ５～１５在５％左右；ｗ（ＥＥ）在２．５０％～７．３３％范围内变动；乳糖含量皆在１％左右；大多数维生素和微量元素含量远高于常见的家畜乳和人乳中相应成分的含量．在分析大熊猫乳汁营养成分含量特点的基础上，探讨了育纳营养对策．

成都麻羊与四川肉用黑山羊地方品种产乳性能研究

测定成都麻羊和四川肉用黑山羊地方品种羔羊哺乳期母羊的产乳量、乳常规营养成分、乳蛋白组分和乳酪蛋白遗传多态性.结果表明,母羊哺乳期的产乳量(kg)成都麻羊、金堂黑山羊、乐至黑山羊、自贡黑山羊和建昌黑山羊相应分别为46.15±1.78,101.67±4.93,85.76±3.36,54.32±6.64和36.65±2.65,成都麻羊极显著低于金堂黑山羊、乐至黑山羊(P<0.01),而极显著高于建昌黑山羊P<0.01)与自贡黑山羊差异不显著(P>0.05);乳中常规营养成分含量(g/L)均较高,范围乳脂为58.59～60.52、乳蛋白为44.18～46.37和乳糖为44.00～47.30;经产母羊常乳主要蛋白组分的相对含量(%)范围α-La为5.35～5.80,β-Lg为14.46～15.18,CN为70.04～71.01,IgG为7.04～7.31,SA为2.02～2.15,品种间差异不显著(P>0.05);酪蛋白电泳染色显示出α-CN和β-CN图带,α-CN均呈现4种不同的带型αS1-CN(H),αS1-CN(L)、αS2-CN(CC)型和αS2CN(CD),其中均以αS2-CN(CD)占优势.β-CN呈现单态,带型为β-CN(AB).

影响牛奶中糠氨酸质量分数变化的因素

综述了影响糠氨酸质量分数的相关因素,并加以归类和概括。系统的阐述了影响牛奶中糠氨酸质量分数的因素,包括杀菌过程中的加热温度和加热时间,储存过程中的储存温度和储存时间以及牛奶自身的理化性质,为科学地检测及反应牛奶中糠氨酸质量分数提供依据。