快速滴定法测定原料乳蛋白质的条件控制

目的:实验快速滴定法直接测定原料奶中蛋白质含量的可行性及掺杂物对该法的干扰程度,为原料奶验收和大批量样品检测提供快速有效的测定方法。方法:分别对快速滴定法的测定条件、操作步骤、终点判定进行反复实验,采用干燥法和凯氏定氮法对结果准确性进行验证。结果:样品取样量为1.00mL,用1.00mL 0.1mol/L盐酸控制酸度时,采用2次滴定法,消耗4.50mL 0.2%SDS,得到理想结果;与凯氏定氮法和仪器法所得结果相比,无显著差异(p0.05)。以凯氏定氮法为标准,得到两种方法之间的数量关系,即消耗1.00mL 0.2%SDS相当于含蛋白质7.53×10-3g。一定浓度范围内的非蛋白氮掺杂物对快速滴定法测定原料奶中蛋白质的含量也无明显影响。结论:本法操作简便、结果准确,可满足原料奶验收、大批样品测定和实时掌控牛奶品质状况的要求,在奶业生产领域具有非常明显的推广应用价值。     

桑葚汁中酵母可同化氮测定方法比较

为顺利完成果酒发酵过程,酿酒前了解果酒发酵液的酵母可同化氮情况非常必要。分别采用精确法(氨基酸分析仪法、靛酚蓝比色法)和速测法(甲醛值法)两种方法测定了不同品种不同园区的18个桑葚汁样品游离氨基酸浓度、铵离子浓度和可同化氮浓度,比较了这两种方法测量值间的关系。结果表明：不同品种、不同园区桑葚汁中都含有17种氨基酸,各种氨基酸浓度及游离氨基酸总浓度差异较大。游离铵离子和甲醛值法测定可同化氮不同品种不同园区差异较大。精确法测定可同化氮浓度均低于速测法测定结果。两种方法间存在明显的线性关系,线性方程为Y=1.1736X+0.7901,且相关系数可达0.9967。可以用甲醛值法快速测定桑葚汁中可同化氮。     

反向流动注射法在线分析皮革废水中的甲醛

为了监控制革废水中甲醛的含量,建立了一种快速、灵敏、精确的反向流动注射光度法,该法基于在碱性环境下,甲醛与间苯三酚生成一种红色物质,在470 nm处有光吸收,从而定量检测样品中甲醛的浓度。该法在范围10~2000μg/L内,浓度与峰高呈线性关系良好,其线性方程为:y=0.0724 x+4.8494(R2=0.9994)。试验过程中对各变量进行了优化,在优化条件下,相对标准偏差为0.27%(n=10),最低检出限为3μg/L。该方法具有使用试剂简单、操作简单、精密度高等优点,可以作为测定皮革废水中甲醛含量的一种可行的检测方法。     

柱前衍生高效液相色谱法测定5种常见食用菌中的甲醛含量

目的建立柱前衍生-高效液相色谱法测定5种常见食用菌中甲醛含量。方法将干制与新鲜食用菌用超纯水浸泡,浸泡液经2,4-硝基苯肼(DNPH)衍生后,采用高效液相色谱法检测;色谱柱:C18(250mm×4.6mm,5μm),流动相:乙腈-水(70:30, V:V);流速为1.0 mL/min;检测波长352 nm;柱温40℃。外标法定量测定食用菌中甲醛含量。结果柱前衍生法对甲醛浓度在10.70～214.00μg/L范围内与其衍生物峰面积呈良好的线性关系,线性回归系数(r~2)为0.9964,方法的检出限为4.20μg/kg(S/N=3)。加标回收率为78.27%～114.26%,精密度1.55%～9.22%(n=6)。5种食用菌样品仅香菇样品检出甲醛。新鲜香菇甲醛含量超标,干制后香菇甲醛含量降低,低至国家标准含量以下。结论本研究的方法简便、快速、准确、稳定,可用于测定食用菌中甲醛含量。     

高效测定纺织品中甲醛含量方法的研究

研究了用超声辅助柱前衍生-高效液相色谱法(UA-HPLC)直接测定纺织品中甲醛含量的可行性.以2,4-二硝基苯肼乙腈溶液-乙酸铵缓冲液为反应液,样品于40℃下衍生反应30 min,快速冷却后直接进行HPLC分析.在印花针织汗布、粘合衬布料两种基质中分别添加5、20、50、100 mg/kg四个浓度水平的甲醛,其回收率在83％～108％,相对标准偏差(n=6)＜5％;此方法的定量限(以信噪比S/N＞10计)为3 mg/kg.该法具有快速、简便,重现性好特点,适用于纺织品中甲醛含量的测定.     

乳清蛋白水解物游离氨基浓度测定方法比较

采用甲醛法、茚三酮法、2,4,6-三硝基苯磺酸(TNBS)法及邻苯二甲醛(OPA)法这4种方法对碱性蛋白酶水解乳清分离蛋白所得水解物中游离氨基浓度进行测定.结果表明,甲醛法和茚三酮法因其灵敏度较低,所测定结果偏低而不适于对水解液中游离氨基进行测定.对TNBS法与OPA法进行比较实验得出结论:OPA队法相比TNBS法具有较高的精确度,能更加安全、简便、快速的测定游离氨基浓度,并且适用范围更宽.     

不同胎次奶牛乳中乳蛋白含量的近红外光谱定量分析

对不同胎次奶牛的牛奶样品进行近红外光谱扫描,并用多功能乳制品分析仪对牛奶样品中蛋白质的含量进行测定。利用正交实验设计,分别采用主成分回归法(PCR)、偏最小二乘法(PLS)、改进偏最小二乘法(MPLS)三种定量校正方法和多种光谱预处理方法建立模型,利用目标函数法对模型进行评定,结果表明:一胎、二胎奶牛乳样中乳蛋白的最优模型相同,其校正相关系数(R2)、定标标准差(SEC)和预测标准差(SEP)分别为:0.9626、0.0531、0.0630和0.9377、0.0810、0.1100;建立了三胎及以上奶牛乳样中乳蛋白的最优模型,R2、SEC和SEP分别为:0.9406、0.0461和0.0500;同时,建立了所有乳样中乳蛋白的最优模型,R2、SEC和SEP分别为:0.9351、0.0687和0.0790。所建模型对于快速、准确、无损、定量检测原料奶中乳蛋白的含量是可行的,该方法为快速检测混合原料奶中乳蛋白含量提供了理论依据。     

不同胎次奶牛乳中乳蛋白含量的近红外光谱定量分析

对不同胎次奶牛的牛奶样品进行近红外光谱扫描,并用多功能乳制品分析仪对牛奶样品中蛋白质的含量进行测定。利用正交实验设计,分别采用主成分回归法(PCR)、偏最小二乘法(PLS)、改进偏最小二乘法(MPLS)三种定量校正方法和多种光谱预处理方法建立模型,利用目标函数法对模型进行评定,结果表明:一胎、二胎奶牛乳样中乳蛋白的最优模型相同,其校正相关系数(R2)、定标标准差(SEC)和预测标准差(SEP)分别为:0.9626、0.0531、0.0630和0.9377、0.0810、0.1100;建立了三胎及以上奶牛乳样中乳蛋白的最优模型,R2、SEC和SEP分别为:0.9406、0.0461和0.0500;同时,建立了所有乳样中乳蛋白的最优模型,R2、SEC和SEP分别为:0.9351、0.0687和0.0790。所建模型对于快速、准确、无损、定量检测原料奶中乳蛋白的含量是可行的,该方法为快速检测混合原料奶中乳蛋白含量提供了理论依据。      

乙酰丙酮法测定啤酒中甲醛含量的研究

目的改进乙酰丙酮法测定啤酒中甲醛含量。方法采用乙酰丙酮比色法测定啤酒中甲醛含量。通过3组加标回收试验,测定不同蒸馏体积、不同反应时间、不同磷酸浓度对乙酰丙酮显色法的干扰,确定最合适的检测条件。结果最佳条件为:蒸馏液为200 mL,加入硫酸浓度为20%,反应时间5 min。甲醛含量在0~50μg范围内具有良好的线性关系,线性方程为Y=0.022X-0.001,r~2=1,回收率大于80%。结论该方法用于检测啤酒中甲醛含量简单、快速、准确,易于推广。     

直接提取-超高压液相色谱-电喷雾串联质谱法检测原料奶及奶制品中的四环素类抗生素

目的 建立直接提取-超高压液相色谱-电喷雾串联质谱法(UPLC-ESIMS/MS)同时测定原料奶及奶粉中土霉素、四环素、金霉素、强力霉素4种四环素类药物的分析方法。方法 原料奶及奶粉样品经少量高氯酸沉淀蛋白、低温冷冻除脂后, 用C18色谱柱分离, 以0.1%甲酸水和乙腈为流动相进行梯度洗脱, 电喷雾串联质谱正离子模式扫描, 多反应监测模式(MRM)检测, 外标法定量。结果 4种四环素族药物在1~1000 ng/mL浓度范围内线性关系良好, 相关系数r均在0.993以上。本方法的定量限为(S/N≥10)为原料奶5μg/kg, 奶粉25 μg/kg, 在10、50、100 μg/kg三个加标水平下, 加标回收率为73.4%~99.4%, 相对标准偏差为0.8%~14.3%(n≥6)。结论 该方法简便快速、灵敏可靠、经济有效, 适用于原料奶及奶粉中土霉素、四环素、金霉素和强力霉素4种四环素族药物残留的测定。     

Quantification of trace elements in raw cow’s milk by inductively coupled plasma mass spectrometry (ICP-MS)

The levels of trace elements are an important component of safety and quality of milk. While certain elements such as chromium are essential at low levels, an excess can result in deleterious effects on human health. International quality control standards for milk are published by the Codex Alimentarious Commission and levels of heavy metals in milk intended for human consumption are routinely monitored. This paper describes a new method for demonstrating the levels of V, Cr, Mn, Sr, Cd and Pb in raw cow’s milk, using an ICP-MS. Samples (n = 24) of raw cow’s milk were collected from dairy farms close to mines in Gauteng and North West Provinces of South Africa. In order to destroy organic matrix, each freeze dried milk sample was mineralised by using a microwave assisted digestion procedure. Concentrations of trace elements in digested milk samples were measured by ICP-MS. A whole milk powder reference material (NIST SRM 8435) was used to evaluate the accuracy of the proposed method. It was found that the levels of V, Cr, Mn, Sr, Cd and Pb obtained using the new method showed concordance with certified values.     

Comparative analysis of bacterial community composition in bulk tank raw milk by culture-dependent and culture-independent methods using the viability dye propidium monoazide

Microbial diversity of 3 raw milk samples after 72 h of storage at 4°C in a bulk tank was analyzed by culture-dependent and -independent methods. The culture-dependent approach was based on the isolation of bacteria on complex and selective media, chemotaxonomic differentiation of isolates, and subsequent identification by 16S rRNA gene sequencing. The culture-independent approach included the treatment of raw milk with the dye propidium monoazide before direct DNA extraction by mechanic and enzymatic cell lysis approaches, and cloning and sequencing of the 16S rRNA genes. The selective detection of viable bacteria improved the comparability between bacterial compositions of raw milk based on culture-dependent and -independent methods, which was the major objective of this study. Several bacterial species of the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were detected by the culture-dependent method, whereas mainly bacteria of the phylum Proteobacteria as well as low proportions of the phyla Bacteroidetes and Actinobacteria were detected by the culture-independent method. This led to the conclusion that the phylum Firmicutes was strongly discriminated by the culture-independent approach. Generally, species richness detected by the culture-dependent method was higher than that detected by the culture-independent method for all samples. However, few taxa could be detected solely by the direct DNA-based method. In conclusion, the combination of culture-dependent and -independent methods led to the detection of the highest bacterial diversity for the raw milk samples analyzed. It was shown that DNA extraction from raw milk as the essential step in culture-independent methods causes the discrimination of taxa by incomplete cell lysis. Treatment of raw milk with the viability dye propidium monoazide was optimized for the application in raw milk without former removal of milk ingredients and proved to be a suitable tool to ensure comparability of bacterial diversity depicted by both methods.     

Nutritional Value and Technological Suitability of Milk from Various Animal Species Used for Dairy Production

Abstract: The analysis of nutritional value and selected traits of technological suitability of milk was performed on the basis of the available literature. This analysis concerned various animal species used for dairy purposes (cattle, buffalo, goats, sheep, camels, donkeys, and horses). It has been stated that a considerable diversity exists in the analyzed parameters and traits of milk, which results in various directions of milk utilization. Cow milk accounts for more than 80% of world milk production. It is the most universal raw material for processing, which is reflected in the broadest spectrum of manufactured products. Sheep and buffalo milk, regarding their high content of protein, including casein, and fat, make a very good raw material for processing, especially cheesemaking. Donkey and horse milk have the most comparable protein composition to human milk (low content of casein, lack of αs₁‐casein fraction and β‐lactoglobulin, and high content of lysozyme). Donkey milk is additionally characterized by a fatty acid profile distinctive from milk of other analyzed animal species. Camel milk also has valuable nutritional properties as it contains a high proportion of antibacterial substances and 30 times higher concentration of vitamin C in comparison to cow milk. The composition of goat milk allows using it as the raw material for dairy processing and also to some extent as a therapeutical product (low content or lack of αs₁‐casein).     

Bacillus cereus spores during housing of dairy cows: factors affecting contamination of raw milk

The contamination of raw milk with Bacillus cereus spores was studied during the indoor confinement of dairy cattle. The occurrence of spores in fresh and used bedding material, air samples, feed, feces, and the rinse water from milking equipment was compared with the spore level in bulk tank milk on 2 farms, one of which had 2 different housing systems. A less extensive study was carried out on an additional 5 farms. High spore concentrations of >100 spores/L in the raw milk were found on 4 of the farms. The number of spores found in the feed, feces, and air was too small to be of importance for milk contamination. Elevated spore contents in the rinse water from the milking equipment (up to 322 spores/L) were observed and large numbers of spores were found in the used bedding material, especially in free stalls with >5 cm deep sawdust beds. At most, 87,000 spores/g were found in used sawdust bedding. A positive correlation was found between the spore content in used bedding material and milk (r = 0.72). Comparison of the genetic fingerprints obtained by the random amplified polymorphic DNA PCR of isolates of B. cereus from the different sources indicated that used bedding material was the major source of contamination. A separate feeding experiment in which cows were experimentally fed B. cereus spores showed a positive relationship between the number of spores in the feed and feces and in the feces and milk (r = 0.78). The results showed that contaminated feed could be a significant source of spore contamination of raw milk if the number of spores excreted in the feces exceeded 100,000/g.     

The mechanism of determining the adulteration of whole milk with milk powder by spectrophotometry

The spectrophotometric method for determination of the reconstituted milk adulteration in the raw milk has been suggested by empirical experiments. However, the mechanism is unclear. In this study, we followed and modified their methods and found that the mechanism is the turbidity difference between homogenized milk and non-homogenized milk. The equation of turbidance S=KBC˙ (d³/d⁴ + λ⁴) is offered as an explanation of this observation. There are linear relationships between transmittance (T[%]) and the amount of there constituted milk added (r=0.99) to the raw milk, non-homogenized milk, and homogenized milk. This method is recommended for detecting the addition of reconstituted milk to raw or non-homogenized milk. The result of the empirical methods showed that the detection rate of adulteration can be as accurate as 2.5%, but this method is not recommended for detecting the adulteration of homogenized milk.     

生物发光快速测定生乳菌落总数的方法

为消除利用ATP生物发光法测定生乳菌落总数时非细菌ATP对测定结果的干扰,建立了一种样品前处理方法。利用ATP生物发光法对经过前处理的生乳样品进行检测,结果表明,生乳菌落总数对数值与生乳细菌ATP发光对数值呈现较好的线性关系(R2=0.982),相关程度为显著相关(P<0.01),说明该前处理方法能够有效排除非细菌ATP的干扰,有利于提高ATP生物发光法定量测定生乳菌落总数准确性。     

指纹图谱技术在生鲜乳掺假检测中的研究进展

生鲜乳是乳制品行业发展的主要原料,是决定乳制品质量的关键因素。然而近年来国内外在乳制品方面的食品安全事件频发,不法分子通过在生鲜乳中掺入虚假物质以获取经济利益的行为已经成为严重的安全问题,对人们健康以及整个乳制品行业造成不良影响。指纹图谱技术是对通过一定的分析工具产生的图像进行判别的一种检测技术,可以对生鲜乳的掺假进行更灵敏、准确和快速的检测。本文通过对生鲜乳的安全现状进行剖析,总结了电泳法、光谱法、色谱法和电子感官技术法4种指纹图谱技术在牛乳掺假检测中的应用,比较了4种技术的优点和局限性,并对未来的研究方向进行了展望,为提高生鲜乳的品质与安全以及保证消费者健康提供理论依据与参考。     

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.     

Bedding and bedding management practices are associated with mesophilic and thermophilic spore levels in bulk tank raw milk

Mesophilic and thermophilic spore-forming bacteria represent a challenge to the dairy industry, as these bacteria are capable of surviving adverse conditions associated with processing and sanitation and eventually spoil dairy products. The dairy farm environment, including soil, manure, silage, and bedding, has been implicated as a source for spores in raw milk. High levels of spores have previously been isolated from bedding, and different bedding materials have been associated with spore levels in bulk tank (BT) raw milk; however, the effect of different bedding types, bedding management practices, and bedding spore levels on the variance of spore levels in BT raw milk has not been investigated. To this end, farm and bedding management surveys were administered and unused bedding, used bedding, and BT raw milk samples were collected from dairy farms (1 or 2 times per farm) across the United States over 1 yr; the final data set included 182 dairy farms in 18 states. Bedding suspensions and BT raw milk were spore pasteurized (80°C for 12 min), and mesophilic and thermophilic spores were enumerated. Piecewise structural equation modeling analysis was used to determine direct and indirect pathways of association among farm and bedding practices, levels of spores in unused and used bedding, and levels of spores in BT raw milk. Separate models were constructed for mesophilic and thermophilic spore levels. The analyses showed that bedding material had a direct influence on levels of spores in unused and used bedding as well as an indirect association with spore levels in BT raw milk through used bedding spore levels. Specific bedding and farm management practices as well as cow hygiene in the housing area were associated with mesophilic and thermophilic spore levels in unused bedding, used bedding, and BT raw milk. Notably, levels of spores in used bedding were positively related to those in unused bedding, and used bedding spore levels were positively related to those in BT raw milk. The results of this study increase the understanding of the levels and ecology of mesophilic and thermophilic spores in raw milk, emphasize the possible role of bedding as a source of spores on-farm, and present opportunities for dairy producers to reduce spore levels in BT raw milk.     

二氧化氯对原料奶保鲜作用的研究

通过在原料奶中加入绿先锋保鲜剂，研究了二氧化氯对鲜牛奶的保鲜作用，以及二氧化氯在牛奶中的衰减过程和二氧化氯对牛奶中各项理化测定指标影响。结果表明，在30℃条件下，加入质量分数为0.05%-0.1%的绿先锋保鲜剂对鲜牛奶具有明显的保鲜效果，保存可延长至24h；该保鲜剂在加入到牛奶中后3-4h内即会衰减完毕，也不会对鲜牛奶中各项理化指标的测定产生干扰影响。