HPLC测定原料乳与乳制品中三聚氰胺质量分数的不确定度评定

建立高效液相色谱法测定测定原料乳与乳制品中三聚氰胺质量分数的不确定度评定方法,采用GB/T22388-2008高效液相色谱法测定测定原料乳与乳制品中三聚氰胺质量分数。建立数学模型,根据《测量不确定度评定与表示》(JJF1059—1999)中有关规定评估其不确定度。结果表明,按数学模型计算奶粉中三聚氰胺质量分数为2.70mg/kg,扩展不确定度为0.064mg/kg,结果表达为(2.70±0.064)mg/kg。该方法建立的数学模型合理、可靠。     

液态奶营养调整对北京居民消费意向影响力的调查

对北京市1301名消费者的液态奶消费行为进行了随机抽样调查，以了解消费者对维生素、矿物质强化和蛋白质、脂肪成分调整液态奶产品的态度。及产品包装上的营养标示对购买意向的影响力。结果表明，消费者对营养宣称产品总体上有积极的购买意向．但对营养强化的认知不足，对营养标示关注不够。建议乳品企业在开发相关产品时更加重视产品的人群针对性，注重健康宣称的告知途径，增大对消费者乳品营养教育投入的力度和系统性。     

Quality at time of purchase of dried milk products commercially packaged in reduced oxygen atmosphere

Nonfat dry milk (NDM) and powdered whey beverages are available at the retail level, packaged in No. 10 cans in a reduced oxygen atmosphere to prolong shelf life. The objective of this research was to determine the sensory and nutritional quality of these dried milk products at the time of purchase. In the 10 brands tested, wide variation existed in headspace oxygen, can seam quality, sensory quality, and vitamin A (with 6 of 10 brands entirely lacking the vitamin). Manufacturers of dried milk products packaged in cans for long-term storage need to give careful attention to can seam quality, product labeling, and vitamin fortification. Consumers would be well advised to evaluate several brands of dried milk products prior to large quantity purchases.     

The effect of vitamin concentrates on the flavor of pasteurized fluid milk

Fluid milk consumption in the United States continues to decline. As a result, the level of dietary vitamin D provided by fluid milk in the United States diet has also declined. Undesirable flavor(s)/off flavor(s) in fluid milk can negatively affect milk consumption and consumer product acceptability. The objectives of this study were to identify aroma-active compounds in vitamin concentrates used to fortify fluid milk, and to determine the influence of vitamin A and D fortification on the flavor of milk. The aroma profiles of 14 commercial vitamin concentrates (vitamins A and D), in both oil-soluble and water-dispersible forms, were evaluated by sensory and instrumental volatile compound analyses. Orthonasal thresholds were determined for 8 key aroma-active compounds in skim and whole milk. Six representative vitamin concentrates were selected to fortify skim and 2% fat pasteurized milks (vitamin A at 1,500–3,000 IU/qt, vitamin D at 200–1,200 IU/qt, vitamin A and D at 1,000/200–6,000/1,200 IU/qt). Pasteurized milks were evaluated by sensory and instrumental volatile compound analyses and by consumers. Fat content, vitamin content, and fat globule particle size were also determined. The entire experiment was done in duplicate. Water-dispersible vitamin concentrates had overall higher aroma intensities and more detected aroma-active compounds than oil-soluble vitamin concentrates. Trained panelists and consumers were able to detect flavor differences between skim milks fortified with water-dispersible vitamin A or vitamin A and D, and unfortified skim milks. Consumers were unable to detect flavor differences in oil-soluble fortified milks, but trained panelists documented a faint carrot flavor in oil-soluble fortified skim milks at higher vitamin A concentrations (3,000–6,000 IU). No differences were detected in skim milks fortified with vitamin D, and no differences were detected in any 2% milk. These results demonstrate that vitamin concentrates may contribute to off flavor(s) in fluid milk, especially in skim milk fortified with water-dispersible vitamin concentrates.     

乳品中维生素K1的测定

在奶粉样品中加入适量的脂酶，酶解后用NaOH皂化，用正己烷萃取，蒸干后用甲醇乙酯混合注溶解；用甲醇作流动相；用液相色谱法测定维生素K1，此法成功地提取了乳粉中的维生素K1，回收率达87．8％，变异系数CV为1．147％。     

Simultaneous determination of water-soluble vitamins in beverages and dietary supplements by LC-MS/MS

An LC-MS/MS method was developed for the simultaneous determination of 15 water-soluble vitamins that are widely used as additives in beverages and dietary supplements. This combined method involves the following simple pre-treatment procedures: dietary supplement samples were prepared by centrifugation and filtration after an extraction step, whereas beverage samples were diluted prior to injection. Chromatographic analysis in this method utilised a multi-mode ODS column, which provided reverse-phase, anion- and cation-exchange capacities, and therefore improved the retention of highly polar analytes such as water-soluble vitamins. Additionally, the multi-mode ODS column did not require adding ion pair reagents to the mobile phase. We optimised the chromatographic separation of 15 water-soluble vitamins by adjusting the mobile phase pH and the organic solvent. We also conducted an analysis of a NIST Standard Reference Material (SRM 3280 Multi-vitamin/Multi-element tablets) using this method to verify its accuracy. In addition, the method was applied to identify the vitamins in commercial beverages and dietary supplements. By comparing results with the label values and results obtained by official methods, it was concluded that the method could be used for quality control and to compose nutrition labels for vitamin-enriched products.     

伏安法快速检测牛乳及乳制品中细菌污染

研究了一种利用伏安法检测牛乳及乳制品中的细菌总数、大肠菌群数的方法。以抽滤的方式将待测样品富集在细菌滤膜上,把细菌滤膜固定在玻碳电极上,在磷酸盐缓冲液中,进行伏安测定,来判断牛乳及乳制品中的细菌污染程度,其结果与常规平板计数比较,差别无显著性。     

高效液相色谱法测定乳与乳制品中双氰胺的残留

建立了乳与乳制品中双氰胺残留的高效液相色谱测定方法.采用水-乙腈提取样品、氨基色谱柱分离、紫外检测器检测、外标法定量测定双氰胺残留.该方法的检出限为牛奶0.01mg/kg,乳粉为0.05 mg/kg(均为质量分数),线性范围为0.25.0 mg/L,并确定了回归方程,相关系-R2=0.9998,样品加标回收率在90％~8％,相对标准偏差为1.2％~2.3％.该法具有样品处理简单方便,灵敏度高,分析时间短等优点,可以满足乳与乳制品中双氰胺残留的测定.     

Does vitamin fortification affect light oxidation in fluid skim milk?

Off-flavors in milk related to light oxidation form due to photoxidation of native riboflavin and tetrapyrroles, resulting in an array of lipid oxidation compounds. Recent work has established that fortification with water-dispersible vitamin A can result in off-flavors in fluid skim milk caused by vitamin A degradation products in the vitamin premix. The objective of this study was to determine the role of vitamin fortification on light oxidation of high temperature, short time pasteurized fluid skim milk. First, the aroma profiles and aroma-active volatile compounds in light-exposed vitamin premixes were determined by exposing the premixes to fluorescent (FL) or light-emitting diode (LED) light at 2,000 lx at 4°C for 0, 2, 4, 8, or 24 h. A trained panel (n = 6) documented aroma profiles of each vitamin premix at each time point. Headspace solid-phase microextraction followed by gas chromatography-olfactometry and gas chromatography-mass spectrometry (GC-MS) were performed to characterize aroma-active compounds in light-exposed vitamin premixes. In the second experiment, commercial vitamin premixes (vitamin A and vitamin D in oil and water matrices) were used to fortify skim milk (vitamin A: 3,000 IU/946 mL; vitamin D: 600 IU/946 mL). Skim milk was pasteurized, homogenized, and packaged in 946-mL high-density polyethylene jugs. Milks were exposed to FL or LED light at 2,000 lx at 4°C for 4, 12, 24, or 48 h. Controls with and without vitamins and light shielding were included. Riboflavin and vitamin A and D degradation were quantified via ultra-high-performance liquid chromatography. A trained panel (n = 8) documented sensory profiles of milks at each time point. Lipid oxidation volatile compounds were quantified via solid-phase microextraction with GC-MS. Vitamin degradation volatile compounds were quantified via solvent-assisted sorptive stir bar extraction with GC-MS. Riboflavin, vitamin A, and vitamin D degradation were consistent with that reported in previous studies. We found no effect of vitamin fortification on development of typical light oxidation–related off-flavors (cardboard and mushroom) or lipid oxidation–related volatiles (hexanal and heptanal). A perfumey/floral flavor was documented in the oil-based vitamin A-fortified milk, suggesting that light exposure affected the off-flavors contributed by water- versus oil-based vitamin fortification. These results show no evidence that vitamin fortification at current levels provides any protection against light oxidation–related off-flavors in fluid milk.     

Aflatoxin M1 in raw,UHT milk and dairy products in Sicily (Italy)

A survey on 73 milk samples from different animal breeds and 24 dairy products samples from Sicily, Italy, was carried out for the presence of aflatoxin M₁ (AFM1) by LC-fluorescence detection after immunoaffinity cleanup. AFM1 was detected in 48% and 42% of the milk and dairy samples at concentration ranges between <5.0–16.0 and <5.0–18.0 ng L^?1, respectively. Within the raw milk samples, 92% had an AFM1 content below 5.0 ng L^?1, in 7% of the cases it was in the range 5.0–10.0 ng L^?1 and 1% was contaminated between 10.0 and 20.0 ng L^?1. For the dairy products, ultra-high-temperature treated (UHT) milk, milk cream and cheese, the incidence was 42%, of which 83% contained less than 5.0 ng L^?1 and 17% contained 10.0–20.0 ng L^?1 AFM1. The levels of contamination found justify continuous monitoring for public health and to reduce consumer exposure.     

Authenticity assessment of dairy products

The authenticity of dairy products has become a focal point, attracting the attention of scientists, producers, consumers, and policymakers. Among many others, some of the practices not allowed in milk and milk products are the substitution of part of the fat or proteins, admixtures of milk of different species, additions of low-cost dairy products (mainly whey derivatives), or mislabeling of products protected by denomination of origin. A range of analytical methods to detect frauds have been developed, modified, and continually reassessed to be one step ahead of manufacturers who pursue these illegal activities. Traditional procedures to assess the authenticity of dairy products include chromatographic, electrophoretic, and immunoenzymatic methods. New approaches such as capillary electrophoresis, polymerase chain reaction, and isotope ratio mass spectrometry have also emerged alongside the latest developments in the former procedures. This work intends to provide an updated and extensive overview since 1991 on the principal applications of all these techniques together with their advantages and disadvantages for detecting the authenticity of dairy products. The scope and limits of different tools are also discussed.     

婴幼儿配方食品和乳粉中核苷酸的测定方法

采用碱性磷酸酶先将样品中的核苷酸酶解为核苷,然后用高效液相色谱法测定婴幼儿配方食品和乳粉中核苷酸总量。试样经水提取,通过调pH值沉淀蛋白质,样液中的核苷酸经碱性磷酸酶水解生成核苷,再通过快速加热的方式终止酶解反应,同时进一步去除杂质,用磷酸二氢钾及甲醇作流动相,用普通C18色谱柱,采用梯度洗脱的模式对5种核苷进行有效分离。本方法回收率在92.4%～103.7%之间,相对标准差2.0%～8.0%。核苷酸各组分定量限:CMP为0.6 mg/100g,UMP为0.7 mg/100g,IMP+AMP为0.5 mg/100 g,GMP为0.4 mg/100 g(均为质量分数)。该方法简便、快速、准确,完全能满足婴幼儿配方食品中核苷酸总量测定的要求。为核苷酸检测开辟了全新的途径。     

乳制品中游离甘氨酸的测定

建立了高效液相色谱法测定乳制品中甘氨酸质量浓度的方法。采用色谱柱为waters氨基酸色谱柱,流动相缓冲液A和缓冲液B,流速为0．4mL／min,激发波长338nm,发射波长425nm。结果表明,甘氨酸的最低检出限为0．03mg／L,回收率为99．88％,变异系数（CV％）为0．42。     

乳与乳制品中细菌总数的检测技术

对各种常用检测乳与乳制品中细菌总数方法的原理、操作、优缺点及应用作了一个较详细的介绍，并对快速检测技术的要求进行了总结。     

食品添加剂中维生素A、D和E的检测方法研究

食品添加剂中脂溶性维生素A、D和E在皂化过程中与脂肪分离，经石油醚萃取后，用高压液相色谱法．由紫外检测器一次性测定3种物质。维生素A、D和E的回收率分别为94．7％．101．7％、96．7％．102．3％、97．5％．103．5％，精密度分别为2．79％、4．16％和1.68％。结果表明，该方法的主要特点为操作快捷、精密度高、重现性好。     

应用高效液相色谱同时测定牛奶中三种四环素的方法研究

应用高效液相色谱法,优化了牛奶中3种四环素的检测方法且力求操作简单、快捷.本方法采用0.1 mol/LEDTA-McIlvaine缓冲液(pH 4.0)提取奶中的残留的三种四环素类抗生素,通过C18固相萃取柱进行提纯、净化,提高了方法的灵敏度.结果表明,该方法最低检出限达到国标的兽药残留最低限量要求,加标回收率103 ％～109％之间.     

Heat-induced changes in dairy products containing sucrose

The aim of the present work was to analyse the influence of the variables reaction temperature, casein–sucrose ratio and pH, on the kinetic parameters of gelation reactions, the gelation time and the functionality of casein micelles in concentrated milk systems containing sucrose.     

高效液相色谱法同时测定乳及乳制品中防腐剂和甜味剂

建立了高效液相色谱法同时测定乳及乳制品中苯甲酸、山梨酸、安赛蜜和糖精钠的方法.通过加入适量沉淀剂除去样品中绝大部分蛋白质后,采用C18色谱柱.以甲醇-0.05mol/L磷酸二氢钾溶液为流动相,用紫外检测器于230 nm波长处检测.回收率在95.0%～103.0%,精密度(RSD)为1.70%2.03%,检出限分别为1.5,1.5,1.5,2.5 μg/g.该方法可用于乳制品中这4种添加剂的同时测定.