液相色谱法测定核桃乳中糠氨酸含量

目的建立液相色谱法测定核桃乳中糠氨酸含量的检测方法。方法样品经酸水解、乙酸铵缓冲溶液定容后,经反相C18色谱柱分离,以甲醇/三氟乙酸溶液为流动相,流速为1.0mL/min,梯度洗脱,在紫外检测器波长为280 nm下检测。结果糠氨酸浓度在2～50μg/L的范围内线性关系良好,相关系数均大于0.999。糠氨酸在2.00、5.00和10.00mg/100g蛋白质添加水平的回收率为88.82%～91.95%,相对标准偏差(relative standard deviation, RSD)小于3.55%(n=6),方法检出限为1.0 mg/100 g蛋白质。结论该方法操作过程简单、方法准确、可靠、重现性好、回收率较高,适合于核桃乳中糠氨酸含量的分析检测。     

HPLC法测定乳品中的糠氨酸

本文采用高效液相色谱法测定乳品中的糠氨酸,应用耐酸的C18色谱柱和紫外检测器.本方法的最低检测限为1.48×10-9g,变异系数CV(%)为1.23,回收率为98.2%～100.8%.     

温度与复原度对巴氏杀菌乳中糠氨酸含量影响的研究

采用农业部标准NY/T 939-2005中的方法对巴氏杀菌乳中的糠氨酸进行检测,测定不同杀菌温度及不同复原度条件下牛乳中的糠氨酸含量。对糠氨酸含量随温度和复原度的变化规律进行研究,得到不同复原度的复原乳在不同温度下的糠氨酸含量数据,并对数据进行分析处理,制定了不同温度下的糠氨酸与复原度的线性回归方程。研究结果可对复原乳进行的定性判别和定量检测,以避免对复原乳的误判。     

HPLC法测定婴幼儿配方食品中的糠氨酸

建立高效液相色谱法测定婴幼儿配方食品中糠氨酸的分析方法。样品经复溶后,经10.6 mol/L盐酸水解,用迪马铂金ODS色谱柱分离,采用紫外检测器在280 nm下进行检测,外标法定量。方法标准曲线线性相关系数r2=0.999 9,精密度RSD为2.23%,加标回收率为96.56%~106.24%,检出限(S/N=3)为0.38μg/mL,检测限(S/N=10)为1.25μg/mL。分析21个婴幼儿配方食品样品(含11个品牌),结果表明,糠氨酸含量水平在468 mg/100 g~1 467 mg/100 g(以蛋白质计)之间,部分样品的蛋白质质量损伤程度较大。     

一种快速检测复原乳的方法

用表面荧光方法,以美拉德反应的产物糠氨酸为指标,检测生乳中添加复原乳的含量,可以检测到添加量5%以上的复原乳。该方法快速简便,不用任何复杂的前处理,5min可检验一个样品,能适应快速检测的需要。同时用高效液相色谱法加以对照,作为表面荧光方法检验的依据。      

一种快速检测复原乳的方法

用表面荧光方法,以美拉德反应的产物糠氨酸为指标,检测生乳中添加复原乳的含量,可以检测到添加量5%以上的复原乳。该方法快速简便,不用任何复杂的前处理,5min可检验一个样品,能适应快速检测的需要。同时用高效液相色谱法加以对照,作为表面荧光方法检验的依据。     

复原乳鉴别指标探讨

选择适宜的鉴别指标,确定并完善复原乳的鉴定方法,不但可为质量监督检验机构的检测和监督工作提供技术支持．而且可有效保护消费者的利益。可以通过检测牛奶在长时间贮藏过程中产生的荧光物质．或检测牛奶中脂肪酸组成分的变化来鉴别鲜奶与复原乳,但难以排除某些干扰因素的影响。近年来复原乳鉴定指标的研究热点主要集中在奶制品经热处理后其中的热损害产物。有两种化学反应产物可用来评价：（1）降解产物：热不稳定组分的降解、变性、失活,如乳清蛋白或酶;（2）新形成物质：如乳果糖或美拉德反应的产物。目前国际上通常用糠氨酸和乳果糖作为评估热处理和贮存对奶制品质量影响的指标。然而各指标也不可避免的存在一定的局限性,因此可能需要不止一个指标来进行综合评价。     

高效液相色谱法测定灭菌乳中糠氨酸的不确定度评定

目的 评定高效液相色谱法测定灭菌乳中糠氨酸含量结果的不确定度.方法 依据NY/T939-2016《巴氏杀菌乳和UHT灭菌乳中复原乳的鉴定》测定灭菌乳中糠氨酸的含量,建立高效液相色谱法测定灭菌乳中糠氨酸含量的不确定度评定的数学模型,全面分析实验过程中各不确定度的来源,并对各不确定度进行分量量化及合成,计算灭菌乳中糠氨酸的...     

影响超高温灭菌纯牛乳糠氨酸含量的关键点分析及控制

牛乳中的乳糖作为还原糖,在热处理过程中与牛乳蛋白之间发生美拉德反应并生成中间产物——乳果糖基赖氨酸(Lactulosyllysine),其经酸水解后可生成呋喃素(Furosine)。呋喃素又称糠氨酸,可作为一个定量指标用于鉴别UHT灭菌纯牛乳或巴氏杀菌乳是否为复原乳。由于加工工艺参数的影响,使得UHT灭菌纯牛乳中的糠氨酸含量时常超出标准范围,为了解决此问题,本文分别对预巴杀温度、浓缩工艺、添加管道滞留奶以及UHT杀菌工艺参数这几个可能影响糠氨酸含量的关键点进行了分析,发现浓缩工艺、添加管道滞留奶以及UHT杀菌工艺参数是影响成品中糠氨酸含量最主要的关键点。      

液相色谱法测定茶氨酸提取物中咖啡因的含量

目的建立一种快速、简便测定茶氨酸提取物中咖啡因的液相色谱方法。方法样品经过前处理,以1-癸烷磺酸钠溶液(1.22 g→850 m L)+乙腈+磷酸=850+150+1(V:V:V)为流动相,流速1.0 m L/min,柱温40℃,进样量10μL,等度洗脱,经Agilent C18柱分离,于280 nm波长处检测,以外标法定量。结果用本方法进行检测,能很好的分离咖啡因,在浓度0.001 mg/m L至0.05 mg/m L之间呈现良好的线性关系,方法的相关系数可达1.000,平均回收率为100.2,在95%~105%之间,相对标准偏差(RSD)为1.0%,定量限为92.78μg/g,检出限为29.03μg/g。结论该方法耗时短、操作简便、准确、重现性好、分离效果明显。可以应用于茶氨酸提取物中咖啡因含量的测定。     

COMPARISON OF WET-CHEMICAL METHODS FOR DETERMINATION OF LIPID HYDROPEROXIDES

Five methods for determination of lipid hydroperoxides were evaluated, including two iodometric procedures involving a titration and a spectrophotometric micro method, and three other spectrophotometric methods namely the ferro, International Dairy Federation (IDF) and FOX2 (ferrous oxidation in xylenol orange). Peroxide values determined in a range of food products by these five methods gave different results. The ferro method required large amounts of solvent (50 mL/sample); the FOX2 method had a low range (0.005–0.04 μmol hydroperoxide); the end point detection of the titration method was subjective and required a large amount of sample (1 g); and the micro method was sensitive to interruptions during execution. Therefore, only the modified IDF method was chosen for further testing and validation. Stability tests of the standard curve showed a variation coefficient of 4% and within runs the highest variation was 5.9% (for blank) and a maximum of 9.6% between runs variation for the lowest concentration. Among the antioxidants tested, only ethylenedi-aminetetraacetic acid (EDTA) affected the peroxide determinations.     

COMPARISON OF METHODS FOR THE DETERMINATION OF CELL VIABILITY IN STORED BAKER'S YEAST

The classical plate method for discriminating between viable and nonviable yeast cells in stored baker's yeast was compared with dead cell staining techniques using methylene blue and three fluorochrome stains. The increase of dead yeast cells during storage of baker's yeast for up to 16 days at 5°C, 20°C and 35°C was determined. During prolonged storage, especially at 35°C, the death rate increased rapidly and the yeast cake began to soften because of autolysis. In these conditions the choice of method for determining the proportion of dead cells proved to be of great importance. Useful results for yeast stored for some time at 35°C could be obtained only by the fluorochrome technique using primuline, acridine orange or acriflavine as fluorochromes.     

A COMPARISON OF MICROBIOLOGICAL AND RADIOIMMUNOASSAY METHODS FOR THE DETERMINATION OF PANTOTHENIC ACID IN FOODS

Seventy-five foods were analyzed for the vitamin pantothenic acid using a microbiological assay and a new radioimmunoassay (RIA). The food sample extract used in both assays was the result of dialysis after enzyme hydrolysis. In the method used previously, the food-enzyme mixture had been filtered.
A very high correlation (r²=.94) between the results from the RIA and the microbiological assay was found. There was a statistically significant difference between the two assay results for all foods and for the subgroups meats, breads and cereals, and fruits and vegetables at p=.05. At p = .01 breads and cereals and fruits and vegetables did not have significantly different results between the two assay methods. For all foods and all subgroups, the microbiological assay produced a higher mean result than the RIA.
The RIA is an acceptable method for assaying pantothenic acid in breads and cereals and fruits and vegetables. Futher study is needed to determine how components of meat interact with one or both assay systems.     

A COMPARISON BETWEEN TWO METHODS FOR THE RECOVERY OF LISTERIA MONOCYTOGENES IN MILK POWDER REFERENCE SAMPLES

Two methods (A and B) for the recovery of Listeria monocytogenes were compared using reference samples based on spray drying of milk containing this pathogen and competitive microflora. For method A, the sample was inoculated in a buffered liquid medium (same as IDF Pre-enrichment Broth) and then passed to IDF Enrichment Broth plus phosphate buffer. For method B, the sample was inoculated in FDA Enrichment Broth (LEB) and then passed to LEB (subenrichment). The solid selective medium used in both cases was Listeria Selective Agar (Oxford formulation). The sensitivity and specificity of method B was 95.2% and 100% vs. 76.1% and 88.8% for method A, respectively.     

HPLC和试剂盒两种测定鳗鱼胆固醇方法的比较

采用高效液相色谱法测定鳗鱼中的胆固醇含量,以C18(4.6mm×250mm,5μm)为固定相,乙腈-异丙醇(60:40)为流动相,流速为1.0 mL/min,检测波长为210 nm,测定结果是,胆固醇浓度在6 mg/L～600 mg/L范围内与色谱峰面积呈良好的线性关系(r=O.999 47),最小检测限为1 mg/L,低、中、高3个浓度的加标回收率分别为98.75、100.7、102.75%,方法精密度(CV)为0.4%.通过比较HPLC与胆固醇试剂盒测定的鳗鱼胆固醇结果表明,两种方法差异显著且试剂盒测定的鳗鱼中胆固醇比HPLC方法平均偏高67.7%,并讨论了试剂盒方法偏高的原因.     

A COMPARISON OF COLORIMETRIC METHODS AND A GAS CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF VICINAL DIKETONES IN BEER

Colorimetric methods recommended by the American Society of Brewing Chemists (Reference method A and Micro method C), the European Brewery Convention and the Institute of Brewing and a new gas chromatographic method have been compared using three beer types (lager, ale and barley wine). Reference method A of the American Society of Brewing Chemists gave the best reproducibility and recovery of added diacetyl for the colorimetric methods but the gas chromatographic method was the best of all the methods and is recommended for quality control use.     

DETERMINATION OF EXTRANEOUS MATTER IN MILK

Improvements in the method used to determine extraneous matter in milk enables the analysis to be completed within a few hours. The new method involves centrifugation to recover the sediment and employs chemical treatment to remove material other than extraneous matter from the sediment.