自动定氮仪测试技术在食品中蛋白质测定的综述评价

凯氏定氮法是测定食品中蛋白质含量的一种普遍使用的常规分析法,目前国内多采用凯氏定氮法,而国际上多采用自动定氮仪进行凯氏定氮法,本文着重对自动定氮仪测定技术的综述评价。     

牛乳中蛋白质的快速测定

采用对牛乳中蛋白质的快速测定与凯氏定氮法测定牛乳中蛋白质的含量,结果相对标准偏差<±0.5%,与凯氏定氮法的结果无差别,且此法操作省时省力,费用低,为一种简便、快速、准确、实用的牛乳蛋白质快速检测方法。     

强化(过氧化)凯氏定氮法在食品蛋白质分析中的应用

<正> 食品蛋白质分析是工业和商业上最频繁出现的分析项目之一。目前国内食品中蛋白质含量测定均采用常规凯氏定氮法,国外亦多采用常规或改良的凯氏定氮法。然而,无论是常规或改良的凯氏定氮法,其蛋白质分析过程均包括碳化—消化—蒸馏—滴定等步骤,操作繁琐,试剂消耗量大、耗时长(约需1～5小时)     

基于有机元素分析的粉状食品中蛋白质含量的测定

目的 建立基于有机元素分析的粉状食品中蛋白质含量的测定方法。方法 采用VarioEL III型元素分析仪对16种粉状食品中蛋白质含量进行测定, 并与传统经典蛋白质测定方法——凯氏定氮法进行比较。结果 元素分析法可准确测定样品中蛋白质含量, 方法重复性和准确度均很好, 与凯氏定氮法相比, 测定结果相近, 并且具有相当的测量精度, 且有操作简单、无需复杂样品前处理、无溶剂和污染、样品需求量少、分析速度快、自动化程度高等优点。结论 元素分析法可作为凯氏定氮法的替代和补充方法, 用于粉状食品中蛋白质含量的测定。     

自动定氮仪测试技术在食品中蛋白质测定的综述评价

凯氏定氮法是测定食品中蛋白质含量的一种普遍使用的常规分析法，目前国内多采用凯氏定氮法，而国际上多采用自动定氮仪进行凯氏定氮法，本文着重对自动定氮仪测定技术的综述评价。     

荞麦中蛋白质含量的分析

用改进的凯氏定氮方法对荞麦中的蛋白质含量进行测定,测得辽宁朝阳、锦州、黑山、铁岭、西丰地区荞麦中蛋白质含量分别为12.48%、9.19%、9.48%、10.16%和11.44%,并用传统凯氏定氮方法进行了验证,结果表明该方法简便、快速、准确可行。     

过氧化凯氏定氮法在食品蛋白质分析中的应用

主要研究了过氧化凯氏定氮法在食品蛋白质分析中的应用,此法较常规或改良凯氏定氮法具有快速简便、精确精密、准确、灵敏度高等优点,且所用的消化设备简单易推广。     

蛋白质检测方法的研究

采用分光光度法、凯氏定氮法和燃烧法测定各种不同食品的蛋白质,通过测得的蛋白质结果,比较3种方法的优缺点。     

凯氏定氮法测定牛奶纤维蛋白质含量

采用凯氏定氮法分析牛奶蛋白纤维中的含氮量,尝试以含氮量变化来表征因染整加工引起的纤维中蛋白质组分的变化.通过正交试验优化了凯氏定氮法消化工艺,研究表明,该法具有消化时间短、测试准确、操作方便等优点,可用于分析牛奶纤维中蛋白质组分的变化,以指导生产.     

凯氏定氮法检测食物中蛋白质含量与误差分析

正越来越多的人开始关注自身健康与食品安全问题,精确地测定食品中蛋白质含量对食品质量检测、食品安全都极为重要。新的国家标准《食品中蛋白质的测定》(GB/T 5009.5-2010)给出凯氏定氮法、分光光度法和燃烧法3种可用于食品中蛋白质的检验方法。其中凯氏定氮法在现阶段检测中的使用最为广泛,其具有适用范围广,检测试验重现性好,准确度和灵敏度高,被测样品用量少等优点,因此本文主要具体介绍凯氏定氮法的步骤和原理并分析其误差。     

Determination of protein in fish meal

A comparison of the Kjeldahl and Lowry methods for the determination of protein in fish meal has been made. The values obtained with the rapid colorimetric Lowry method, using extracts of total fish meal proteins, were lower than those obtained by the Kjeldahl method. For fish meal from different species the general factor 1.19±0.03 (confidence limit for P<0.01) may be used to convert protein values obtained by the Lowry method into protein values obtained by the Kjeldahl method.     

广西水牛奶和荷斯坦牛奶中蛋白质和氨基酸的含量及组成分析

目的研究广西区内生水牛奶和荷斯坦生牛奶中蛋白质、氨基酸含量及其组成特性,分析水牛奶和荷斯坦牛奶的差异。方法采用盐酸水解法处理牛奶样品,通过氨基酸自动分析仪测定氨基酸含量,分析水牛奶和荷斯坦牛奶氨基酸的含量和组成;通过凯氏定氮法测定牛奶中蛋白质含量。结果 18份牛奶样品中蛋白质、氨基酸的测定结果表明,生水牛奶的蛋白质和氨基酸含量均高于荷斯坦生牛奶,而水牛奶和荷斯坦牛奶中各氨基酸含量占氨基酸总量的比值相近。结论该方法为广西生水牛奶和荷斯坦生牛奶的鉴别提供参考。     

Über das Protein in Kartoffel-, Mais- und ReisstärkeHerrn Prof. Dr. Erwin Welte,Direktor des Instituts für Agrikulturchemie der Universität Göttingen,zum 60. Geburtstag gewidmet.

On the Protein in Potato, Maize and Rice Starch The protein content of potato, maize and rice starch was determined, and 21 amino acids could be identified. With the usual hydrochloric acid hydrolysis to set free the amino acids a portion (residual protein) remains in the dark residue (melanine), and can be isolated only after destruction of the latter, e.g. with sodium chlorite, and analyzed for amino acids. As shown by the nitrogen determination after Kjeldahl and amino acid analysis potato starch has the lowest, maize starch a mean and rice starch a high content of amino acids. The total amount of nitrogen in the amino acids compared with the Kjeldahl nitrogen is only 83% for potato protein and 80% for maize and rice protein. The residue from hydrolysis can vary substantially.     

重量法结合氨基酸分析法测定婴幼儿配方乳粉中小分子蛋白肽含量

目的:建立婴幼儿配方乳粉中小分子肽含量的定量分析方法。方法:分别采用凯氏定氮法、重量法、离子交换色谱等方法测定婴幼儿配方乳粉中总蛋白、高分子蛋白和游离氨基酸含量,通过计算求得小分子蛋白肽含量。结果:高分子蛋白检测精密度RSD (n=6)为0.74%;17种氨基酸回收率为91.0%～103.2%,检测结果的相对偏差为0.6%～2.5%;小分子蛋白肽添加回收率为95.2%～98.2%。结论:所建方法精密度和回收率良好,可用于婴幼儿配方乳粉中小分子肽含量的测定。     

Comparison of a short method for Kjeldahl digestion using a trace of selenium as catalyst,with other methods

A short digestion method for Kjeldahl nitrogen determination, using a trace of selenium as catalyst and described in this paper, gives results comparable to the American Association of Cereal Chemists (1976) method using mercuric oxide catalyst, for all compounds tested except for nicotinic acid. However, nicotinic acid is a minor component of food materials and it is not normally assayed by the Kjeldahl method. Selenium, like mercury, is known to be toxic⁷ but mercury ranks more highly than selenium as an environmental problem.     

CALCULATION OF MOLECULAR WEIGHTS AND KJELDAHL NITROGEN-TO-PROTEIN CONVERSION FACTORS FOR MYOFIBRILLAR PROTEINS FROM AMINO ACID SEQUENCES

The objectives of this research were to calculate the molecular weights and Kjeldahl conversion factors for the major myofibrillar proteins from knowledge of their primary structures. Kjeldahl nitrogen-to-protein conversion factors for the myofibrillar proteins myosin, actin, and tropomyosin were calculated from amino acid sequences found in the literature. The molarity of pure protein solutions can be determined without the use of a primary standard with the Kjeldahl nitrogen determination method and use of calculated Kjeldahl nitrogen-to-protein conversion factors. The molecular weights of bovine myosin (519,725), actin (41,549), alpha-tropomyosin (32,680), and beta-tropomyosin (32,811) were calculated. The nitrogen-to-protein conversion factors for these proteins were calculated to be respectively 6.05, 6.29, 6.24, and 6.25. The molecular weights of myosin light chains L1, L2, L3, and L4 and the myosin heavy chain were calculated and their respective nitrogen-to-protein conversion factors were: 6.18, 6.34, 6.34, 6.32, and 6.01.     

杜马斯燃烧法测定油料作物中粗蛋白质含量的 方法优化及其与凯氏定氮法的比较研究

目的建立杜马斯燃烧法测定油料作物中粗蛋白质含量的方法,并与凯氏定氮法进行比较。方法以芝麻、大豆、油菜和花生为研究对象,对杜马斯燃烧法的称样量和氧气系数进行优化。分别用杜马斯燃烧法和凯氏定氮法测定4种样品的粗蛋白含量,并对2种测试方法的结果进行比较分析。结果杜马斯燃烧法的测定值略高于凯氏定氮法,但2种方法的测定值间没有显著性差异(P0.05),杜马斯燃烧法比凯氏定氮法的测定精密度和准确度更高。测定结果的相关性分析表明两种方法的测定值呈显著相关(r~2=0.9988)。结论杜马斯燃烧法的精密度和准确度更好,可以替代凯氏定氮法测定油料作物的粗蛋白质含量。     

羊乳酒在发酵过程中主要参数变化的研究

以新鲜羊奶为原料,采用乳酸菌和酵母菌共发酵方法,在29 ℃条件下振荡发酵羊乳,以pH值、酒精度、总氮及非蛋白氮含量为评价指标,通过凯氏定氮法、十二烷基硫酸钠-聚丙烯酰氨凝胶电泳法（SDS-PAGE）,对羊乳酒在发酵过程的不同时期蛋白质降解的动态变化进行了研究。研究结果表明,羊乳酒在发酵的过程中的pH值呈现先降低后升高再降至稳定的趋势;酒精度呈现缓慢增长的趋势;总氮含量变化不大;非蛋白氮含量随着乳酒发酵的进行缓慢升高;SDS-PAGE结果显示,羊乳酒中蛋白质发生了不同程度的降解,小分子蛋白增多,蛋白分子质量主要分布在17～35 kDa。     

国内外乳品真蛋白检测方法的进展

介绍了乳品真蛋白的定义,比较了国内外牛乳蛋白质检测的标准方法,简述了乳品真蛋白的快速检测方法,提出了我国国家标准需要改进的方向,即在样品处理前先用150g/L的三氯乙酸溶液使乳中的蛋白质沉淀,用滤纸分离,再用凯氏定氮法分别测定沉淀和滤液中的蛋白态氮含量和非蛋白态氮含量,计算蛋白质含量。如果改用pH4.6来沉淀酪蛋白,同样的方法还可以用于测定乳品中酪蛋白。     

Analysis of Protein and Total Usable Nitrogen in Beer and Wine Using a Microwell Ninhydrin Assay

In this study we present a ninhydrin based microwell assay that can be utilized in place of the traditional Kjeldahl method for the determination of the protein content of beer or wine. In addition, the assay is ideal for the determination of free amino acids in beer (FAN), a term understood and used by brewers, and yeast assimilable nitrogen (YAN) used by enologists. The assay only measures alpha amino acids and ammonia so other nitrogen sources are not detected, resulting in a 30% reduction in total protein of a variety of beers compared to the Kjeldahl method, which measures nitrogen from all sources. The results also showed that only 25% of the total “protein” in beer is actually derived from peptides larger than 3,500 Kd. Analysis of beer or wine with the microwell assay for total usable nitrogen was compared to the standard FAN and YAN methods and conditions were determined for maximal efficiency and precision. Superior results were obtained with low reaction volumes and a stable sodium acetate buffered ninhydrin reagent at pH 5.5. As an alternative, for use with cuvettes, a reduced volume FAN assay using the same pH 5.5 sodium acetate buffered ninhydrin reagent gave comparable results. The assay is economical, rapid, accurate and applicable to large numbers of samples.