配方注册婴幼儿配方乳粉中蛋白质及三聚氰胺含量测定分析

目的通过测定婴幼儿配方乳粉中蛋白质及三聚氰胺含量,对我国现阶段配方注册的婴幼儿配方乳粉安全状况进行监测。方法婴幼儿配方乳粉中蛋白质的含量依照GB 5009.5-2016《食品安全国家标准食品中蛋白质的测定》中"第一法凯氏定氮法"进行检测;三聚氰胺的含量依照GB/T22388-2008《原料乳与乳制品中三聚氰胺检测方法》中"第一法高效液相色谱法"进行检测。结果样品中蛋白质含量均符合食品安全国家标准规定,且满足测定值不小于标签标示值80%的规定;三聚氰胺的含量均为未检出或低于检出限,符合原卫生部公告的限量值规定。结论根据食品安全国家标准或推荐标准的检测方法和评价指标,所检测的样品中蛋白质项目满足配方注册要求。     

Spectra-Quad实现三聚氰胺含量在线检测

在麦麸、奶粉或其他富含蛋白质面粉的生产中,进行三聚氰胺含量的测定是一项重要的安全措施。不法企业常利用三聚氰胺少量添加即可大大提高氮含量的特性,向产品中添加三聚氰胺,造成蛋白质含量的虚假增高,以达到产品蛋白质含量达标的目的。     

人为添加非蛋白质氮乳与乳制品中蛋白质含量测定方法的研究

本研究分别用GB/T5009.5《食品中蛋白质的测定》和NY/T1678《乳与乳制品中蛋白质的测定——双缩脲比色法》,测定了添加非蛋白氮物质的乳及乳制品中的蛋白质含量。结果表明GB/T5009.5方法不能区分样品中的蛋白氮与非蛋白氮;采用NY/T1678-2008方法可以较好的实现蛋白氮和非蛋白氮物质的分离,有效地排除三聚氰胺、尿素、甘氨酸和水解蛋白等多种非蛋白氮对乳及乳制品中蛋白质含量检测的影响,该方法前处理方法快速、简单,检测结果准确。 更多还原     

电位滴定法测定牛乳中蛋白质含量

为排除三聚氰胺等非蛋白氮的干扰,探索研究了牛乳中蛋白质含量快速准确的测定方法——电位滴定法。用甲醛固定蛋白质中的氨基从而释放出游离的羧基。并用氢氧化钠标准溶液滴定,通过测定牛乳中蛋白质的游离氨基酸的含量,可以计算蛋白质中的氮含量,从而求得牛乳中蛋白质含量。经t检验t〈t0.95,5,电位滴定法和凯氏定氮法之间未发现有显著性差异,且测定时间只需10min左右。本方法操作简便、测定结果准确,并有效地排除了三聚氰胺等非蛋白氮的干扰．适用于牛乳中蛋白质的快速定量检验。     

荔枝果干蛋白质组成及其抗氧化性研究

分析荔枝干果肉蛋白组成并比较不同组份蛋白质的抗氧化性。采用等电点法提取不同组份蛋白质,利用氨基酸自动分析仪测定不同组份蛋白及总蛋白的氨基酸组成,用超高压液相质谱联用系统Q1扫描测定不同等电点组份中小分子蛋白分子量分布,用抗氧化试剂盒测定不同等电点组份蛋白质的抗氧化性。试验结果表明荔枝浆浸泡2 h为蛋白质的最佳提取时间,测得pH 3.5、pH 5.5、pH 6.5和pH 7.5为荔枝蛋白的4个等电点,且4个等电点组份蛋白含量分别占果肉总蛋白的12.03%、14.37%、17.18%、9.45%;不同组份蛋白氨基酸种类相同、含量不同;pI 3.5和pI 5.5组份中含量较高的小分子蛋白集中在5000 Da附近,pI6.5和pI7.5组份中含量较高的小分子蛋白主要集中在1000 Da和5000 Da附近。说明不同组份荔枝蛋白抗氧化性不同。荔枝蛋白四个等电点组份的蛋白氨基酸含量、分子量分布及抗氧化性不同。     

关于GB/T 21704-2008方法改进和适用范围的研究

目的 对GB/T 21704-2008《乳与乳制品中非蛋白氮含量的测定》中前处理部分提出方法改进,明确方法的适用范围。方法 用不同剂量的三氯乙酸溶液沉淀样品中蛋白质,过滤后测定滤液中非蛋白氮含量；加水完全溶解三组不同质量的三聚氰胺,加入不同体积的三氯乙酸溶液,观察三聚氰胺在不同浓度三氯乙酸溶液中的析出情况；加标不同量的三聚氰胺,测定计算回收率确定仪器的检测限。结果 样品中蛋白质含量低于20 g/ 100 g 时,20 mL 15%三氯乙酸溶液可完全沉淀样品中蛋白质；三氯乙酸浓度越高,三聚氰胺溶解度越小,越容易析出；本实验用的全自动凯氏定氮仪最低可准确稳定检测2 mg三聚氰胺/10g样品。结论 国标方法改进后可以节约试剂,在消化环节缩短加热时间,提高实验效率；三聚氰胺在三氯乙酸溶液中的溶解度情况和仪器检测限的限制框定方法的适用范围是2 mg -20 mg三聚氰胺/10g样品。     

燕麦麸蛋白质的Osboren分类及SDS-PAGE电泳分析

根据微量凯氏定氮法测定了燕麦麸中蛋白质含量,40～60目之间的燕麦麸蛋白质含量最高,平均为19.42%;并对其进行Osboren蛋白质分类以及分类后各类蛋白质组分含量的测定,结果表明,燕麦麸中清蛋白、球蛋白、醇溶蛋白、谷蛋白占蛋白质总量依次为63.40%、15.18%、8.18%、13.24%。SDS-PAGE电泳分析各类蛋白的组成结果表明,燕麦麸中清蛋白含量最高且蛋白质亚基分布广泛。清蛋白必需氨基酸含量高,溶解性好,易于消化吸收,为优质的营养蛋白。     

一种快速鉴别三聚氰胺毒奶粉蛋白质含量的检测方法

为了建立一种快速检测含三聚氰胺奶粉蛋白质含量的简便方法,本研究分别用考马斯亮蓝法、双缩脲法以及纳氏法测定了三聚氰胺毒奶粉中蛋白质的含量,并对测定结果进行了比较。通过高温变性法、改良三氯乙酸法、Sevage法和透析法考察了去除蛋白氮和非蛋白氮-三聚氰胺的效果。结果表明,考马斯亮蓝和双缩脲不与非蛋白氮三聚氰胺发生反应,采用改良三氯乙酸法可以较好的实现蛋白氮与非蛋白氮三聚氰胺的分离。因此,用考马斯亮蓝法或者双缩脲法可以准确测出含毒奶粉中蛋白氮的含量,通过改良三氯乙酸法配合纳氏法可以检测奶粉中的非蛋白氮-三聚氰胺。     

食品中蛋白质快速检测技术的研究

蛋白质是生命的物质基础。随着社会生活水平的提高,人们更加注重对食物中蛋白质的摄入。三聚氰胺事件的发生促使了蛋白质检测工作的重大变革,相关部门更加重视对蛋白质含量的检测工作。本文综述了快速测定蛋白质的各种方法,分析它们的检测原理、检测时间,将其与传统的凯氏定氮法相比较并对其以后的应用前景进行了展望,为进一步研究蛋白质检测工作提供一定的参考价值。     

豆奶蛋白质中巯基含量的测定

Ellman法是测定蛋白质中游离巯基和二硫键含量的快速、简便的方法,但该法用于测定豆奶等的巯基含量时,由于溶液高度混浊和巯基含量不高,给测定带来了困难。本实验先采用丙酮将豆奶中的蛋白质沉淀分离,再用含8mol/L尿素的Tris-甘氨酸缓冲溶液或不含尿素的Tris-甘氨酸缓冲溶液溶解,使蛋白质溶液的混浊度大大下降,从而能达到用分光度法准确测定豆奶蛋白质中巯基含量的目的。采用大豆分离蛋白作对照实验表明,丙酮处理不会影响蛋白质中的巯基含量,说明丙酮处理是测定高混浊度蛋白质溶液如牛奶、豆奶中的蛋白质巯基含量的一种有效方法。     

Melamine and cyanuric acid do not interfere with Bradford and Ninhydrin assays for protein determination

In the fall of 2007 pet food contaminated with melamine and cyanuric acid caused kidney stones in thousands of animals. In the summer of 2008, a more serious outbreak of adulterated dairy food resulted in the deaths of six infants and sickened about 290,000 children in China. In all cases, melamine was likely concentrations added to inflate the apparent protein content of the foods. To determine if we could measure protein without interference from melamine and cyanuric acid we tested these compounds in the Bradford and Ninhydrin assays, two common dye-based assays for protein, as well as by ammonia release, the most common assay used in the food industry. Neither compound was detected in the Ninhydrin and Bradford assays at concentrations of >100 μg/ml. The ammonia assay detected melamine but was inconclusive with respect to cyanuric acid. To develop an accurate test for food that would not detect either chemical as a protein, assays were run on cat food and reconstituted milk powder. The Bradford assay readily measured the protein content of each food, and importantly, the addition of melamine or cyanuric acid to reconstituted milk did not affect the readings. The protein concentrations obtained for reconstituted milk powder were as expected, but those for the cat food were 10–30-fold lower, due to its low solubility. We conclude that dye-binding assays can be employed to detect protein in food without interference from melamine and cyanuric acid, thus reducing the incentive to use them as additives.     

食品和饲料中三聚氰胺检测方法研究进展

三聚氰胺是一种三嗪类含氮杂环有机化合物。由于其较高的含氮量而被添加于食品和饲料中,对动物和人体造成了一定的危害。本文综述了近期的食品和饲料中三聚氰胺检测的样品前处理技术和分析方法,主要包括高效液相色谱法、气相色谱- 质谱法、液相色谱- 质谱法和酶联免疫法等。     

乳制品中三聚氰胺检测方法的现状及研究进展

三聚氰胺是一种三嗪类含氮杂环有机化合物,三聚氰胺分子中含氮量达66.7%,一些不法企业将其添加到牛奶、乳制品中,造成粗蛋白质虚高的假相,不仅对乳制品、养殖业等产业产生不利影响,对人类健康也构成严重威胁。因此,对乳制品中三聚氰胺的检测方法的研究,在食品安全检测方面早已成为了社会的热点。本文着重论述了近年来乳制品中三聚氰胺检测方法的研究现状,检测方法主要包括液相色谱-质谱联用法、气相色谱-质谱法、表面增强拉曼光谱、电化学分析方法、红外光谱法和荧光光度法等。随着仪器和科学技术的发展,开发操作简单、成本低廉、方便携带、准确快速、灵敏高效的乳制品中三聚氰胺的检测技术,是今后三聚氰胺技术研究的重要方向。     

三聚氰胺的毒性毒理及检测最新进展

三聚氰胺是用途广泛的化工原料,含氮量高达66%,被不法分子作为蛋白替代品添加到乳品、饲料中,导致婴幼儿、宠物患泌尿结石甚至死亡。本文对三聚氰胺及其同系物的理化性质、代谢、毒性毒理、检测最新进展全面综述,并对其添加原因进行初步分析。     

三聚氰胺在罗非鱼体内的残留和消除规律研究

以罗非鱼(Tilapia)为研究对象,通过在罗非鱼饲料中添加不同剂量三聚氰胺进行罗非鱼摄食生长试验,研究三聚氰胺在罗非鱼肝脏和肌肉中的残留和消除规律。实验结果表明:(1)罗非鱼连续饲喂含三聚氰胺的饲料50d,添加不同剂量的三聚氰胺对各组罗非鱼的平均体重增长无显著影响(P>0.05);(2)肝脏和肌肉中三聚氰胺的残留量随着各实验组饲料中添加量的增加呈显著递增趋势(P<0.05),低剂量组(1000、5000mg/kg)的肝脏和肌肉中的残留量在2～20mg/kg间,高剂量组(10000、50000mg/kg)的残留量均超过40mg/kg,各组中肝脏的残留量均显著高于肌肉(P<0.05)。停药5d后,罗非鱼的肝脏和肌肉中三聚氰胺的残留量均内显著下降,各实验组的三聚氰胺残留量均降至2.0mg/kg以下,此后则缓慢下降。各实验组中,肌肉的消除时间比肝脏的消除时间长。     

Total Protein Methods and Their Potential Utility to Reduce the Risk of Food Protein Adulteration

Abstract: Kjeldahl and combustion (Dumas) methods are widely accepted for total protein determination but lack analytical selectivity for protein because they measure protein on the basis of sample nitrogen content. Adulteration incidents exploiting this analytical vulnerability (for example, melamine) demonstrate that these methods are no longer sufficient to protect the public health. This article explores the challenges and opportunities to move beyond total nitrogen based methods for total protein measurement. First, it explores the early history of protein measurement science, complexities of current global protein measurement activities, and ideal analytical performance characteristics for new methods. Second, it comprehensively reviews the pros and cons of current and emerging approaches for protein measurement, including their selectivity for protein, ability to detect adulteration, and practicality for routine use throughout the supply chain. It concludes that some existing highly selective methods for food protein measurement have potential for routine quality control. It also concludes that their successful implementation will require matrix‐specific validation and the use of supporting reference materials. These methods may be suitable only for food ingredients that have a low degree of compositional variability and are not complex finished food products.     

Quantitation and Risk Assessment of Chemical Adulterants in Milk Using UHPLC Coupled to Photodiode Array and Differential Refractive Index Detectors

Milk can be adulterated illegitimately with formaldehyde, melamine, urea, and sugars for preservation, protein content enhancement, and taste improvement, respectively. In the present study, formaldehyde, melamine, urea, and sugars (fructose, glucose, lactose, sucrose) were analyzed using ultra-fast high performance liquid chromatography in 30 fresh and pasteurized milk samples. Satisfactory chromatographic retention and peak shape investigated and method has been validated by means of recovery experiments in samples spiked at two levels. Average recoveries ranged between 95–105 % with excellent precision; RSD lower than 5 % was achieved. Among the tested samples, formaldehyde was detected in all samples while seven and 20 samples were positive for melamine and sucrose, respectively. Monitoring of these adulterants in milk could help to reduce the human health hazards. Exposure to formaldehyde, melamine, and urea from consumption of milk was estimated, and these were less than 3.3, 1, and 700 μg/mL, respectively, which is an oral reference dose suggested by the World Health Organization and US Food and Drug Administration.     

High-performance liquid chromatographic method for the simultaneous detection of the adulteration of cereal flours with melamine and related triazine by-products ammeline, ammelide, and cyanuric acid

Melamine has been used for the adulteration of cereal flours in order to increase their apparent protein content. Crude melamine may contain several by-products, i.e. ammeline, ammelide, and cyanuric acid. The simultaneous analysis of all four chemicals is difficult because of the formation of an insoluble salt between melamine and cyanuric acid. A simple and convenient high-performance liquid chromatography (HPLC) method for the detection of the adulteration of cereal flours with all four chemicals is proposed herein. The precipitate formation between melamine and cyanuric acid was prevented by using alkaline conditions (pH 11-12) for both standards preparation and sample extraction. The method uses matrix-matching, which involves the construction of a calibration curve on a blank (negative control) matrix, which is then used for the quantitation of melamine and by-products in adulterated (positive) samples. Matrix-matching compensates for analyte losses during sample preparation, and for matrix effects. The method was successfully applied to wheat, corn, and rice flours, and is expected to be applicable (with some modifications) to soy flour as well. The method allows for the detection of melamine, ammeline, and ammelide at approximately 5 µg g^-1, and cyanuric acid at approximately 90 µg g^-1 in wheat flour.