A review of traditional and novel detection techniques for melamine and its analogues in foods and animal feed

Melamine, a nitrogen-rich chemical, has received much attention in recent years due to a series of highly publicized food safety incidents, including 2007 pet food recalls in North America and 2008 melamine contamination in milk, infant formula, and other milk-derived products in China. Current analytical methods fortesting melamine are time-consuming, expensive, and labor-intensive. Therefore, there is an increasing interest in the food science and analytical chemistry field to develop simple, quick, sensitive, and cost-effective methods for detection of melamine and its analogues (e.g., cyanuric acid, melamine cyanurate, ammelide, and ammeline) in food ingredients, processed food, and animal feed. This review aims to summarize traditional and novel analytical techniques that have been used or show great potential to detect, characterize, and quantify melamine and its analogues in foods and animal feed.     

A review of traditional and novel detection techniques for melamine and its analogues in foods and animal feed

Melamine, a nitrogen-rich chemical, has received much attention in recent years due to a series of highly publicized food safety incidents, including 2007 pet food recalls in North America and 2008 melamine contamination in milk, infant formula, and other milk-derived products in China. Current analytical methods for testing melamine are time-consuming, expensive, and labor-intensive. Therefore, there is an increasing interest in the food science and analytical chemistry field to develop simple, quick, sensitive, and cost-effective methods for detection of melamine and its analogues (e.g., cyanuric acid, melamine cyanurate, ammelide, and ammeline) in food ingredients, processed food, and animal feed. This review aims to summarize traditional and novel analytical techniques that have been used or show great potential to detect, characterize, and quantify melamine and its analogues in foods and animal feed.     

能量转移荧光法测定牛奶中的三聚氰胺

在pH 3.5的Britton-Robinson缓冲溶液中,酸性染料荧光素与碱性染料中性红之间能够发生有效的能量转移,在波长508nm处的荧光值与三聚氰胺的加入量有线性关系,据此建立了一种测定三聚氰胺的荧光光度法,并研究了测定三聚氰胺的最佳条件和干扰离子对体系的影响。方法的线性范围是0.4～100mg/L,检出限为0.015mg/L。将方法用于牛奶中三聚氰胺的测定,结果满意。     

原料乳及乳制品中三聚氰胺的快速测定

建立了一种快速测定原料乳及乳制品中三聚氰胺的高技液相色谱方法.样品中的三聚氰胺经三氯乙酸-甲醇-水混合溶液超声提取,离心过滤后进行HPLC测定.三聚氰胺浓度在0.2～100.0μg/mL范围内呈现良好的线性关系,相关系数R<'2>=0.9999.三聚氰胺的平均回收率为96.0%～102.8%,相对标准偏差为1.9%～7...     

On Measurement of Food Powder Reconstitution Properties

Dissolution of powdered ingredients is of particular importance to manufacturers and consumers as a benchmark of consumption quality. Standard methods gauging the reconstitution properties of milk powders in the dairy industry are available, although they are relatively crude with poor reproducibility. Since most procedures were developed based on “traditional” dairy powders, they may fail to recognize the important characteristics of specialty products. A critical review is presented that identifies the properties of interests and methods for analysis. It is argued that more reliable techniques tailored for different food products can be developed to predict their behaviors for specific end usage.     

Preparation and chemical and nutritional evaluation of an infant food based on sweet lupine, wheat and milk

This paper deals with the development of a food for infants and young children based upon a mixture of 27.5% wheat flour, 20% sweet lupin flour and 20% powdered milk (GL) (18% fat content) with added vitamins and minerals. The blend of wheat and lupin flour was processed in an extrusion-cooker (Wenger X 25) before mixing with the other ingredients. The proximate chemical analysis performed on the wheat-lupin-milk blend (LTL) showed 18.7% protein and 12.5% fat with a calculated caloric value of 427 kcal/100 g. Amino acid analysis indicated a deficiency of methionine + cystine and of threonine in the blend. Nevertheless, studies with rats on the biological quality of the protein, such us protein efficiency ratio and apparent digestibility, revealed that this blend was as good as the reference diet (powdered egg). It is therefore felt that the LTL blend may be a useful substitute in food programs directed to infants and school children.     

On Measurement of Food Powder Reconstitution Properties

Dissolution of powdered ingredients is of particular importance to manufacturers and consumers as a benchmark of consumption quality. Standard methods gauging the reconstitution properties of milk powders in the dairy industry are available, although they are relatively crude with poor reproducibility. Since most procedures were developed based on “traditional” dairy powders, they may fail to recognize the important characteristics of specialty products. A critical review is presented that identifies the properties of interests and methods for analysis. It is argued that more reliable techniques tailored for different food products can be developed to predict their behaviors for specific end usage.     

密胺塑料中三聚氰胺在食品模拟物中的迁移规律研究

采用超高效液相色谱串联质谱(UPLC-MS/MS)法,研究食品模拟物种类、接触时间、接触温度、乙酸浓度、乙醇浓度、重复使用和微波加热等迁移条件下,密胺塑料中三聚氰胺在水、4%乙酸(w/v)、10%乙醇(v/v)、95%乙醇(V/V)和异辛烷等5种食品模拟物和牛奶样品中的迁移规律。结果表明:模拟物的属性对迁移行为有显著影响,迁移量随温度的升高和时间的增加而变大。酸性食品和牛奶中的三聚氰胺迁移风险较高,且需控制密胺塑料的使用温度、盛放时间、重复使用次数及微波加热功率和时间以降低密胺塑料中三聚氰胺迁移风险。     

Computational design of molecularly imprinted polymer for direct detection of melamine in milk

A novel protocol for use of molecularly imprinted polymer (MIP) in analysis of melamine is presented. Design of polymer for melamine has been achieved using a combination of computational techniques and laboratory trials, the former greatly reducing the duration of the latter. The compatibility and concerted effect of monomers and solvents were also investigated and discussed. Two novel open-source tools were presented which are the online polymer calculator from mipdatabase.com and the application of the Gromacs modelling suite to determine the ideal stoichiometric ratio between template and functional monomer. The MIP binding was characterised for several structural analogues at 1–100 μM concentrations. The use of divinylbenzene (DVB) as cross-linking polymer and itaconic acid as functional monomer allowed synthesis of MIP with imprint factor (IF) of 2.25 for melamine. This polymer was used in high-performance liquid chromatography (HPLC) for the rapid detection of melamine in spiked milk samples with an experimental run taking 7–8 min. This approach demonstrated the power of virtual tools in accelerated design of MIPs for practical applications.     

The Determination of n-3 Fatty Acid Levels in Food Products Containing Microencapsulated Fish Oil Using the One-Step Extraction Method. Part 1: Measurement in the Raw Ingredient and in Dry Powdered Foods

An optimized one-step extraction and methylation method (OSE) for the determination of n-3 fatty acid levels in microencapsulated fish oil products has been described. Validation of the method for the food ingredient powder MEG-3^® (a commercial microencapsulated fish oil product manufactured by Ocean Nutrition Canada Ltd, with a gelatin shell matrix) has been demonstrated and compared to a method that combines enzymatic digestion of the shell material, gravimetric determination of released oil payload and an official method of fish oil analysis. Excellent agreement between the two methods was also achieved using a microencapsulated standard of pure ethyl palmitate. The OSE method was applied to an infant formula containing microencapsulated fish oil powder and is shown to be a valid method for such dry powdered foods.     

非线性化学指纹图谱鉴别和区分牛奶及其制品

非线性化学指纹图谱技术是基于化学振荡反应,从非线性化学角度来对试样进行分析的一种新的技术。牛奶及其制品是一种营养价值比较全面的食品,今天已成为人们日常生活不可缺少的一部分。本文考察利用非线性化学指纹图谱来对15种牛奶及其制品进行快速、准确的鉴别和区分的可行性。实验结果表明:牛奶及其制品的非线性指纹图谱具有较强的直观特征性,能很好的鉴别和区分,利用聚类分析(CA)和主成分分析(PCA)的方法得到15个样品的非线性化学指纹图谱的特征数据能够很好的反映它们的指纹图谱的特征。     

Identification of extrinsic proteins in boneless cooked ham by SDS-PAGE: detection level in model systems

Protein extraction and separation in polyacrylamide slab gel electrophoresis with Laemmli system (SDS-PAGE) were used to establish the detection level of protein raw materials in mixtures with porcine meat in boneless cooked ham. Model systems of boneless cooked ham with soy protein isolates, caseinate, skim powdered milk, bovine plasma, porcine plasma and whey proteins were studied. The quantification level of this method was 0.5% for soy protein isolates, caseinate and bovine plasma and 1.0% for porcine plasma, milk powder and whey proteins in boneless cooked ham. The electrophoretic method proved to be useful to identify some proteinic raw materials in porcine meat products and verify compliance with Argentine legislation. It may be used as a control methodology.     

粉末NBR和超细碳酸钙填充粉末NBR硫化胶力学性能的研究*

以高分子树脂膜为包覆剂,采用凝聚共沉法制备非填充型粉末ＮＢＲ和超细碳酸钙填充粉末ＮＢＲ。研究了包覆剂及超细碳酸钙的用量对产物粒径及其硫化胶力学性能的影响。结果表明,当包覆剂用量为１０份时,粒径≤０９ｍｍ的产物占９９８％,加入超细碳酸钙后可进一步减小产物的粒径;极性适宜的包覆剂及超细碳酸钙对粉末ＮＢＲ硫化胶有显著的补强作用,故非填充型粉末ＮＢＲ及超细碳酸钙填充粉末ＮＢＲ均有良好的力学性能。扫描电镜分析表明,极性适宜的包覆剂与ＮＢＲ有一定的相容性,并以粒径约０５μｍ的微粒均匀分布于ＮＢＲ基体中;超细碳酸钙则以原生粒子和粒径≤０５μｍ的团粒存在,它在粉末ＮＢＲ中的分散性比块状ＮＢＲ／超细碳酸钙混炼体系有显著改善     

The rapid determination of aflatoxin M1 in dairy products

A method for aflatoxin M₁ in dairy products is presented. It decreases the analysis time compared to currently accepted methods. Samples are extracted in a blender or separatory funnel for 1 min with chloroform and saturated sodium chloride solution. The chloroform extracts are partially purified on a small silica gel column (2 g), and M₁ is determined by thin layer chromatography (TLC) and densitometry. Recoveries of M₁ added to milk are about 80%. Recovery of M₁ from cheeses is variable depending on the type of cheese. The method gave results for a naturally contaminated powdered milk comparable to analyses by accepted methods. The determination limit of the method is about 0.1 μg/kg.     

Melamine/epichlorohydrin prepolymers: syntheses and characterization

The basic catalysis of melamine with epichlorohydrin gives prepolymers that can be used in the preparation of energetic materials. In this work, sodium hydroxide and triethylamine were used as catalysts and ethyleneglycol as initiator. Different reaction conditions were tested and the characterization of the products was carried out by IR and NMR spectroscopy and MS spectrometry, hydroxyl groups content, vapour pressure osmometry and elemental and thermal analysis. Epichlorohydrin reacts with the amine groups of melamine and forms lateral chains with hydroxyl and epoxide end groups, which can be used for curing purposes. The two catalysts lead to similar products, confirmed both by the structure and number of the lateral chains. The melamine/epichlorohydrin ratio was found important for the structure of the final compounds. Chlorine atoms leave the molecules during reaction due to basic catalysis. In the light of the use of the prepolymers in energetic materials, the presence of the 1,3,5-s-triazine ring and the lateral chains with end groups curable by e.g. isocyanates was accomplished with success. However, the loss of chlorine atoms limits to a certain extent their possible substitution by energetic groups.     

三聚氰胺产业现状及市场分析

经过五十多年的发展,我国已经成为世界最大的三聚氰胺生产基地和出口国,国内三聚氰胺产品也在国际市场处于强势地位。本文介绍近期国内三聚氰胺的产能、价格、出口、市场及下游产品开发应用等方面的一些情况。     

Direct pyrolysis mass spectrometry analyses of polyamide‐6 containing melamine and boron compounds

In this work, the thermal degradation characteristics of polyamide 6 (PA6) containing melamine (Me) and a boron‐containing additive, borophosphate (BPO₄), zinc borate (ZnB) or a boron and silicon‐containing oligomer (BSi) are investigated systematically via direct pyrolysis mass spectrometry. In the presence of boron compounds, not only the release of melamine and its degradation products but also thermal characteristics of PA6 are affected significantly and the interactions between melamine and PA6 are enhanced. For the composite involving BPO₄, sublimation of melamine and degradation of PA6 are slightly shifted to high temperatures. Whereas, for the composites involving ZnB and BSi, sublimation of melamine is depressed due to the glassy surface formed by ZnB and BSi and release of thermal degradation products of PA6 are shifted to lower temperatures noticeably. The glassy surface generated by ZnB allows the release of degradation products of melamine to a certain extent. Conversely, for the composite involving BSi, reduction in the yields of degradation products of melamine is also noted. The trap of degradation products of melamine in the polymer matrix causes significant decrease in the the temperature region where thermal degradation products of PA6 are recorded. POLYM. COMPOS. 34:1389–1395, 2013. © 2013 Society of Plastics Engineers     

近红外透反射光谱用于掺假牛奶的快速识别初探

为快速识别掺加违禁物质的假牛奶,在市售纯奶基础上按不同比例添加水+糊精、水+糊精+三聚氰胺(硝酸铵、尿素)的溶液,配制掺假牛奶,测试真、假牛奶样品的近红外透反射光谱,分别采用PLS-DA、KNN、LDA、改进与简化的KNN(IS-KNN)模式识别方法和不同光谱预处理方法进行真、假牛奶的识别。各模式识别方法在不同预处理光谱下对真、假两类牛奶的识别正确率最高为95.12%和96.34%并且在最高正确率下对所有掺假牛奶均能正确识别。表明采取适宜的近红外光谱预处理方法和模式识别方法,可以良好地对纯奶和掺假牛奶进行区分。     

二步法三聚氰胺热气冷却单元的新工艺

在两步法三聚氰胺工艺生产中,由于热气过滤单元温度高,产出的粗品三聚氰胺纯度低,副产物多,需要在精制过程中利用蒸汽,重新加热溶解粗品三聚氰胺,并送入结晶塔降温结晶,得到纯度高的三聚氰胺成品,此过程消耗了大量的蒸汽,增加了生产成本。提出了一种新的生产工艺,首次在二步法三聚氰胺工艺中增加了热气冷却单元,降低了热气温度,并副产了部分蒸汽,分离出了高沸点反应副产物,净化了热气,得到了纯度高的粗品三聚氰胺,同时改变了精制工艺,极大地降低了蒸汽消耗,节约了生产成本,提高了产品市场竞争力。