三聚氰胺是怎么加到牛奶中的how melamine is added to milk in the
| 方舟子：三聚氰胺是怎么加到牛奶中的 |
许多人喝牛奶是为了补钙，不过你如果留心一下国内鲜牛奶包装上的标注，一般没有列出钙的含量，标明的营养成分含量只有两种：脂肪和蛋白质。鲜牛奶有全脂、低脂、脱脂之分，其脂肪含量各不相同，而且在脂肪被视为健康杀手的今天，一般人不会在乎脂肪含量是否达标。蛋白质才是牛奶中的主要营养成分，鲜牛奶包装上都会注着蛋白质含量为100毫升≥2.9克,以表明符合鲜牛奶的国家标准（100毫升≥2.95克）。
生鲜牛奶的蛋白质含量一般在3%以上，所以一般都能达到国家标准，除非往原奶中兑水。要提防有人拿水卖出奶的价钱，就有必要在收购生鲜牛奶时检测蛋白质的含量。根据蛋白质的化学性质，有几种检测方法，各有优缺点。食品工业上普遍采用的、被定为国家标准的是凯氏定氮法。这是19世纪后期丹麦人约翰·凯达尔发明的方法，原理很简单：蛋白质含有氮元素，用强酸处理样品，让蛋白质中的氮元素释放出来，测定氮的含量，就可以算出蛋白质的含量。牛奶蛋白质的含氮率约16%，根据国家标准，把测出的氮含量乘以6．38，就是蛋白质含量。
所以凯氏定氮法实际上测的不是蛋白质含量，而是通过测氮含量来推算蛋白质含量，显然，如果样品中还有其他化合物含有氮，这个方法就不准确了。在通常情况下，这不是个问题，因为食物中的主要成分只有蛋白质含有氮，其他主要成分（碳水化合物、脂肪）都不含氮，因此凯氏定氮法是一种很准确的测定蛋白质含量的方法。但是如果有人往样品中偷加含氮的其他物质，就可以骗过凯氏定氮法获得虚假的蛋白质高含量，用兑水牛奶冒充原奶。
常用的一种冒充蛋白质的含氮物质是尿素。不过尿素的含氮量不是很高（46.6%），溶解在水中会发出刺鼻的氨味，容易被觉察，而且用一种简单的检测方法（格里斯试剂法）就可以查出牛奶中是否加了尿素。所以后来造假者就改用三聚氰胺了。三聚氰胺含氮量高达66.6%（含氮量越高意味着能冒充越多的蛋白质），白色无味，没有简单的检测方法（要采用“高性能液体色谱”这种高科技去检测），是理想的蛋白质冒充物。三聚氰胺是一种重要的化工原料，广泛用于生产合成树脂、塑料、涂料等，目前的价格大约是1吨12000元。在生产三聚氰胺过程中，会出现废渣，废渣中还含有70%的三聚氰胺。造假者用来冒充蛋白质的就是三聚氰胺渣，有些“生物技术公司”在网上推销“蛋白精”，其实就是三聚氰胺渣。在饲料、奶制品中添加“蛋白精”冒充蛋白质。
三聚氰胺是怎么加到牛奶中的呢？有两种可能途径。一种是奶站加到原奶中。这样做有一定的局限，因为三聚氰胺微溶于水，常温下溶解度为3．1克／升。也就是说，100毫升水可以溶解0．31克三聚氰胺，含氮0．2克，相当于1．27克蛋白质，由此可以算出，要达到100毫升≥2.95克蛋白质的要求，100毫升牛奶最多只能兑75毫升水（并加入0．54克三聚氰胺）。另一种途径是在奶粉制造过程中加入三聚氰胺，这就不受溶解度限制了，想加多少都可以。
三聚氰胺之所以被不法之徒当成“蛋白精”来用，可能是因为觉得它毒性很低，吃不死人。大鼠口服三聚氰胺，半致死量（毒理学常用指标，指能导致一半的实验对象死亡）大约为每千克体重3克，和食盐相当。大剂量喂食大鼠、兔、狗也未观察到明显的中毒现象。三聚氰胺进入体内后似乎不能被代谢，而是从尿液中原样排出，但是，动物实验也表明，长期喂食三聚氰胺能出现以三聚氰胺为主要成分的肾结石、膀胱结石。我们无法拿人体做试验，而即使患肾结石的人曾经服用过偷加了三聚氰胺的食物，也很难确定三聚氰胺就是罪魁祸首，除非患者的食物来源很单一，例如只吃配方奶粉的婴儿——没想到还真有人敢拿婴儿来做试验证明了它能吃死人！
有人认为既然蛋白质检测法的缺陷导致了致命的造假，还不如干脆取消蛋白质检测，默许牛奶兑水得了。其实凯氏定氮法的缺陷并不难弥补，只要多一道步骤即可：先用三氯乙酸处理样品。三氯乙酸能让蛋白质形成沉淀，过滤后，分别测定沉淀和滤液中的氮含量，就可以知道蛋白质的真正含量和冒充蛋白质的氮含量。这是生物化学的常识，也早成为检测牛奶氮含量的国际标准（ISO 8968）。“蛋白精”骗局在国内出现已有一些年头，“三鹿奶粉”事件不过是把这一“行业秘密”摆在了公众面前。只有改进国家标准，堵住漏洞，才能挽回人们对国产乳业的信心。
Fang: how melamine is added to milk in the
Many people drink milk for calcium, but if you look carefully to the domestic fresh milk packaging on the mark, generally do not list the calcium content, indicating the nutritional content of the content, there are only two: fat and protein. A fresh full-fat milk, low-fat, skim it, the fat content varied, but also in fat is considered healthy today, the killer, most people will not care about whether the fat content standards. Milk protein is the main nutrients, fresh milk packaging will be injected with the protein content of 100 ml for ≥ 2.9 grams of fresh milk in order to show that in line with the national standard (100 ml ≥ 2.95 grams).
Fresh milk protein content in general more than 3%, so in general to achieve the national standard, unless the original milk to Duishui. Thinner should be alert when the price of milk sold, there is a need to detect when to buy fresh milk protein content. According to the chemical properties of the protein, there are several methods of detection, each with advantages and disadvantages. On the food industry generally adopted as the national standard by the Kjeldahl method. This is the late 19th century Denmark John Dahl who invented the method, the principle is simple: contain protein nitrogen, with strong acid sample handling, so that the protein nitrogen released, the determination of nitrogen content, you can calculate the protein content. Milk protein nitrogen rate of about 16 percent, according to national standards, to measure the nitrogen content of 6.38 times, that is, the protein content.
So Kjeldahl method is not actually measured the protein content, but by measuring the content of nitrogen to project protein content, it is clear that if there are other samples contain nitrogen compounds, this approach is not accurate. Under normal circumstances, this is not a problem because food proteins contain only the major components of nitrogen and other major components (carbohydrates, fats) are not nitrogen, the Kjeldahl method is a very accurate determination of protein content . However, if someone stole samples to add nitrogen and other substances, can deceive Kjeldahl method to obtain a false high protein content, milk Duishui posing as the original milk.
Posing as a common protein material is urea nitrogen. However, the urea nitrogen content is not very high (46.6%), dissolved in water will be issued by the sharp An Wei, easy to detect, and a simple method of testing (Tigris reagent) can be found in milk Does the addition of urea. So are false later on the use of melamine. Melamine nitrogen content as high as 66.6 percent (the higher the nitrogen content means pretending to be able to more protein), white and tasteless, there is no simple method of testing (to a "high-performance liquid chromatography" to such a high-tech detection), Posing as an ideal protein structures. Melamine is an important chemical material widely used in the production of synthetic resins, plastics, paint and so on, the current price of about 1 metric ton of 12,000 yuan. Melamine production process, there will be waste, the waste contains 70% of melamine. Those who used false impersonation of the protein is melamine residue, some of the "biotechnology company" in the online marketing of "precision protein" is actually one of the melamine residue. In the feed, dairy products added to the "protein fine," posing as protein.
Melamine is added to milk in how it? There are two possible ways. A station is added to milk in the original milk. This has some limitations, because melamine micro-soluble in water, at room temperature for the solubility of 3.1 grams / liter. In other words, can be dissolved in 100 ml of water 0.31 grams of melamine, containing 0.2 grams, the equivalent of 1.27 grams of protein, which can be worked out, it is necessary to reach 100 ml ≥ 2.95 grams of protein requirements, 100 ml Milk was up to 75 ml of water (and add 0.54 grams of melamine). Another way in the manufacture of milk powder in the process of adding melamine, which is not the solubility limit, and would like to increase the number can be.
Melamine was the reason why criminals as a "precision protein", probably because it felt very low toxicity, eat dead people. Rat oral melamine, semi-lethal dose (toxicology commonly used indicator that can lead to the death of half of the subjects) about every 3 g kg body weight, salt and fairly. High-dose fed rats, rabbits, dogs are not clearly observed toxicity. Melamine appears to be entering the body after metabolism can not be, but as it is discharged from the urine, but animal experiments have shown that long-term feeding of melamine in order to be able to appear as the main ingredient of melamine kidney and bladder stones. We can not take the body to do the pilot, and even those who suffer from kidney stones have been stolen to increase the use of melamine in food, it is hard to determine melamine is the culprit, unless the patient is a single source of food, such as eating only baby milk formula -- Ganna really did not expect someone to do tests to prove baby eat its dead!
Some people think that since the detection of the protein deficiency false led to the fatal, just not as good as the abolition of detecting protein, milk Duishui had acquiesced. In fact, Kjeldahl method is not difficult to make up for deficiencies, as long as a multi-step process: first TCA to deal with samples. TCA can form a protein sedimentation, filtration, filtration and precipitation were measured in the nitrogen content, will be able to know the real content of protein and protein nitrogen content pretending. This is the biochemistry of common sense, but also become the early detection of nitrogen content in milk of international standards (ISO 8968). "Sperm protein" fraud occurred at home, some years, "Sanlu milk powder" incident, however this is the "trade secrets" before the public. Only by improving national standards, close the loopholes in order to restore people's confidence in the domestic dairy industry.
(The original "," fine-"fraud" 2008-09-17)
Many people drink milk for calcium, but if you look carefully to the domestic fresh milk packaging on the mark, generally do not list the calcium content, indicating the nutritional content of the content, there are only two: fat and protein. A fresh full-fat milk, low-fat, skim it, the fat content varied, but also in fat is considered healthy today, the killer, most people will not care about whether the fat content standards. Milk protein is the main nutrients, fresh milk packaging will be injected with the protein content of 100 ml for ≥ 2.9 grams of fresh milk in order to show that in line with the national standard (100 ml ≥ 2.95 grams).
Fresh milk protein content in general more than 3%, so in general to achieve the national standard, unless the original milk to Duishui. Thinner should be alert when the price of milk sold, there is a need to detect when to buy fresh milk protein content. According to the chemical properties of the protein, there are several methods of detection, each with advantages and disadvantages. On the food industry generally adopted as the national standard by the Kjeldahl method. This is the late 19th century Denmark John Dahl who invented the method, the principle is simple: contain protein nitrogen, with strong acid sample handling, so that the protein nitrogen released, the determination of nitrogen content, you can calculate the protein content. Milk protein nitrogen rate of about 16 percent, according to national standards, to measure the nitrogen content of 6.38 times, that is, the protein content.
So Kjeldahl method is not actually measured the protein content, but by measuring the content of nitrogen to project protein content, it is clear that if there are other samples contain nitrogen compounds, this approach is not accurate. Under normal circumstances, this is not a problem because food proteins contain only the major components of nitrogen and other major components (carbohydrates, fats) are not nitrogen, the Kjeldahl method is a very accurate determination of protein content . However, if someone stole samples to add nitrogen and other substances, can deceive Kjeldahl method to obtain a false high protein content, milk Duishui posing as the original milk.
Posing as a common protein material is urea nitrogen. However, the urea nitrogen content is not very high (46.6%), dissolved in water will be issued by the sharp An Wei, easy to detect, and a simple method of testing (Tigris reagent) can be found in milk Does the addition of urea. So are false later on the use of melamine. Melamine nitrogen content as high as 66.6 percent (the higher the nitrogen content means pretending to be able to more protein), white and tasteless, there is no simple method of testing (to a "high-performance liquid chromatography" to such a high-tech detection), Posing as an ideal protein structures. Melamine is an important chemical material widely used in the production of synthetic resins, plastics, paint and so on, the current price of about 1 metric ton of 12,000 yuan. Melamine production process, there will be waste, the waste contains 70% of melamine. Those who used false impersonation of the protein is melamine residue, some of the "biotechnology company" in the online marketing of "precision protein" is actually one of the melamine residue. In the feed, dairy products added to the "protein fine," posing as protein.
Melamine is added to milk in how it? There are two possible ways. A station is added to milk in the original milk. This has some limitations, because melamine micro-soluble in water, at room temperature for the solubility of 3.1 grams / liter. In other words, can be dissolved in 100 ml of water 0.31 grams of melamine, containing 0.2 grams, the equivalent of 1.27 grams of protein, which can be worked out, it is necessary to reach 100 ml ≥ 2.95 grams of protein requirements, 100 ml Milk was up to 75 ml of water (and add 0.54 grams of melamine). Another way in the manufacture of milk powder in the process of adding melamine, which is not the solubility limit, and would like to increase the number can be.
Melamine was the reason why criminals as a "precision protein", probably because it felt very low toxicity, eat dead people. Rat oral melamine, semi-lethal dose (toxicology commonly used indicator that can lead to the death of half of the subjects) about every 3 g kg body weight, salt and fairly. High-dose fed rats, rabbits, dogs are not clearly observed toxicity. Melamine appears to be entering the body after metabolism can not be, but as it is discharged from the urine, but animal experiments have shown that long-term feeding of melamine in order to be able to appear as the main ingredient of melamine kidney and bladder stones. We can not take the body to do the pilot, and even those who suffer from kidney stones have been stolen to increase the use of melamine in food, it is hard to determine melamine is the culprit, unless the patient is a single source of food, such as eating only baby milk formula -- Ganna really did not expect someone to do tests to prove baby eat its dead!
Some people think that since the detection of the protein deficiency false led to the fatal, just not as good as the abolition of detecting protein, milk Duishui had acquiesced. In fact, Kjeldahl method is not difficult to make up for deficiencies, as long as a multi-step process: first TCA to deal with samples. TCA can form a protein sedimentation, filtration, filtration and precipitation were measured in the nitrogen content, will be able to know the real content of protein and protein nitrogen content pretending. This is the biochemistry of common sense, but also become the early detection of nitrogen content in milk of international standards (ISO 8968). "Sperm protein" fraud occurred at home, some years, "Sanlu milk powder" incident, however this is the "trade secrets" before the public. Only by improving national standards, close the loopholes in order to restore people's confidence in the domestic dairy industry.
(The original "," fine-"fraud" 2008-09-17)
No comments:
Post a Comment