Clipping Board » Illness Enters through Mouth ─ The information that has been made public is often just the tip of the iceberg...
Many people drink milk to supplement calcium, but if you pay attention to the labels on domestic fresh milk packaging, the calcium content is generally not listed. The nutritional components listed are usually only two: fat and protein. Fresh milk can be categorized as whole, low-fat, or skim, with varying fat content. In today's world where fat is often seen as a health hazard, most people don't care much about whether the fat content meets standards. Protein is the main nutritional component in milk, and fresh milk packaging typically states that the protein content is ≥2.9 grams per 100 milliliters, indicating compliance with the national standard for fresh milk (≥2.95 grams per 100 milliliters).
The protein content of raw fresh milk is generally above 3%, so it usually meets the national standard unless water is added to the raw milk. To prevent people from selling water at the price of milk, it is necessary to test the protein content when purchasing raw fresh milk. Based on the chemical properties of protein, there are several testing methods, each with its own advantages and disadvantages. The Kjeldahl method, widely adopted in the food industry and established as a national standard, is a method invented by Danish chemist Johan Kjeldahl in the late 19th century. The principle is simple: protein contains nitrogen, and by treating the sample with strong acid to release the nitrogen from the protein, the nitrogen content can be measured to calculate the protein content. The nitrogen content of milk protein is about 16%, and according to the national standard, the measured nitrogen content is multiplied by 6.38 to determine the protein content.
Therefore, the Kjeldahl method does not actually measure protein content directly but estimates it by measuring nitrogen content. Obviously, if the sample contains other nitrogen-containing compounds, this method becomes inaccurate. Under normal circumstances, this is not a problem because the main components in food that contain nitrogen are proteins, while other main components (carbohydrates, fats) do not contain nitrogen. Thus, the Kjeldahl method is a very accurate way to measure protein content. However, if someone adds other nitrogen-containing substances to the sample, they can deceive the Kjeldahl method into showing a falsely high protein content, allowing diluted milk to pass as raw milk.
A commonly used nitrogen-containing substance to fake protein is urea. However, urea's nitrogen content is not very high (46.6%), and when dissolved in water, it emits a pungent ammonia smell, making it easy to detect. Additionally, a simple testing method (the Griess reagent method) can determine whether urea has been added to milk. As a result, counterfeiters later switched to using melamine. Melamine has a high nitrogen content of 66.6% (the higher the nitrogen content, the more protein it can fake), is white and odorless, and lacks a simple detection method (requiring high-tech methods like "high-performance liquid chromatography" for detection), making it an ideal protein substitute. Melamine is an important industrial chemical widely used in the production of synthetic resins, plastics, coatings, etc., with a current price of about 12,000 yuan per ton. During the production of melamine, waste residue is generated, which still contains 70% melamine. Counterfeiters use this melamine residue to fake protein, and many "biotech companies" in China promote "protein essence" online, which is essentially melamine residue. Adding "protein essence" to feed and dairy products to fake protein has become an open secret, and its popularity has driven up the price of this otherwise free industrial waste to 300–400 yuan per ton.
How is melamine added to milk? There are two possible ways. One is adding it to raw milk at milk collection stations. This has certain limitations because melamine is slightly soluble in water, with a solubility of 3.1 grams per liter at room temperature.In other words, 100 milliliters of water can dissolve 0.31 grams of melamine, containing 0.2 grams of nitrogen, equivalent to 1.27 grams of protein. From this, it can be calculated that to meet the requirement of 100 milliliters containing at least 2.95 grams of protein, a maximum of 75 milliliters of water can be added to 100 milliliters of milk (along with 0.54 grams of melamine). Another method is to add melamine during the production of milk powder, which is not limited by solubility and allows for any amount to be added.
The reason melamine has been used as a "protein enhancer" domestically is likely due to the perception that it has very low toxicity and is not lethal. The oral lethal dose (LD50, a common toxicological indicator referring to the dose that causes death in half of the test subjects) of melamine in rats is about 3 grams per kilogram of body weight, similar to that of table salt. High-dose feeding of melamine to rats, rabbits, and dogs has not shown significant signs of poisoning. Melamine seems not to be metabolized in the body but is excreted unchanged in urine. However, animal experiments have also shown that long-term feeding of melamine can lead to kidney and bladder stones composed mainly of melamine and can induce bladder cancer. In 2007, pet food exported from China to the United States caused kidney failure and death in many pets, with investigations suggesting that melamine contamination in the pet food was the cause. So, does melamine have the same toxicity to humans? We cannot conduct experiments on humans, and even if people with kidney stones have consumed food adulterated with melamine, it is difficult to confirm melamine as the culprit unless the patient's food source is very limited, such as infants who only consume formula milk—unexpectedly, someone dared to use infants as test subjects to prove that it can be lethal!
Some argue that since the flaws in protein testing methods have led to fatal adulteration, it might as well be better to abolish protein testing altogether and tacitly allow the dilution of milk with water. In fact, the flaws in the Kjeldahl method are not difficult to remedy; it only requires an additional step: treating the sample with trichloroacetic acid first. Trichloroacetic acid can precipitate proteins, and after filtration, the nitrogen content in the precipitate and the filtrate can be measured separately to determine the true protein content and the nitrogen content masquerading as protein. This is a basic principle in biochemistry and has long been an international standard (ISO 8968) for testing nitrogen content in milk. The "protein enhancer" scam has been around domestically for some years, and the "Sanlu milk powder" incident merely brought this "industry secret" to public attention. Only by improving national standards and plugging loopholes can we restore public confidence in the domestic dairy industry.
Source: http://blog. sina. com. cn/ s/ blog_474068790100au5o. html
2008/09/23 10:48
The "Protein Essence" Scam
The protein content of raw fresh milk is generally above 3%, so it usually meets the national standard unless water is added to the raw milk. To prevent people from selling water at the price of milk, it is necessary to test the protein content when purchasing raw fresh milk. Based on the chemical properties of protein, there are several testing methods, each with its own advantages and disadvantages. The Kjeldahl method, widely adopted in the food industry and established as a national standard, is a method invented by Danish chemist Johan Kjeldahl in the late 19th century. The principle is simple: protein contains nitrogen, and by treating the sample with strong acid to release the nitrogen from the protein, the nitrogen content can be measured to calculate the protein content. The nitrogen content of milk protein is about 16%, and according to the national standard, the measured nitrogen content is multiplied by 6.38 to determine the protein content.
Therefore, the Kjeldahl method does not actually measure protein content directly but estimates it by measuring nitrogen content. Obviously, if the sample contains other nitrogen-containing compounds, this method becomes inaccurate. Under normal circumstances, this is not a problem because the main components in food that contain nitrogen are proteins, while other main components (carbohydrates, fats) do not contain nitrogen. Thus, the Kjeldahl method is a very accurate way to measure protein content. However, if someone adds other nitrogen-containing substances to the sample, they can deceive the Kjeldahl method into showing a falsely high protein content, allowing diluted milk to pass as raw milk.
A commonly used nitrogen-containing substance to fake protein is urea. However, urea's nitrogen content is not very high (46.6%), and when dissolved in water, it emits a pungent ammonia smell, making it easy to detect. Additionally, a simple testing method (the Griess reagent method) can determine whether urea has been added to milk. As a result, counterfeiters later switched to using melamine. Melamine has a high nitrogen content of 66.6% (the higher the nitrogen content, the more protein it can fake), is white and odorless, and lacks a simple detection method (requiring high-tech methods like "high-performance liquid chromatography" for detection), making it an ideal protein substitute. Melamine is an important industrial chemical widely used in the production of synthetic resins, plastics, coatings, etc., with a current price of about 12,000 yuan per ton. During the production of melamine, waste residue is generated, which still contains 70% melamine. Counterfeiters use this melamine residue to fake protein, and many "biotech companies" in China promote "protein essence" online, which is essentially melamine residue. Adding "protein essence" to feed and dairy products to fake protein has become an open secret, and its popularity has driven up the price of this otherwise free industrial waste to 300–400 yuan per ton.
How is melamine added to milk? There are two possible ways. One is adding it to raw milk at milk collection stations. This has certain limitations because melamine is slightly soluble in water, with a solubility of 3.1 grams per liter at room temperature.In other words, 100 milliliters of water can dissolve 0.31 grams of melamine, containing 0.2 grams of nitrogen, equivalent to 1.27 grams of protein. From this, it can be calculated that to meet the requirement of 100 milliliters containing at least 2.95 grams of protein, a maximum of 75 milliliters of water can be added to 100 milliliters of milk (along with 0.54 grams of melamine). Another method is to add melamine during the production of milk powder, which is not limited by solubility and allows for any amount to be added.
The reason melamine has been used as a "protein enhancer" domestically is likely due to the perception that it has very low toxicity and is not lethal. The oral lethal dose (LD50, a common toxicological indicator referring to the dose that causes death in half of the test subjects) of melamine in rats is about 3 grams per kilogram of body weight, similar to that of table salt. High-dose feeding of melamine to rats, rabbits, and dogs has not shown significant signs of poisoning. Melamine seems not to be metabolized in the body but is excreted unchanged in urine. However, animal experiments have also shown that long-term feeding of melamine can lead to kidney and bladder stones composed mainly of melamine and can induce bladder cancer. In 2007, pet food exported from China to the United States caused kidney failure and death in many pets, with investigations suggesting that melamine contamination in the pet food was the cause. So, does melamine have the same toxicity to humans? We cannot conduct experiments on humans, and even if people with kidney stones have consumed food adulterated with melamine, it is difficult to confirm melamine as the culprit unless the patient's food source is very limited, such as infants who only consume formula milk—unexpectedly, someone dared to use infants as test subjects to prove that it can be lethal!
Some argue that since the flaws in protein testing methods have led to fatal adulteration, it might as well be better to abolish protein testing altogether and tacitly allow the dilution of milk with water. In fact, the flaws in the Kjeldahl method are not difficult to remedy; it only requires an additional step: treating the sample with trichloroacetic acid first. Trichloroacetic acid can precipitate proteins, and after filtration, the nitrogen content in the precipitate and the filtrate can be measured separately to determine the true protein content and the nitrogen content masquerading as protein. This is a basic principle in biochemistry and has long been an international standard (ISO 8968) for testing nitrogen content in milk. The "protein enhancer" scam has been around domestically for some years, and the "Sanlu milk powder" incident merely brought this "industry secret" to public attention. Only by improving national standards and plugging loopholes can we restore public confidence in the domestic dairy industry.
Source: http://blog. sina. com. cn/ s/ blog_474068790100au5o. html
2008/09/26 04:33