"Leather Milk"

From Scientific Squirrels. Translated and edited by Dennis Nichols Ming and Chou Sichang

As an academic of Food Engineering, I am surprised by the “creativity” and “courage” of the Chinese food industry. Maybe it is because of our thousand-year examination tradition that we are capable of finding shortcuts.

“Leather Milk” is another classic example. The standard test for milk all over the world is to multiply the nitrogen content by a variable to calculate the protein content. A few years back, a Shanzhai Chinese milk company added urea to reach that standard protein content. However, urea is stinky and easy to detect, so it was replaced by Melamine which led to the Melanine Scare (this topic is “sensitive” and won’t be detailed) that entirely broke the confidence people built on Chinese milk. Since the Melamine Scare, Melamine and other toxic chemical inspections have become routine.

The food inspection department can use many techniques to detect “fake” milk with low-quality protein and/or toxic chemicals. Nevertheless, the Shanzhai industry is always pushing ahead. Now, the industry has found a way to recycle the collagen from leather waste. Toxic chemical reagents and heavy metals such as chrome stick to leather during leather production. So far, heavy metal content for leather milk has yet to be determined. The World Health Organization allows less then 0.05mg of heavy metals in 1 liter of water, but heavy metals are not the only thing to consider. Even pure collagen milk made from non-toxic ingredients contains low-quality protein.

Turning Leather into protein
Leather and hair are mainly consisted of collagen. Collagen needs to go through a process called hydrolysis before it can dissolve in water. The normal way to do it is to heat it in strong acid or alkali such as protease until the collagen breaks down. These protein pieces become polypeptides and can dissolve.

Basically, hydrolyzing collagen at a high-level yields purer protein but also costs more money. For example Gelatin, a harmless food and cosmetics additive, is a low-level hydrolyzed collagen widely used as a thickening agent and contains low-quality protein. Though harmless, gelatin is not hydrolyzed to a high-level, so its protein is of low-quality with a different amino acid structure and lacks necessary nutrients.

And now Shanzhai milk factories are taking this model and using low-level hydrolysis to make protein which means more profit for them, increasing protein rate on the cheap. The problem is that we think of milk as a healthy food and expect high-quality protein and nutrition. But the protein from collagen is not of high quality and includes elements that humans don’t need. In addition, collagen milk lacks tryptophan, which humans need. Ten grams of real milk can give people everything they need for a day while collagen milk lacks them entirely. It is an inferior product.

Detecting “leather milk” is not difficult. There is plenty of hydroxyproline in collagen, but not pure milk. Also, milk has some tryptophan, collagen doesn’t. But this kind of inspection is not cheap. Wide inspections will cost lot of money which will reflect in either the price of milk or the bill for taxpayers.

To the government’s credit, it is knocking “leather milk” down before it has had a chance to spring up which was not the case for the melamine scare. We can see that some progress has been made.

The orignal article link is here: