主题：【整理】2012年国内食品质量状况，看数据说话 -- 文青

caseins ares not "presenting" 80% of the total protein, themsevles ARE the 80% of the total protein and they are also the very component that is most interesting to the consumers. When talking about taking protein from cow milk, we are talking about eating casein. In every liter of cow milk, there is >30 grams of protein, and 80% of these protein are caseins.

In such case the quantitation should be very easy because we are testing a class of protein that exists in amounts greater than 20 grams per liter of sample. Nothing could be easier. Simplest way is to pick one most abundant casein and use that as a standard. Or doing it more carefully, we can test a few caseins. Technically these are all no problem. Similar tests have been widely used for blood or urine samples for detecting much more difficult targets. All the technologies have been well developed.

The main obtacle would be that milk is too cheap, and people may not want to spend much money on such tests. But if there are people who are willing to painstakingly smuggle in milk power from a foreign country, then a market for consumer QC kits may emerge. The industry only need to find a way to make profit.

Also there is a very low-tech method for estimating how much protein you have in your milk: we can simply precipitate all the casein by adding acid(vinegar) to it (ie, making yogurt/cheese, people knew how to do this for thousands of years already) and quantitate the total weight of the pellet. The pellet will contain the precipitated casein, some milk fat and some water. As long as we have an idea how much pellet we should get from real milk, this experiment will let we know how dilute our milk is (but of course, to test toxins like melamine we still need those high-tech methods).