To get back on the subject: There are several different methods of measuring the "quality" of different proteins but they all have their different strengths and weaknesses so at this moment I personally think that it is very hard to rate different kinds of proteins against each others and be a 100% sure that you are right. And when eating a varied diet and getting more than the minimal needed amount of protein needed to survive I don't think it matters all that much.
I just today ran across an article explaining the different methods of rating protein quality, and here are the more important parts of it:
The quantity of protein in the diet may in fact add importance to the scoring assessment of a given protein. In fact, if you only eat 35- 45 grams a protein a day you better make sure you chose the highest quality protein you can find. On the other hand, if you eat quantities of protein common among bodybuilders, say 1.6 - 1.8 grams per kilogram, the large amount of amino acids overcome slight differences in scoring. Once you achieve a certain levels of quality in a protein supplement, increasing it further will not significantly change it¹s effectiveness when consumed in quantities sufficient to pack on muscle.
Here is a quick overview of the various methods used to determine protein quality. Keep in mind that tests used to determine protein quality use the lower threshold of protein requirements. This creates a metabolic environment far different from that seen in a well fed bodybuilder or athlete.
Chemical Scoring
The most obvious way to determine the quality of a given protein is to break it down into it's individual amino acids. This amino acid profile is then compared to a standard profile. Egg protein is the standard that is used in a Chemical Scoring scale for protein quality and has a rating of 100. Take for example a protein that has a limited amount of a specific amino acid. This amount is then com-pared to the amount found in egg protein. If the amount in the test protein is 75% of that found in egg then the test protein gets a rating of 75. From this you would assume that if you could feed a person an amount of this protein that is exactly his requirement, you would see nitrogen excreted in the urine in the amount of 25 percent of the nitrogen fed.
Although it is relatively easy and inexpensive to do a chemical scoring of any protein, it does not always accu-rately predict how well the body can utilize it. So the ad-vantages of chemical scoring in determining the quality of protein are that it is easy and inexpensive. It's drawback is that it cannot tell you anything about the digestibility of the protein. Chemical scoring also involves a procedure that may destroy certain amino acids and this may lead to inaccurate values. It is also insensitive to substances in a given protein that can adversely effect digestibility. To discover this variable the test would have to utilize living animals.
Biological value (BV)
Biological value (BV) scoring does utilize in vivo testing. To determine the actual amount of a given protein that will be used by the body it is necessary to measure not only urinary, but also fecal losses of nitrogen when that protein is fed to human beings. This method is used inter-nationally.
When measuring the BV of a protein source, two nitrogen studies are done. The first study determines how much nitrogen is lost from the body even when no protein is fed. This amount of nitrogen loss is assumed to be inevitable and that the body will naturally lose it regardless of the amount of nitrogen in the diet. In the second study an amount of the protein is fed that is slightly below what is required. As before, the nitrogen losses are then measured, but this time they are compared to the amount of nitrogen consumed. To determine the actual BV of the protein the re-sults are then derived using this formula:NPU = (N retained / N intake) x 100
This method often involves animal test subjects and is more frequently used. It's draw backs are that if a low NPU is obtained, it is impossible to know if it is because of a poor amino acid profile or low digestibility.
Protein efficiency Ratio (PER)
Protein Efficiency Ratio (PER) is the best known procedure for evaluating protein quality and is used in the United States as the basis for regulations regarding food labeling and for the protein RDA. This method involves rats who are fed a measured amount of protein and weighed periodically as they grow. The PER is expressed as: PER = weight gain (g) / protein intake (g)
The benefits of this method are it's expense and simplicity. It's drawbacks are that it is time consuming; the amino acid needs of rats are not those of humans; and the amino acid needs of growing animals are not those of adult animals (growing animals and humans need more lysine, for example).
The PER is used to qualify statements about daily pro-tein requirement in the United States. You are assumed to eat protein with a PER that is equal to or better than that of the milk protein casein; if the protein's PER is lower, you must eat more of it to meet the RDA. Food labels have to take protein quality into consideration, using the PER of casein as a reference point. If a food has a protein quality equal or better than that of casein, the RDA is 45 grams. If the protein quality is less than casein you need 65 grams for the RDA.
You may be wondering if it makes any difference if you eat your protein from a supplement or from food. Remember that by the time it gets absorbed into the blood stream, all your body knows is how much of each amino acid was present in the food you ate. If you have the money, it is certainly convenient to just drink down a high quality protein supplement. Beyond that, it makes no difference in what form you get your protein from as long as its a complete protein and sufficiently digestible.
Protein digestibility-corrected amino acid score (PDCAA)
As outlined above, protein quality can be measured by the quantity of indispensable amino acids they contain. If a protein contains all the amino acids essential for life, it is called a complete protein and is given a high score. Because some proteins are not as efficiently digested there arose a need to not only test for the amino acid composition of proteins but also for digestibility. This type of testing is called protein digestibility-corrected amino acid score (PDCAA). It is now a federally accepted standard for determining protein quality for preschool aged children.
Some foods however, contain anti-nutritional factors. These factors sometimes occur naturally like in some beans, or are a result of heating and/or cooking, and inhibit the ability of the body to digest and thus absorb certain amino acids. Research has shown the PDCAA method of scoring protein often over estimates the quality of foods containing anti-nutritional factors.12
The take home message from all this is that arguments about who¹s protein scored highest on this test or that test are really meaningless to the average well fed athlete.
The whole article can be found at:
http://www.hypertrophy-specific.com/hsn ... myths.html
by ssrvj » Sun Sep 09, 2007 1:30 am 
Hahah... this thread took me 1½h to read... I had ignored it for a very long time cause I figured it would anoy me... it did, but amusment was also a factor 
