What is the best method for testing the protein quality of food?

Answer

The biochemistry of the body is very complex. There are essential proteins (9), that you have to get thru your diet and non-essential proteins (11) which your body synthesizes. The absorption of protein has many different transport mechanisms. The liver is the primary site for the uptake of most amino acids following ingestion of a protein containing meal. The liver monitors the absorbed amino acids and adjusts the rate of their metabolism according to the needs of the body. There are tons of factors that determine the absorption rate. There are fast proteins such as whey and soy protein which is utilized differently compared to slow proteins such as casein. Hormones also play a role in amino acid utilization. Your energy exertion rate is another factor. The digestibility of a protein is a measure of the amounts of amino acids absorbed following ingestion of given protein. In general, animal protein is 90-99% digestible and considered a compete protein because it includes all 9 essential proteins. Plant proteins are 70-90% digestible, considered incomplete because the don’t include all 9 essential proteins, but if you eat a varied diet of plants this is not an issue for example beans and rice combined include all 9 essential proteins. There are several method to determine protein quality of food

1. PROTEIN DIGESTIBILITY CORRECTED AMINO ACID SCORE or PDCAAS. Example of foods with a PDCAAS of 100 include milk, egg white, ground beef and tuna. Soy bean protein is 94. This measure is commonly used and compares the amount of the limiting amino acid for a test protein to the amount of the same amino acid in 1 g of a reference protein (usually egg or milk).
2. PROTEIN EFFICIENCY RATION (PER). Represents body weight gained on a test protein divided by the grams of protein consumed - used by food manufactures to assess protein quality especially for items such as baby formula.
3. CHEMICAL OR AMINO ACID SCORE. Involves determination of the amino acid composition of a test protein, done in a lab.
4. BIOLOGICAL VALUE. Measures of how much nitrogen (by product of amino acids) is retained in the body for maintenance and growth rather than absorbed. Eggs have BV of 100, meaning that 100% of the nitrogen absorbed from egg protein is retained.
5. NET PROTEIN UTILIZATION. Measures retention of food nitrogen consumed, used more experimental.
6. NET DIETARY PROTEIN CALORIES PERCENTAGE. Helpful in the evaluation of human diets in which the protein calorie ratio varies greatly.

Food Labels are required to indicate the amount of protein in grams and the % daily value for a protein serving of food. The PDCAAS method is used to establish the protein quality for % daily value on food labels.

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