Protein Dispersibility Index

Protein Dispersibility Index

The Protein Dispersibility Index (PDI) is a means of comparing the solubility of a protein in water, and is widely used in the soybean product industry.

A sample of the soybeans are ground, mixed with a specific quantity of water, and the two are then blended together at a specific rpm for a specific time. The resulting mixture and original bean flour then have their protein content measured using a combustion test, and the PDI is calculated as the percentage of the protein in the mix divided by the percentage in the flour - a PDI of 100 therefore indicates total solubility. [cite web|url=|title=Illinois Crop Improvement Association Soybean Tests|accessdate=2007-06-26] [cite web|url=|title=University of Illinois Extension - Soy in Animal Nutrition Databases|accessdate=2007-06-26]

It has been shown that the PDI can be affected, not only by the type of soybean used, but also by manufacturing processes - heat has been shown to lower the PDI. [cite web|url=|title=Protein dispersibility index as an indicator of adequately processed soybean meal|author=AB Batal, MW Douglas, AE Engram, and CM Parsons|accessdate=2007-06-26]

The PDI required of a soyflour is dependent on the purpose to which the soybeans are to be put. Manufacturers of soymilk and tofu products want a high PDI to ensure the maximum protein content in their products. However, manufacturers of soy-based fish feed require a low PDI to avoid loss of valuable protein into the surrounding water. [cite web|url=|title=Protein Dispersibility Index (PDI) As A Quality Control Measure For Soy Flour Used In Brown Trout Starter Feed|accessdate=2007-06-26]


* Dudley-Cash, W.A. 1999. Methods for determining quality of soybean meal protein important. Feedstuffs. 71(1):10-11.

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