- 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 thesoybean 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=http://www.ilcrop.com/ipglab/soybtest/soybdesc.htm|title=Illinois Crop Improvement Association Soybean Tests|accessdate=2007-06-26] [cite web|url=http://www.livestocktrail.uiuc.edu/sand/definitions.cfm|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=http://ps.fass.org/cgi/content/abstract/79/11/1592|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 andtofu 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=http://afs.allenpress.com/perlserv/?request=get-abstract&doi=10.1577%2F1548-8640(1984)46%3C161%3APDIPAA%3E2.0.CO%3B2|title=Protein Dispersibility Index (PDI) As A Quality Control Measure For Soy Flour Used In Brown Trout Starter Feed|accessdate=2007-06-26]References
* Dudley-Cash, W.A. 1999. Methods for determining quality of soybean meal protein important. Feedstuffs. 71(1):10-11.
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