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.[1][2]
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.[3]
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.[4]
References
- ^ "Illinois Crop Improvement Association Soybean Tests". Archived from the original on 2007-08-13. Retrieved 2007-06-26.
- ^ "University of Illinois Extension - Soy in Animal Nutrition Databases". Archived from the original on 2007-03-11. Retrieved 2007-06-26.
- ^ AB Batal; MW Douglas; AE Engram & CM Parsons. "Protein dispersibility index as an indicator of adequately processed soybean meal". Archived from the original on 2007-09-27. Retrieved 2007-06-26.
- ^ Reinitz, Gary (1984). "Protein Dispersibility Index (PDI) As A Quality Control Measure For Soy Flour Used In Brown Trout Starter Feed". The Progressive Fish-Culturist. 46 (3): 161. doi:10.1577/1548-8640(1984)46<161:PDIPAA>2.0.CO;2. ISSN 1548-8640. Retrieved 2007-06-26.[permanent dead link]
- Dudley-Cash, W.A. 1999. Methods for determining quality of soybean meal protein important. Feedstuffs. 71(1):10-11.