Protein dispersibility index

The severity of agitation and separation determines whether the separated medium is considered to have proteins in solution (protein solubility values) or in dispersion (protein dispersion values). The terms Nitrogen Solubility Index (NSI) and Protein Dispersibility Index (PDI) are to be used only when the official... 

Protein dispersibility index Dry product is dispersed in water by blending, then centrifuged at 880 x g for I0 min Protein dispersibility index (%) = (% water-dispersible prolein/% total protein) x 100 Advantages Tested in a collaborative study and found to be reproducible between laboratories. Disadvantages Limited to soy products protein is determined by Kjeldahl analysis, which can be a lengthy procedure. AOCS Method B a 10-65 (AOCS, 1999) AACC Method 46-24 (AACC, 2000)... 

Laboratory tests such as urease activity, protein dispersibility index (PDI), nitrogen solubility index (NSI), thiamine, and water absorption have been found valuable in monitoring daily production for protein quality. But biological chick and/or rat assays are the only reliable means currently available for predetermining the nutritional value of whole soybean protein they must be conducted periodically to verify results of chemical tests (31). If whole soybeans are to be used in a mixture containing 20% or more soybean meal, 5% or more urea, and 20% or more molasses, or an equivalent mixture, and exposed to hot, humid storage conditions, it is advisable that the urease activity of the whole soybeans not exceed 0.12 increase in pH (31). Extruded or roasted soybeans properly treated for cattle to increase bypass protein should have urease values of less than 0.05 pH rise. A urease rise of 0.05-0.20 is an indication of proper treatment for swine and poultry. 

Of obvious concern in any DT application is the potential for overtoasting the meal and adversely affecting the water solubility of the protein, often expressed in terms of the protein dispersion index, or PDl. For certain edible flour and other applications demanding a high PDI, the DTDC process may be replaced with a flash desolventizing system. These systems, which typically use superheated solvent to evaporate volatiles present in the freshly extracted white flakes, maintain the high PDI while desolventizing the feedstock. 

Figure 13. Effect of extrusion temperature on protein dispersibility index (PDI) and lipoxygenase enzymes activity (LOX).

A patent owned by E.I. du Pont (Crank and Kerr, 1999) described procedures for preparing isoflavone-rich soy protein products with desirable flavor and functionality. A low-stachyose soybean variety was dehulled, flaked (0.25-0.6 mm), defatted by hexane and desolventized by vacuum to yield a 90 PDI (protein dispersibility index) of soymeal. A water extraction at 80°C was carried out for 6-10 min, and it was then cooled to 40-45°C by adding more water. The extract after centrifugation was neutralized and spray-dried. The product contained 2.5 mg/g isoflavone. 

Wang and Johnson (2001) reported on test measurement methods that were major indicators of soybean oil quality. These tests included peroxide value, anisidine value, FFA content, phospholipid content, total tocopherol content, oxidative stability index, color, and moisture content. For soybean meal, they reported on urease activity, protein dispersibility index (PDI), rumen bypass or rumen undegradable protein, trypsin inhibitor activity, moisture content, residual oil content, protein content, fiber content, color, amino acid profiles, and protein solubility under alkaline (KOH) conditions. 

Protein Dispersibility Index is a standard AOCS method (Ba 10-65) for measuring the amount of heat treatment used in the processing of soybean meal products. 

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