Protein nitrogen solubility

Cell contents (soluble in neutral detergent) Cell wall constituents (fibre insoluble in neutral detergent) Lipids Sugars, organic acids and water-soluble matter Pectin, starch Non-protein nitrogen Soluble protein... 

Activity of soluble protein Nitrogen catabolism regulation Translation termination Not known Not known Not known... 

Nitrogen Solubility Index. Nitrogen solubility index (NSI) indicates the extent of denaturation of a protein and correlates well with the functional characteristics of protein ingredients. 

Nitrogen solubility index is inversely related to protein level, i.e., as the protein level increases, NSI decreases (8). Another factor related to solubility of seed nitrogen in a flour and distilled water suspension is the concentration of water-soluble naturally occurring salts, since salt-soluble globulins are the major proteins found in peas (21). Also, differences in pea mineral content may play a role in NSI. 

Water Absorption. Water absorption of pea protein isolates depends on pH and processing method used to produce the isolate. Isoelectric pea protein isolate absorbed 2.7 to 2.8 times its weight of water at pH 7 while UF pea protein isolate absorbed 3.3 times its weight of water at pH 2.5 and twice its weight in water at pH 8.5 (13). These low water absorption values may be due to the high nitrogen solubilities of these proteins (35). 

The protein fraction showed low nitrogen solubility and rather low water hydration and oil absorption values relative to those of the proteinates but oil emulsification was quite high. Refined legume fiber had a water hydration capacity of over 20 g/g product. 

The field pea and fababean flours, which were ground to 60-mesh, showed hieh nitrogen solubility (Table III). However, the orocess of oin milling reduced the NSI values to approximately one-half that of the original flours. The air classified protein... 

Figure 4, Mean nitrogen solubility index (%) for protein flour dry roasted under various processing conditions bean/bean ration (1/10, 1/15) residence time (1, 2 min) and bead...

Precipitation by ethanol in the cold was used effectively by J.Mellanby in 1908 to obtain diptheria antitoxin two years later Hardy and Gardiner reported the precipitation of plasma proteins by cold ethanol or acetone. The resulting proteins remained soluble in water, i.e. they were not denatured, and subsequent estimation of protein as nitrogen was helped by the use of nitrogen-free precipitants. Separations using organic solvents were considerably extended by Edsall,... 

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... 

Ingredients most commonly used in textured vegetable protein products are defatted soy flours or grits. Preferably, the defatted soy flour should contain a minimum of 50% protein with a nitrogen solubility index of 50 to 70, a maximum of 30% insoluble carbohydrate, and less than 1% fat (9). ... 

Sekul et al. (29) studied the nitrogen solubility properties of enzyme-hydrolyzed peanut proteins. A deionized water dispersion of peanut flour (1 10, w/v) was treated with papain (0.5% total volume) at 45OC for 15 min. Solubility was tested over a range of pH 1 to 9. In general, papain treatment improved solubility at all levels examined except pH 2 and 8 (Figure 6). 

Figure 6. Nitrogen solubility (Kjeldahl) of peanut proteins P.H.P. = partial hydrolysis by 5% papain CON. = control (no papain) (2i).

In any quantitative work on protein hydrolysis, it is necessary to have a measure of the extent of the hydrolytic degradation. The measurement of the number of peptide bonds cleaved during a hydrolytic process is related to the activity of proteinolytic enzymes and the extent of hydrolysis. Various techniques that evaluate the progress of hydrolysis have been reported, such as the trichloroacetic acid (TCA) solubility index, which evaluates the percentage of nitrogen soluble in TCA after partial hydrolysis of the protein. 

Solubility. The results from the solubility experiments are given in Figures 4 and 5. The broken curve is the solubility curve for the original soy protein isolate (Purina 500 E) the nitrogen solubility of this product at neutral pH is below 40%, which indicates that the isolate has been partly denatured during its processing. The sample denoted as DH = 1.0% is the control and it is clearly demonstrated that the acid treatment has caused further aggregation and denaturation. The definitely positive DH-value... 

Figure 4. Nitrogen solubility tw. pH for soy protein hydrolysates. The hydrolyses were carried out using alcalase(B> at pH 8.0 as described in the experimental...

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. 

Figure 5. Liberation of nonprotein nitrogen (soluble in 12% TCA) from milk protein fractions by rennin (149). (a) 2% first cycle casein (largely whole casein) (b) total when protein (c) 2% second cycle casein—fraction P (mostly a8- and ft-caseins) (a) 1% second cycle casein—fraction S (mostly k- and ft-caseins) (d) 1 % K-casein and (f) 2% a-casein.

The extent of denaturation of soybean by heating influences significantly the rate of protein isolation. The extent of aenaturation can be shown by the NSI (nitrogen solubility index). It was shown to be adequate to use a mixed enzyme solution at concentrations of 0.2 to 1.0% (usually 1.0 to 3.0% of substrate). Although good results were obtained by enzymatic treatment of raw soybeans and defatted soybean cakes with NSI of 24 (for brewing of soysauce and fermented soybean... 

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