Protein Dispersibility

The quantity of water is two to three times the weight of the hides. The salt from the cure dissolves in the water and the reverse of the curing takes place. The water is drawn into the hides by osmotic forces. The concentration of the salt solution is about 3-5 g/lOO mL. At this concentration some of the soluble proteins disperse. The soak water removes the salt, some proteins, some loose fat, blood, dirt, and manure. 

Figure 4.58 Effect of axial ratio, alb, and concentration on friction coefficient ratio for aqueous protein dispersions. Reprinted, by permission, from P. Hiemenz, Principles of Colloid and Surface Chemistry, 2nd ed., p. 88. Copyright 1986 by Marcel Dekker, Inc.

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... 

A wide variety of gel formation conditions and a wide variety of measurement parameters have been used to describe these functional properties, Heat-Induced gel formation techniques generally Involve heating protein dispersions at appropriate concentrations In sealed test tubes (7,13.14.15.16.24.25). In sealed cans... 

The data presented In Table II summarize differences In composition, preparation method and time required for gel formation of lOX protein dispersions of WPC heated at 100°C. Differences In gelling time could not be related entirely to compositional differences and appear to be related to other additional factors (I.e., preparation technique, protein denaturation level, etc.)... 

Figure 3. Response surface contour plots (15) for cysteine (x,) and CaCh (Xi) addition to 10% whey protein dispersions at pH 7.0 on hardness (y,), cohesiveness (yi), springiness (ys), and compressible water (yj of gels prepared by heating at 100°C for 15 min...

Table III. Dialysis effect on gel characteristics of 10% protein dispersions of whey protein concentrate (WPG) heated at 100 C for 15 rain.

Additives had substantial effects on the aeration properties of bromelain-modified succinylated fish protein (50). Foam volume was increased with up to 2% sodium chloride in the system however there was a decrease in foam stability when greater than 0.3% salt was used. Sucrose, at concentrations up to 50%, increased foam stability. When fat was added to treated fish protein dispersions... 

FIG. 2.9 Variations of the ratio ///0 with asymmetry and hydration for aqueous protein dispersions. (Redrawn from L. Oncley, Ann. NY Acad. Sci. 41, 121 (1941). 

Protein additives Protein amino acids a-l-Protemase inhibitor Protein-based mimetncs Protein Ca [42617-41-4] Protein channels Protein chromatography Protein crystal growth Protein dispersibility Protein engineering... 

For the test protein, disperse 6.25 mg protein (1.0 mg nitrogen as determined by Kjeldahl method see unitbi.2) in 10 ml distilled water into a small reaction vessel or vial. Adjust the pH of the suspension with 0.1 N NaOH while stirring at 37°C. 

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)... 

J.M. Perri, Jr. and F. Hazel, Effect of electrolytes on the foaming capacity of alpha soybean protein dispersions, J. Phys. Colloid Chem. 51 (1947) 661-666. 

Pectate, alginate, and CMC have held proteins dispersed under conditions that might otherwise have caused precipitation (Imeson et al., 1977). Polysaccharide stabilizers, in the order of decreasing thermodynamic compatibility with proteins, are pectin > CMC > alginate > gum arabic > dextran (Tolstoguzov, 1986). 

Figure 2. The effects of progressive succinylation on the viscosity (v/v — 1 )/C) and uv absorption, i.e. tyrosine (At 287) of peanut protein dispersions...

The limited studies have revealed some of the potential benefits of chemical derivatization for increasing the use of novel proteins by expanding their functional properties. Some of the properties imparted by succinylation may have very specific or unique applications, e.g. as thermo-stable protein dispersions in coffee whiteners, beverages. Derivatization can be used to impart functionality into denatured, insoluble proteins, and thereby increase their value as functional ingredients. 

When a protein dispersion is heated a gel may form. The gelation mechanism, the gel structure and the gel properties are highly dependant on processing conditions as well as factors such as pH and ionic strength. Differences in gel structures are demonstrated in Finures 1 and 2. where electromicrographs of two gel structures of exactly the same protein preparation, formed at different ionic strengths are shown. 

Whey protein concentrate. The whey protein used was prepared by ultrafiltration and spray drying. Protein content (N x 6.55) was 68% (dry weight). Lipid content was 7.1% (dry weight). In order to study heat induced aggregation by spectrophotometric methods the turbidity of the dilute protein dispersions was too high. The turbidity of whey protein dispersions is caused by lipids associated with proteins probably in the form of emulsified oil droplets. This fraction was removed by precipitation at pH 4.5 from dispersions made in dist. water and separated by centrifugation at 40 000 xg. 

When protein dispersions of soy and whey proteins are heated, they become turbid due to aggregation. Spectrophotometric methods can therefore not be used and few denaturation studies have been made on such systems. Differential scanning calorimetry is an interesting alternative method, since the physical state of the system is unimportant for this analytical tool. 

Figure 3 shows DSC thermograms of 10 soy protein dispersions at varying pH in distilled water. Two peaks can be observed in the pH range 4-9. The 7S globulin is responsible for the first and the 11S globulin for the second peak (1 ). 

Figure 3. DSC thermograms of 10% soy protein dispersions in distilled water at pH 2.0—10.0. The sensitivity was 0.5 meal sec 1 and the heating rate 10°C min1 (1).

Even if salt had little influence on the position of the peak onsets, salt seemed to have an effect on the areas under the peaks for whey proteins. Figure 6 shows DSC thermograms of 10% whey protein dispersions at varying pH in 0.2 M NaCl. 

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