Water-soluble proteins from peanut

Figure 2. Typical disc polyacrylamide gel electrophoretic patterns of water-soluble proteins from peanut flours. Reproduced with permission from Ref. 2. Copyright 1980, Institute of Food Technologists.

Burnett and others (37,41,42) have prepared water-soluble glues from peanut protein isolated from defatted peanut meal. The glues are re-wettable, flexible, and nonwarping and are suitable for making gummed tape and paper. 

Water-Soluble Proteins. Historically, several water-soluble plant and animal proteins have been used as adhesives, both industrially and in conservation work. Currently, only the milk-based casein products are in significant industrial use. Casein glues have also been used in conservation work, but formulations designed for high water resistance could be difficult to reverse. Plant proteins, especially those from legumes such as soybeans and peanuts, have been used industrially, some until fairly recently. Presumably at least some forms of plant protein glues would be reversible enough to be of interest to conservators. 

Data in Figure 6 show the effect of varying the pH and sodium chloride concentration on emulsion capacity of peanut protein isolate. Shifting the pH to levels above or below the isoelectric point improved emulsion capacity of peanut protein isolate in O.IM or 0.2M NaCl. Similar trends were noted when distilled water was used as the continuous phase (data not.shown). At the 0.5M NaCl concentration, however, little difference was noted in emulsion capacity at pH 3, 4, or 5 appreciable increases occurred when the pH was raised to 6 and above. At the highest salt concentration (1.OM NaCl), a gradual increase in emulsion capacity occurred when the pH was increased from 3 to 10. An overall suppression in emulsion capacity occurred as salt concentration increased except at pH 5 and 6. These emulsion-capacity curves closely resemble the protein-solubility curves of peanut protein shown in Figure 7... 

The percentages of proteins in water-soluble extracts of suspensions of peanut meal adjusted from pH 6.7 to 4.0, then back to either 6.7 or 8.2, were less than those of the initial extract and the one-step pH change, respectively (Figure 5). Percentage of protein in soluble extracts at pH 6.7 or 8.2 was not altered greatly by the two-step pH adjustment. 

Protein Solubility. The effects of moist heat on functionality of peanut proteins have been investigated (10,12,14) by heating shelled kernels in water in a temperature-controlled retort at 50, 75, and 100eC for 15-min intervals ranging from 15-90 min. Levels of soluble protein generally decreased as heating time incr eased from 15 to 90 min at all three temperatures (Figure 9). 

Succinylation significantly enhances the rate of hydration of soy, peanut and cottonseed proteins (12,38,43). It causes a marked improvement in the water solubility of soy protein and also of leaf protein concentrate (12). It decreased the isoelectric point of both soy and peanut proteins by approximately 0.5 pH unit (from pH 4.5 to 5.0) significantly enhanced solubility between the isoelectric point and pH 6, but progressively reduced solubility of both soy and peanut protein below the isoelectric point (12,43). 

Since peanut proteins are very soluble in water in their native state, Sugarman (188) has proposed the simultaneous extraction of oil and proteins from macerated kernels by vigorously mixing the kernels with water and then separating the oil, proteins, and insoluble constituents by centrifugation. 

In 1880 Ritthausen (172) reported the isolation of a protein product from oil-free peanut meal, using aqueous sodium chloride solution as the solvent for extraction of the protein. Lichnikov (131) in 1913 proposed the classification of peanut protein into three fractions, albumin, globulin, and gluten components, based on their relative solubilities in water, salt solutions, and aqueous potassium hydroxide, respectively. 

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