Proteins, functional properties solubility

In particular, we have concentrated on developing techniques for isolating protein to attain this objective we have studied the practical use of chemical modification. The application of chemical modification to food proteins has been explored for several purposes to block deteriorative interactions between reactive groups (e.g., e-NH2 and reducing sugars) to improve functional properties (solubility, flavor, and thermal stability) to enhance nutritive value and digestibility to facilitate the elucidation of interrelationship between structure and functional properties (6,7,8,9) and, as discussed herein, to facilitate the preparation of protein isolates. 

Partial proteolysis of soy protein isolate with neutral protease from Aspergillus oryzae altered certain functional properties ( ). Solubility was increased in the enzyme-treated soy isolate at both neutral pH and at the isoelectric point (pH... 

Egg white is composed of about 10% protein and 0.5% glucose. Maillard reaction of egg white proteins with glucose proceeds during the production of dried egg white powder, resulting in the formation of brownish pigments and the alteration of powdered protein functional properties such as solubility, emulsifying activity, gelling property (4). 

The number of different proteins in a membrane varies from less than a dozen in the sarcoplasmic reticulum to over 100 in the plasma membrane. Most membrane proteins can be separated from one another using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), a technique that has revolutionized their study. In the absence of SDS, few membrane proteins would remain soluble during electrophoresis. Proteins are the major functional molecules of membranes and consist of enzymes, pumps and channels, structural components, antigens (eg, for histocompatibility), and receptors for various molecules. Because every membrane possesses a different complement of proteins, there is no such thing as a typical membrane structure. The enzymatic properties of several different membranes are shown in Table 41-2. 

Characteristically, legume seeds are rich in protein and contain intermediate to high levels of lysine and threonine which are important in balancing the deficiencies of these essential amino acids in cereal diets. Certain legume proteins, such as soybean, also exhibit strong functional properties, especially water solubility, water and fat binding and emulsification. Thus soybean flours, protein concentrates and isolates have been used widely as nutritional supplements and functional ingredients in foods. 

The present study was conducted to obtain additional information on changes in soy protein subunits during limited proteolysis. Enzymatic soy protein deamidation that occurred, in addition to limited proteolysis, during germination of soybean seeds was investigated. The effects of proteolysis and deamidation on solubility and emulsifying activity were compared. Phosphorylation of soy protein with a commercially available protein kinase and its effects on subsequent changes in functional properties of the protein were also studied. 

For comparison, the solubility-pH profile of the deamidated protein was added to the plot containing the profiles for the pronase E-treated proteins (Figure 5). The deamidated protein, with 2.6% peptide bond hydrolysis, showed improved minimum solubility, comparable to the protein with 5.7% peptide bond hydrolysis and no deamidation. The shape of solubility-pH profile for the deamidated sample resembled that of the intact protein more than those of the pronase E-treated samples. For the deamidated sample, both the increase in solubility and the slight shift of minimum solubility to the acid side were the result of the increase in negative charges from deamidation. Obviously, deamidation was more capable of maintaining the original protein structure than proteolysis, which is essential for the development of desirable functional properties. 

The effect of phosphorylation at 13 /xmoles/g protein on functional properties was minimal. Both solubility and EAI of the phosphorylated protein were slightly higher, compared to those of intact protein (not shown). Phosphorylation with protein kinase from bovine cardiac muscle is restricted by the limited number of potential phosphorylation sites in soy proteins. Experiments are... 

As functional properties of soy proteins, viscosity and solubility are alike in that they are non-equilibrium properties of the system. In the case of solubility, there is at least evidence of steady state equilibrium which allows for the possibility of some qualitative thermodynamic interpretation. In the case of viscosity, steady state equilibrium is not reached. Thus, thermodynamic interpretation is impossible. Molecular dynamics data are needed. 

Water absorption or hydration is considered by some as the first and the critical step in imparting desired functional properties to proteins. Most additives are in dehydrated form the interaction with water is important to properties such as hydration, swelling, solubility, viscosity, and gelation. Protein has been reported to be primarily responsible for water absorption,... 

Q The most detailed studies were reported by Hermansson and Akesson ( , 41) and Hermansson (42) in which the properties of a soy isolate, caseinate, WPC, and model test systems of additive and lean beef or pork were studied. Solubility, swelling, and viscosity (properties reviewed as related to water absorption) were correlated with moisture loss in the raw systems. In cooked systems, the best predictability of meat texture as affected by additive was a statistical model that included the functional properties of swelling and gel strength of protein additive dispersions. 

Pallavicini et al. (16) utilized a-chymotrypsin immobilized on chitin to catalyze plastein formation from leaf protein hydrolyzates. When analyzed by gel exclusion chromatography, the products were comparable to those produced by soluble enzymes. Modification of Specific Functional Properties... 

The functional properties that govern the role of proteins in food applications are color flavor texturization solubility viscosity adhesion or cohesion gelation coagulation aeration or foamability water and oil absorption and emulsification. 

The effective utilization of proteins in food systems is dependent on tailoring the protein s functional characteristics to meet the complex needs of the manufactured food products. Many food proteins require modification to improve such functional properties as solubility, foaming and emulsifying activity (EA). Reviews on classical food protein modifications for improved functionality are available in the literature (Means and Feeney, 1971 Feeney and Whitaker, 1977, 1982, 1986). 

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