Functional properties of proteins

Tolstoguzov VB (1986) Functional properties of protein-polysaccharide mixtures. In Mitchell JR, Ledwards, DA (eds) Functional properties of food macromolecules. Elsevier, London, p 385... 

Schmitt, C., Sanchez, C., Desobiy-Banon, S., Hardy, J. (1998). Structure and techno-functional properties of protein-polysaccharide complexes. Critical Reviews in Food Science and Nutrition, 38, 689-753. 

Tolstoguzov, V.B. (1986). Functional properties of protein-polysaccharide mixtures. In Led ward, D.A., Mitchell, J.R. (Eds). Functional Properties of Food Macromolecules. London Elsevier Applied Science, pp. 385 115. 

Many methods of classifying the functional properties of protein products have been proposed (3). They are based on the preferences and intentions of the researcher. 

The factors influencing the functional properties of protein products are the innate characteristics (physico-chemical) of proteins, and processing and modification steps that alter them. Physico-chemical properties include ... 

Protein is utilized in many foods for the particular characteristics that it contributes to the final product (1 ). In order for protein products to maintain or enhance the quality and acceptability of a food, the protein ingredients should possess certain functional properties that are compatible with the other ingredients and environmental conditions of the food system. Consequently, an important aspect of the development of new protein additives and their incorporation into food systems is the establishment of their functional properties. Functional properties of proteins are physicochemical properties through which they contribute to the characteristics of food. Study of functionality should provide information as to how a protein additive will perform in a food system (, A). These properties are... 

Kinsella Q) reviewed the principal categories of functional properties of proteins in foods and outlined various factors affecting them from the point of view of the food chemist and technologist. 

Existing uses of proteases in foods have been discussed in the foregoing section. Expanding such applications in the future depends upon our ability to control both the processes themselves and their costs. The development of continuous reactors utilizing free or immobilized enzymes will address each of these constraints. Furthermore, our understanding of the chemical basis for the various functional properties of proteins must be expanded... 

Kinsella, J.E. 1976. Functional properties of proteins in foods A survey. CRC Crit. Rev. Food Sci. Nulr. (1976) 219-280. 

The literature is replete with methods to measure protein functional properties. For example, Kneifel et al. (1991) listed about 70 published methods to measure the water-holding ability of dairy proteins. Table B5.1.1, Table B5.1.2, and Table B5.1.3 list some common tests used to evaluate the functional properties of proteins. The methods in these tables should serve as examples only. Selection of the proper test to evaluate a particular functional property is difficult. A functional property test must meet the needs of the user and answer the question(s)... 

The a-helix is the most abundant secondary structural element, determining the functional properties of proteins as diverse as a-keratin, hemoglobin and the transcription factor GCN4. The average length of an a-helix in proteins is approximately 17 A, corresponding to 11 amino acid residues or three a-helical turns. In short peptides, the conformational transition from random coil to a-helix is usually entropically disfavored. Nevertheless, several methods are known to induce and stabilize a-helical conformations in short peptides, including ... 

Many databases provide information on functional annotation of the genomes of organisms. One such high-quality standard database is Pfam (19). Pfam is fundamentally a protein domain family database derived based on sequence similarity. Pfam provides details on the functional properties of protein domains of known function. Out of 1,590, 1,495, and 1,536 proteins encoded in the genomes of 26695, J99, and HPAG1 strains of H. pylori, respectively, 1,113, 1,130, and 1,143 proteins have at least 1 protein domain associated (defined by Pfam) with the amino acid sequence. Therefore, for these domains of H. pylori proteins, preliminary indication of their functions is available. 

The earliest commercial milk protein enzymatic modification dates back to the 1940s, when the first formulas for allergenic infants were made. The aims of this process were to reduce allergenicity as well as to change the functional properties of proteins while preserving their nutritional value for clinical use. Unfortunately the hydrolysates thus obtained were characterized by bitter taste, and for mainly this reason proteolysis, as a technological process, enjoyed very little popularity. 

Functional properties of proteins are closely related to their size, structural conformation, and level and distribution of ionic charges. Chemical treatments, which could cause alteration of these properties, include reactions that either introduce a new functional group to the protein or remove a component part from the protein. Consequently, reactions such as acylation, phosphorylation, esterification, glycation, limited hydrolysis, and deamidation have been used to impart improved functional properties to the dairy proteins. 

Functional Properties. Functional properties of food proteins (106) such as gelling ability, solubility, and the viscosity of their solutions obviously contribute to the nature of a food product in which they are present. Kinsella (100) has classified the functional properties of proteins in terms of their contribution to the complete food (see Table VI) his review and the papers from the recent symposium edited by Pour-El (106) contain a detailed discussion of the subject. 

Table VI. Typical Functional Properties of Proteins Important in Food Applications0...

Limiting essential amino acids covalently attached to proteins by using activated amino acid derivatives can improve the nutritional quality and change the functional properties of proteins. The best chemical methods for incorporating amino acids into water-soluble proteins involve using car-bodiimides, N-hydroxysuccinimide esters of acylated amino acids, or N-carboxy-a-amino acid anhydrides. The last two methods can give up to 75% incorporation of the amount of amino acid derivative used. With the anhydride method, as many as 50 residues of methionine have been linked to the 12 lysine residues of casein. The newly formed peptide and isopeptide bonds are hydrolyzed readily by intestinal aminopeptidase, making the added amino acids and the lysine from the protein available nutritionally. 

Table V. Changes in Functional Properties of Proteins Due to Succinylation °...

Hermansson, A-M. 1975. Functional properties of proteins for foods-flow properties. J. Text. Stud. 8, 425-439. 

Klompong, V., Benjakul, S., Kantachote, D., and Shahidi, F. 2007 (In press). Antioxidative activity and functional properties of protein hydrolysate of yellow stripe trevally (Selaroides leptolepis) as influenced by the degree of hydrolysis and enzyme type. Food Chem. 

Photosensitive systems are convenient objects for analysing a possible correlation between the dynamic and functional properties of proteins. After a short light pulse, it is possible to observe a chemical reaction and to trace the dynamical state of the matrix with the aid of internal and external physical labels. 

It is of interest to obtain quantitative information concerning the role of chemical structure and conformation on the functional properties of proteins. Such information is useful in determining effective methods for altering functionality or in plant breeding to build in desirable traits or increase the yields of those proteins having more desirable properties. 

Chemical derivatization to modify the functional properties of proteins for food applications has received limited attention (10,11,12). Intentional chemical alteration of proteins by... 

Acetylated cottonseed protein demonstrated significantly higher water and oil holding capacities and improved foaming properties (38) compared to unmodified proteins (Table III). Thus, while acetylation does not significantly enhance functional properties of proteins, it improves thermal stability and since acetylated proteins are susceptible to enzyme hydrolysis in vivo it affords a useful reagent for protection of e-NH groups of lysine (11). 

Solubility is a critical functional characteristic because many functional properties depend on the capacity of proteins to go into solution initially, e.g. gelation, emulsification, foam formation. Data on solubility of a protein under a variety of environmental conditions (pH, ionic strength, temperature) are useful diagnostically in providing information on prior treatment of a protein (i.e. if denaturation has occurred) and as indices of the potential applications of the protein, e.g. a protein with poor solubility is of little use in foams). Determination of solubility is the first test in evaluation of the potential functional properties of proteins and retention of solubility is a useful criterion when selecting methods for isolating and refining protein preparations (1). Several researchers have reported on the solubility of extracted microbial proteins (69,82,83,84). In many instances yeast proteins demonstrate very inferior solubility properties below pH 7.5 because of denaturation. 

Enzyme hydrolysis is occasionally used to modify the functional properties of proteins and yeast autolyzates are used commercially as food flavorants (66,86). Partial proteolysis of... 

Chemical modification of yeast protein has received limited attention though as described above it has potential as a method for facilitating recovery of yeast protein. Current studies are concerned with determination of the functional properties of proteins succinylated during the extraction. The composition of yeast proteins prepared by different methods is shown (Table 8). Noteworthy is the protein and nucleic acid concentration in the yeast isolate which differed from the concentrate in that cell wall material was removed by centrifugation. 

The emulsifying properties of proteins have been a subject of concern for those dealing with functional properties of proteins. The studies so far have been restricted to two main approaches emulsifying capacity and emulsion stability measurements. The former measures the maximum oil addition until inversion or phase separation of the emulsion occurs, whereas the latter measures the ability of the emulsion to remain unchanged. 

Although the functional properties of proteins are of the greatest concern to the food scientist, our knowledge of them remains empirical. Observations are but rarely related back to fundamental physicochemical properties such as conformation. 

Friedman, M. (1977). Effects of lysine modification on chemical, physical, nutritive, and functional properties of proteins. In "Food Proteins", J. R. Whitaker and S. R. Tannenbaum, Eds., Avi, Westport, Connecticut, pp. 446-483. 

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