Protein modifying functional properties

Hydrolyzed Vegetable Protein. To modify functional properties, vegetable proteins such as those derived from soybean and other oil seeds can be hydrolyzed by acids or enzymes to yield hydrolyzed vegetable proteins (HVP). Hydrolysis of peptide bonds by acids or proteolytic enzymes yields lower molecular weight products useful as food flavorings. However, the protein functionaHties of these hydrolysates may be reduced over those of untreated protein. 

Attention has been directed toward modifying functional properties of peanut proteins by chemical, enzymatic, and physical approaches. Chemical modification has included acetylation and succinylation treatments (28, 29). Marked improvement in emulsion capacity occurred as a result of this treatment if the proteins were extracted in acid 28). Beuchat et al. 

Chemical derivatization of proteins to modify functional properties has received limited consideration. Cationic derivatives of food proteins are routinely used (e.g. sodium soy isolates and sodium and calcium caseinates) to improve wettability, dispersibility and handling properties of these proteins (27). 

Before the first indication of the existence of cannabinoid receptors, the prevailing theory on the mechanism of cannabinoid activity was that cannabinoids exert their effects by nonspecific interactions with cell membrane lipids (Makriyannis, 1990). Such interactions can increase the membrane fluidity, perturb the lipid bilayer and concomitantly alter the function of membrane-associated proteins (Loh, 1980). A plethora of experimental evidence suggests that cannabinoids interact with membrane lipids and modify the properties of membranes. However, the relevance of these phenomena to biological activities is still only, at best, correlative. An important conundrum associated with the membrane theories of cannabinoid activity is uncertainty over whether cannabinoids can achieve in vivo membrane concentrations comparable to the relatively high concentrations used in in vitro biophysical studies (Makriyannis, 1995). It may be possible that local high concentrations are attainable under certain physiological circumstances, and, if so, some of the cannabinoid activities may indeed be mediated through membrane perturbation. 

It is also essential that any functional properties of the mutant protein that can be assessed be assessed. Although the substitution of one particular residue for another may be made in an attempt to determine the effect of the mutation on a specific property of a protein, it is quite possible that other properties that are not of immediate concern may be modified unintentionally and that these modifications may have important, otherwise occult, implications for the functional studies that are of immediate interest (vide infra). In the case of electron transfer proteins it may be useful, for example, to produce a family of mutants the members of which differ from each other only in their reduction potentials. This result may prove to be difficult to achieve because many mutations that perturb the reduction potential of a protein may also change its electrostatic properties or its reorganizational barrier to electron transfer. Depending on the experiments to be conducted with the mutants, these other properties may prove to be more important considerations than the reduction potentials of the mutants. In summary, new mutant proteins are ideally studied as if they were altogether new proteins of the same general class as the wild-type protein, and assumptions regarding the properties of such mutants should be kept to a minimum. 

These transglutaminase-catalysed reactions can be nsed to modify the functional properties of food proteins. Transglutaminase has been nsed to catalyze the cross-hnking of a nnmber of proteins, such as whey proteins, soy proteins, glnten, myosin and... 

Adler-Nissen and Olsen (40) studied the influence of peptide chain length on the taste anT functional properties of enzymatically modified soy protein. The emulsifying capacity of modified proteins could be improved significantly compared to unmodified control samples by controlling the extent of hydrolysis. 

Considerable effort has been devoted to the improvement of functional properties of fish protein concentrate. Spinelli et al. (44) conducted a study to determine the feasibility of modifying myofibrillar fish proteins by partially hydrolyzing them... 

The expanded use of enzymes to modify protein functional properties has great promise for the food industry. Major advantages of using proteases compared to other agents include their specificity, their effectiveness at low concentrations and... 

The most important feature affecting the functional and organoleptic properties of a protein is its surface structure. Surface structures affect the interaction of a protein with water or other proteins. By modifying the structure of the protein, particular functional and organoleptic properties are obtained. Functional properties of a protein are physicochemical characteristics that affect the processing and behavior of protein in food systems (Kinsella, 1976). These properties are related to the appearance, taste, texture, and nutritional value of a food system. Hydrolysis is one of the most important protein structure modification processes in the food industry. Proteins are hydrolyzed to a limited extent and in a controlled manner to improve the functional properties of a foodstuff. 

The functionality of a protein is dictated by the molecular properties of the protein as modified by processing treatments, environmental factors, and interactions with other components. Environmental conditions, such as pH, ionic strength, type of salts, moisture content, and oxidation-reduction potential, may alter the functional properties of a protein in a food. Protein functional properties are also influenced by unit operations during processing... 

Primary structure of proteins can be chemically modified in order to improve their functional properties. This approach has been used with success to study the structure-function relationships (enzymatic function, biological function, physico-chemical and functional properties). Deliberate chemical modification of food proteins can result in alteration of the nutritive value, formation of potentially toxic amino acid derivatives, and contamination by toxic chemicals. 

Adler-Nissen, J. and Olsen, H.S. 1979. The influence of peptide chain length on taste and functional properties of enzymatically modified soy protein In Functionality and Protein Structure , Advances in Chemical Series 92 (A. Pour-El ed.), pp. 125-146. American Chemical Society, Washington, DC. 

Kim, S.Y., Park, P.S.W., and Rhee, K.C. 1990. Functional properties of proteolytic enzyme modified soy protein isolate. J. Agric. Food Chem. 38, 651-656. 

Some physical and functional properties of casein modified by the covalent attachment of amino acids are given in Table IX. Despite extensive modification, the relative viscosities of 2% solutions of the modified proteins did not change significantly, with the exception of aspartyl casein which was more viscous. There was some decrease in the solubilities of aspartyl casein and tryptophyl casein as compared with the casein control. It is anticipated that adding some 11.4 tryptophyl residues per mole of casein would decrease the aqueous solubility of the modified protein. However the results with aspartyl casein are unexpected. The changes in viscosity, solubility, and fluorescence indicate that aspartyl casein is likely to be a more extended molecule than the casein control. There was a marked decrease in the fluorescence of aspartyl casein and tryptophyl casein (see Table IX). The ratios of the fluorescences of acetylmethionyl casein to methionyl casein and t-BOC-tryptophyl casein to tryptophan casein were 1.20 and 2.01, respectively, indicating the major effects that these acyl groups have on the structure of the casein. 

---