Peptides 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. 

Deamidation of soy and other seed meal proteins by hydrolysis of the amide bond, and minimization of the hydrolysis of peptide bonds, improves functional properties of these products. For example, treatment of soy protein with dilute (0.05 A/) HCl, with or without a cation-exchange resin (Dowex 50) as a catalyst (133), with anions such as bicarbonate, phosphate, or chloride at pH 8.0 (134), or with peptide glutaminase at pH 7.0 (135), improved solubiHty, whipabiHty, water binding, and emulsifying properties. 

A peptide is essentially comprised of L-amino acid residues, and the peptide backbone may be critical to provide physicochemical and functional properties. Diverse functionalities induced by peptides in natural protein hydrolysates are being received with much interest in food industries or alternative-medicinal food sciences. The latest year s researches... 

The application of high-performance capillary zone electrophoresis (HP-CZE) in its various selectivity modes has become a very valuable adjunct to HPLC for the analysis of peptides. For synthetic peptides, in particular, both HPLC and HP-CZE now form essential components of the analytical characterization of these molecules. Increasingly, zonal, micellar, or (biospecific) affinity-based HP-CZE procedures with open tubular capillary systems are adapted to allow resolution with extremely high separation efficiencies (e.g., >105 plates per meter) of synthetic or naturally occurring peptides as part of the determination of their structural, biophysical, or functional properties. Illustrative of these capabilities are the results shown in Figure 19 for the separation of several peptides with different charge and Stokes radius characteristics by HP-CZE. 

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. 

Discarded fish bones and cutoffs may contain considerable amounts of muscle proteins. These muscle proteins are nutritionally valuable and easily digestible with well-balanced amino acid composition (Venugopal et al., 1996). Therefore, fish proteins derived from seafood processing by-products can be hydrolyzed enzymatically to recover protein. Protein hydrolysates from several marine species have been analyzed for their nutritional and functional properties, and researches have mainly explored the possibility of obtaining biologically active peptides (Benkajul and Morrissey, 1997). Moreover, skipjack tuna muscle (Kohama et al., 1988), sardine muscle (Bougatef et al., 2008), and shark meat (Wu et al., 2008) have been used to separate potential peptides. 

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. 

Enzymatic hydrolysis of food proteins yields peptides that are of great interest to the food industry and are utilized for various purposes, e.g., improving the functional properties of foods, parenteral feeding (casein hydrolyzates), or milk protein substitutes in cases of intolerance. 

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 ... 

Looking back, the variety of substituents, including crosslinks, encountered in physiological research, is really remarkable and raises the important question of their implications in the area of foods. In principle, any of the above types of substituents could be present on proteins, peptides, and amino acids found in foods (see Section 3.1 below). Under appropriate conditions, the crosslinks would be expected to be able to affect texture, in particular, but also other functional properties. 

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. 

Haque, Z.U. and Mozaffar, Z. 1992. Casein hydrolysate. II. Functional properties of peptides. Food Hydrocoil. 5, 559-571. 

A whey protein hydrolysate BioZate , containing ACE-inhibitory peptide was recently developed by Davisco Foods International Inc. The effect on blood pressure was studied with 30 unmedicated, non-smoking, borderline hypertensive men and women, and daily dose was 20 g. The results indicated that there was a significant drop in both systolic and diastolic blood pressure after 1-week treatment, which persisted throughout the study of 6 weeks. The application of this product is varied and flexible. In addition to the bioactive peptides, it has functional properties such as emulsification and foaming (Klink, 2002). 

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. 

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