Acid Hydrolysates of Proteins

ML Gardner. Cysteine A potential source of error in amino acid analysis of mercaptoethane sulfonic or hydrochloric acid hydrolysates of proteins and peptides. Anal Biochem 141. -429-431, 1984. 

Acid Hydrolysates of Proteins occur as liquids, pastes, powders, or granules. They are composed primarily of amino acids, small peptides (peptide chains of five or fewer amino acids), and salts resulting from the essentially complete hydrolysis of peptide bonds in edible proteinaceous materials, catalyzed by food-grade acids and/or heat. Cleavage of peptide bonds typically ranges from a low of 85% to essentially 100%. In processing, the protein hydrolysates may be treated with safe and suitable alkaline materials. The edible proteinaceous materials used as raw materials are derived from corn, soy,... 

Acid Calcium Phosphate, 68, (Sl)9, (S2)4 Acid Ferric Sulfate TS, 852 Acid Hydrolysates of Proteins, 13, (Sl)l Acid-Hydrolyzed Milk Protein, 13, (Sl)l Acid-Hydrolyzed Proteins, 13, (Sl)l Acidified Sodium Chlorite Solutions, (S3)3... 

In the production of acid hydrolysates of proteins using hydrochloric acid, the residual sterols and their esters occurring in the starting materials yield small amounts of 3-chloro derivatives by replacement of the C-3 hydroxyl group with chlorine. Possible intermediates in the formation of 3-chlorosterok maybe 3,5-dienes derived from sterols (Figure 3.91). 

It is common to find laevulinic (4-oxopentanoic) acid (8-69) in foods containing carbohydrates, as it is one of the final dehydration products of hexoses via 5-hydroxymethylfuran-2-carbaldehyde in acidic media. It is present in very high concentrations (about 1-2% tv/w) in acid hydrolysates of proteins. 

As described above, Steinhardt and Fugitt81 found that the catalytic activity of polystyrenesulfonic acid 37 (HPSt) was higher than that of mineral acid for the add hydrolyses of proteins. Lawrence and Moore82 investigated the hydrolysis rates of glycylpeptides more quantitatively by using cationic... 

Block, R. J. Amino acid analysis of protein hydrolysates, in A laboratory manual of analytical methods of protein chemistry". Vol. 2, 1 —57. Ed. P. Alexander u. R. J. Block, Pergamon Press, 1960. 

The antioxidant activity of peptides has been shown to be a result of the cooperative effect of their entire amino acid sequence however, there is still little information concerning the structural characteristics of antioxidative peptides. At present, the main strategy has been to identify and characterize antioxidative peptides from the hydrolysates of proteins ... 

E Tatar, M Khalifa, G Zaray, I Molnar-Perl. Comparison of the recovery of amino acids in vapor-phase hydrolysates of proteins performed in a Pico Tag work station and in a microwave hydrolysis system. J Chromatogr A 672 109-115, 1994. 

J Csapo, Z Csapo-Kiss, S Folestad, A Tivesten. Mercaptoethanesulphonic acid as a protecting and hydrolysing agent for the determination of the amino acid composition of proteins using an elevated temperature for protein hydrolysis. Anal Chim Acta 289 105-111, 1994. 

U Butikofer, D Fuchs, JO Bosset, W Gmur. Automated HPLC-amino acid determination of protein hydrolysates by precolumn derivatization with OPA and FMOC and comparison with classical ion exchange chromatography. Chromatographia 31 441-447, 1991. 

Various applications of PITC in analyses of acid hydrolysates of purified proteins and peptides (91) and of hydrolysates of feeds (92) have been described. Bidlingmeyer et al. (93) showed reversed-phase chromatographic analysis of free amino acids and hydrolysates of foods (soybean flour, mozzarella cheese, beer, and soy sauce) with formation of PITC derivatives to be a fast, reproducible method that presented a very good correlation with the results obtained by ion-exchange chromatography. 

Usually the amino acid analyzer is first standardized by running through it a sample containing known quantities of amino acids to account for any differences in their ninhydrin reaction properties. In this way it is possible to relate directly the amount of amino acid present to the amount of colored product formed, as measured by the area under the peak produced on the strip-chart recorder (see fig. 3.15). Similarly, the amino acid hydrolysate of a protein of unknown composition can be run through the analyzer, and the relative peak areas can be used to estimate the ratios of the different amino acids present. 

The amino acid composition of keratin, the protein of hair and wool, includes a greater-than-average proportion of the sulphur-containing amino acid, cystine. Since this is the least soluble of the protein amino acids it can readily be isolated after carefully neutralising an acid hydrolysate of hair (Expt 5.187). Protein hydrolysis is usually effected by boiling for about 10-20 hours with 20 per cent hydrochloric acid. The hydrolysis of hair for the isolation of cystine is, however, best achieved using a mixture of hydrochloric and formic acids. 

It should be noted that for a protein having 20 residues of one amino acid (e.g. leucine), the precision of the results obtained by analysis of acid hydrolysates of this protein would usually indicate 20 + 1 residues. 

Direct Determination of the Contents of Amino Acids in Proteins. Amino acid contents of proteins are presently determined, with few exceptions, on an acid hydrolysate of the protein. In some instances, however, a particular amino acid may be at least partially destroyed by the conditions for acid hydrolyses. In other instances, a particular derivative of an amino acid of the protein may be hydrolyzed by the acid condition to regenerate the original amino acid. An analysis of such a chemically modified protein would thus need to be done on the protein before acid hydrolysis. In still other instances, there may be a need to perform a large number of analyses of different proteins for a single amino acid. The availability of a simple, direct chemical method for determination of such a single amino acid would be desirable. 

Because an analysis for amino acids in an acid hydrolysate of a protein gives no information about the state of that particular amino acid in the original protein, chemical methods that do not distort the conformation of the protein can thus provide information on the state of the side chain of that particular amino acid in the protein in solution or in a crystal state. Thus, poorly reactive (sometimes called masked ) sulfhydryl groups of cysteine show different degrees of reactivity, depending upon the chemical agents used (Table III). 

Peptones are small polypeptides that are intermediate products in the hydrolysis of proteins. The term is often used for any partial hydrolysate of proteins, e.g., bacteriological peptone, which is used as a medium for the growth of microorganisms. Peptones are water-soluble protein derivatives obtained by the partial hydrolysis of a protein by an acid or enzyme during digestion. 

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