Destruction of amino acids

Excessive heat can cause destruction of amino acid residues. The amino acid most susceptible to direct heat destruction is cystine. Although not an essential amino acid, cystine does have a sparing effect on the dietary requirement for methionine. As a result, cystine destruction can be nutritionally important. In addition, many vegetable proteins are limiting in the sulfur amino acids. Cystine destruction would be particularly harmful for these proteins. 

G values for the destruction of amino acids and formation of amide-like nitrogen were calculated from the initial slopes of linear plots of yield-dose data. For doses up to 1 Mrad in 0.1% solution, these were straight lines. 

The presence of O2 causes an increase in the destruction of amino acids and in the amount of amide nitrogen formed and also influences the modification of amino acid side chains. Thus, a major product from PGA irradiated in 02 is aspartic acid, which is formed only in traces in the absence of O2. The inversion of glutamate residues is reduced in O2. 

Destruction of Amino Acids and Peducing Sugars on Heating Chocolate Aroma Precursor Extract... 

Destruction of Amino Acids After Heating With Glucose at Different Temperatures for One Hour... 

In alkaline solution, proteins are known to undergo the following types of reactions (a) denaturation, (b) hydrolysis of some peptide bonds, (c) hydrolysis of amides (asparagine and glutamine), (d) hydrolysis of arginine, (e) some destruction of amino acids, (f) e elimination and racemization, (g) formation of double bonds and (h) formation of new amino acids. 

A linear extrapolation to zero-time of hydrolysis based on zero-order kinetics has been used to estimate the destruction of each amino acid (Smith and Stockell, 1954 Wilcox et al. 1957). In contrast, Hirs et al. (1954) measured the destruction of amino acids in a mixture of serine, threonine, aspartic acid, and glutamic acid and showed that first-order kinetics are applicable to the destruction observed. 

Luse and M(iLaren (1963) have reviewed published research on the photolysis products and quantum yields tor the destruction of amino acids and have attributed the photochemical inactivation of the enzymes chymo-trypsin, lysozyme, ribonuclease, and trypsin by UV light at 254 m i primarily to destruction of the cystyl and tryptophyl residues. The destruction of these residues in proteins was suggested to be a function of the product of the number of residues present, the molecular extinction coefficient, and the quantum yield for destruction of each residue. Cysteine and tryptamine were identified among the irradiation products from cystine and tryptophan, respectively. Tyrosine, histidine, and phenylalanine were also shown to be degraded by UV, histidine yielding histamine, urocanic acid, and other imidazole derivatives, and phenylalanine yielding tyrosine and dihydroxyphenylalanine. Destruction of these three amino acids was not considered to contribute appreciably to the enzyme inactivation. 

The main disadvantage of alkaline hydrolysis is that much more destruction of amino acids occurs than with acid. The chief amino acids to be affected are cysteine, serine, threonine and arginine. Wieland and Wirth (1949) have used paper chromatography to study the effect of strong alkali on certain amino acids. They found that serine broke down to give appreciable quantities of glycine and alanine, threonine... 

Peroxidation of hpids (discoloration of the product) Total destruction of amino acids... 

Further breakdown of amino acids occurs as a result of plant enzyme action, although this is considered to be limited. Most destruction of amino acids in silage is brought about by microbial activity rather than by plant enzymes. 

The presence in the FTlR-speetrum of the line corresponding to HCOO, is essential, for it proves the eorreetness of the earned out estimation of the current efficiency of the processes of the anodic destruction of amino acid anions. In a broader sense, this result confirms, in our opinion, the validity of a four-electron scheme of a "gentle" electrooxidation of glycine anions and the possibility of its appUcation to oxidation of a-alanine anion suggested in [19]. The appearance in the FTIR-spectra obtained at the potentials of aminoacid anions anodic oxidation, of the bands corresponding to the formation of adsorbed species (-CH2-NH2)ads [33], as well as the presence of HCOO and CN proposed in the [19] scheme electrooxidation of Gly and a-Ala, presenting the process (9) as follows ... 

Following the formation of the deoxyketosyl derivative, the reactions leading to the formation of the brown pigments or melanoidins (Fig. 3) are not well defined. These reactions, however, are responsible for numerous flavours and odours, possibly for toxicity, and for a further reduction in protein nutritive value via destruction of amino acids and reduced digestibility. There are thought to be three main pathways in the advanced Maillard reaction. 

Maillard reaction) or in the relative absence of sugars (lean meat protein). The reaction leads to a fall in protein digestibility and in the availability of most amino acids, in addition to that of lysine. Destruction of amino acids can also occur. 

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