Amino acid pyrolysates

Sato T, Nagase H, Sato K, et al. 1994. Enhancement of the mutagenicity of amino acid pyrolysates by phthalate esters. Environ Mol Mut 24 325-331. 

Of course, in 1971 when Patterson et al. offered this suggestion, the presence in amino acid pyrolysates of the so-called cooked food mutagens and the inordinately high mutagenicity of several of them were unknown. 

Amino acid pyrolysates Phenylalanine Lysine Tryptophan... 

The 3-amino-1 -mcthyl-5//-pyrido[4,3-b]indolc derivatives (31 Trp-P-1) and (32 Trp-P-2) were found as tryptophane pyrolysates in broiled fish and meat and in pyrolysates of protein and amino acids by Sugimura and coworkers198. These mutagens are heterocyclic amines and exhibit mutagenicity in the Ames test supplemented with S-9 mix198. The pyridoindole derivatives Trp-P-1 and Trp-P-2 are /V-hydroxylated at the exocyclic amino group to form proximate reactive compounds. 

The 2-amino-dipyrido[ 1,2-a 3, 2 -d]imidazoles (33 Glu-P-1) and (34 Glu-P-2) were first isolated from glutamic acid pyrolysates. As observed with Trp-P-1 and Trp-P-2,... 

The first intimation that mutagens could be formed from natural food substances came from the laboratory of Sugimura, where it was found that mutagenic activity was found in smoke condensates or in DMSO extracts of the charred surface of fish and meat. This activity could not be accounted for by the amounts of BaP and PAH known to be present. Extracts of pyrolysates of various proteins and amino acids were also mutagenic (14). 

Mutagens Isolated from Pyrolysates of Amino Acids and Protein, and from Cooked Foods... 

From fried beef, another new compound, 2-amino-3,8-dimethy1-imidazo[4,5-/]quinoxaline (MelQx), was isolated, and its structure was confirmed by chemical synthesis (15). The structures of all the compounds isolated from pyrolysates of amino acids and a protein, and from cooked fish and meat, are shown in Table II. 

Amino acids were first studied as their esters by mass spectrometry in the late 1950 s and early 1960 s [136-138]. Although many free amino acids can be directly sublimed and give useful spectra, some decompose on heating while others, most noteably arginine and cystine, pyrolyse. These undesirable features prompted the search for derivatives which would permit either direct or reservoir introduction into the mass spectrometer of as many of the biological amino acids as possible. This was prior to the... 

The amino acid pyrolysis is relevant for protein pyrolysis because certain compounds in the pyrolysate are the same when the substance to be pyrolysed is the amino acid or a peptide formed from that specific amino acid (see Section 13.2). The main pyrolysis products of several amino acids are given in Table 12.1.2 [3,4]. 

Besides the determination of major pyrolysis products for amino acids, a special issue is the formation of several mutagenic compounds (heterocyclic amines) during pyrolysis. These types of compounds were detected in traces in the pyrolysates of amino acids, and the finding is very important as the amino acids are components of proteins and are present in food. Some of these compounds isolated from pyrolysates performed at 550 C from several amino acids [5,6] are shown below ... 

The type of DKP formed and the amount that can be detected in the pyrolysate may also be influenced by the nature and stability of the R group of a particular amino acid in the peptide sequence. In addition to this, the pyrolysis conditions were found to influence the amount of DKPs. Milder pyrolytic conditions favored more DKP formation, while higher temperatures of pyrolysis generated more small molecules, as expected. 

In this reaction, the formation of two series of compounds is proposed because in the chromatographic separations of polypeptide pyrolysates, an additional peak is noticed for each 3-alkenyl-5-alkyl-pyrrolidin-2,4-dione. This second peak is assigned to the corresponding 2,4-dialkyl-3,5-diketopyrroline (position isomers are not possible when R2 and R3 are identical) [1]. The list of different compounds from these two classes that may be formed during laser irradiation of different mammalian tissues [13a] due to peptide (protein) pyrolysis and the amino acid pair that can generate them is given in Table 12.2.3. 

Tobacco leaf has a complicated chemical composition including a variety of polymers and small molecules. The small molecules from tobacco belong to numerous classes of compounds such as hydrocarbons, terpenes, alcohols, phenols, acids, aldehydes, ketones, quinones, esters, nitriles, sulfur compounds, carbohydrates, amino acids, alkaloids, sterols, isoprenoids [48], Amadori compounds, etc. Some of these compounds were studied by pyrolysis techniques. One example of pyrolytic study is that of cuticular wax of tobacco leaf (green and aged), which was studied by Py-GC/MS [49]. By pyrolysis, some portion of cuticular wax may remain undecomposed. The undecomposed waxes consist of eicosyl tetradecanoate, docosyl octadecanoate, etc. The molecules detected in the wax pyrolysates include hydrocarbons (Cz to C34 with a maximum of occurrence of iso-Czi, normal C31 and anti-iso-C32), alcohols (docosanol, eicosanol), acids (hexadecanoic, hexadecenoic, octadecanoic, etc ). The cuticular wax also contains terpenoids such as a- and p-8,13-duvatriene-1,3-diols. By pyrolysis, some of these compounds are not decomposed and others generate closely related products such as seco-cembranoids (5-isopropyl-8,12-dimethyl-3E,8E,12E,14-pentadecatrien-2-one, 3,7,13-trimethyl-10-isopropyl-2,6,11,13-tetradecatrien-1al) and manols. By pyrolysis, c/s-abienol, (12-Z)- -12,14-dien-8a-ol, generates mainly frans-neo-abienol. 

In 1969, at the 4th ASIC symposium in Amsterdam, Merritt et al. (1970) asserted that the object of research on the composition of the constituents of coffee aroma is not the mere compilation of lists, but the relationship of the compounds to their precursors, in order to establish a mechanism for their formation, and ultimately for controlling the quality of the product. Merritt et al. (1970) tried to correlate the composition of green and roasted coffees and gave a list of some pyrolysis products of various amino acids, observing that proteins containing the same amino acids produce the same pyrolysates. After having identified 16 other constituents, the authors hoped that new techniques will lead to more direct correlations between the aroma and their precursors, providing a more secure basis to evaluate and control the quality of coffee. 

GC-MS Gas chromatography-mass spectrometry is the most versatile method. It can be used for pyrolysates (see above), but also for the detection of PAHs in extracts. In combination with commercially available derivatization protocols, amino acids can be analyzed as well. If chiral columns are used, enantiomeric separation of chiral compounds is possible. Usually, either quadrupole or ion trap mass spectrometers are used as detectors, but Time-of-flight (ToF) MS can also be used. 

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