Protein pyrolysates

The silylated pyrolysate of the two albumins shows the presence of levoglucosan, which is a marker for the sugar moiety indicating the presence of carbohydrates. Besides the compounds seen by GC techniques, probably protein pyrolysates contain larger molecules, which are kept in the char that is formed in abundance in protein pyrolysis. 

Most compounds given in Tables 12.3.3 and 12.3.4 can be traced back to protein pyrolysates. However, two other groups of compounds were identified in the pyrograms. 

Protein pyrolysates Albumin Soybean globulin Calf thymus Egg white Serum albumin Casein collagen ... 

Nagao, M., M. Honda, Y. Seino, T. Yahagi, T. Kawachi, and T. Sugimura Mutagenicities of protein pyrolysates Cancer Lett. 2 (1977) 335-340. 

T. Sugiraura, Mutagenicities of protein pyrolysates. Cancer Lett. 2 335 (1977). 

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 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. 

The ions with m/z = 59, 73, 83, 97, 109,125, 137,139, 151 in the two spectra were attributed to the presence of acetamido-2-deoxy-glycosyl residues, while the ions with m/z = 60, 68, 96,112,114, 126 were attributed to the presence of uronic acid residues. The ion with m/z = 64 is the only ion generated by SO2 and is a marker for sulfation. The Py-MS study on several glycosaminoglycans [3] showed that the sample purity (separation from the protein) plays an important role in the spectrum appearance. Also, the fact that these compounds were pyrolysed in salt form may have reduced some of the potential differences in the spectra. 

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 ... 

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. 

In protein analysis one important element is the purity of the enzyme and the procedure to obtain it. In many situations protein purification is not a simple step because of the lability of proteins. In many cases, the protein is associated with other components of the material from which it was obtained. As an example, the results for the analysis of the pyrolysate obtained from gluten at 510° C are discussed below. Gluten in this sample contained about 80% protein, 7% fats, and carbohydrates. The pyrolysis was first performed in a Curie point system and analyzed by on-line GC/MS on a Carbowax column in conditions similar to those previously described for the albumin analysis. The chromatogram is shown in Figure 12.3.5. 

Numerous studies done on conjugated proteins were oriented toward the differentiation of the material without performing special separations. For example, direct pyrolysis of several enzymes showed a significant difference in the chromatographic profile of the pyrolysate. The enzymes analyzed by this procedure included a-chymotrypsin, creatine kinase, lactate dehydrogenase, catalase, acetylcholinesterase, and urease [19,20]. 

The main components of wood are cellulose, hemicelluloses, lignin, proteins, and small molecules including several inorganic compounds. The pyrolysis products of each individuai type of macromolecular component of wood were described in Part 2 of this book. Some differences are seen in the pyrolysis of pure macromolecular components as compared to the pyrolysis results of the same component from the wood matrix. This is seen mainly for cellulose and hemicelluloses. However, the pyrolysis components are well recognizable, and it is common to use wood pyrolysates to trace a certain group of compounds to celiulose, hemicellulose, lignin, small molecules existent in wood, etc. 

In a long-term assay (about 500 d), an intake of 2 g of pyrolysates of tryptophan or arginine-tryptophan per kg of diet containing 12% of protein appeared to induce a sex-dependent decrease in the growth of rats. Pyroly-sate withdrawal in accustomed rats (second and third generations) demonstrated an acquired inurement to these products. Indeed, their removal caused increased food consumption and growth.286... 

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. 

Components in Pyrolysates from Amino Acids (Proline and Glycine) and Proteins (Casein and Collagen) (1647)... 

During the isolation of these pyrolysis products of the amino acids and proteins from the charred pyrolysates, Sugimura et al. 

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