2.6- Diethyl-3 -methylpyrazine

Dilution and concentration experiments on samples of dried black pepper berries from India and Malaysia, as well as enantioselec-tive analysis of optically active monoterpenes, indicated ( )-linalool, (-i-)-a-phellandrene, (-)-limonene, myrcene, (-)-a-pinene, 3-methylb-utanal and methylpropanal as the most potent odorants of black pepper. Additionally, 2-iso-propyl-3-methoxypyrazine and 2,3-diethyl-5-methylpyrazine were detected as important odorants of the black pepper sample from Malaysia, which had a mouldy, musty off-flavour (Jagella and Grosch, 1999a). Gamma irradiation was an effective means of decon-... 

Coffee (Arabica) /3-Damascenone, 2-furylmethanethiol, 3-sulfanyl-3-methylbutyl formate (126), homofuronol (127), furaneol, guaiacol, 4-vinylguaiacol, methional, sotolone, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, vanillin, 4-ethylguaiacol, homosotolone (128) 147... 

Tomato (fresh) Solanum 2-acetyl-1 -pyrroline, dimethyl trisulfide, 2,3-diethyl-5-methylpyrazine (Z)-3-Hexenal, hexenal, 1 -octen-3-one, methional 131,169... 

Pepper, black Musty, mouldy 2,3-Diethyl-5-methylpyrazine, 2-Isopropyl-3-methoxypyrazine [83]... 

Pyrazine, 2,3-diethyl-5-methyl-, 2,3-diethyl-5-methylpyrazine, 5,6-diethyl-2-methylpyrazine [18138-04-0] FEMA 3336... 

These authors synthesized it together with the above isomer from 2,3-diethyl-5-methylpyrazine (0.27) which was treated by /V-bromosuccinimide. The two bromo derivatives were separated by TLC, then treated with dicyclohexylamine to give the vinyl compounds. The two alkenylpyrazines could not be separated in the coffee volatiles of arabica and robusta. The mixture was therefore treated with hydrogen bromide, the bromides analyzed by high resolution GC and their EI-MS compared with data of the bromides from 0.27. 

Guan and collaborators studied the effect of 14 alkylpyrazines, known to be ant alarm pheromones, in combination with bait on fire ants (Figure 12) (14JAF11924).Testing at a dose range ofO.l—1000ng,it was found that out of the 14 alkylpyrazines, 4 compounds,2,3,5-trimethylpyrazine (88),2,3-diethyl-5-methylpyrazine (89), and a mixture of 2-ethyl-3,6-dimethylpyrazine (90) and 2-ethyl-3,5-dimethylpyrazine (91) promoted a significant increase in the alarm responses. Furthermore, it was determined that out of the mixture of 2-ethyl-3,6-dimethylpyrazine (90) and 2-ethyl-3,5-dimethylpyrazine (91), the former was substantially more active than the latter. 

The potent volatiles from freshly prepared French fries were evaluated by aroma extraction dilution and headspace GC-olfactometry (Table 12.2). The most potent odorants included methional, 2-ethyl-3,6-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, trans,trans-2,4-dec (iiem, dimethyltrisulfide, and... 

Chang et al. [73] and Nawar et al. [74] have identified many of the volatiles formed during deep fat frying. They have found numerous acids, alcohols, aldehydes, hydrocarbons, ketones, lactones, esters, aromatics, and a few miscellaneous compounds (e.g., pentylfuran and 1,4-dioxane) as products of deep fat frying. More recently, Wagner and Grosch [75] have studied the key contributors to French fry aroma. The list of key aroma compounds in French fries includes 2-ethyl-3,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 3-isobutyl-2-methoxypyrazine, (E,Z), (E,E)-2,4-decadienal, trans-4,5-epoxy-(E)-2-decenal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, methylpropanal, 2- and 3-methylbutanal, and methanethiol. If one examines this list, it is obvious that the Maillard reaction (pyrazines, branched chain aldeydes, furanones, and methional), and lipid oxidation (nnsaturated aldehydes) are the primary sources of this characteristic aroma. 

Schnermann and Schieberle [54] reported 13 odorants with the highest flavor dilution factors in milk chocolate as 3-methylbutanal (malty) 2-ethyl-3,5-dimetbylpyrazine (potato chip-like) 2- and 3-methylbutanoic acid (sweaty) 5-methyl-(E)-2-hepten-4-one (hazelnut-like) l-octen-3-one (mushroom-Uke) 2-ethyl-3,6-dimethylpyiazine (nutty, earthy) 2,3-diethyl-5-methylpyrazine (potato chip-like) (Z)-2-nonenal (green, tallowy) (E,E)-2,4-decadienal (fatty, waxy) (E,E)-2,4-nonadienal (fatty) 8-decalactone (sweet, peach-like) and 2-methyl-3-(methyldithio)furan. 

Cemy, C., W. Grosch, Precursors of ethyldimethylpyrazine isomers and 2,3-diethyl-5-methylpyrazine in roasted beef, Zeitschrift Lebens. Untersuch. Forsch, 198, 3, p. 210, 1994. 

Fig. 5.8. FD chromatogram of the volatile fraction of French fries. Ordinate n, number of 1 + 1 dilutions. Abscissa retention index (RI) on the capillary SE-54. The following odorants were identified 1 methional, 2 2-acetyl-1-pyrroline, 3 dimethyltrisulfide, 4 l-octen-3-one, 5 phenylacetaldehyde, 6 2-ethyl-3,6-dimethyl-pyrazine, 7 2-ethyl-3,5-dimethylpyrazine, 8 nonanal, 9 (Z)-2-nonenal, 10 2,3-diethyl-5-methylpyrazine, 11 (E)-2-nonenal, 12 2-ethenyl-3-ethyl-5-methylpyrazine, 13 2-isobutyl-3-methoxypyrazine, 14 dimethyltetrasulfide, 15 (E,E)-2,4-nonadienal, 16 (Z)-2-decenal, 17 (E,Z)-2,4-decadienal, 75 (E,E)-2,4-decadienal, 79trans-4,5-epoxy-(E)-2-decenal (according to Wagner and Grosch, 1997)...

Isobutyl-2-methoxyp)trazine and 2,3-diethyl-5-methylpyrazine belong to the key aroma substances in raw potatoes. These two pjtrazines are also essential for the aroma of boiled potatoes. The substances responsible for the aroma of boiled potatoes are shown in Table 17.10. 

The potato aroma note can be reproduced with an aqueous solution (pH 6) of methanethiol, dimethylsulfide, 2,3-diethyl-5-methylpyrazine, 3-isobutyl-2-methoxypyrazine and methional in the concentrations given in Table 17.10. Although it smeUs of boiled potatoes, methional only rounds off this aroma quality. In the drying of blanched potatoes to give a granulate, the concentrations of the two pyrazines decrease and, therefore, the intensity of the potato note also decreases. 

---