2.6- Dimethyl-3-alkylpyrazine

Lipid-Protein-Carbohydrate Interactions. Evidence for such complex interaction was recently reported by Huang et al (36) who observed that the addition of corn lipids to zein and corn carbohydrates enhanced the formation of alkylpyrazines, indicating that lipid-derived free radicals may accelerate the rate of Maillard reactions. Two of the alkylpyrazines, identified in such mixtures after heating for 30 minutes at 180°C, have 5-carbon alkyl substitution at the pyrazine ring and could only be explained by interaction of lipid or lipid decomposition products. These authors suggested that condensation of amino ketones, formed by protein-carbohydrate interaction, may yield 3,6-dihydropyrazine which would in turn react with pentanal, a lipid oxidation product, to form 2,5-dimethyl-3-pentylpyrazine. 

Other furans included methyl- 2-furfural [4], 2-acetylfuran [5], 2-propionylfuran [6], l-(2-furanyl)-2-propanone [7] and l-(-2-furanyl)-3-butanone [8]. Several alkylpyrazines were also found, with the 2,5-dimethyl [9] and 2-methy 1-5-ethyl [10] the most abundant derivatives, and some 2-acyl-l-methylpyrroles of which only the formyl [11] and acetyl [12] derivatives were conclusively identified. 

The Strecker reactant, i.e., the a-dicarbonyl, picks up ammonia during the Strecker reaction and can then form heterocyclic volatiles, particularly pyrazines. The most powerful odorants among these are the 2-ethyl-3,5-dimethyl- (0.04) and the 2,3-diethyl-5-methyl-derivatives (0.09). It is worth noting that most other alkylpyrazines have much higher thresholds and thus make relatively little contribution to the aroma of heated foods. 

Citral (123), formic acid (124), and n-undecane (125) are among a host of other compounds identified as formicid alarm pheromones. Recently, Wheeler and Blum (126) reported that alkyl-pyrazines were secreted by Odontomachus spp. in response to foreign stimuli. Some species produced 2,5-dimethyl-3-isopentylpyrazine (XXIX) whereas 2,5-dimethyl-3-pentylpyrazine (XXX) and related compounds were produced by others. Although these compounds are attractants that release attack behavior in Odontomachus workers, ponerine species that form small colonies utilize one of the alkylpyrazines to release escape behavior (127). 

The important aroma compounds of roasted cumin are the pyrazines, their various alkyl derivatives - particularly, 2,5- and 2,6-dimethyl pyrazine - and also substituted pyrazines 2-alkoxy-3-alkylpyrazines ... 

Alkylpyrazines, which are commonly produced in the mandibular glands of ants and wasps (1 ), appear to have a limited distribution in the venoms of ants. 2,5-Dimethyl-3-ethylpyrazine (XXII) has been identified as a trace constituent in the venom of Atta sexdens (15), a myrmicine species that also produces a pyrrole (X) as a poison gland product. 

Cocoa Butter Cocoa butter is one of the most Uked and highly prized food ingredients because of its desirable flavor and unique melting behavior. As early as 1961, van Elzakker and van Zutphen (32) studied and identified 23 volatile compounds in the vacuum steam distillate of cocoa butter. Later, Rizzi (33) identified nine alkylpyrazines including methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-5-methylpyrazine, trimethylpyra-zine, 2,5-dimethyl-3-ethylpyrazine, 2,6-dimethyl-3-ethylpyrazine, and tetramethyl-pyrazine in the basic fraction of a vacuum steam distillate of cocoa butter. 

Various other heterocycles have also been converted to pyrazines. Thus tetra-phenylpyrrole with lead tetraacetate and potassium carbonate in chloroform has been shown to give a 20% yield of tetraphenylpyrazine (498) 5-amino-3,4-dimethyl-isoxazole (117) and 50% hydrazine hydrate, when heated on a water bath and the product treated with hot concentrated hydrochloric acid, pve tetramethylpyrazine (499). Treatment of 3-amino-24iydroxy-4,4-dimethyltetrahydrofuran (118) with strong alkali gave 2,5-bis(hydroxy-f-butyl)pyrazine (119) (500) and catalytic hydrogenation of furylamines (120) over platinum at 220-225° gave alkylpyrazines (121) (500a). 

Cheese flavor. C. f. is formed from milk fat, milk protein, lactose during the maturation of cheese mainly through enzymatic and microbial processes. Quantitative and, sometimes, qualitative differences are responsible for the diversity of cheese flavors. Typical aroma substances are the free C4-C,2 fatty acids, C7, C and C, 2-alkanones (also in Roquefort cheese), the butter aroma substances acetoin, 2,3-butanedione, and 5- alkanolides, (-)-(R)-l-octen-3-ol (fungus note in Camembert), 4-alkanolides and alkylpyrazines with nut-like nuances, indole, skatole, and phenols with stable-like odors, as well as numerous sulfur compounds such as methional, methyl mercaptan (moldy, coal-like), dimethyl sulfide and dialkyl polysulfides with, in part, onion- and garlic-like nuances. Furaneol" and homofuraneol (see hydroxyfura-nones) are responsible for the sweetish odor of Em-mental cheese. 

Despite the acknowledged importance of these furan- and thiophenethiols and their disulfides in meat-like flavors, it is only recently that compounds of this type have been reported in meat itself (8-10). Grosch and co-workers (11) have suggested that the 2-methyl-3-furanthiol and its disulfide are more important in the aroma of boiled meat than in roast beef where alkylpyrazines, 2-acetyl-2-thiazoline and 2,5-dimethyl-4-hydroxy-3(2 -fiiranone make greater contributions. 

Important components of hard cheeses (Gouda type) include some carboxylic acid esters (ethyl butanoate, ethyl hexanoate), as well as carboxylic acids (acetic, butyric, isobutyric, valeric, isovaleric, 2-methylbutyric and caproic acids). Cheeses manufactured using bacteria of the genus Propionibacterium (such as Emmental and Gruyere) contain propionic acid and other lower fatty acids, methyl thioacetate, some oxocarboxylic acids, various alcohols, esters (such as ethyl butanoate), lactones (such as 8-decalactone), amines and other basic compounds (also skatole in addition to aliphatic amines), alkylpyrazines (e.g. 2-sec-butyl-3-methoxypyrazine), 4-hydroxy-2,5-dimethyl-2H-furan-3-one (furaneol), 2-ethyl-4-hydroxy-5-methyl-2H-furan-3-one (homofuraneol) and a range of other compounds. 

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