Coffee, 2,6-dimethyl pyrazine

Pyrazines. In the thirties, the attention on pyrazines was focused on its industrial role in dyes, photographic emulsions and chemotherapy. Its importance in life processes was indicated in its derivative, vitamin B2 (riboflavin, 6,7-dimethyl-9-(l -D-ribityl isoalloxazine). Later,in the midsixties, it was identified in foods and its contributions to the unique flavor and aroma of raw and processed foods attracted the attention of flavor chemists Pyrazine derivatives contribute to the roasting, toasting, nutty, chocolaty, coffee, earthy, caramel, maple-like, bread-like, and bell pepper notes in foods. The reader is referred to the reviews on Krems and Spoerri (88) on the chemistry of pyrazines, and the review of pyrazines in foods by Maga and Sizer (89, 90) Table XVI summaries sensory description and threshold of selected pyrazines. 

As mentioned above, Vitzthum and Werkhoff (1975) reported for the first time 17 alkylated five-and six-membered bicyclic pyrazines in roasted coffee The tetrahydroquinoxalines reference standards were synthesized according to the IFF British Patient 1 310771. The mass spectra of these new constituents are discussed and fragmentation pathways for 2-ethyl-5,6,7,8-tetrahydroquinoxaline 0.69 and 2,3-dimethyl-5,6,7,8-tetrahydroquinoxaline 0.70 are commented upon in detail. 

Others. For example, the odour of 2,5-dimethylpyrazine resembles roasted hazelnuts, and 2,6-dimethylpyrazine and trimethylpyrazine have a chocolate-like odour. Important components of coffee aroma include a number of pyrazines, such as 2,3-diethyl-3-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. The flavour-active components of popcorn and white bread are acetylpyrazine, 2-ethyl-3-methylpyrazine, 3-ethyl-2,5-dimethylpyrazine and 5-methyl-6,7-dihydro-5H-cyclopenta[fo] pyrazine. Cyclopentapyrazines, specihcaUy 6,7-dihydro-5H-cyclopenta[fo]pyrazines, are formed in reactions of cyclopen-tenolones with aminoketones and ammonia. 

Significant aliphatic sulfur compounds are methional, 3-methyl-but-2-ene-1-thiol, 3-mercapto-3-methylbutan-l-ol (8-124), its ester 3-mercapto-3-methylbutyl formate, methanethiol and dimethyltrisulfide. 3-Mercapto-3-methyl-l-ol also occurs in passion fruit and blackcurrant, and as a putative cat pheromone in cat urine, where it is formed as a degradation product of amino acid L-felinine (see Section 2.2.1.2.2). Of more than 70 known pyrazines, the most important compounds in roasted coffee are isopropylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. Pyridine and its alkyl derivatives and bicyclic pyridines have a negative impact on the quality of coffee aroma. Important aromatic... 

---