2-Methoxy-3-isopropylpyrazine

The aposematic beetle, Metriorrhynchus rhipidius, contains three pyrazines as warning odor components and two amides as bitter principles (Tables III, V, and VIII) (97). Of the three components with the beetlelike odor, the most characteristic is 2-methoxy-3-isopropylpyrazine (24b). The other two components are 2-methoxy-3-methylpyrazine (24a) and 2-methoxy-3-sec-butylpyrazine (24d). It would seem likely that these compounds will occur in the defensive systems of the aposematic beetles. The two amide components, detectable in the hemo-lymph exuded by adult beetles, are 3-phenylpropanamide (130) and l-methyl-2-quinolone (57), the latter being the major component. It seems likely that these bitter principles contribute to distastefulness to potential predators. 

Cacao mass 2-/3-Methylbutanoic acid, 3-methylbutanal, ethyl 2-methylbutanoate, hexanal, 2-methoxy-3-isopropylpyrazine (132), ( )-2-octenal, 2-methyl-3-(methyldisulfanyl)furan (133) 150... 

Volatile fungal metabolites contribute to the organoleptic properties of several other foodstuffs. Surface mould ripened cheeses such as Brie and Camembert are produced using Penicillium camembertii and, more commonly, P. caseicolum. Oct-l-en-3-ol accompanied by smaller amounts of octa-l,5-dien-3-ol and 3-one are major contributors to the aroma. These organisms also have the ability to produce 2-alkanones from fatty acids and these contribute to the odour of the cheese. 2-Methylisoborneol (7.70) and 2-methoxy-3-isopropylpyrazine (7.71) have been detected in mature cultures. An unpleasant earthy flavour encountered in some aged cultures has been attributed to the excessive produetion of 7.71. 

Methoxy-3 -isobutylpyrazine 2-Methoxy-3 -isopropylpyrazine 2-Methoxy-3 -sec-butylpyrazine... 

One must recognize that microorganisms can accomplish a wide range of chemical transformations thereby potentially producing a host of different oflf-flavors. Earlier in this section, several oflf-notes have been described as being the result of microbes. One can add other sensory notes such as faceal (indole and skatole in rotting potatoes [147]), musty potato (2-methoxy-3-isopropylpyrazine [148]), mousy (wine, 2-acetyl-1,4,5,6-tetrahydropyridine [149]), and musty, dirty dishcloth (machine oils 2,6-dimethyl-3-methoxypyrazine [150]). 

Fenugreek (11) Linalool, 3-isobutyl-2-methoxypyrazine, 2-methoxy-3-isopropylpyrazine,... 

Musty taints and off-flavors in foodstuffs have been a source of concern in the food industry for many years. Although a list of potential compounds causing this defect is long [1], the main ones responsible for it are 2-methoxy-3-isopropylpyrazine (IPMP), 2-methoxy-3-isobutylpyrazine (IBMP), 2,4,6-trichloroanisole (TCA), 2-methylisoborneol (MIB), and geosmin (GEO) (Fig. 1). 

Methoxy-3-alkylpyrazines are often associated with musty-earthy and potato-like odors. 2-methoxy-3-isopropylpyrazine is responsible for the musty, potato-bin odor and contributes to off-flavor notes in wines 2-methoxy-3-isobutylpyrazine is a main constituent of green bell pepper and jalapenios flavor. It is known that alkylpyrazines are formed in thermal reactions but can be also produced by microorganisms, mainly bacteria, such as Pseudomonas species [2]. 

Figure 2 Influence of water content in the wheat grain matrix on the amounts of compounds isolated by solid-phase microextraction (SPME). IPMP, 2-methoxy-3-isopropylpyrazine IBMP, 2-methoxy-3-isobutylpyrazine MIB, 2-methylisobomeol TCA, 2,4,6-trichloroanisole GEO, geosmin.

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