Flavor pyrazines responsible

Minuscule quantities of naturally-occurring pyrazines have been found in some foodstuffs and are largely responsible for their flavor and aroma. For example, 3-isopropyl-2-methoxypyrazine is isolated from green peas and wine and a seasoned wine connoisseur can identify a ppt quantity. In addition, 2-methyl-6-vinylpyrazine exists in coffee. 

The pH of the steam distillate was 6.2 in all cases. The total flavor isolate (by SDE) of plain cashews had, on the whole, a strong pungent and green aroma, reminiscent of the cashew nut testa and cashew shell, whereas the flavor isolates from roasted samples had the characteristic mildly nutty aroma also. The flavor fractions obtained by selective extraction method gave some information about the chemical nature of compounds responsible for the characteristic flavor notes. Accordingly, the basic fraction of roasted nuts, (both oven-and oil-roasted), had the typical nutty aroma associated with pyrazine. compounds. The basic fraction of plain cashews did not have any characteristic flavor in particular. 

There are many reports of Pseudomonas cultures producing musty, earthy, and potato-like odors ( l-6). The work of Morgan et al. (T) established 2-methoxy-3-isopropyl pyrazine to be partially responsible for these odors. Subsequently, 2-methyoxy-3-isopropyl pyrazine was found in bell peppers (8), a similar compound 2-methoxy-3-secbutyl pyrazine was identified in galbanum oil (9), and several 2-methoxy-3-alkyl pyrazines were identified in various raw botanicals (10). The odor threshold exhibited by 2-methoxy-3-isobutyl pyrazine (1 part in 10 indicates flavor significance for these compounds even at the exceptionally low concentrations in which they occur in foods and other natural products Producing these compounds from microbial fermentations could be an economical source of flavor for the food industry. 

The carbonyls are represented by peaks 4, 6, 7, 11 and 16 on Figure 3. They were identified as isobutyraldehyde, isovaler-aldehyde, 2-methyl butanal, pentanal cUid hexanal. The pyrazines are represented by peaks 13, 18, 20, 25 cind 26. They were identified as pyrazine, 2-methyl pyrazine, 2,5-dimethyl pyrazine, 2-ethy1-5-methyl pyrazine and 2-ethyl-3-methyl pyrazine. The authors observed a decrease in carbonyls (which are responsible for harsh green flavor notes) euid increase in pyrazines (which are responsible for roasted notes) with longer roasting time. 

The pyrazines were responsible for the roasted nutty flavor of fresh roasted peeinuts (Mason et al) (15, 16), (Johnson 25, 26). According to Mason et al (15), the low molecular weight aldehydes are responsible for the harsh aroma associated with fresh roasted nuts. 

The roasting process subjects peanuts to internal temperatures of 130 -150 C during which the typical roast peanut flavor is produced. The most important constituents of peanuts responsible for flavor formation are the amino acids, sugars, protein and lipids. There are close to 300 flavor compounds identified in roasted peanuts. Pyrazines contribute roasted nutty aroma and aldehydes are responsible for harsh green aroma. Recent development in the research include application of an absorption polymer Tenax GC to collect volatiles, quantitation of flavor components and computer aided correlation of instrmental and sensory data. 

Red currant flavor The flavor of red currants is principally due to ( )-2- hexenal, ( )-2- hexen-l-ol, and hexanal (see alkanals). In black currants the im-pact compound 4-methoxy-2-methyl-2-butanethiol (C6H14OS, Mr 134.24, CAS [94087-83-9]) is responsible for the typical feline note. Terpene compounds such as 1,8- cineole, linalool, a-terpineol (see p-menthenols), citronellol and /S- damascenone, fruit esters (e.g., ethyl butanoate), the butter note of 2,3-butanedione, 4-methoxyacetophenone (CgHmOj, Mr 150.18, CAS [100-06-1]) and 2-isopropyl-3-methoxy-pyrazine (see pyrazines) complete the aroma. In the aroma industry buchu leaf oil is used to generate the black currant note. 

Several methods have been employed (20) in the extraction of flavor volatiles from their chemical and physical bonds in the complex muscle matrix. These methods include steam distillation, solvent extraction, headspace analysis and supercritical fluid extraction. Each method had specific advantages and shortcomings when used in the isolation of numerous compound types such as carbonyls, sulfur-containing compounds such as thiols and thiazoles, pyrazines, furans, and pyrroles (27, 22). The mechanisms responsible for the formation of these flavor volatiles have been proposed and developed based on such experimentation (25, 24). 

In the case of bread, aroma has been largely studied and many methods have been developed to identify the compoimds responsible of flavor [5]. More than 540 different compounds have been described in the complex volatile fraction of bread [39], being alcohols, aldehydes, esters, ketones, acids, pyrazines and pyrrolines the most important quantitatively, but fii-rans, hydrocarbons and lactones were also identified [30]. 

Pyrazines are also produced by microorganisms. For example, 2-isopropyl-3-methoxypyrazine has been identified as a metabolic byproduct of Pseudomonas perolans and Pseudomonas taetrolens. This pyrazine is responsible for a musty/earthy off-flavor in eggs, dairy products and fish. 

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