Hydrocarbons Alcohols and Carbonyl Compounds

Earlier studies of volatiles of cooked poultry identified a variety of hydrocarbons, alcohols, acids, aldehydes, and ketones. Of these classes, the carbonyl group (aldehydes and ketones) has often been suggested to be associated with meat flavor. Lipids are the principal precursors of these compounds, and many carbonyls probably originate from oleic, mevalonic, linoleic, and arachidonic acids (5,16). The flavor threshold values of some of the carbonyl compounds (up to C9) are as low as a few parts per billion. The presence of highly unsaturated fatty acids, primarily in the phospholipids in chicken, is the basis for the development of the characteristic carbonyl profile that differentiates poultry flavor from the flavors of other species (14,24). At least nine compounds have been identified exclusively or predominantly in chicken, including 3-methyloctane, 2,2,6-trimethyloctane, 4-ethylbenzaldehyde, 1,2-dibutylcyclo-pentane, 2,6-bis(l,l-dimethylethyl)-4methylphenol, diethyl phthalate, 1,12-dodecanedial, 2(E), 4(E)-deca-dienal, and y-dodecalactone (21,22). Aroma extract dilution analysis of volatiles obtained by the simultaneous distillation/extraction of chicken broth resulted in the identifications of nonanal, 2(E)-nonenal, 2(E), 4(E)-nonadienal, 2(E), 4(E)-decadienal, 2-undecenal, /?-ionone, y-decalac-tone, and ยก-dodecalactone as primary chicken odorants. Al-kanals, generated from turkey skin, contributed to meaty and turkeylike flavor, and the alk-2-enal group had a strong, oxidized, and brothlike flavor (25). Utilizing a supercritical carbon dioxide extraction technique followed by identification of compounds in isolated fractions, it was concluded that excess concentrations of enal aldehyde and ketones are related to the oxidized aroma and flavor of chicken broth (26).

In addition to the pathway of lipid oxidation, carbonyls can be derived from nonenzymatic browning (Maillard re-

Table 1. Representative Flavor Compounds in Poultry

Aliphatic Hydrocarbons (over 45 compounds)

n-decane n-dodecane n-heptane

1-octene n-tridecane

Aromatic hydrocarbons (over 50 compounds)

benzene n-propylbenzene toluene p-xylene

1,2,3-trimethylbenzene

Alcohols (over 45 compounds)

n-butanol n-hexanol n-heptanol n-pentanol

2-methylpropanol- l-ol

Aldehydes (over 75 compounds)

acetaldehyde n-butanal

2-methylbutanal n-hexanal trans-2-hexenal

Ketones (over 55 compounds)

acetone 2-butanone

2-heptanone 2,3-butanedione

3-octen-2-one

Amino acids, amines, and peptides (over 25 compounds)

cysteine cystine glutathione methionine dimethylamine

Fatty acids and esters (over 40 compounds)

pentanoic ethyl acetate hexanoic

2(3)-methylbutyric ethyl lactate

Lactones (in fat drippings) (over 24 compounds)

4-hydroxybutanoic acid lactone 4-hydroxyhexanoic acid lactone 4-hydroxyoctanoic acid lactone

Pyrrols, pyridines, and pyrazines (over 50 compounds)

2-methylpyrazine pyridine pyrrole

3-ethylpyridine 2,6-dimethylpyrazine

Table 1. Representative Flavor Compounds in Poultry

(continued)

Sulfur compounds (over 45 compounds)

methyl disulfide thiophene 2-methyl thiophene thiazole ethane thiol

Furans (over 20 compounds)

2-butyl furan 2-hexyl furan 2-octyl furan

Miscellaneous (over 35 compounds)

hydrogen sulfide ribose inosine-monophosphate chloroform

4,5-dimethyloxazole action), Strecker degradation, and Amadori transformation reactions. The condensation of carbohydrates with amino acids during heating causes the formations of complex cyclic carbonyls. Carbonyl compounds could be important in secondary reactions; they resulted in furanones and mercapto compounds with roast meat aroma and meaty aroma (27).

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