Lipids rancid odor from

Aldehydes are by far the most numerous compounds identified as dry-cured ham odorants, with different odors (green, rancid, toasted) and thresholds in air ranging from 0.09 to 480 ng/L (Table 1). Most of them were identified in the first works focused on dry-cured ham volatile compounds (7,2). Aldehydes are essential for meat flavor (70), but large quantities in meat and meat products have been related to lipid oxidation and deterioration (77). The effect of several quality factors has been researched and it was found that the rearing system of pigs (S) and ripening conditions (7) influence on the contribution to odor and the content of some aldehydes. 

Evidence indicates that VSCs are most responsible for the off-odor due to irradiation. This evidence includes 1) The irradiation odor is different from rancidity, which is believed to be caused mainly by lipid oxidation. 2)... 

The rancid lipid odor profile is made up of a mixture of several volatile compounds. Among them, the trans, cw-alkadienals, and vinyl ketones have the lowest flavor threshold in oils, while the threshold of hydrocarbons (alkanes and alkenes) is the highest (Min, 1998). The sensory effects depend on the composition of the participating compounds and on the composition of the food matrix, while the rancid off-odors and off-flavors of foods emanate from the interactions between lipids and other components, especially proteins. 

The sensitivity of taste or odor panels can be measured by the ability of individuals to detect sensory characteristics. Threshold values are measures of the least concentrations of volatile compounds detected in a food matrix (oil or water) or minimum detectable level by at least 50% of the panelists. This definition is, however, now commonly used to refer to detection by 100% of the panelists. There is a considerable difference in the flavor significance of volatile decomposition products formed in oxidized or rancid lipids. Hydrocarbons have the highest threshold values ranging from 90 to 2150 ppm, and the least impact on flavor. Substituted furans with threshold values of 2-27 ppm, vinyl alcohols with threshold values of 0.5-0.3 ppm, and 1-alkenes... 

Preparation and storage of products from both oilseeds is often inhibited by rancidity and bitter aroma defects caused mostly by volatile aroma active carbonyl compounds, e. g., (Z)-3-hexenal, (Z)-l,5-octadien-3-one and 3-methyl-2,4-nonan-dione. The rancidity-causing compounds are formed through peroxidation of linolenic acid, accelerated by the enzyme lipoxygenase and/or by hem(in) proteins (cf. 3.T.2.2). Furan fatty acids are the precursors in the case of the dione (cf. 14.3.2.2.5). Lipid peroxidation is also involved in the formation of another very potent odorant, 2-pentylpyridine, which produces grassy aroma defects in soybean products. Defatted soybean protein isolates contained 60-510 pg/kg of this compound, which with an odor threshold... 

Lipid components associated with meat fat, especially unsaturated aldehydes, play a significant role in species-characterization flavors. For example, ( ,Z)-2,4-decadienal exhibits the character impact of chicken fat and freshly boiled chicken (66). ( , )-2,6-Nonadienal has been suggested as the component responsible for the tallowy flavor in beef and mutton fat (63). 12-Methyltridecanal was identified as a species-specific odorant of stewed beef and provides a tallowy, beeflike flavor character (67). Aldehydes provide desirable flavor character to cooked meat, but they can contribute rancid and warmed-over flavors at high concentrations, resulting from autoxidation of lipids (68). 

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