Hexenal odor profile

Examples are (E)-2-hexenal and (E)-2-decenal which have clearly different odor profiles (cf. Fig. 5.2 a and 5.2 f). If the ratio of the odor intensities is approximately one, the odor notes of both aldehydes can be recognized in the odor profile of the mixture (Fig. 5.2 d). But if the dominating odor intensity is that of the decenal (Fig. 5.2 b), or of the hexenal (Fig. 5.2 e), that particular note determines the odor profile of the mixture. 

Fig. 5.2. Odor profiles of (E)-2-decenal (D), (E)-2-hexenal (H) and mixtures of both aldehydes (according to Laing and Willcox, 1983). The following concentrations (mg/kg) dissolved in di-2-ethylhexyl-phthalate were investigated 50 (D) 2 (H ) 3.7 (H ) 11 (H ) and 33...

The mixture in Fig. 5.2, c gives a new odor profile because definite features of the decenal (stale, paint-like, rancid) and the hexenal (like apples, almonds, sweet) can no longer be recognized in it. The examples show clearly that the aroma profiles of foods containing the same aroma substances can be completely dissimilar owing to quantitative differences. For example, changes in the recipe or in the production process which cause alterations in the concentrations of the aroma substances can interfere with the balance in such a way that an aroma profile with unusual characteristics is obtained. ... 

The potent odorants identified in two apple varieties with fruity/green (Elstar) and fruity/sweet/aromatic (Cox Orange) odour are shown in Table 6.40. The fruity note in the aroma profile of both varieties is produced by acetic acid esters nos. 4-6. Ethyl esters, which on molar basis are more aroma-active than acetates [72, 73[ and which predominate in some other fmits, e.g. olives (Table 6.37) and orange (Table 6.38), are of minor importance for the aroma of apples. Hexanal (no. 7), (Z)-3-hexenal (no. 9) and (Z)-2-nonenal (no. 10) are responsible for the green/apple-like note. (E)-p-damas-... 

Unsaturated aldehydes have particularly irritating odors, and this is further increased by the presence of a triple bond. Like alcohols, some of the mid chain length unsaturated aldehydes such as trans-2-hexenal have very desirable green but more spicy odors. The di unsaturated aldehydes, e.g., 2,4-decadienal and 2,6-non-adienal, are important aroma contributors to meaty and fried aromas, and cucumber aroma, respectively. The aromatic aldehydes are powerful and display a wide spectrum of profiles, depending on their complexity. 

The fruity note in the aroma profile of both varieties is produced by acetic acid esters. On the other hand, there is a decrease in the ethyl esters, which are more odor active than the acetates (cf. 5.3.2.2) and dominate in some other fruits, e. g., oranges and olives. Hexanal, (Z)-3-hexenal and (Z)-3-nonenal are responsible for the green/apple-like note. (E)-P-Damascenone, which smells of cooked apples, has the highest aroma value in both varieties due to its much lower odor threshold. Eugenol and (E)-anethol contribute to the aniseed-like note which is a characteristic especially of the aroma of the peel of the Cox Orange. 

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