Hexanal Z -3-Hexen

The edible portion of broccoli Brassica oleracea var. italica) is the inflorescence, and it is normally eaten cooked, with the main meal. Over 40 volatile compounds have been identified from raw or cooked broccoli. The most influential aroma compounds found in broccoli are sulfides, isothiocyanates, aliphatic aldehydes, alcohols and aromatic compounds [35, 166-169]. Broccoli is mainly characterised by sulfurous aroma compounds, which are formed from gluco-sinolates and amino acid precursors (Sects. 7.2.2, 7.2.3) [170-173]. The strong off-odours produced by broccoli have mainly been associated with volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl disulfide and trimethyl disulfide [169,171, 174, 175]. Other volatile compounds that also have been reported as important to broccoli aroma and odour are dimethyl sulfide, hexanal, (Z)-3-hexen-l-ol, nonanal, ethanol, methyl thiocyanate, butyl isothiocyanate, 2-methylbutyl isothiocyanate and 3-isopropyl-2-methoxypyrazine... 

Table I lists the compounds identified in a headspace sample of pineapple crowns. The sample was characterized by low levels of very few volatiles. The Ce compounds, hexanal, (Z)-3-hexenal, (E)-2-hexenal and (Z)-3-hexenol were probably produced enzymatically in response to tissue damage from cutting (12). Hydrocarbons identified include styrene, and the monoterpenes, a- and p-pinene.

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. 

The aroma of peaches is characterized by y-lactones (C6-C12) and 5-lactones (Cio and Cl2). The main compound in the lactone fraction is (R)-l,4-decanolide, which has a creamy, fruity, peach-like odor. Other important compounds should be benzaldehyde, benzyl alcohol, ethyl cinnamate, isopentyl acetate, linalool, a-terpineol, a- and 3-ionone, 6-pentyl-a-pyrone (Formula 18.39, VIII), hexanal, (Z)-3-hexenal, and (E)-2-hexenal. Aroma differences in different varieties of peaches are correlated with the different proportions of the esters and monoterpenes. In the case of nectarines (Prunus persica L., Batsch var. nucipersica Schneid), the lactones y-C8-Ci2 and 5-Cio belong to the compounds with the highest aroma values. 

Elderberry (Sambucus nigra) is cultivated on small scale in Europe. The fruits have a high concentration of red and purple anthocyanins and a relatively low concentration of sugars, organic acids and aroma compounds, which make this juice attractive as a natural colour ingredient in other red fruit products [126-129]. The fresh green odour of elderberry juice is associated with volatile compounds with typical green notes such as 1-hexanol, 1-octanol, (Z)-3-hexen-l-ol, ( )-2-hexen-l-ol, hexanal and ( )-2-hexenal, whereas the floral aroma is mainly due to the presence of hotrienol and nonanal [127-130]. 

The fruit of pumpkin (Cucurbita pepo) is eaten boiled or baked. About 30 compounds have been identified in the volatile extracts of raw pumpkin, with the major classes of compounds being aliphatic alcohols and carbonyl compounds, furan derivatives and sulfur-containing compounds. Hexanal, ( )-2-hexenal, (Z)-3-hexen-l-ol and 2,3-butanedione have been identified as important for the flavour of freshly cooked pumpkins (Table 7.7) [35] however, studies using GC-O techniques are needed to get a better understanding of the character-impact compounds of pumpkins. 

Another pathway is the fatty acid hydroperoxidase lyase (HPL) pathway. This pathway produces C6-aldehydes and C12-oxo acids. 2 C6-volatiles, including ( )-2-hexenal, (Z)-3-hexenal, hexanal, as well as their corresponding alcohols or esters, are produced from mechanically wounded plant tissue.197,203 C6-aldehydes are also formed during hypersensitive response to infection by bacterial pathogens, after insect feeding, and after exogenous application ofJA.204,205 As already shown in this chapter, some of C6-volatiles are known to be attractants of parasitoids and predators. 

Analysis of the vacuum volatile constituents of fresh tomatoes was carried out using capillary GLC-MS and packed column GLC separation with Infrared, NMR and CI-MS analysis. Evidence was obtained for the presence of the unusual components 3-damascenone, 1-nltro-2--phenylethane, 1-nltro-3-methylbutane, 3-cyclocltral and epoxy-3-1onone. A method for the quantitative analysis of the volatile aroma components In fresh tomato has been Improved and applied to fresh tomato samples. The quantitative data obtained have been combined with odor threshold data to calculate odor unit values (ratio of concentration / threshold) for 30 major tomato components. These calculations Indicate that the major contributors to fresh tomato aroma Include (Z)-3-hexenal, 3-lonone, hexanal, 3-damascenone, 1-penten-3-one, 3-methylbutanal, (E)-2-hexenal, 2-lso-butylthlazole, 1-nltrophenylethane and (E)-2-heptenal. 

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-... 

Z)-3-Hexen-l-ol, (E)-2-hexenal, hexanol, (E)-2-hexen-l-ol, and hexanal are formed in bell peppers (Capsicum annuun var. grossum, Sendt) after tissue disruption (Buttery and Ling, 1992). 

To understand the sensitivity of the extracts to artifact formation it is informative to review the volatiles in kiwifruit. Quantitatively, peroxidation products of unsaturated fatty acids (11, 12), which include (E)-2-hexenal (77.87%), (E)-2-hexen-l-ol (6.80%), 1-hexanol (3.40%), hexanal (1.78%), (Z)-2-hexenal (0.87%), (E)-3-hexen-l-ol (0.32%) and (Z)-3-hexen-l-ol (0.17%), constitute over 90% of the total volatiles. Other major constituents include the esters, methyl butanoate (2.54%) and ethyl butanoate (3.52%). The presence of large amounts of saturated and unsaturated aldehydes in the extract is noteworthy since they are quite susceptible to free-radical oxidation. We therefore expected that at least some of the artifacts were the products of autoxidation. 

Six-carbon volatile alcohols and aldehydes have been found in all freshwater fish surveyed (23-24). However, these compounds have not been found in either salmon residing in saltwater (unpublished data) or in oysters (26). Hexanal has been found in modestly fresh (5-6 days old) saltwater fish (24), but its formation may be the result of autoxldation rather than via enzyme-mediated reactions. Thus, data for the occurrence of hexanal in freshly harvested saltwater fish remains to be developed. Hexanal and (E)-2-hexenal contribute coarse, green-plant-like, aldehydic aroma notes to freshly harvested finfish where their aroma dominates the overall odors within seconds after the death of the fish. (Z)-3-Hexen-l-ol contributes a clean, green-grass-like aroma note. Hexanal always occurs in substantially greater abundance than 1-hexanol in fish. 

Guava flavor G.f., resembling pear and quince flavor, contains )8- caryophyllene, numerous fruit esters, e.g., ethyl butanoate and ethyl hexanoate, cinna-myl acetate (see cassia oil) and the green notes from hexanal, ( )-2- hexenal, and (Z)-3- hexen-l-ol. Important trace components are C -C,g-dienals, Fura-neol, some pyrazines and thiazoles, as well as 6-mercapto-I-hexanol(CiHnOS, Mr 134.24,CAS [1633-78-9]) ... 

Green peas (raw) 2-alkyl-3-methoxypyrazines (2-isopropyl-, 2-isobutyl-, and 2-sec-butyl-, see pyrazines) together with ( )-2-nonenal (see alkenals) ( ,Z)-2,6- nonadienal, ( , )- 2,4-decadienal, hexan-l-ol, and (Z)-3- hexen-l-ol. 

The aspen leaves were wounded using scissors in the experiment, for which the plant chamber was quickly opened and closed (Figure 52.8). A rapid peak of mass (Z)-3-hexenal emission is observed. This behavior is consistent with the role of (Z)-3-hexenal as the precursor in the degradation process (see Figure 52.7). The rapid decline in (Z)-3-hexenal takes place simultaneously with the rise of other hexenyl derivates.The detection of hexanal is complicated by the lack of unique fragments, but the time evolution of n-hexanol and... 

Linoleic and linolenic acids in fruits and vegetables are subjected to oxidative degradation by lipoxygenase alone or in combination with a hydroperoxide lyase, as outlined in sections 3.7.2.2 and 3.7.2.3. The oxidative cleavage yields oxo acids, aldehydes and allyl alcohols. Among the aldehydes formed, hexanal, (E)-2-hexenal, (Z)-3-hexenal and/or (E)-2-nonenal, (Z)-3-nonenal, (E,Z)-2,6-nonadienal and (Z,Z)-3,6-nonadienal are important for aroma. 

Except for the pair (E/Z)-6-nonenal, the odor threshold of the E-isomer exceeds that of the corresponding Z-isomer. In particular, the values for (E)- and (Z)-3-hexenal differ greatly. Some of the aldehydes listed in Table 5.44 and 5.45 are formed by the peroxidation of unsaturated fatty acids (cf. 3.7.2.1.9). However, they play a role in aromas only when they are produced in foods in a concentration higher than their odor threshold concentration. The aroma active aldehydes usually include hexanal, which appears as the main product in the volatile fraction of peroxidized linoleic acid and, therefore, can surmount the relatively high odor threshold (Table 5.44). (E)-2-Nonenal also belongs to this... 

Among a large number of volatile compounds, (Z)-3-hexenal, 3-ionone, hexanal, P-damasce-none, l-penten-3-one, and 3-methylbutanal are of special importance for the aroma of tomatoes (cf. Table 17.12). 

In tomato paste, for example (cf. Table 17.12), it was found that the changes in aroma caused by heating are primarily due to the formation of dimethylsulfide, methional, the furanones HD2F and HD3F and the increase in P-damascenone, and a substantial decrease in (Z)-3-hexenal and hexanal. 

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