Aroma cucumber

In addition to the straight-chain saturated aldehydes, a number of branched-chain and unsaturated aliphatic aldehydes are important as fragrance and flavoring materials. The double unsaturated 2-trviolet leaf aldehyde (the dominant component of cucumber aroma), is one of the most potent fragrance and flavoring substances it is, therefore, only used in very small amounts. 2-frfatty odor character is indispensible in chicken meat flavor compositions. 

In Table V some results with cucumbers (Cucumis sativus) are summarized. The enzyme system has been studied by Phillips and Galliard (1 9) and by Phillips et al. ( ). Cucumbers possess a lipoxygenase system which forms D-9-LOOK and L-13-LOOK which are decomposed into (E)-2-isomerase (E3) which converts ( Z)-enals into ( )-enals. Therefore, the "labile" ( )-3-enols were detected by Hatanaka for the first time in 1975 (21 ). They are the precursors of other Cg-con-stituents in cucumber aroma concentrates. 

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 following aldehydes play an important role in cucumber aroma (E,Z)-2,6-nonadienal and (E)-2-nonenal. Linoleic and linolenic acids, as shown in Fig. 3.31, are the precursors for these and other aldehydes (Z)-3-hexenal, (E)-2-hexenal, (E)-2-nonenal. 

Nonadienol is a powerful fragrance substance. It is used in fine fragrances to create refined violet odors and to impart interesting notes to other blossom compositions. In aroma compositions it is used for fresh-green cucumber notes. FCT 1982 (20) p.771. 

In general, microwave cake appeared to lack many of the nutty, brown, and caramel-type aromas observed in the conventional cake and was in fact more similar to the batter. Table 2 summarizes the predominant aranas noted from each extract in decreasing order. The predominant aromas in both batter and microwave cake were green vegetable notes. Brown, caramel, and potato notes were observed less frequently. The conventional cake profile contained more brown, caramel notes followed by butter, cucumber, potato, and finally, green vegetable aromas. 

Hexenal (leaf aldehyde) is a constituent responsible for the smell of green leafs, ( )-2-octenal a main component of the aroma of raw potatoes ( )-2-nonenal is the organoleptic main constituent of the smell of cucumbers and is found in carot root oil, tomatoes, beef and raspberries 158). ( )-2-Decenal and ( )-2-dodecenal are components of some essential oils, ( )-2-tridecenal is responsible for the bug-like smell of coriander seed oil1S8). 

In some cases the action of lipoxygenase leads to development of a characteristic aroma. Galliard et al. (1976) found that the main aroma compounds of cucumber, 2-trans hexenol and 2-trans, 6-cis-nonadienal, are produced by reaction of linolenic acid and lipoxygenase to form hydroperoxide... 

Figure 10-20 Lipoxygenase Catalyzed Formation of Aroma Compounds in Cucumber. Source Reprinted from Biochim. Biophys. Acta., Vol. 441, T. Galliard, D.R. Phillips, and J. Reynolds, The Formation of cw-3-nonenal, mwu-2-nonenal and Hexanol from Linoleic Acid Hydroperoxide Isomers by a Hydroperoxide Cleavage Enzyme System in Cucumber (Cucumis Sativus) Fruits, p. 184, Copyright 1976, with permission from Elsevier Science.

In contrast, odour intensity of other components related to off flavours ( herbal , sawdust , greasy , and cucumber ) can be seen to decrease with toasting. The same happened with the intensity of fruity and floral aromas of linalool oxide, p-damascenone, or 2-phenylethanol, and the oak lactones odour descriptors. 

The taste of the muskmelon is very sweet creamy with a strong, sweet, floral fruity-sulphurous and typical melon-like, fatty, green aroma. The taste of watermelon is very watery, juicy, sweet with a weak green, fatty, cucumber-like aroma. 

CIC In both melon types the lipid degradation products (Z)-6-nonenol, (Z,Z)-3,6-nonadienol and the corresponding aldehydes are responsible for the typical green, fatty, cucumber melon aspect. Ethyl propionate imparts an overripe character to muskmelon flavour, supported by the sweet, caramelic aspect of 2-methyl-5-ethyl-4-hydroxy-furan-3(2H)-one and the fmity-sulphurous aroma of S-methyl thioacetate and methyl thiobutyrate. 

Although for many years lipoxygenase activity in fish was discounted (14-17), plant lipoxygenases were easily demonstrated, and became well-accepted. Research into the biosynthesis of the six-, eight-, and nine-carbon volatile aroma compounds of mushrooms (27, 56) and cucumber/melon-fruits (37, 57-58) showed the concerted activities of both site-specific lipoxygenases and hydroperoxide lyases. Because animal lipoxygenases exhibit self-inactivation properties (59-60), early experimentation failed to detect an active lipoxygenase from fish, and this led to conclusions that autoxidation was responsible for the... 

The relative ratios of alcohols and carbonyls for the six-, eight- and nine-carbon volatiles in fish (23-24) and oysters (26) parallel those encountered in cucumber fruits (37) and mushrooms (27, 56) if the two systems are combined. Therefore, the use of plant-based enzyme systems for the controlled generation of fresh seafood flavors and aromas has been under consideration in our laboratory as a means to overcome some of the self-inactivating problems associated with fish lipoxygenases. 

When mushroom homogenates were incubated with surimi, enhanced plant-like aromas somewhat reminiscent of oysters were produced, and this treatment also resulted In the masking of some of the fish-like aromas of the surimi. Cucumber homogenates developed strong cucumber, cardboard-like aromas which appear to be contributed principally by 2-nonenal and 2,6-nonadienal. As a result, the cucumber homogenates caused undesirable and unbalanced aromas that did not suppress unpleasant fishiness. Watermelon fruit extracts behaved similarly, and also provided unbalanced sweet aromas to surimi. Tests to date have been limited to short-term incubations of crude enzyme preparations with surimi. Further exploration of more purified and controlled plant-based flavor-generating enzyme systems for the production of fresh seafood-like aromas, and especially those for the eight-carbon volatile aroma compounds, appear warrented. 

Alkenals. A. are formed from fatty acids by autooxidation or enzyme action and are widely distributed in essential oils and aromas. The Cs-Cu-A. (see also hexenals) have sensory effects even in low concentrations. Odors of (0-2-A. resemble those of the alka-nals but are stronger and less fatty Ci citrus, orange C,2 orange, mandarine. Clearly different are the odors of the (Z)-A. (see table, p. 20). C, green, fatty cream C9 cucumber, melon C, citrus, flowery. ... 

Occurrence E)-2-A. Cg-C,3 in citrus oils, especially bitter orange, Cg also in guava and ginger aromas, C, in bread, cucumber, carrot (see vegetable flavors) and rice flavor, c,o in coriander oil, butter, chicken and guava aroma, C,2 in coriander oil, peanut and meat flavor. (Z)-4-Heptenal is found, among others, in "butter, seafood and tea flavor, (Z)-3- and (Z)-6-nonenal in cucumber, melon and fish aroma, and (Z)-4-decenal in calamus oil and Citrus junos oil. ... 

Unripe cucumbers, after addition of dill herb and, if necessary, other flavoring spices (vine leaf, garlic or bay leaf), are placed into 4-6% NaCl solution or are sometimes salted dry. Usually, the salt solution is poured on the cucumbers in a barrel and then allowed to ferment and, if necessary, glucose is added. Fermentation takes place at 18-20 °C and yields lactic acid, CO2, some volatile acids, ethanol and small amounts of various aroma substances. Homo-and heterofermentative lactic acid bacteria Uke Lactobacillus plantarum, L. brevis and Pediococ-... 

Green-note compounds are responsible of the fresh, green odor of cut leaves and are important components of the flavor of fruits and vegetables, such as apples, cherries, kiwifruits, raspberries, strawberries, and tomatoes. They include six-carbon aldehydes and alcohols, such as (2 )-hexenal (leaf aldehyde) and (3Z)-hexenol (leaf alcohol). Nine-carbon aldehydes and alcohols, which are found in the aroma of cucumbers and melons, are also considered green-note compounds. 

R. T. Marsili and N. MUler, Determination of major aroma impact compounds in fermented cucumbers by sohd-phase microextraction-gas chromatography-mass spectrometry-olfactometry detection, J. Chromatogr. Sci. 38 307 (2000). 

Of the significant odor-active compounds observed in brine samples, only cis- and fran -4-hexenoic acids and phenyl ethyl alcohol (or phenyl acetaldehyde, an oxidation product of phenyl ethyl alcohol) were present in all brine samples tested. (Note Phenyl acetaldehyde has a fioral/lilac/hyacinth aroma.) Therefore, these highly odiferous chemicals are likely to be key impact-odor components of fermented cucumbers. This was confirmed by detection frequency olfactometry experiments and by recombination studies. 

Recent aroma research has been devoted to the identification of key flavor compounds in vegetables and is the subject of several contemporary reviews (31,34,35). Cucumbers, sweet com, and tomatoes are botanically classified as fmits however, for flavor considerations they are regarded as vegetables, because they are typically consumed with the savory portion of the meal. Overall, the knowledge base of character impact compounds for vegetables is much smaller than other flavor categories and warrants further investigation. 

Key parsley aroma compounds were recently identified (41). The primary flavor contributors were found to include p-mentha-l,3,8-triene (terpeny, parsleylike), myrcene (metallic, herbaceous), 2-sec-butyl-3-methoxypyrazine (musty, earthy), myristicin (spicy), linalool (coriander), (Z)-6-decenal (green, cucumber), and (Z)-3-hexenal (green). 

The fishy aroma of seafood is incorrectly attributed to trimethyl amine. Flavor formation in fresh and saltwater fish results from complex enzymatic, oxidative, and microbial reactions of n-3 polyunsaturated fatty acid precursors (e.g., eicosapentaenoic acid) (69,70). Hence, fish flavor is mostly composed of non-characterizing planty or melon-like aromas from lipid-derived unsaturated carbonyl compounds. Examples are (Z)-l,5-octadien-3-one ( geranium-like ) in boiled cod (71) and (7i,Z)-2,6-nonadienal ( cucumber-like ) in boiled trout (72). 

P. Schieberle, S. Ofner, and W. Grosch, Evaluation of potent odorants in cucumbers (Cucumis sativus) and muskmelons (Cucumis melo) by aroma extract dilution analysis, J. Food Sci. 55 193 (1990). 

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