Cucumber aldehyde

The variety of aldehyde oxidases discovered in other plants have similarities to the maize enzyme, but also have some very important differences. Enzymes contained in a cell wall fraction from barley seedlings were able to oxidize IAAld to form IAA at a pH optimum of 7 and Km of 5 pmol 1 1, which was very similar to the enzyme found in maize.113 Two aldehyde oxidases from potato have also been identified 101 they had a similar pH optimum (between 7 and 8), but preferred aliphatic aldehydes to aromatic aldehydes. Although oat and cucumber aldehyde oxidases have been shown to oxidize IAAld to produce IAA,102 114 the oat enzyme had a lower pH optimum and higher Km than the maize enzyme, and the cucumber enzyme was inhibited by synthetic auxin and activated by 2-mercaptoethanol, which was not true for the maize enzyme. The difference in the enzymes makes it difficult to envision a common evolutionary origin for the IAAld pathway in plants if these particular enzymes are involved in each case. 

SYNS CUCUMBER ALDEHYDE FEMA No. 3317 2,6-NONADIENAL trans,cis-2,6-NONADIENAL trans-2,ds-6-NONADIENAL VIOLET LEAF ALDEHYDE... 

Enzymatically active materials (fruits, vegetables and some fats) contain a large number of other aldehydes that are produced from essential fatty acids, mainly linoleic and Knolenic acids (Table 8.9) by oxidation reactions catalysed by lipoxygenases. In some vegetables (e.g. in cucumbers), aldehydes also result from a-oxidation of fatty acids (Figure 8.15). The primary oxidation products of essential fatty acids are hydroperoxides, which break down to aldehydes and other products under the action of lyases and can be... 

Essential oils are known to have detrimental effects on plants. The inhibitory components have not been identified, but both alde-hydic (benzol-, citrol-, cinnamal-aldehyde) and phenolic (thymol, carvacol, apiol, safrol) constituents are suspected. Muller et al. (104) demonstrated that volatile toxic materials localized in the leaves of Salvia leucophylla, Salvia apiana, and Arthemisia californica inhibited the root growth of cucumber and oat seedlings. They speculated that in the field, toxic substances from the leaves of these plants might be deposited in dew droplets on adjacent annual plants. In a subsequent paper, Muller and Muller (105) reported that the leaves of S. leucophylla contained several volatile terpenes, and growth inhibition was attributed to camphor and cineole. 

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. 

The overwhelming consideration in regard to lipid deterioration is the resulting off-flavors. Aldehydes, both saturated and unsaturated, impart characteristic off-flavors in minute concentrations. Terms such as painty, nutty, melon-like, grassy, tallowy, oily, cardboard, fishy, cucumber, and others have been used to characterize the flavors imparted by individual saturated and unsaturated aldehydes, as well as by mixtures of these compounds. Moreover, the concentration necessary to impart off-flavors is so low that oxidative deterioration need not progress substantially before the off-flavors are detectable. For example, Patton et al (1959) reported that 2,4-decadienal, which imparts a deep-fried fat or oily flavor, is detectable in aqueous solution at levels approaching 0.5 ppb. 

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). 

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. 

The oxidation products of lipids include volatile aldehydes and acids. Therefore, lipids are one of the major sources of flavors in foods. For example, much of the desirable flavors of vegetables such as tomatoes, cucumbers, mushrooms, and peas (Ho and Chen, 1994) fresh fish (Hsieh and Kinsella, 1989), fish oil (Hu and Pan, 2000) and cooked shrimp (Kuo and Pan, 1991 Kuo et al., 1994), as well as many deep-fat fried foods such as French-fried potatoes (Salinas et al., 1994) and fried chicken (Shi and Ho, 1994), are contributed by lipid oxidation. LOX-catalyzed lipid oxidation produces secondary derivatives, e.g., tetradecatrienone, which is a key compound of shrimp (Kuo and Pan, 1991). The major difference between the flavors of chicken broth and beef broth is the abundance of 2,4-decadienal and y-dodeca-lactone in chicken broth (Shi and Ho, 1994). Both compounds are well-known lipid oxidation products. A total of 193 compounds has been reported in the flavor of chicken. Forty-one of them are lipid-derived aldehydes. 

Compound identifications were based on comparison of mass spectral data and co-chromatography of plant components with standards as reported (8,9). A sample of 3,6-nonadien-l-ol was isolated from melon (10) whereas 8,11—heptadecadienal and 8,11,14-heptadecatrienal were obtained from cucumber fruit (11). Of primary interest in the present study is the identification of Cg aldehydes and alcohols including nonanal and nonanol which are effective promotors of wheat rust spore germination. The unsaturated Cg compounds have not been evaluated for activity but their close structural relationships to nonanal and nonanol make them candidates for germination promotors. 

Mascerated cucumber Lacks masking effect Green-vine-like C9 Aldehydes... 

Galliard and Matthew (5) have reported the biogenesis of C15, C14, C13 and C12-saturated fatty aldehydes from palmitic acid in cucumber fruits. However, that of the unsaturated Cn-aldehydes such as (Z, Z, Z)-8,11,14-heptadecatrienal, (Z, Z)-8, 11-heptadecadienal and (Z)-8-heptadecenal had not been studied so far. Thus, the enzymatic formation of the long-chain aldehydes from unsaturated fatty acids in a green seaweed, U. pertusa, was explored. 

The surprising feature of this fruit is the quantity of six-carbon alcohols and aldehydes. Taken as a group, these conpounds constitute over 70% of the total volatiles. We had fully expected to find a variety of nine-carbon compounds in our essence and we specifically looked for them since they are the major volatiles in other Cucurbitaceae. For exanple, nonanal, 2-nonenal, 6-nonenal and 2,6-nonadienal are some of the major components of cucumber ( ) and 6-nonenol is the major compound in frozen muskmelon ( ). None of these compounds were found if present, they are below the 1% level. 

The enzymic formation of aldehydes, ketones, alcohols, and oxoacids (from linoleic and linolenic acids) on disruption of plant tissues is an important biosynthetic pathway by which fruit and vegetable volatiles are formed. Some examples are (E)-2-hexenal ("leaf aldehyde") and ( )-3-hexenol ("leaf alcohol") in tea (E)-2-hexenal in apples (E,Z)-2,6-nonadienal ("violet Teaf aldehyde") and (E)-2-nonenal in cucumber ( Z)-5-nonenal in musk melon (Z,Z) -3,6-nonadienol in water melon, and 1-octen-3-ol ("mushroom alcohol") in certain edible mushrooms and Fungi. The enzyme system is highly substrate specific to a (Z,Z)-1,4-pentadiene system (like lipoxygenase) splitting the >C = C< double bond at the W - 6 and/or W - 9 position. Therefore linoleic-, linolenic-, and arachidonic acids are natural substrates. It seems to be a common principle in leaves, fruits, vegetables, and basidiomycetes. 

E,Z)-2,6-N. (violet leaf aldehyde) bp. 88 °C (1.3 kPa), LD50 (rat p.o.) >5 g/kg fatty-green odor of violet leaves in which it was first detected in 1925, ( ,Z)-structure assigned in 1944. It also occurs in vegetable flavors ( impact compound in cucumber), fruit flavors (guava, melon, mango), meat, and seafood flavors. For synthesis, see Lit.. ... 

Other plant systems effect degradation of the hydroperoxides to short-chain aldehydes which have important flavour properties. For example, when cucumber cells are broken and the enzymes liberated, lipolysis, enz5rmic oxidation and subsequent chain hssion give hexanal (from 18 2),... 

It has long been recognized that unsaturated fatty acids are the source of volatile compounds with characteristic odors in various plants, e.g., the so-called leaf alcohols and aldehydes and the flavor of cucurbitaceous fruits (cucumbers, melons, etc.). Evidence that these compounds were formed by enzymatic reactions had accumulated (see Eriksson, 1975), but the enzymatic pathways have only recently been identified. 

As shown in Fig. 3, the initial products from the 9- and 13-hydroperoxides of linoleic acid are the volatile aldehydes c/j-3-nonenal and hexanal and the corresponding C9 and C12 0x0 acid fragments. Analagous volatile products from linolenic acid are cw-3,c/s-6-nonadienal and cw-3-hexenal. However, in most plants, an isomerase enzyme converts the cis-3-enals to the trans-2 isomers (see Fig. 3). Such an enzyme cis-Z, trans-l-emA isomerase has been partially purified from cucumber fruits (Phillips et al., 1979). 

Although LOX from tomato fruits forms predominantly 9-hydroperoxides from linoleic and linolenic acids (Matthew et al., 1977), the cleavage enzyme from tomato does not attack these positional isomers but, rather, is specific for the 13-hydroperoxy isomers, producing hexanal or c/5-3-hexanal, respectively (Galliard and Matthew, 1977). Thus one can rationalize the formation of both Cg and C9 volatiles aldehydes in cucumber extracts with less specificity of LOX and cleavage enzymes and the absence of C9 volatiles in tomato with the substrate specificity of the cleavage enzyme. 

Three indoleacetaldehyde reductases were purified from cucumber seedlings [ 1,4]. The enzyme requiring NADH as a cofactor occurred in the cytosol one of the two NADPH-specific reductases was associated with a microsomal fraction. The latter reduced phenylacetaldehyde at about half the rate observed for indoleacetaldehyde and exhibited minor activity on some of the aliphatic aldehydes tested. The NADH-requiring enzyme acted only on indoleacetaldehyde and phenylacetaldehyde. None of the three enzymes would catalyze the reverse oxidation of tryptophol. 

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