Limonene, -, aroma, orange

Many essential oils, such as those of citrus fruits, contain terpene hydrocarbons which contribute little to aroma but are readily au-tooxidized and pol)merized ( resin formation ). These undesirable oil constituents (for instance, limonene from orange oil) can be removed by fractional distillation. Fractional distillation is also used to enrich or isolate a single aroma compound. Usually, this compound is the dominant constituent of the essential oU. Examples of single aroma confounds isolated as the main constituent of an essential oil are 1,8-cineole from eucalyptus, 1(—)-menthol from peppermint, anethole from anise seed, eugenol from clove, or citral (mixture of geranial and neral, the pleasant odorous... 

The oils have a high terpene hydrocarbon content (>90%, mainly (+)-limonene), but their content of oxygen-containing compounds differs and affects their quality. Important for aroma are aldehydes, mainly decanal and citral, and aliphatic and terpenoid esters. The sesquiterpene aldehydes a-sinensal [17909-77-2] and/3-sinensal [6066-88-8], which contribute particularly to the special sweet orange aroma, also occur in other citrus oils, although in lower concentration [369-370a, 370d, 394,421, 430-438]. 

Limonene [138-86-3] - [ANALYTICALMETHODS - TRENDS] (Vol 2) -aroma chemical [PERFUMES] (Vol 18) -in Bergamot oil [OILS, ESSENTIAL] (Vol 17) -in caraway oil [OILS, ESSENTIAL] (Vol 17) -in asms oil [OILS, ESSENTIAL] (Vol 17) -in citronella oils [OILS, ESSENTIAL] (Vol 17) -in eucalyptus oil [OILS, ESSENTIAL] (Vol 17) -in expectorants [EXPECTORANTS, ANTITUSSIVES AND RELATED AGENTS] (Vol 9) -m jumperberry oil [OILS, ESSENTIAL] (Vol 17) -in lavender [OILS, ESSENTIAL] (Vol 17) -in lavender [OILS, ESSENTIAL] (Vol 17) -in lime oil [OILS, ESSENTIAL] (Vol 17) -in neroli oil [OILS, ESSENTIAL] (Vol 17) -m oilbanum [OILS, ESSENTIAL] (Vol 17) -in orange oil [OILS, ESSENTIAL] (Vol 17) -in sweet basil oil [OILS, ESSENTIAL] (Vol 17)... 

Limonene, a terpene hydrocarbon, is the major component of orange oil (3), and it is present in orange juice at a level almost 800 times its taste threshold in water. Limonene possesses a weak, citrus-like aroma but does not by itself impart an orangelike flavor note to a bland orange juice base (5 6). Limonene and the other terpene hydrocarbons probably make a significant... 

Tocopherol was effective and ascorbic acid ineffective in the protection of citrus oils evaluated by aroma (13). In a typical study, 5 g of orange oil was oxidized in 75-mL open brown bottles at 45°C and was evaluated by a panel after 6 d, at which time it was ranked as off-odor, "terpeney. The peroxide value of the initial oil was zero the oxidized material had a PV of 100. As a result, days to reach 100 PV was used as an endpoint. Comparative antioxidant effects on a number of citrus oils and on D-limonene [cyclohexene, l-methyl-4-(l-methylethenyl)-(R)-5989-27-5] are presented in Table X. BHA is the most active while AP has no activity alone but does synergize with tocopherol. 

The odour intensities of volatiles showing similar odour qualities are partially additive [68]. To substantiate such additive effects, three groups of odorants (terpene hydrocarbons, esters or aldehydes) were omitted from the aroma model for orange juice. For all groups, a significant difference from the complete model was observed (Table 6.39). Omission of esters nos. 12,14 and 15 with ethyl butanoate (no. 13) still present was clearly detectable. This indicates that the fruity quality in the odour profile is enhanced by additive effects. In contrast, no difference was perceivable when (R)-a-pinene (no. 17) and myrcene (no. 18) were omitted. The concentration of the odorants in juice differs depending on the variety. Thus, the weaker citrus note of Navel oranges compared with the above discussed variety Valencia late is due to a 70% lower content of (R)-limonene [67]. 

One enantiomer of the compound carvone is associated with the smell of spearmint the other produces the aroma of caraway seeds or dill. One mirror-image form of limonene smells like lemons the other has the aroma of oranges. 

Examples of the dependence of aroma scalping on plastic/migrant combination are illustrated by the data on partition of key orange oil aroma constituents into four types of common plastics (see Table 8.7) (Charara et al., 1992). The nonpolar limonene is readily absorbed by LDPE a polar polymer such as PET would absorb much less of the compound. 

The aromatic properties of essential oils are perhaps the most conspicuous and account for a wide range of traditional applications. Many terpenoids have characteristic odors, some of them are presented in Tables 96.3 and 96.4 [55-57]. The odor thresholds however may vary greatly and depend on the matrix. (—)-Limonene with citrus-like aroma is a key odorant of orange juice and neral/ geranial the key odorants of lemons. l-p-Menthene-8-thiol present in grapefruit juice and responsible for the grapefruit aroma has with 0.02 ng/L one of the lowest odor threshold values [42]. 

Orange juice from rediluted concentrate differs in its aroma. This can be the result of big losses of acetaldehyde and (Z)-3-hexenal, the formation of carvone by peroxidation of limonene and a large increase in the vanillin concentration, probably due to the degradation of ferulic acid. 

Chiral compounds are frequently foimd among the flavor volatiles of fruits and, like many naturally occurring chiral compounds, one enantiomer usually exists with a greater preponderance when compared with its antipode. Chiral odor compounds may show qualitative and quantitative differences in their odor properties (7). For example, (/ )-(+)-limonene has an orange-like aroma while (5)-(-)-limonene is turpentine-like (5)-(+)-carvone is characteristic of caraway while its enantiomer has a spearmint odor (2). However, other chiral compounds, such as y 6-lactones, show very little enantioselectivity of odor perception (7). The occurrence of chiral flavor compounds in enantiomeric excess provides the analyst with a means of authenticating natural flavorings, essential oils, and other plant extracts. The advent of cyclodextrin-based gas chromatography stationary phases has resulted in considerable activity in the analysis of chiral compounds in flavor extracts of fruits, spices and other plants (i-7). 

Table 2 Headspace Saturation of rf-Limonene at Different Pulp Contents in 11.8 °Brix Orange Juice Diluted from Aroma-Free 65 Brix Evaporator Pump-out, Spiked...

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