Limonene-1,2-epoxides and carvone

Gas Chromatographic Analysis. The contribution of limonene-1, 2-epoxides and carvone to the development of oxidized flavor of encapsulated orange oil has been investigated (5). The concentrations of these two compounds were reported to provide a reliable index of the stability of the encapsulated orange oil. 

The identification of limonene-1,2-epoxides and carvone was accomplished by retention indices and mass spectra, obtained separately by GC-MS, in comparison to authentic reference compounds. 

Cold pressed orange oil contains over 95 by weight monoterpene hydrocarbons. The principal constituent, d-limonene, ranges from 83-97 percent (9), Limonene degradation has been well docu-meted in the literature (LO, 1 1). Anandaraman identified limonene-1,2-epoxide and carvone as two of the earliest degradation products of d-limonene (12, 13). 

C. Samples were withdrawn every two days from the samples stored at 45 C and every three days from the samples stored at 37 C. Pulled samples were stored in screw cap vials at 0 C until analsis by gas chromatography (GC). The products were monitored for the formation of limonene-1,2-epoxide and L-carvone, both oxidation products of d-limonene (3). 

An alternative process for the production of (-)-carvone has recently been elaborated. Starting from (-i-)-limonene 1,2-epoxide, a regioselective rearrangement of the epoxide leads to (-)-carveol (trans- -.[2102-58-1] cis- -.[2102-59-2]). The reaction is effected by the use of a catalyst consisting of a combination of metal salts and phenolic compounds. 

Limonene (68) was biotransformed via limonene-l,2-epoxide (69) to 8-p-menthene 1,2-frani -diol (71b). On the other hand, (-i-)-carvone (93) was biotransformed via (-)-isodihydrocarvone (101b) and la-hydroxydihydrocarvone (72) to (-i-)-8-p-menthene-l,2-tran5 -diol (71a) (Noma et al., 1985a, 1985b) (Figure 14.28). A soil Pseudomonad formed 1-hydroxydihydrocarvone (72), 8-p-menthene-l,2-tra i-diol (71b) from (-i-)-limonene (68). Dhavalikar and Bhattacharyya (1966) considered that the formation of 1-hydroxy-dihydrocarvone (66) is from dihydrocarvone (64). 

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