Figure 13-8 Average variation in the citral, limonene and ¿3-pmene content (A) and limonene, o-terpineol and nonanai content (B) for lemon oil for each month of the productive season (Dugo etal., 1992).
Cartoni etal. (1986), using two columns, one of PEG-20M and one of SE-54, in series, obtained a good separation of the critical pairs />-cymene/limonene, and sabinene//3-pinene, otherwise not separated by using SE-54 columns, and of the pairs a-thujene/a-pinene and geranial/3-bisabolene, otherwise not separated on a PEG-20M column.
Mazza (1987b) during a study for the detailed analysis of lemon oil composition, identified by GC/MS, in two samples of lemon oil obtained by FMC, the following components not listed in Table 13.15:/>-cymenene, 5-acoradiene, a-selinene, (E)-2-decenal, hexadecanal, hexanal, (E)-2-nonenal, pentadecanal, (E)-2-tetradecenal, myrtenal, isopiperitone, heptanol, carvacrol, cis- and fra/w-carveol, />-cymen-8-ol, y-isogeraniol, cis- and trans-isopiperitenol, cis- and ftw»j-p-mentha-2,8-dien-l-ol, 5-terpineol, cis- and trans-p-memh&-\(J), 8-dien-2-ol, />-mentha-l,8(10)-dien-9-ol, cis- and toKj-l-acetoxy-3,7-dimethyl-2,7-octadien-6-ol, perilla alcohol, thymol; hepthyl acetate, ^-mentha-l,8(10)-dien-9-yl acetate; ethyl benzoate, 1,4-cineole, acetic acid, octanoic acid.
Lakszner and Szepesy (1988), as mentioned for bergamot oil, proved the possibility to use a selective GC detector for oxygen containing components, for the determination of lemon oil genuineness.
Sawamura etal. (1990) reported the presence of valencene (0.05 per cent).
Munari etal. (1990) were the first who used an automated HPLC-GC system to fractionate lemon oil by HPLC and transfer the fractions onto the GC system. The advantage was that, with such method, the GC analysis of simple fractions avoided peak overlapping.
Micali etal. (1990) and Lanuzza etal. (1991), using a coupled HPLC-GC system identified in a lemon oil the n-alkanes from C21 to C33 and the correspondent 'iso' isomers, along with /3-caryophyllene, bergamotene* (probably the /nwj-a-bergamotene), a-humulene, bisabolene*. Using a similar system Mondello etal. (1995b) identified the following sesquiterpene hydrocarbons listed in decreasing amount order: /3-bisabolene, /TiZOT-a-bergamotene, /3-caryophyllene, cxr-a-bergamotene, valencene1, (Z)-/3-farnesene, /3-santalene, a-humulene, 7-curcumene, (Z)-7-bisabolene, (E)-7-bisabolenet, (E)-/3-far-nesenec. Chamblee etal. (1997) using a GC/FT-IR system identified for the first time in lemon oil bicyclogermacrene and (Z)-a-bisabolene.
Some authors refer to commercial lemon oils of not specified origin. The results of these analyses are reported in Table 13.16. The values obtained by Inoma etal. (1989) are not reported in this table, since, although they referred to lemon oil, the composition reported resulted extremely different from that of such citrus oil. In fact some of the values obtained by these authors were: limonene (90 per cent), other monoterpene hydrocarbons almost absent, linalool (1.95 per cent), decanal (1.56 per cent), valencene (0.53 per cent), 7-cadinene (0.47 per cent).
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