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Bound volatile compounds from Osage orange fruit (Maclura pomifera) in comparison with its essential oil

The type of compounds isolated from the various parts of Osage orange, Maclura pomifera (Raf.) Schneid (Moraceae), belong to different classes such as flavonoids, xanthones, triterpenes and stilbenes (Lee et al., 1998). The fruit of Osage orange has been utilized as an insect repellent (Peterson et al., 2002). Among others, volatility is viewed as being important to repellent activity. Phytochemical studies of this fruit made no attempt to compare its free and bound volatiles. If the bound volatile aglycones are compared with the corresponding free volatiles of the same plant, only limited similarity turns out (Stahl-Biskup et al., 1993). In the literature, only one reference about M. pomifera fruit oil of American origin was found (Peterson et al., 2002). Mostly sesquiterpenoids were determined to be present in the fruit volatile isolates and many of them were repellent to German cockroaches. As a part of our research project (Croatian grant No. 0011010), we have studied the free and bound volatile composition of M. pomifera fruit by GC and GC-MS. The free volatiles (230 mg kg-1) were obtained by hydrodistillation (Clevenger apparatus) and bound volatiles (10 mg kg-1) were liberated after the hydrolysis of the glycosidic fraction (obtained by water extraction and purified by 'flash' CC-chromatography) using β -glucosidase. The oil (50 μ L) was separated in two fractions – with hydrocarbons and oxygen-containing compounds, respectively – by eluting the oil on a silica gel microcolumn with subsequently n-pentane and diethyl ether. Identified compounds consist of aliphatic constituents (free 28.3% ; bound 29.1%), phenylpropane derivatives along with related compounds (free 5.1% ; bound 36.0%), monoterpenes along with sesquiterpenes (free 55.2% ; bound 19.3%) and other compounds (bound 3.5%). In total, 43 bound volatiles were identified, with eugenol (9.9%) and p-cresol (9.6%) being the major components. As far as we know, this is the first report on bound volatiles of Osage orange fruit and 12 compounds were established to be identical by comparison with the free volatiles. The principal constituents of the essential oil were elemol (19.2%), 1-dodecanol (9.7%), trans-caryophyllene (5.6%) and hexyl hexanoate (5.4%).

Maclura pomifera; essential oil; glycosidically bound volatiles; GC-MS

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