Inter-Tree Variation in the Chemical Composition of Boswellia papyrifera Oleo-Gum-Resin
Abstract Frankincense is a fragrant resin produced by Boswellia species, and has been used for centuries as a perfume, medicine, and incense, and is an important cosmetic and therapeutic product today. A number of studies have been conducted on the resin essential oils, but many have used commercial sources outside of the country of origin, leading to potential taxonomic confusion or misidentification. Individual Boswellia papyrifera resin samples were each obtained directly from 11 individual trees in Sudan, hydrodistilled, the volatile phytochemicals determined by gas chromatographic methods, and the chemical compositions subjected to cluster analysis. All samples were very similar, with high levels of octyl acetate (49.5%-81.0%) and octanol (6.5%-13.7%), and varying levels of diterpenoids (6.6%-32.7%). The cluster analysis indicated 3 highly similar groups, defined by (1) relatively higher levels of octyl acetate (58.9%-81.0%), but with low levels of diterpenoids (6.6%-18.6%); (2) relatively lower levels of octyl acetate (49.5%-61.3%), but with a higher proportion of diterpenoids (19.0%-22.8%); and (3) with octyl acetate (51.6%) and diterpenoids (32.7%).
Introduction Frankincense is a natural plant resin widely valued for its aromatic and therapeutic uses.1 It is produced by species in the genus Boswellia (Burseraceae: Sapindales), a group of approximately 24 species of small trees often featuring compound leaves, exfoliating bark, and a deep red resiniferous bark layer.2 The resin is produced and stored in resin canals in the bark, and is exuded when the bark is broken, either by an animal (such as a boring beetle) or intentionally by humans to extract the resin.2 Frankincense has been used and traded internationally for thousands of years for its use in traditional medicine, perfumery, cosmetics, and religious ceremonies. It is still used for these purposes today.1 In addition, essential oils and extracts derived from frankincense resins have become ingredients in supplements, aromatherapy, and complementary/alternative medicine. The essential oils and heavy terpenes in the resins have shown notable biological activity.3 A number of studies have been conducted on frankincense essential oils, but many of these used resins obtained from commercial sources outside of the country of origin, potentially leading to taxonomic confusion. Most Boswellia species produce essential oils dominated by mono- and sesquiterpenes, particularly α-pinene, α-thujene, sabinene, limonene, myrcene, p-cymene, and β-caryophyllene.3 Boswellia occulta is a unique exception, with an essential oil dominated by methoxyalkanes.4 Boswellia papyrifera is found across Sahelian east and central Africa, with major populations in Ethiopia, Eritrea, and Sudan, and is perhaps the most-traded frankincense species in terms of volume.2, 5 The essential oil has been reported to contain high levels of octyl acetate and octanol; however, many of these studies have been conducted on commercial samples obtained outside of the species’ range states.6–10 Significant concerns about the conservation status and sustainability of trade of B papyrifera have been raised, making proper identification of these resins a key priority.5 In this study, we present a characterization of the resin essential oils of vouchered single-tree samples taken in South Kordofan, Sudan.Results The B papyrifera resin essential oils of 11 individual trees (samples A-K) were obtained by hydrodistillation in yields of 1.32% to 2.72% (w/w) as colorless to pale yellow oils. The chemical composition of each sample is reported in Table 1.