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. 2019 Jul 14;8(7):223. doi: 10.3390/plants8070223

Chemical Composition of the Oleogum Resin Essential Oils of Boswellia dalzielii from Burkina Faso

Anjanette DeCarlo 1,*, Stephen Johnson 1, Amadé Ouédraogo 2, Noura S Dosoky 1, William N Setzer 1,3,*
PMCID: PMC6681306  PMID: 31337133

Abstract

Frankincense, the oleogum resin from members of Boswellia, has been used as medicine and incense for thousands of years, and essential oils derived from frankincense are important articles of commerce today. A new source of frankincense resin, Boswellia dalzielii from West Africa has been presented as a new, alternative source of frankincense. In this work, the oleogum resins from 20 different Boswellia dalzielii trees growing in Burkina Faso, West Africa were collected. Hydrodistillation of the resins gave essential oils that were analyzed by GC-MS and GC-FID. The essential oils were dominated by α-pinene (21.0%–56.0%), followed by carvone (2.1%–5.4%) and α-copaene (1.8%–5.0%). Interestingly, there was one individual tree that, although rich in α-pinene (21.0%), also had a substantial concentration of myrcene (19.2%) and α-thujene (9.8%). In conclusion, the oleogum resin essential oil compositions of B. dalzielii, rich in α-pinene, are comparable in composition to other frankincense essential oils, including B. sacra, B. carteri, and B. frereana. Additionally, the differences in composition between samples from Burkina Faso and those from Nigeria are very slight. There is, however, a rare chemotype of B. dalzielii that is dominated by myrcene, found both in Burkina Faso as well as Nigeria.

Keywords: frankincense, olibanum, essential oil composition, α-pinene

1. Introduction

Frankincense is an aromatic oleoresin with a volatile fraction typically composed primarily of terpenoids and more rarely ethers or fatty esters/alcohols [1]. The oleoresin is produced by the 20 members of the genus Boswellia (Burseraceae: Sapindales), which are distributed across sub-Saharan Africa, Arabia, and the Indian subcontinent [1,2,3]. In nature, the oleoresins defend the trees against infection and pests such as boring beetles, while humans have used them for up to 5000 years for medicine and incense [4]. Today, the oleoresins of many species are traded internationally and distilled into essential oil for aromatherapy and perfumery. The oleoresin essential oils have been characterized for most of the Boswellia genus, with the exceptions of B. microphylla Chivo., B. ogadensis Vollesen, and B. globosa Thulin [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21].

Despite being one of the most wide-ranging species, the oleoresin essential oil of Boswellia dalzielii has only recently been examined [21]. Boswellia dalzielii (see Figure 1) inhabits wooded to open savannahs from Chad to Mali; the most significant populations appear to be in Burkina Faso, Nigeria, and Mali. The trees are 4–13 m tall, typically with papery or scaly bark, fragrant white flowers, serrated compound leaves, and aromatic resin [22]. Although resin harvesting has only recently increased, the bark is harvested extensively for its use in tinctures to treat malaria, toothaches, sores, and snakebites [23,24,25,26,27,28].

Figure 1.

Figure 1

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Boswellia dalzielii tree in situ (A); Grove of B. dalzielii trees (B); Oleogum resin from self-exuded by a B. dalzielii tree (C).

Although there have been a number of studies on the compounds in the bark, there has been little work on the volatile compounds in this species. Two studies have examined the hydrodistilled leaf essential oils of B. dalzielii; Kohoude et al. found that the oil was dominated by δ-3-carene (27.7%) and α-pinene (15.2%) with smaller amounts of p-cymene (9.5%), β-phellandrene (8.5%), isolongifolene (6.2%), and myrcene (5.7%) [29], while Kubmarawa et al. found oils dominated by α-pinene (45.7%) and α-terpinene (11.5%) [30]. Recent work by DeCarlo et al. provided the first study on B. dalzielii oleoresin essential oil, examining single-tree oleoresin samples from northern Nigeria [21]. They found that the majority of essential oils were dominated by α-pinene (21.7%–76.6%), some with lower levels of α-thujene (2.0%–17.6%) and p-cymene (0.3%–15.6%); a second, much rarer chemotype was rich in myrcene (up to 35.2%), sometimes with a significant level of limonene (up to 32.9%). These samples were found to be rich in monterpenes but almost devoid of sesquiterpenes.

Along with Nigeria, Burkina Faso hosts one of the largest populations of B. dalzielii. The species is widespread across three of the four phytogeographic zones of the country (from 500 to 900 mm annual rainfall range). Populations are gregarious and colonize more often rocky hills and glacis. Mean density of trees in natural stands ranges between 7 and 10 trees per 1000 m2 according to phytogeographic zones in Burkina Faso [31]. The regeneration is very poor due to human disturbances (bushfire, pasture, agriculture) and climate pejoration (drought, rain fluctuations) [32,33].

The prior work on B. dalzielii oleoresin essential oil from Nigeria found multiple chemotypes as well as intrachemotypic compositional variation [21], and several other Boswellia species are known to display multiple chemotypes [1,5,11,19] (unpublished results from our laboratory). Given the extensive geographical range of B. dalzielii, it’s likely that additional chemical diversity is present beyond that captured in the study from Nigeria. Therefore, in this study, we examine the essential oils from oleoresins taken directly from individual trees in Burkina Faso to determine if additional chemical variation is present. Each oleoresin sample was hydrodistilled using the same apparatus (Clevenger) and analyzed by GC-MS and GC-FID by the same operators under the same conditions.

2. Results

Essential oils were obtained by hydrodistillation of the B. dalzielii oleogum resin samples in yields of 1.69%–17.0% (v/w) as pale-yellow essential oils. The chemical compositions of the essential oils are compiled in Table 1. Nineteen of the twenty samples were dominated by α-pinene (26.3%–56.0%), with minor levels of α-copaene (1.8%–5.0%), carvone (2.1%–5.0%), bornyl acetate (1.6%–3.5%), α-cubebene (1.2%–3.4%), myrcene (0.4%–5.5%), α-thujene (0.5%–9.2%), and γ-terpinene (0.8%–2.6%). One sample contained almost equal levels of myrcene (19.2%) and α-pinene (21.0%), with moderate α-thujene (9.8%) and α-copaene (3.8%).

Table 1.

Chemical compositions of Boswellia dalzielii oleogum resin essential oils from Burkina Faso.

RI a RI b Compound Re190227M Re190125O Re190125Q Re190125R Re190125S Re190125T Re190125U Re190125V Re190125W Re190125X
906 906 Santolina triene c 1.2 ± 0.0 d 1.0 ± 0.0 1.0 ± 0.0 1.8 ± 0.0 1.2 ± 0.0 1.5 ± 0.0 1.1 ± 0.0 1.0 ± 0.0 1.0 ± 0.0 1.3 ± 0.0
918 919 5,5-Dimethyl-1-vinylbicyclo [2.1.1] hexane 1.1 ± 0.0 1.1 ± 0.0 0.6 ± 0.0 1.0 ± 0.0 1.1 ± 0.0 1.0 ± 0.0 1.4 ± 0.0 0.9 ± 0.0 0.7 ± 0.0 1.5 ± 0.0
920 921 Tricyclene 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0
923 924 α-Thujene 1.4 ± 0.0 3.1 ± 0.0 9.2 ± 0.0 0.7 ± 0.0 3.0 ± 0.2 5.0 ± 0.1 0.7 ± 0.0 1.1 ± 0.0 0.5 ± 0.0 9.8 ± 0.2
932 932 α-Pinene 39.6 ± 1.5 56.0 ± 0.0 41.3 ± 0.1 34.9 ± 0.6 43.3 ± 2.3 26.3 ± 0.3 44.1 ± 0.6 43.5 ± 0.1 49.7 ± 0.0 21.0 ± 0.4
945 945 α-Fenchene tr e tr tr --- tr tr tr tr tr tr
947 946 Camphene 0.9 ± 0.0 1.1 ± 0.0 0.8 ± 0.0 0.8 ± 0.0 1.3 ± 0.1 1.1 ± 0.0 0.7 ± 0.0 1.0 ± 0.0 0.8 ± 0.0 0.8 ± 0.0
951 953 Thuja-2, 4(10)-diene 0.8 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 1.0 ± 0.0 0.8 ± 0.0 1.0 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.4 ± 0.0 0.8 ± 0.0
953 954 β-Fenchene 0.2 ± 0.0 0.4 ± 0.0 0.1 ± 0.0 0.5 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 tr
970 969 Sabinene 1.3 ± 0.0 1.3 ± 0.0 1.5 ± 0.0 1.1 ± 0.0 1.2 ± 0.0 1.4 ± 0.0 0.9 ± 0.0 0.1 ± 0.0 0.8 ± 0.0 1.9 ± 0.0
975 974 β-Pinene 1.4 ± 0.0 2.0 ± 0.0 1.6 ± 0.0 0.8 ± 0.0 1.5 ± 0.1 1.4 ± 0.0 1.7 ± 0.0 1.3 ± 0.0 1.4 ± 0.0 1.1 ± 0.0
985 984 trans-p-Mentha-2, 8-diene --- --- --- --- --- --- --- --- --- ---
986 988 Myrcene 1.0 ± 0.0 0.9 ± 0.0 0.5 ± 0.0 0.9 ± 0.0 0.8 ± 0.1 1.1 ± 0.0 1.6 ± 0.1 1.0 ± 0.0 0.4 ± 0.0 19.2 ± 0.3
988 989 3, 3, 7-Trimethylcyclohepta-1, 3, 5-triene 0.1 ± 0.0 tr tr 0.2 ± 0.0 --- tr --- 0.1 ± 0.0 tr ---
996 997 (E)-2,6-Dimethyl-2, 6-octadiene --- --- --- --- --- --- --- --- --- ---
998 1001 δ-2-Carene --- --- --- --- --- --- --- --- --- ---
999 995 cis-p-Menth-8-ene 0.7 ± 0.0 0.9 ± 0.0 0.6 ± 0.0 0.8 ± 0.0 0.6 ± 0.0 0.8 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 0.4 ± 0.0
1002 1003 p-Mentha-1(7), 8-diene --- --- --- --- --- --- --- --- --- tr
1003 1002 α-Phellandrene tr 0.1 ± 0.0 tr --- tr tr tr tr 0.1 ± 0.0 ---
1004 1006 1,5,8-p-Menthatriene 0.4 ± 0.0 0.4 ± 0.0 0.4 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.7 ± 0.0
1006 1005 o-Cresol methyl ether tr 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 tr 0.1 ± 0.0 0.1 ± 0.0 --- tr
1006 1008 δ-3-Carene --- 0.2 ± 0.0 tr 0.2 ± 0.0 tr tr tr tr 0.1 ± 0.0 0.1 ± 0.0
1015 1014 α-Terpinene 0.5 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 0.5 ± 0.0
1017 1022 m-Cymene 0.6 ± 0.0 0.9 ± 0.0 0.6 ± 0.0 0.7 ± 0.0 0.7 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.6 ± 0.0 0.3 ± 0.0 0.5 ± 0.0
1021 1021 p-Menth-1-ene --- --- --- --- --- --- --- --- tr tr
1022 1024 p-Cymene 0.5 ± 0.0 1.2 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 1.0 ± 0.0 1.1 ± 0.0 0.3 ± 0.0 1.1 ± 0.0 0.3 ± 0.0 0.4 ± 0.0
1024 1026 2-Acetyl-5-methylfuran 0.1 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 tr 0.1 ± 0.0 tr tr
1027 1024 Limonene 0.2 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 tr 0.1 ± 0.0 0.2 ± 0.0
1028 1025 β-Phellandrene tr 0.1 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 tr tr tr 0.1 ± 0.0 0.1 ± 0.0 0.4 ± 0.0
1029 1026 1,8-Cineole 0.9 ± 0.0 1.8 ± 0.0 1.0 ± 0.0 0.6 ± 0.0 0.9 ± 0.0 0.9 ± 0.0 0.6 ± 0.0 1.0 ± 0.0 0.9 ± 0.0 1.3 ± 0.0
1031 1032 (Z)-β-Ocimene 0.2 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.1 ± 0.0 0.1 ± 0.0
1032 1039 o-Cymene 1.2 ± 0.0 2.0 ± 0.0 1.1 ± 0.0 1.5 ± 0.0 1.1 ± 0.1 1.4 ± 0.0 1.2 ± 0.0 1.1 ± 0.0 1.0 ± 0.0 1.5 ± 0.0
1043 1044 (E)-β-Ocimene 0.1 ± 0.0 0.3 ± 0.0 0.1 ± 0.0 --- 0.1 ± 0.0 tr 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.3 ± 0.0
1055 1054 γ-Terpinene 1.9 ± 0.0 0.8 ± 0.0 2.0 ± 0.0 2.0 ± 0.1 1.9 ± 0.1 2.6 ± 0.0 1.8 ± 0.0 2.0 ± 0.0 1.5 ± 0.0 1.9 ± 0.0
1068 1065 cis-Sabinene hydrate tr tr tr 0.1 tr 0.1 ± 0.0 tr tr tr tr
1083 1086 Terpinolene 1.2 ± 0.0 0.5 ± 0.0 1.1 ± 0.0 1.5 ± 0.0 1.3 ± 0.1 1.3 ± 0.0 1.4 ± 0.0 1.5 ± 0.0 1.0 ± 0.0 1.3 ± 0.0
1088 1089 p-Cymenene 0.1 ± 0.0 --- --- --- --- --- 0.1 ± 0.0 0.1 ± 0.0 --- ---
1088 1090 6,7-Epoxymyrcene --- --- --- --- --- --- --- --- --- tr
1090 1095 6-Camphenone --- --- --- --- --- --- --- --- --- ---
1094 1091 Rosefuran tr --- --- --- --- --- --- tr --- ---
1096 1102 Perillene tr tr --- --- --- --- 0.1 ± 0.0 tr --- tr
1097 1095 Linalool 1.3 ± 0.0 0.6 ± 0.0 1.0 ± 0.0 1.4 ± 0.0 1.2 ± 0.0 1.8 ± 0.0 1.3 ± 0.0 1.0 ± 0.0 1.0 ± 0.0 1.1 ± 0.0
1097 1099 α-Pinene oxide tr 0.2 ± 0.0 0.1 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 ---
1099 1098 trans-Sabinene hydrate --- --- tr 0.1 ± 0.0 --- tr --- tr tr 0.1 ± 0.0
1103 1101 cis-Thujone 1.2 ± 0.0 0.6 ± 0.0 1.2 ± 0.0 1.4 ± 0.0 1.6 ± 0.0 1.8 ± 0.0 1.7 ± 0.0 1.3 ± 0.0 1.2 ± 0.0 1.4 ± 0.0
1110 1112 (E)-2, 4-Dimethylhepta-2, 4-dienal --- --- tr --- --- tr tr --- --- ---
1116 1112 trans-Thujone 0.6 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.7 ± 0.0 0.9 ± 0.0 0.8 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.6 ± 0.0
1117 1119 Myrcenol --- --- --- --- --- --- 0.1 ± 0.0 --- --- tr
1117 1118 exo-Fenchol --- --- --- --- --- --- --- 0.1 ± 0.0 tr ---
1117 1119 trans-p-Mentha-2, 8-dien-1-ol tr --- --- --- --- --- --- --- --- ---
1119 1124 Chrysanthenone 0.2 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.2 ± 0.0
1122 1118 cis-p-Menth-2-en-1-ol --- --- --- --- --- --- --- --- --- tr
1125 1122 α-Campholenal 2.0 ± 0.0 1.1 ± 0.0 1.7 ± 0.0 2.3 ± 0.0 1.9 ± 0.0 2.8 ± 0.1 2.1 ± 0.0 2.2 ± 0.0 1.8 ± 0.0 1.8 ± 0.0
1130 1132 cis-Limonene oxide --- --- --- --- --- --- --- --- --- ---
1135 1137 trans-Limonene oxide --- --- --- --- --- --- --- --- --- ---
1137 1137 trans-Sabinol --- --- tr --- --- 0.1 ± 0.0 --- --- --- ---
1139 1135 trans-Pinocarveol 2.4 ± 0.0 1.3 ± 0.0 1.6 ± 0.0 2.7 ± 0.0 2.0 ± 0.1 2.8 ± 0.0 2.5 ± 0.0 2.3 ± 0.0 1.9 ± 0.0 1.3 ± 0.0
1139 1137 cis-Verbenol 0.6 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 1.2 ± 0.0 0.2 ± 0.0 0.5 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.2 ± 0.0 tr
1143 1140 trans-Verbenol 1.6 ± 0.0 1.4 ± 0.0 0.9 ± 0.0 2.9 ± 0.3 1.6 ± 0.0 2.2 ± 0.0 1.9 ± 0.0 2.8 ± 0.0 1.2 ± 0.0 0.6 ± 0.0
1145 1141 Camphor 0.2 ± 0.0 tr 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.2 ± 0.0
1148 1150 α-Phellandren-8-ol 0.7 ± 0.0 0.2 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 0.7 ± 0.0 0.8 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 0.8 ± 0.0 0.5 ± 0.0
1158 1158 trans-Pinocamphone 0.5 ± 0.0 0.4 ± 0.0 0.6 ± 0.0 0.8 ± 0.0 0.4 ± 0.0 0.8 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.5 ± 0.0
1160 1160 Pinocarvone 0.5 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 0.4 ± 0.0
1167 1168 trans-Phellandrene epoxide --- --- 0.1 ± 0.0 --- --- 0.1 ± 0.0 --- tr tr tr
1169 1166 p-Mentha-1, 5-dien-8-ol 1.5 ± 0.0 0.5 ± 0.0 1.2 ± 0.0 1.3 ± 0.0 0.9 ± 0.0 1.8 ± 0.0 1.1 ± 0.0 1.1 ± 0.038 1.3 ± 0.0 1.0 ± 0.0
1170 1165 Borneol --- --- --- --- --- --- --- --- --- tr
1174 1172 cis-Pinocamphone tr tr tr tr tr 0.1 ± 0.0 tr 0.1 ± 0.0 tr ---
1178 1174 Terpinen-4-ol 0.4 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.2 ± 0.0
1185 1179 p-Cymen-8-ol 0.8 ± 0.0 0.5 ± 0.0 0.8 ± 0.0 0.8 ± 0.0 0.7 ± 0.0 1.4 ± 0.0 0.7 ± 0.0 0.8 ± 0.0 0.9 ± 0.0 0.7 ± 0.0
1192 1186 α-Terpineol 1.2 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 1.1 ± 0.0 0.9 ± 0.0 1.4 ± 0.0 0.9 ± 0.0 1.2 ± 0.0 1.0 ± 0.0 0.9 ± 0.0
1193 1195 Myrtenal 1.8 ± 0.0 1.1 ± 0.0 1.6 ± 0.0 2.1 ± 0.0 1.5 ± 0.0 1.8 ± 0.0 1.6 ± 0.0 1.6 ± 0.0 1.7 ± 0.0 1.1 ± 0.0
1205 1204 Verbenone 2.8 ± 0.0 1.2 ± 0.0 2.0 ± 0.0 3.0 ± 0.0 2.2 ± 0.0 2.9 ± 0.0 2.4 ± 0.0 2.7 ± 0.0 2.5 ± 0.0 2.1 ± 0.0
1216 1215 trans-Carveol 0.1 tr --- --- --- tr tr 0.2 ± 0.0 tr ---
1242 1239 Carvone 5.1 ± 0.1 2.1 ± 0.1 4.3 ± 0.0 4.4 ± 0.2 4.2 ± 0.1 5.4 ± 0.1 4.6 ± 0.1 4.7 ± 0.0 5.0 ± 0.0 4.3 ± 0.1
1246 1254 Linalyl acetate --- --- tr --- --- tr tr tr tr ---
1261 1265 3, 5-Dimethoxytoluene --- tr tr --- --- tr tr tr --- tr
1281 1287 Bornyl acetate 3.4 ± 0.2 1.6 ± 0.0 2.9 ± 0.0 3.5 ± 0.3 2.6 ± 0.1 3.5 ± 0.1 2.6 ± 0.0 3.0 ± 0.0 2.9 ± 0.0 2.6 ± 0.0
1286 1289 Thymol --- --- tr --- --- tr --- --- --- tr
1294 1298 Carvacrol 2.2 ± 0.0 0.9 ± 0.0 1.6 ± 0.0 2.1 ± 0.0 1.7 ± 0.0 1.9 ± 0.0 1.7 ± 0.0 1.8 ± 0.0 1.8 ± 0.0 1.6 ± 0.0
1343 1346 α-Terpinyl acetate 2.1 ± 0.0 0.8 ± 0.0 1.5 ± 0.0 2.1 ± 0.0 1.6 ± 0.0 2.5 ± 0.0 1.7 ± 0.0 1.6 ± 0.0 1.9 ± 0.0 1.6 ± 0.0
1345 1345 α-Cubebene 3.4 ± 0.0 1.2 ± 0.0 2.7 ± 0.0 2.7 ± 0.1 2.6 ± 0.0 2.8 ± 0.0 2.4 ± 0.0 2.5 ± 0.0 2.7 ± 0.0 2.4 ± 0.0
1373 1374 α-Copaene 4.8 ± 0.4 1.8 ± 0.0 3.9 ± 0.0 4.7 ± 0.1 3.8 ± 0.1 5.0 ± 0.1 4.1 ± 0.1 3.6 ± 0.0 4.1 ± 0.0 3.8 ± 0.0
1409 1411 cis-α-Bergamotene --- tr tr --- --- --- tr tr tr tr
1416 1417 β-Caryophyllene --- --- --- --- --- --- tr --- --- tr
1429 1432 trans-α-Bergamotene --- tr tr --- --- --- tr tr 0.2 ± 0.0 tr
1441 1440 (Z)-β-Farnesene --- --- --- --- --- --- --- --- --- tr
1441 1449 α-Himachalene --- --- --- --- --- --- --- --- --- ---
1452 1452 α-Humulene --- --- --- --- --- --- --- --- --- ---
1486 1489 β-Selinene --- --- --- --- --- --- tr --- --- tr
1493 1498 α-Selinene --- --- --- --- --- --- --- --- --- ---
1579 1582 Caryophyllene oxide --- --- --- --- --- --- tr tr --- tr
1942 1944 m-Camphorene 0.1 ± 0.0 0.2 ± 0.0 --- --- 0.1 ± 0.0 --- 0.1 ± 0.0 --- 0.1 ± 0.0 0.2 ± 0.0
1948 1947 (3E)-Cembrene A 0.1 ± 0.0 0.4 ± 0.0 0.1 ± 0.0 0.7 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.4 ± 0.0
1977 1977 p-Camphorene tr tr --- --- tr --- 0.2 ± 0.0 --- --- tr
1993 1992 α-Pinacene --- tr tr --- --- --- tr tr tr tr
2130 2138 Cembrenol 0.1 ± 0.0 0.4 ± 0.0 0.1 ± 0.0 0.5 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.1 ± 0.0 0.2 ± 0.0
2143 2144 Incensole + Serratol 0.4 ± 0.0 0.9 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 0.9 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.8 ± 0.0
Monoterpene hydrocarbons 56.6 76.4 65.1 52.5 62.4 49.6 60.5 59.9 61.5 65.9
Oxygenated monoterpenoids 33.9 17.8 27.0 36.7 29.6 39.8 31.2 33.1 30.5 26.1
Sesquiterpenoids 8.2 3.0 6.7 7.5 6.4 7.7 6.5 6.1 7.0 6.3
Diterpenoids 0.7 1.8 0.7 1.8 0.6 1.3 1.4 0.6 0.6 1.6
Others 0.1 0.1 0.4 0.5 0.3 0.5 0.1 0.2 0.0 0.0
Total Identified 99.6 99.1 99.8 99.0 99.3 99.0 99.8 99.9 99.5 99.9
RI a RI b Compound Re190227G Re190227H Re190227I Re190227K Re190227L Re190227N Re190227O Re190227P Re190416A Re190416B
906 906 Santolina triene c 1.2 ± 0.0 d 1.4 ± 0.0 1.0 ± 0.0 1.2 ± 0.0 1.1 ± 0.0 1.4 ± 0.0 0.9 ± 0.0 1.3 ± 0.0 0.9 ± 0.0 0.9 ± 0.0
918 919 5, 5-Dimethyl-1-vinylbicyclo [2.1.1] hexane 0.8 ± 0.0 0.9 ± 0.0 1.4 ± 0.0 1.3 ± 0.0 0.8 ± 0.0 1.4 ± 0.0 1.2 ± 0.0 0.8 ± 0.0 0.6 ± 0.0 0.6 ± 0.0
920 921 Tricyclene 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0
923 924 α-Thujene 1.4 ± 0.0 2.7 ± 0.0 0.8 ± 0.0 3.4 ± 0.0 0.9 ± 0.0 2.3 ± 0.0 0.5 ± 0.0 2.0 ± 0.0 2.0 ± 0.0 2.1 ± 0.0
932 932 α-Pinene 51.0 ± 0.2 41.8 ± 0.3 44.9 ± 0.4 39.6 ± 0.3 38.2 ± 0.3 47.1 ± 0.5 40.3 ± 0.3 42.0 ± 0.3 55.2 ± 0.4 54.2 ± 0.2
945 945 α-Fenchene tr e tr tr tr tr tr tr tr tr tr
947 946 Camphene 0.8 ± 0.0 1.1 ± 0.0 1.0 ± 0.0 1.0 ± 0.0 0.9 ± 0.0 0.8 ± 0.0 0.8 ± 0.0 0.8 ± 0.0 1.0 ± 0.0 1.1 ± 0.0
951 953 Thuja-2, 4(10)-diene 0.6 ± 0.0 0.9 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.6 ± 0.0 0.4 ± 0.0 0.6 ± 0.0 0.8 ± 0.0 0.7 ± 0.0 0.7 ± 0.0
953 954 β-Fenchene 0.1 ± 0.0 0.1 ± 0.0 0.5 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.5 ± 0.0 0.3 ± 0.0
970 969 Sabinene 0.7 ± 0.0 1.4 ± 0.0 0.8 ± 0.0 1.0 ± 0.0 1.0 ± 0.0 1.3 ± 0.0 1.1 ± 0.0 1.0 ± 0.0 1.1 ± 0.0 1.1 ± 0.0
975 974 β-Pinene 1.6 ± 0.0 2.6 ± 0.0 1.8 ± 0.0 1.5 ± 0.0 1.2 ± 0.0 1.4 ± 0.0 1.4 ± 0.0 1.1 ± 0.0 2.0 ± 0.0 1.9 ± 0.0
985 984 trans-p-Mentha-2, 8-diene --- --- tr --- tr tr --- --- tr tr
986 988 Myrcene 0.6 ± 0.0 0.5 ± 0.0 1.9 ± 0.0 3.7 ± 0.0 0.8 ± 0.0 5.5 ± 0.1 2.7 ± 0.0 0.7 ± 0.0 0.5 ± 0.0 0.7 ± 0.0
988 989 3, 3, 7-Trimethylcyclohepta-1, 3, 5-triene --- 0.1 ± 0.0 tr tr --- --- 0.1 ± 0.0 --- tr tr
996 997 (E)-2, 6-Dimethyl-2, 6-octadiene --- --- tr tr --- --- --- --- 0.1 ± 0.0 tr
998 1001 δ-2-Carene --- --- tr tr --- --- --- --- tr tr
999 995 cis-p-Menth-8-ene 0.5 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.7 ± 0.0 0.7 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 ---
1002 1003 p-Mentha-1(7), 8-diene --- --- --- --- --- --- --- --- --- ---
1003 1002 α-Phellandrene tr tr 0.1 ± 0.0 tr tr 0.2 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0
1004 1006 1,5,8-p-Menthatriene 0.3 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.4 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 --- 0.3 ± 0.0
1006 1005 o-Cresol methyl ether 0.1 ± 0.0 tr 0.1 ± 0.0 tr 0.1 ± 0.0 tr 0.3 ± 0.0 0.1 ± 0.0 --- 0.1 ± 0.0
1006 1008 δ-3-Carene tr tr 0.1 ± 0.0 tr tr tr tr tr tr 0.1 ± 0.0
1015 1014 α-Terpinene 0.3 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.4 ± 0.0
1017 1022 m-Cymene 0.5 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 0.6 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.4 ± 0.0
1021 1021 p-Menth-1-ene --- --- --- --- --- --- 0.1 ± 0.0 --- 0.6 ± 0.0 0.6 ± 0.0
1022 1024 p-Cymene 0.5 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 0.6 ± 0.0 0.4 ± 0.0 0.8 ± 0.0 0.4 ± 0.0 0.5 ± 0.0 0.5 ± 0.0
1024 1026 2-Acetyl-5-methylfuran --- 0.2 ± 0.0 tr 0.1 ± 0.0 --- tr tr --- 0.1 ± 0.0 tr
1027 1024 Limonene tr 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.1 ± 0.0
1028 1025 β-Phellandrene 0.4 ± 0.0 --- 0.1 ± 0.0 tr 0.1 ± 0.0 0.2 ± 0.0 tr 0.3 ± 0.0 tr tr
1029 1026 1,8-Cineole 1.3 ± 0.0 3. ± 0.0 2.1 ± 0.0 4.6 ± 0.1 5.1 ± 0.0 1.3 ± 0.0 1.2 ± 0.0 6.1 ± 0.1 1.4 ± 0.0 1.3 ± 0.0
1031 1032 (Z)-β-Ocimene 0.1 ± 0.0 0.3 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.5 ± 0.0 0.1 ± 0.0
1032 1039 o-Cymene 1.3 ± 0.0 1.2 ± 0.0 1.4 ± 0.0 1.2 ± 0.0 1.3 ± 0.0 1.4 ± 0.0 1.4 ± 0.0 1.0 ± 0.0 0.7 ± 0.0 1.1 ± 0.0
1043 1044 (E)-β-Ocimene 0.1 ± 0.0 tr 0.6 ± 0.0 0.2 0.5 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.5 ± 0.0 0.2 ± 0.0 0.2 ± 0.0
1055 1054 γ-Terpinene 1.5 ± 0.0 1.8 ± 0.0 1.8 ± 0.0 2.0 ± 0.0 2.0 ± 0.0 1.5 ± 0.0 2.4 ± 0.0 1.9 ± 0.0 1.5 ± 0.0 1.4 ± 0.0
1068 1065 cis-Sabinene hydrate --- tr tr tr --- --- tr tr tr tr
1083 1086 Terpinolene 1.1 ± 0.0 1.0 ± 0.0 1.3 ± 0.0 1.3 ± 0.0 1.2 ± 0.0 1.0 ± 0.0 1.5 ± 0.0 0.9 ± 0.0 1.0 ± 0.0 1.1 ± 0.0
1088 1089 p-Cymenene --- --- --- --- --- --- --- --- --- ---
1088 1090 6,7-Epoxymyrcene tr --- --- --- --- --- --- tr --- ---
1090 1095 6-Camphenone --- --- --- --- --- --- --- --- 0.1 ± 0.0 0.1 ± 0.0
1094 1091 Rosefuran --- --- --- --- --- --- --- --- --- ---
1096 1102 Perillene 0.1 ± 0.0 --- --- --- 0.1 ± 0.0 0.1 ± 0.0 tr tr --- ---
1097 1095 Linalool 0.8 ± 0.0 1.3 ± 0.0 0.9 ± 0.0 1.1 ± 0.0 1.4 ± 0.0 0.9 ± 0.0 1.1 ± 0.0 1.2 ± 0.0 tr ---
1097 1099 α-Pinene oxide --- tr tr --- 0.1 ± 0.0 --- tr --- --- 0.1 ± 0.0
1099 1098 trans-Sabinene hydrate --- tr --- --- --- --- --- tr 0.6 ± 0.0 0.6 ± 0.0
1103 1101 cis-Thujone 1.3 ± 0.0 1.2 ± 0.0 1.3 ± 0.0 ± 0.0 1.3 ± 0.0 1.3 ± 0.0 1.2 ± 0.0 1.6 ± 0.0 0.9 ± 0.0 --- ---
1110 1112 (E)-2, 4-Dimethylhepta-2, 4-dienal --- tr --- --- --- --- --- --- tr ---
1116 1112 trans-Thujone 0.4 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 0.6 ± 0.0 0.7 ± 0.0 0.5 ± 0.0 1.0 ± 0.0 0.4 ± 0.0 0.4 ± 0.0 0.5 ± 0.0
1117 1119 Myrcenol --- --- --- --- --- --- --- --- --- ---
1117 1118 exo-Fenchol --- --- --- --- --- --- --- --- --- ---
1117 1119 trans-p-Mentha-2, 8-dien-1-ol --- --- --- --- --- --- --- --- --- ---
1119 1124 Chrysanthenone 0.2 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0
1122 1118 cis-p-Menth-2-en-1-ol --- --- --- --- --- --- --- --- --- ---
1125 1122 α-Campholenal 1.6 ± 0.0 1.7 ± 0.0 1.4 ± 0.0 1.6 ± 0.0 2.1 ± 0.0 1.4 ± 0.0 1.8 ± 0.0 1.7 ± 0.0 1.5 ± 0.0 1.5 ± 0.0
1130 1132 cis-Limonene oxide --- 0.1 ± 0.0 --- tr tr tr 0.1 ± 0.0 --- tr tr
1135 1137 trans-Limonene oxide --- 0.2 ± 0.0 tr tr tr tr 0.1 ± 0.0 --- --- ---
1137 1137 trans-Sabinol --- --- --- --- --- --- --- --- --- ---
1139 1135 trans-Pinocarveol 1.4 ± 0.0 2.1 ± 0.0 1.7 ± 0.0 1.7 ± 0.0 1.3 ± 0.0 1.5 ± 0.0 1.9 ± 0.0 2.5 ± 0.0 2.0 ± 0.0 1.6 ± 0.0
1139 1137 cis-Verbenol tr 0.7 ± 0.0 tr 0.3 ± 0.0 tr tr 0.6 ± 0.0 0.1 ± 0.0 0.4 ± 0.0 0.2 ± 0.0
1143 1140 trans-Verbenol 0.7 ± 0.0 1.3 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 1.7 ± 0.0 0.8 ± 0.0 0.7 ± 0.0 2.0 ± 0.0 2.0 ± 0.1 1.3 ± 0.0
1145 1141 Camphor 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.1 ± 0.0
1148 1150 α-Phellandren-8-ol 0.5 ± 0.0 0.7 ± 0.0 0.5 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 0.5 ± 0.0 0.7 ± 0.0 0.7 ± 0.0 0.5 ± 0.0 0.5 ± 0.0
1158 1158 trans-Pinocamphone 0.4 ± 0.0 0.5 ± 0.0 0.6 ± 0.0 0.8 ± 0.0 0.6 ± 0.0 0.4 ± 0.0 0.7 ± 0.0 0.6 ± 0.0 0.5 ± 0.0 0.5 ± 0.0
1160 1160 Pinocarvone 0.3 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 0.5 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.2 ± 0.0
1167 1168 trans-Phellandrene epoxide --- tr tr tr --- --- --- --- tr tr
1169 1166 p-Mentha-1,5-dien-8-ol 1.1 ± 0.0 1.3 ± 0.0 1.0 ± 0.0 1.1 ± 0.0 1.4 ± 0.0 1.1 ± 0.0 1.3 ± 0.0 1.4 ± 0.0 1.0 ± 0.0 0.9 ± 0.0
1170 1165 Borneol --- --- --- --- --- --- --- tr --- ---
1174 1172 cis-Pinocamphone tr tr tr tr tr tr tr tr tr tr
1178 1174 Terpinen-4-ol 0.4 ± 0.0 0.4 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.3 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.3 ± 0.0 0.2 ± 0.0
1185 1179 p-Cymen-8-ol 0.5 ± 0.0 0.8 ± 0.0 0.7 ± 0.0 0.7 ± 0.0 0.9 ± 0.0 0.6 ± 0.0 1.0 ± 0.0 0.8 ± 0.0 0.6 ± 0.0 0.6 ± 0.0
1192 1186 α-Terpineol 0.7 ± 0.0 0.8 ± 0.0 0.9 ± 0.0 1.1 ± 0.0 1.0 ± 0.0 0.8 ± 0.0 1.0 ± 0.0 1.0 ± 0.0 0.7 ± 0.0 0.6 ± 0.0
1193 1195 Myrtenal 1.2 ± 0.0 1.5 ± 0.0 1.2 ± 0.0 1.2 ± 0.0 1.7 ± 0.0 1.2 ± 0.0 1.5 ± 0.0 1.7 ± 0.0 1.3 ± 0.0 1.2 ± 0.0
1205 1204 Verbenone 1.9 ± 0.0 2.3 ± 0.0 2.2 ± 0.0 2.0 ± 0.0 2.7 ± 0.0 1.7 ± 0.0 2.6 ± 0.0 2.2 ± 0.0 1.8 ± 0.0 1.8 ± 0.0
1216 1215 trans-Carveol --- 0.3 ± 0.0 tr 0.1 --- --- 0.2 ± 0.0 --- 0.2 ± 0.0 0.1 ± 0.0
1242 1239 Carvone 4.2 ± 0.1 4.2 ± 0.0 4.3 ± 0.1 4.4 ± 0.1 3.3 ± 0.0 3.6 ± 0.0 5.1 ± 0.1 4.4 ± 0.0 3.7 ± 0.1 3.4 ± 0.3
1246 1254 Linalyl acetate --- --- --- --- --- --- --- --- --- ---
1261 1265 3,5-Dimethoxytoluene tr --- --- --- --- --- --- --- --- ---
1281 1287 Bornyl acetate 2.4 ± 0.0 2.8 ± 0.0 2.7 ± 0.0 2.6 ± 0.0 3.0 ± 0.0 2.4 ± 0.0 3.1 ± 0.0 2.4 ± 0.0 2.3 ± 0.0 2.4 ± 0.0
1286 1289 Thymol --- tr --- --- --- --- --- --- --- ---
1294 1298 Carvacrol 1.7 ± 0.0 1.7 ± 0.0 1.9 ± 0.0 1.6 ± 0.0 1.9 ± 0.0 1.3 ± 0.0 2.0 ± 0.0 1.9 ± 0.0 --- ---
1343 1346 α-Terpinyl acetate 1.9 ± 0.0 1.6 ± 0.0 1.8 ± 0.0 1.6 ± 0.0 1.4 ± 0.0 1.4 ± 0.0 2.0 ± 0.0 1.7 ± 0.0 1.3 ± 0.0 1.5 ± 0.0
1345 1345 α-Cubebene 2.6 ± 0.0 2.2 ± 0.0 2.5 ± 0.0 2.4 ± 0.0 2.9 ± 0.0 2.2 ± 0.0 2.9 ± 0.0 2.5 ± 0.0 2.1 ± 0.0 2.0 ± 0.0
1373 1374 α-Copaene 3.8 ± 0.0 3.5 ± 0.0 3.7 ± 0.1 3.6 ± 0.1 2.9 ± 0.0 3.2 ± 0.0 4.1 ± 0.0 3.7 ± 0.0 2.5 ± 0.0 3.5 ± 0.1
1409 1411 cis-α-Bergamotene tr tr tr tr 0.2 ± 0.0 tr tr tr tr 0.1 ± 0.0
1416 1417 β-Caryophyllene tr tr tr tr tr tr tr tr --- tr
1429 1432 trans-α-Bergamotene tr tr tr tr 0.2 ± 0.0 tr tr tr tr 0.1 ± 0.0
1441 1440 (Z)-β-Farnesene --- --- --- --- --- --- --- --- --- ---
1441 1449 α-Himachalene --- --- --- --- tr tr --- --- --- ---
1452 1452 α-Humulene tr --- --- --- tr --- --- --- --- ---
1486 1489 β-Selinene tr --- --- tr tr --- --- --- --- ---
1493 1498 α-Selinene tr --- --- --- tr --- --- --- --- ---
1579 1582 Caryophyllene oxide tr tr --- --- tr tr tr tr --- ---
1942 1944 m-Camphorene 0.3 ± 0.0 --- 1.8 ± 0.0 0.8 ± 0.0 1.8 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 tr --- ---
1948 1947 (3E)-Cembrene A 0.7 ± 0.0 0.2 ± 0.0 0.5 ± 0.0 0.1 ± 0.0 0.9 ± 0.0 0.4 ± 0.0 0.2 ± 0.0 0.4 ± 0.0 0.1 ± 0.0 0.2 ± 0.0
1977 1977 p-Camphorene 0.1 ± 0.0 --- --- --- 2.1 ± 0.0 0.6 ± 0.0 tr tr --- ---
1993 1992 α-Pinacene tr tr tr --- 0.1 ± 0.0 tr tr tr --- 0.1 ± 0.0
2130 2138 Cembrenol 0.4 ± 0.0 0.1 ± 0.0 0.8 ± 0.0 tr 0.5 ± 0.0 0.2 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 0.6 ± 0.0
2143 2144 Incensole + Serratol 0.7 ± 0.0 0.6 ± 0.0 0.6 ± 0.0 0.3 ± 0.0 0.2 ± 0.0 0.1 ± 0.0 0.3 ± 0.0 0.5 ± 0.0 0.3 ± 0.0 1.0 ± 0.0
Monoterpene hydrocarbons 65.7 60.1 62.7 61.5 53.8 69.2 58.5 57.9 70.9 70.0
Oxygenated monoterpenoids 25.1 32.5 27.1 30.5 33.8 23.5 33.0 34.6 23.0 21.4
Sesquiterpenoids 6.4 5.7 6.2 5.9 6.1 5.4 7.0 6.1 4.6 5.7
Diterpenoids 2.3 0.9 3.7 1.1 5.6 1.6 0.9 1.0 0.6 1.9
Others 0.1 0.2 0.1 0.1 0.1 0.0 0.4 0.1 0.1 0.1
Total Identified 99.6 99.4 99.8 99.1 99.4 99.6 99.8 99.7 99.2 99.0
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a RI: Retention Index determined in reference to a homologous series of n-alkanes on a ZB-5ms column. b RI: Retention Index from the databases. c Entries in boldface were used in the cluster analysis. d Percentages are average of three runs (±standard deviations). e tr = “trace” (<0.05%).

A hierarchical cluster analysis of the essential oil compositions revealed two major groups (Figure 2): One dominated by high α-pinene, and one rich in myrcene. Although unusual, the myrcene sample is only moderately dissimilar to the predominant α-pinene samples; we therefore conclude that there is a single, α-pinene dominant chemotype with a rare subchemotype rich in myrcene. The chemical compositions do not appear to correlate with the geographical locations from which they were taken, either within central Burkina Faso or between central and western Burkina Faso.

Figure 2.

Figure 2

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Dendrogram obtained from the agglomerative hierarchical cluster analysis of 20 Boswellia dalzielii oleogum resin essential oil compositions from Burkina Faso.

3. Discussion

The oleogum resin essential oil of Boswellia dalzielii has only been described once previously, to our knowledge, in oleoresins taken from trees in northern Nigeria [21]. Our results are largely consistent with the findings of that study: In both areas, the essential oils are most commonly dominated by α-pinene, with a small number of samples showing high levels of myrcene. Levels of α-pinene were generally higher in Nigeria (42.6%–72.1%) compared to Burkina Faso (21.0%–56.0%) and α-thujene and p-cymene were less prevalent in this study. Additionally, in contrast to the samples from Nigeria, the samples from this study were found to contain an appreciable percentage of sesquiterpenes, particularly α-copaene.

The leaf essential oils of B. dalzielii have also been observed to contain a significant proportion of α-pinene, although other major components in those oils such as δ-3-carene, α-terpinene, and p-cymene were only observed in minor quantities in the oleoresin essential oils [29,30]. Boswellia dalzielii is rich in monoterpenes, particularly α-pinene, similar to many Boswellia species; Boswellia sacra and Boswellia carteri oleoresin essential oils are most commonly dominated by α-pinene, as well as lesser amounts of α-thujene, limonene, myrcene, sabinene, and p-cymene [11,13,18,34,35,36]. Many B. frereana essential oils are similarly dominated by α-pinene, with lower levels of sabinene and p-cymene [7,13,19]. A second chemotype of B. frereana is dominated by α-thujene, as are the oleoresins of B. serrata from India and B. ameero, B. dioscoridis, B. elongata, B. nana, and B. popoviana from Socotra Island, Yemen [12,17,37,38] (unpublished results from our laboratory). By contrast, several Boswellia species have completely different chemical profiles: B. papyrifera essential oils are dominated by octyl acetate and to a lesser degree octanol [8,13,39]; B. occulta oils have methoxyalkanes as the major components [11,40,41]; and B. bullata produces an unusual mix of δ-cadinene, β-caryophyllene, (E)-β-farnesene, α-cadinol, and several unidentified components [37]. The Boswellia dalzielii oleoresin essential oils are therefore fairly similar to those of several commonly traded commercial species (B. frereana, B. sacra, B. carteri).

Further work will be necessary to determine if the essential oils from Burkina Faso versus Nigerian B. dalzielii oleoresins show differential biological activities. In general, the reason for the diversity of terpenes and especially the importance of minor constituents is not clear [42]. The differential profiles likely convey some ecological benefits, though, as even essential oils from the same species, showing only modest chemical differences, do vary significantly in the degree to which they inhibit different strains of microbial pathogens [34]. This may indicate that the variation is related to variation in pathogenic threats.

The myrcene-dominated resins are intriguing as they represent only a small number of samples and differ greatly from the dominant α-pinene chemotype in both Nigeria and Burkina Faso. Environmental conditions can influence the chemical composition of plant volatiles [43,44,45]; although there was no geographic pattern observed here with regard to chemical variation, the myrcene chemotype samples taken in Nigeria were from the same geographic location. However, biotic factors also play a role: in a study of the heartwood essential oil of Santalum insulare in the Marquesas Islands, different chemotypes were observed in trees only a few meters apart, implying differences based on genetics or possibly pathogen attack history [46]; our laboratory has also observed different oleoresin chemical compositions in Boswellia carteri trees only a few meters apart in Somaliland (unpublished results from our laboratory). Further work is thus necessary to elucidate the reasons for the observed chemotypic differences in B. dalzielii.

4. Materials and Methods

4.1. Collection of Oleogum Resins

Twenty Boswellia dalzielii oleoresin samples were collected directly from source trees in six locations across central and western Burkina Faso (Figure 3). Samples were collected during the dry season (February–March 2019), and each sample location was GPS tagged (Table 2). All samples were taken from fresh resin exuding either naturally from tree branches or from wounds left by recent bark harvesting; consequently, age differences in the resin were not enough to significantly alter the resins′ chemical compositions. The trees were identified in the field by Anjanette DeCarlo and Stephen Johnson. A voucher specimen (Voucher number OUA6892) was deposited at the University of Ouagadougou herbarium and the identification confirmed by Amadé Ouédraogo, a botanist working there.

Figure 3.

Figure 3

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Locations where B. dalzielii oleogum resin samples were collected.

Table 2.

Geographical collection locations of Boswellia dalzielii oleogum resins.

Sample Code GPS Coordinates Elevation, m
Re190227M 12°21′13.92″ N 3°16′57.72″ W 290
Re190125O 12°41′43.74″ N 1°10′48.18″ W 291
Re190125P 12°41′43.74″ N 1°10′48.18″ W 291
Re190125Q 12°41′43.74″ N 1°10′48.18″ W 291
Re190125R 12°41′43.74″ N 1°10′48.18″ W 291
Re190125S 12°41′43.74″ N 1°10′48.18″ W 291
Re190125T 12°29′36.54″ N 1°15′40.20″ W 321
Re190125U 12°29′36.54″ N 1°15′40.20″ W 321
Re190125V 12°29′36.54″ N 1°15′40.20″ W 321
Re190125W 12°21′28.98″ N 1°3′15.60″ W 284
Re190125X 12°20′5.58″ N 0°59′10.14″ W 318
Re190227G 12°21′13.92″ N 3°16′57.72″ W 290
Re190227H 12°21′13.92″ N 3°16′57.72″ W 290
Re190227I 12°21′13.92″ N 3°16′57.72″ W 290
Re190227K 12°21′13.92″ N 3°16′57.72″ W 290
Re190227L 12°21′13.92″ N 3°16′57.72″ W 290
Re190227N 12°21′13.92″ N 3°16′57.72″ W 290
Re190227P 12°21′13.92″ N 3°16′57.72″ W 290
Re190416A 12°46′53.88″ N 1°19′20.16″ W 348
Re190416B 12°45′56.70″ N 1°54′19.56″ W 372
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4.2. Hydrodistillation of Oleogum Resins

Hydrodistillations of the Boswellia dalzielii oleoresin samples were carried out in an all-glass Clevenger-type apparatus as previously described [21].

4.3. Gas-Chromatographic-Mass Spectral Analysis

Each of the B. dalzielii oleogum resin essential oils was analyzed by GC-MS as previously described [21]: Shimadzu GCMS-QP2010 Ultra (Shimadzu Scientific Instruments, Columbia, MD, USA), ZB-5ms capillary column (Phenomenex, Torrance, CA, USA). Identification of the essential oil components was based on their retention indices determined by reference to a homologous series of n-alkanes, and by comparison of their mass spectral fragmentation patterns with those reported in the literature [47], and our in-house library.

4.4. Gas Chromatographic-Flame Ionization Detection

Analysis of the B. dalzielii oleogum resin essential oils by GC-FID was carried out as previously described [21]: Shimadzu GC 2010 with flame ionization detector (Shimadzu Scientific Instruments, Columbia, MD, USA), ZB-5 capillary column (Phenomenex, Torrance, CA, USA). The percent compositions listed in Table 1 are averages from three separate runs of the essential oils were determined from peak areas and corrected using response factors for the different classes of chemical components [48].

4.5. Hierarchical Cluster Analysis

The chemical compositions of the B. dalzielii oleoresin essential oils were used in the hierarchical cluster analysis. The 20 essential oil compositions were treated as operational taxonomic units (OTUs), and the concentrations (percentages) of 23 major components were used to determine the chemical associations between these frankincense essential oils using agglomerative hierarchical cluster (AHC) analysis using XLSTAT Premium, version 2018.5.53172 (Addinsoft, Paris, France). Dissimilarity was determined using Euclidean distance, and clustering was defined using Ward’s method.

5. Conclusions

Boswellia dalzielii oleoresin essential oils from Burkina Faso are similar to those from Nigeria in that they are generally dominated by α-pinene, but unlike the samples from Nigeria, those in the current study contained a significant percentage of sesquiterpenes. The reason for these differences is not clear, but it potentially points to different biological and ecological activity due to different pathogenic threats. A rare chemotype or subchemotype dominated by myrcene was observed both in this study and in samples from Nigeria; this is potentially also related to specific pathogenic threats that may exist in both locations, or possibly genetic factors. This species thus offers a promising option for future work to elucidate the drivers of intraspecific chemical variation.

Acknowledgments

This work was carried out as part of the activities of the Aromatic Plant Research Center (APRC, https://aromaticplant.org/). We are grateful to Roland Traore, Denis Dipama, and Zongo Daouda, who helped collect samples.

Author Contributions

Conceptualization, A.D. and S.J.; methodology, A.D. and S.J.; validation, A.D., S.J. and W.N.S.; formal analysis, N.S.D. and W.N.S.; investigation, A.D., S.J., A.O., N.S.D., and W.N.S.; resources, A.D.; data curation, W.N.S.; writing—original draft preparation, S.J., A.O., and W.N.S.; writing—review and editing, A.D., S.J., A.O., N.S.D., and W.N.S.; supervision, A.D.; project administration, A.D.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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