Sage Journals: Discover world-class research

Abstract

The Burseraceae is an important family of resin-producing trees and shrubs, which have yielded biologically active essential oils. Boswellia dalzielii and Canarium schweinfurthii are members of the family that are used in West African traditional medicine for a variety of ailments. The leaf essential oils of B. dalzielii have been obtained from 2 different locations in north-central Nigeria, while the leaf and stem bark essential oils of C. schweinfurthii have been obtained from 3 locations. The chemical compositions of the essential oils have been determined by gas chromatography-mass spectrometry and show wide variation, especially for the leaf essential oils. The leaf essential oils of B. dalzielii and C. schweinfurthii have been screened for antibacterial and antifungal activity; C. schweinfurthii leaf essential oil showed remarkable activity against Aspergillus niger with a minimum inhibitory concentration of 78.1 μg/mL.

Keywords

essential oil chemical composition α-pinene β-pinene limonene α-terpineol germacrene B juniper camphor incensole

The Burseraceae is composed of 18 genera and around 640 species of mainly tropical trees and shrubs.¹ Historically and commercially important members of the family include frankincense (Boswellia spp.) and myrrh (Commiphora myrrha).² Several genera, especially Boswellia, Bursera, Canarium, Commiphora, Dacryodes, and Protium, have yielded biologically active essential oils.³

The genus Boswellia ranges across Africa, the Arabian Peninsula, and India, and is the source of the aromatic oleo-gum resin frankincense. The West African species, Boswellia dalzielii Hutch, ranges from western Chad, through Nigeria and Burkina Faso, to Mali.⁴ Bark decoctions of B. dalzielii have been used in traditional medicine to treat various maladies, including malaria, toothaches, sores, abscesses, mental disorders, yellow fever, asthma, wounds, and dysentery,^5

-9 while the leaves have been used to protect stored food from insect pests.^10,11

The leaf essential oil from Adamawa State, Nigeria, yielded an essential oil rich in α-pinene (45.7%) and γ-terpinene (11.5%),¹² while the leaf essential oil from Ségbana region, Benin, had α-pinene (15.2%), myrcene (5.7%), δ-3-carene (27.7%), p-cymene (9.5%), β-phellandrene (8.5%), and isolongifolene (6.2%), as major constituents.¹³ Oleo-gum resin essential oils from Nigeria were found to contain α-pinene (21.7%-76.6%), α-thujene (2.0%-17.6%), myrcene (up to 35.2%), p-cymene (0.3%-15.6%), and limonene (1.1%-32.9%),⁴ while oleo-gum resin essential oils from Burkina Faso were dominated by α-pinene (21.0%-56.0%), followed by carvone (2.1%-5.4%) and α-copaene (1.8%-5.0%).¹⁴ Two chemotypes of B. dalzielii, based on oleo-gum resin essential oil compositions, have been described, 1 dominated by α-pinene and the other with myrcene as the major component.^4,14

Most of the species of Canarium are found in tropical Asia and the Pacific,¹ but 2 species are found in tropical Africa, Canarium madagascariense Engl., found along the eastern coast of Africa and the western and central regions of Madagascar and Canarium schweinfurthii Engl., found in the rainforest belt of central and West Africa.¹⁵ A decoction of the bark of C. schweinfurthii is used traditionally to treat dysentery, gonorrhea, cough, chest pains, pulmonary affections, stomach complaints, and food poisoning; the pounded bark is used to treat leprosy and ulcers; and the oleo-gum resin is taken internally for roundworm infections and other intestinal parasites, and externally for skin infections and eczema.¹⁶ Oleo-gum resin essential oils from Cameroon¹⁷ and Gabon¹⁸ have been dominated by limonene (42.7%-52.1%), while a resin essential oil from Uganda showed γ-terpinene (34.5%), α-phellandrene (17.9%), α-thujene (14.0%), β-phellandrene (12.9%), and p-cymene (8.5%) as the major components.¹⁹

As part of our ongoing exploration of the essential oils of the Burseraceae, we have examined the essential oils of B. dalzielii and C. schweinfurthii growing in the wild in north-central, Nigeria.

Results and Discussion

Essential Oil Compositions

Boswellia dalzielii

Hydrodistillation of leaves of B. dalzielii collected from Zaria, Kaduna State, and Bukuru, Plateau State, Nigeria (Figure 1(A)), yielded essential oils with yields of 1.76% and 1.65%, respectively. The essential oils were analyzed by gas chromatography-mass spectrometry (GC-MS) (Table 1).

Figure 1

Collection sites of Boswellia dalzielii (A) and Canarium schweinfurthii (B).

Table 1

Chemical Compositions of the Leaf Essential Oils of Boswellia dalzielii from Nigeria.

RI_calc ^a	RI_db ^b	Compound	% Composition^c
RI_calc ^a	RI_db ^b	Compound	Bukuru, Nov. 2019	Zaria, Mar. 2019
920	919	5,5-Dimethyl-1-vinylbicyclo[2.1.1]hexane	0.5	-
922	923	Tricyclene	0.1	-
925	927	α-Thujene	0.3	-
932	933	α-Pinene	20.1	4.7
947	948	α-Fenchene	tr^d	-
949	953	Camphene	0.6	0.4
952	953	Thuja-2,4(10)-diene	1.3	0.2
972	972	Sabinene	0.1	0.3
977	978	β-Pinene	0.6	2.9
988	991	Myrcene	0.6	-
990	989	3,7,7-Trimethylcyclohepta-1,3,5-triene	0.2	-
1005	1006	3-Ethenyl-1,2-dimethylcyclohexa-1,4-diene	0.3	-
1006	1007	α-Phellandrene	0.1	0.2
1017	1018	α-Terpinene	0.1	-
1024	1025	p-Cymene	2.6	1.1
1027	1023	p-Menth-1-ene	0.1	-
1029	1030	Limonene	0.3	3.5
1030	1031	β-Phellandrene	0.1	0.2
1031	1030	1,8-Cineole	0.1	0.6
1057	1057	γ-Terpinene	0.1	0.1
1068	1067	cis-Linalool oxide (furanoid)	-	0.1
1083	1082	Terpinolene	-	0.1
1084	1084	trans-Linalool oxide (furanoid)	-	0.2
1089	1093	p-Cymenene	0.8	0.3
1097	1098	Perillene	0.2	-
1097	1101	Linalool	-	1.1
1104	1103	Nonanal	0.1	2.5
1125	1125	α-Campholenal	1.0	0.2
1140	1141	trans-Pinocarveol	0.3	0.5
1146	1149	Camphor	0.1	1.0
1149	1150	α-Phellandren-8-ol	0.2	0.1
1159	1160	trans-Pinocamphone	0.4	0.2
1161	1161	Pinocarvone	0.5	0.5
1170	1170	Borneol	-	0.4
1175	1176	cis-Pinocamphone	0.5	0.9
1180	1180	Terpinen-4-ol	0.2	1.1
1190	1190	Methyl salicylate	-	1.1
1193	1195	α-Terpineol	-	2.3
1194	1197	Myrtenal	0.6	-
1196	1197	cis-Dihydrocarvone	0.2	0.4
1206	1208	Verbenone	0.3	0.1
1217	1219	β-Cyclocitral	-	0.2
1241	1247	Cuminaldehyde	0.1	-
1242	1246	Carvone	0.2	-
1247	1249	Carvotanacetone	0.2	-
1276	1277	Phellandral	0.1	-
1283	1285	Bornyl acetate	0.3	-
1347	1349	α-Cubebene	2.1	-
1376	1375	α-Copaene	3.0	1.0
1384	1382	β-Bourbonene	0.1	0.3
1386	1390	β-Elemene	-	0.3
1387	1392	β-Cubebene	0.3	-
1407	1406	α-Gurjunene	0.1	0.3
1413	1416	cis-α-Bergamotene	0.1	0.4
1416	1417	(E)-Caryophyllene	0.5	5.1
1418	1421	(E)-α-Ionone	-	0.5
1425	1427	γ-Elemene	-	4.1
1427	1427	β-Duprezianene	0.1	-
1433	1432	trans-α-Bergamotene	0.1	0.3
1444	1447	Geranyl acetone	-	0.3
1449	1448	cis-Muurola-3,5-diene	0.1	-
1449	1452	(E)-β-Farnesene	-	0.1
1453	1454	α-Humulene	0.1	0.9
1458	1457	allo-Aromadendrene	0.1	0.3
1472	1472	trans-Cadina-1(6),4-diene	0.3	-
1474	1478	γ-Muurolene	0.1	0.1
1475	1481	(E)-β-Ionone	-	0.5
1480	1480	ar-Curcumene	0.1	1.0
1483	1489	cis-Eudesma-6,11-diene	-	0.6
1486	1494	10,11-Epoxycalamenene	0.1	-
1488	1487	β-Selinene	0.4	0.8
1489	1491	Eremophilene	-	0.2
1491	1490	γ-Amorphene	0.4	-
1492	1492	α-Selinene	0.1	0.8
1495	1497	α-Muurolene	0.4	0.1
1501	1505	α-Bulnesene	0.1	-
1507	1508	β-Bisabolene	0.1	0.2
1512	1512	γ-Cadinene	tr
1518	1518	δ-Cadinene	1.7	0.9
1519	1523	β-Guaiene	-	1.1
1521	1519	trans-Calamenene	1.0	-
1522	1521	Zonarene	0.3	-
1529	-	Unidentified^e	0.7	1.2
1532	1536	trans-Cadina-1,4-diene	0.2	-
1533	1538	γ-Calacorene	0.1	-
1533	1540	Selina-4(15),7(11)-diene	-	7.0
1538	1546	Selina-3,7(11)-diene	-	4.8
1540	1541	α-Calacorene	0.6	-
1555	1557	Germacrene B	-	8.1
1565	1571	iso-Shyobunone	0.7	-
1568	1573	(3E)-Hexenyl benzoate	-	1.3
1581	1587	Caryophyllene oxide	0.9	2.1
1601	1598	Dehydroxyisocalamendiol	0.3	-
1601	1605	Ledol	-	0.3
1606	1607	Humulene epoxide I	0.2	0.3
1609	1614	Tetradecanal	-	0.5
1627	1630	Caryophylla-4(12),8(13)-dien-5α-ol	0.3	-
1628	1628	1-epi-Cubenol	0.3	-
1632	1632	Cedr-8(15)-en-9-one	0.2	-
1640	1645	τ-Muurolol	-	0.2
1642	1643	Cubenol	0.7	-
1645	1644	Selina-3,11-dien-6α-ol	-	0.7
1652	1655	α-Cadinol	-	0.6
1655	1661	neo-Intermedeol	-	1.3
1666	1668	Intermedeol	-	1.8
1672	1681	Mustakone	0.6	-
1672	1677	Cadalene	0.7	-
1685	-	Unidentified^f	-	1.2
1694	1696	Eudesm-7(11)-en-4-ol (=Juniper camphor)	-	8.1
1708	-	Unidentified^g	-	1.6
1711	1715	Pentadecanal	-	1.4
1767	-	Unidentified^h	-	1.5
1794	1793	α-Phellandrene dimer A	0.4	-
1836	1841	Phytone	-	1.5
1953	1960	Neocembrene	3.3	-
1968	1968	Cembrene	0.5	-
1998	1992	α-Pinacene	0.2	-
2016	2022	(E,E)-Geranyl linalool	-	0.5
2104	2106	Phytol	-	2.4
2143	2138	iso-Cembrol	6.8	-
2151	2143	Serratol	6.2	-
2174	2184	Incensole	27.5	-
		Monoterpene hydrocarbons	29.0	13.9
		Oxygenated monoterpenoids	5.6	9.8
		Sesquiterpene hydrocarbons	13.3	38.9
		Sesquiterpenoid derivatives	0.0	1.3
		Oxygenated sesquiterpenoids	4.2	15.4
		Benzenoids	0.0	2.5
		Fatty acid derivatives	0.1	4.4
		Diterpenoids	44.9	4.4
		Total identified	97.1	90.6

MS, mass spectrometry; EI, electrospray ionization.

^aRI_calc = Retention index calculated with respect to a homologous series of n-alkanes on a ZB-5ms column

^bRI_db = Retention index from the databases.^20

-23

^cAverage of 3 measurements; SDs were small and for clarity are not shown.

^dtr = trace (<0.05%).

^eMS (EI): 204 (100%), 189 (99%), 175 (12%), 161 (90%), 147 (36%), 134 (31%), 133 (86%), 119 (62%), 107 (44%), 105 (89%), 95 (41%), 93 (37%), 91 (75%), 81 (40%), 79 (37%),77 (30%), 67 (29%), 55 (40%), 53 (20%), 43 (23%), 41 (60%).

^fMS (EI): 222 (2%), 204 (2%), 162 (2%), 147 (2%), 126 (100%), 111 (22%), 97 (14%), 84 (10%), 81 (8%), 55 (14%), 43 (14%), 41 (14%).

^gMS (EI): 220 (54%), 205 (37%), 202 (41%), 187 (40%), 177 (18%), 173 (18%), 162 (85%), 149 (72%), 147 (56%), 121 (88%), 119 (77%), 107 (80%), 105 (75%), 97 (69%), 93 (85%), 91 (87%), 79 (57%), 67 (73%), 55 (70%), 53 (37%), 43 (98%), 41 (100%).

^hMS(EI): 220 (68%), 205 (6%), 202 (15%), 187 (23%), 177 (73%), 159 (100%), 145 (31%), 135 (66%), 123 (66%), 107 (79%), 105 (73%), 93 (80%), 91 (80%), 81 (67%), 79 (59%), 67 (77%), 55 (63%), 53 (38%), 43 (64%), 41 (89%).

The 2 leaf essential oils of Nigerian B. dalzielii show significant quantitative differences. The sample from Zaria, Kaduna State, which was collected during the dry season, had low concentrations of monoterpene hydrocarbons (13.9%), but relatively large concentrations of sesquiterpene hydrocarbons (38.9%) and oxygenated sesquiterpenoids (15.4%). The major components in the Zaria sample were germacrene B (8.1%), juniper camphor (8.1%), selina-4(15),7(11)-diene (7.0%), and (E)-caryophyllene (5.1%). The concentration of α-pinene was low, only 4.7%. In contrast, the leaf essential oil from Bukuru, Plateau State, which was collected during the rainy season, was rich in monoterpene hydrocarbons (20.1% α-pinene) and the diterpenoids incensole (27.5%), iso-cembrol (6.8%), and serratol (6.2%). The leaf essential oil of B. dalzielii from Gombi, Adamawa State, Nigeria, showed α-pinene (45.7%) and γ-terpinene (11.5%) as the major components, with only low concentrations of sesquiterpene hydrocarbons (2.5%) or oxygenated sesquiterpenoids (2.6%); diterpenoids were absent.¹² The major components in the leaf essential oil of B. dalzielii from Ségbana, North Benin, were δ-3-carene (27.7%), α-pinene (15.2%), p-cymene (9.5%), β-phellandrene (8.5%), isolongifolene (6.2%), and myrcene (5.7%).¹³ No diterpenoids were reported in the Benin sample. Thus, the essential oils from the leaves of B. dalzielii show a wide variation in chemical composition. It is difficult, however, to account for these variations at this time. The 4 samples were collected from different geographical locations and at different times of the year, both factors of which may profoundly affect the chemical compositions.

Canarium schweinfurthii

Leaves and stem bark samples were obtained from C. schweinfurthii from Azare, Bauchi State; Bukuru, Plateau State; and Donga, Taraba State, Nigeria (Figure 1B). The leaf essential oils were obtained in 1.35%, 1.42%, and 1.82% yield, respectively, while the bark essential oils were obtained in 1.83%, 1.76%, and 1.85% yield, respectively. The chemical compositions of C. schweinfurthii leaf and bark essential oils are compiled in Tables 2 and 3, respectively.

Table 2

Chemical Compositions of the Leaf Essential Oils of Canarium schwienfurthii from Nigeria.

RI_calc ^a	RI_db ^b	Compound	% Composition (March 2019)^c
RI_calc ^a	RI_db ^b	Compound	Azare	Bukuru	Donga
930	933	α-Pinene	4.1	17.4	4.3
947	953	Camphene	-	0.7	0.2
950	953	Thuja-2,4(10)-diene	-	-	0.3
975	978	β-Pinene	2.9	10.9	2.9
986	991	Myrcene	-	-	0.7
1005	1006	α-Phellandrene	-	0.9	-
1022	1024	p-Cymene	1.2	5.2	0.4
1027	1030	Limonene	7.2	19.3	0.4
1028	1031	β-Phellandrene	-	0.6	0.1
1084	1080	trans-Linalool oxide (furanoid)	0.7	2.9	-
1088	1093	p-Cymenene	-	-	0.2
1096	1098	Perillene	-	-	0.1
1097	1101	Linalool	-	-	1.0
1103	1107	Nonanal	0.7	-	0.8
1117	1119	endo-Fenchol	-	-	0.1
1125	1125	α-Campholenal	-	-	0.1
1139	1141	trans-Pinocarveol	1.6	0.6	0.4
1146	1149	Camphor	-	-	tr^d
1161	1164	Pinocarvone	0.7	-	0.4
1170	1170	Borneol	-	-	0.1
1173	1174	trans-Linalool oxide (pyranoid)	-	0.9	-
1175	1176	cis-Pinocamphone	0.6	-	0.3
1179	1180	Terpinen-4-ol	0.7	-	0.5
1191	1192	Methyl salicylate	3.0	1.4	2.2
1194	1195	α-Terpineol	4.8	2.1	1.8
1197	1198	neo-Dihydrocarveol	-	-	0.2
1206	1208	Verbenone	1.1	-	-
1217	1219	β-Cyclocitral	-	-	0.2
1242	1246	Carvone	-	-	0.1
1262	1259	Dodecanoic acid	-	-	0.2
1276	1277	Phellandral	-	-	0.2
1332	1335	δ-Elemene	-	-	tr
1343	1346	α-Cubebene	-	-	0.1
1349	1357	Eugenol	1.1	-	-
1372	1375	α-Copaene	-	-	0.6
1380	1382	β-Bourbonene	-	-	0.1
1386	1390	β-Elemene	-	-	0.4
1403	1403	α-Gurjunene	-	-	0.3
1409	1416	cis-α-Bergamotene	-	-	0.5
1417	1417	(E)-Caryophyllene	18.7	0.9	14.6
1418	1421	(E)-α-Ionone	0.4	-	0.5
1426	1427	γ-Elemene	-	1.2	7.1
1429	1432	trans-α-Bergamotene	-	-	0.3
1444	1447	Geranyl acetone	-	-	0.3
1452	1454	α-Humulene	3.4	-	2.7
1454	1451	(E)-β-Farnesene	-	-	0.1
1457	1457	allo-Aromadendrene	-	-	0.1
1470	1475	Selina-4,11-diene	-	-	0.2
1471	1466	cis-Muurola-4(14),5-diene	-	-	0.1
1473	-	Unidentified^e	1.0	-	0.4
1475	1481	(E)-β-Ionone	-	-	0.7
1477	1482	ar-Curcumene	-	-	0.4
1477	1480	Germacrene D	-	-	0.5
1483	1489	cis-Eudesma-6,11-diene	-	-	0.4
1486	1487	β-Selinene	0.8	-	1.2
1489	1492	Valencene	-	-	0.2
1493	1494	α-Selinene	1.2	-	1.5
1495	1497	α-Muurolene	-	-	0.1
1504	1500	β-Bisabolene	-	-	0.2
1514	1518	δ-Cadinene	-	-	0.5
1516	1502	trans-β-Guaiene	-	-	0.7
1534	1540	Selina-4(15),7(11)-diene	0.6	4.0	4.7
1539	1546	Selina-3,7(11)-diene	-	2.7	4.0
1556	1557	Germacrene B	0.5	3.2	14.6
1557	1560	(E)-Nerolidol	0.6	-	-
1568	1573	(3Z)-Hexenyl benzoate	-	-	3.2
1579	1587	Caryophyllene oxide	9.1	-	3.3
1607	1607	Humulene epoxide I	2.2	-	0.5
1609	1614	Tetradecanal	-	-	0.4
1635	1636	Caryophylla-4(12),8(13)-dien-5β-ol	0.9	-	-
1641	1645	τ-Muurolol	0.7	-	-
1645	1645	Selina-3,11-dien-6α-ol	-	-	0.5
1652	1650	α-Cadinol	3.6	-	0.6
1655	1658	neo-Intermediol	2.6	1.0	1.0
1666	1668	Intermediol	-	0.8	0.8
1695	1696	Eudesm-7(11)-en-4α-ol (=Juniper camphor)	3.8	16.1	3.5
1708	-	Unidentified^f	0.5	1.1	2.1
1711	1715	Pentadecanal	1.6	-	1.4
1733	1734	14-Hydroxy-α-humulene	3.7	-	-
1768	-	Unidentified^g	-	1.9	2.0
1836	1841	Phytone	2.0	-	0.5
2017	2018	(E,E)-Geranyl linalool	2.6	1.6	0.7
2104	2106	Phytol	6.3	2.7	0.6
		Monoterpene hydrocarbons	15.5	54.9	9.5
		Oxygenated monoterpenoids	10.2	6.5	5.5
		Sesquiterpene hydrocarbons	25.1	12.0	56.1
		Sesquiterpenoid derivatives	0.4	0.0	1.5
		Oxygenated sesquiterpenoids	27.0	17.9	10.1
		Benzenoids	4.1	1.4	5.4
		Fatty acid derivatives	2.3	0.0	2.8
		Diterpenoids	10.9	4.3	1.8
		Total Identified	95.5	97.0	92.9

MS, mass spectrometry; EI, electrospray ionization.

^aRI_calc = Retention index calculated with respect to a homologous series of n-alkanes on a ZB-5ms column.

^bRI_db = Retention index from the databases.^20

-23

^cAverage of 3 measurements; SDs were small and for clarity are not shown.

^dtr = trace (<0.05%).

^eMS (EI): 140 (12%), 126 (100%), 111 (8%), 98 (37%), 95 (20%), 81 (20%), 70 (24%), 67 (26%), 55 (28%), 53 (17%), 43 (51%), 41 (42%).

^fMS (EI): 220 (44%), 205 (25%), 202 (31%), 187 (30%), 162 (77%), 149 (56%), 147 (50%), 135 (29%), 121 (71%), 119 (75%), 107 (68%), 105 (66%), 97 (53%), 93 (67%), 91 (71%), 79 (49%), 67 (63%), 55 (59%), 53 (28%), 41 (100%), 41 (83%).

^gMS (EI): 220 (71%), 205 (7%), 202 (10%), 187 (18%), 177 (79%), 159 (100%), 145 (27%), 135 (62%), 123 (66%), 107 (78%), 105 (66%), 93 (76%), 91 (76%), 81 (63%), 67 (73%), 55 (68%), 43 (70%), 41 (95%).

Table 3

Chemical Compositions of the Stem Bark Essential Oils of Canarium schwienfurthii from Nigeria.

RI_calc ^a	RI_db ^b	Compound	% Composition (March 2019)^c
RI_calc ^a	RI_db ^b	Compound	Azare	Bukuru	Donga
930	933	α-Pinene	1.3	1.7	2.9
947	953	Camphene	0.1	0.1	-
975	978	β-Pinene	1.2	1.7	2.8
1005	1006	α-Phellandrene	0.1	0.3	0.5
1022	1025	p-Cymene	1.0	2.8	4.3
1027	1030	Limonene	18.3	5.7	3.4
1028	1031	β-Phellandrene	0.2	0.4	0.7
1030	1032	1,8-Cineole	0.6	0.9	0.7
1056	1056	γ-Terpinene	0.1	0.1	-
1068	1069	cis-Linalool oxide (furanoid)	0.5	0.5	0.4
1083	1086	Terpinolene	0.1	0.2	-
1084	1086	trans-Linalool oxide (furanoid)	0.2	0.2	0.3
1087	1091	Fenchone	0.1	0.1	-
1088	1093	p-Cymenene	0.3	0.3	-
1098	1101	Linalool	0.9	0.2	-
1103	1104	Nonanal	0.1	0.1	-
1117	1119	endo-Fenchol	0.5	0.9	0.7
1120	1120	trans-p-Mentha-2,8-dien-1-ol	0.8	0.2	-
1122	1124	cis-p-Menth-2-en-1-ol	0.1	0.2	0.3
1125	1125	α-Campholenal	0.4	0.3	0.2
1129	1131	Terpin-3-en-1-ol	-	0.1	-
1135	1137	cis-p-Mentha-2,8-dien-1-ol	0.7	0.2	-
1137	1139	Nopinone	0.2	0.3	0.4
1139	1141	trans-Pinocarveol	2.6	2.7	3.8
1141	1139	trans-p-Menth-2-en-1-ol	-	0.2	-
1144	1145	trans-Verbenol	0.4	0.1	-
1146	1149	Camphor	0.2	0.4	-
1147	1149	cis-β-Terpineol	0.5	0.5	0.5
1149	1150	α-Phelandren-8-ol	0.6	0.4	0.5
1153	1156	Camphene hydrate	0.2	0.3	0.3
1158	1163	(2E)-Nonenal	0.2	0.2	-
1159	1161	trans-Pinocamphone	0.2	0.3	0.5
1161	1164	Pinocarvone	0.9	1.0	1.5
1166	1169	trans-β-Terpineol	0.1	0.1	-
1169	1171	p-Mentha-1,5-dien-8-ol	1.3	0.3	0.3
1170	1173	Borneol	0.7	3.2	3.3
1174	1176	cis-Pinocamphone	0.3	0.6	0.9
1177	1179	2-Isopropenyl-5-methyl-4-hexenal	0.6	0.2	-
1179	1180	Terpinen-4-ol	3.6	8.6	8.1
1183	1188	p-Methylacetophenone	0.2	0.2	-
1185	1186	p-Cymen-8-ol	2.0	2.9	5.4
1194	1195	α-Terpineol	24.1	38.1	28.2
1197	1197	cis-Dihydrocarvone	1.6	0.7	-
1198	1198	cis-Isopiperitenol	1.5	0.5	-
1201	1202	cis-Sabinol	0.6	1.4	2.9
1203	1204	trans-Dihydrocarvone	0.5	0.2	-
1205	1208	Verbenone	1.3	1.2	1.6
1217	1223	trans-Carveol	5.2	1.6	0.7
1227	1228	cis-p-Mentha-1(7),8-dien-2-ol	0.2	0.1	-
1230	1232	cis-Carveol	2.0	0.7	-
1236	1239	Carvacryl methyl ether	-	0.1	-
1238	-	Unidentified^d	-	0.6	1.6
1241	1241	Cuminal	-	0.4	1.0
1242	1246	Carvone	4.5	1.3	0.5
1248	1249	Carvotanacetone	-	0.5	1.0
1252	1254	Piperitone	0.1	0.4	0.7
1260	1267	iso-Myrtanol	-	0.2	0.6
1267	1270	iso-Piperitenone	0.2	0.1	-
1274	1277	Perilla aldehyde	0.5	0.2	-
1276	1277	Phellandral	0.2	0.6	1.1
1287	1293	Thymol	-	0.2	0.5
1290	1291	p-Cymen-7-ol	-	0.4	0.6
1295	1300	Carvacrol	0.2	1.1	3.5
1297	1299	Perilla alcohol	0.5	0.3	-
1317	1322	(2E,4E)-Decadienal	0.4	0.2	-
1408	1408	cis-5-Hydroxy-p-menth-6-en-2-one	-	0.2	0.8
1409	1416	cis-α-Bergamotene	3.7	2.3	2.2
1415	1418	α-Santalene	0.2	-	-
1416	1416	trans-5-Hydroxy-p-menth-6-en-2-one	tr	1.3	3.5
1429	1432	trans-α-Bergamotene	0.7	0.5	0.4
1444	1447	Geranyl acetone	0.2	0.1	-
1450	1452	(E)-β-Farnesene	0.7	0.2	-
1454	1455	Sesquisabinene	0.2	0.1	-
1467	1473	4,5-di-epi-Aristolochene	0.2	0.1	-
1472	-	Unidentified^e	1.0	1.1	1.9
1478	1480	ar-Curcumene	0.2	0.2	-
1480	1483	trans-β-Bergamotene	0.4	0.2	-
1486	1489	β-Selinene	0.6	0.5	1.2
1492	1501	α-Selinene	0.3	0.3	1.0
1504	1508	β-Bisabolene	0.6	0.3	-
1506	1511	β-Curcumene	0.2	0.1	-
1514	1511	(Z)-γ-Bisabolene	0.2	0.1	-
1520	1524	β-Sesquiphellandrene	0.2	0.1	-
1557	1561	(E)-Nerolidol	1.2	0.4	1.1
1630	1634	α-Acorenol	0.2	0.1	-
1652	1653	Pogostol	0.2	0.1	-
1666	1670	epi-β-Bisabolol	0.4	0.2	-
1667	1671	β-Bisabolol	0.3	0.1	-
1682	1686	epi-α-Bisabolol	0.3	0.1	-
1684	1688	α-Bisabolol	0.1	0.1	-
		Monoterpene hydrocarbons	22.7	13.2	14.5
		Oxygenated monoterpenoids	62.2	77.0	75.1
		Sesquiterpene hydrocarbons	8.4	5.0	4.8
		Oxygenated sesquiterpenoids	2.6	1.1	1.1
		Others	1.2	1.1	0.4
		Total Identified	97.1	97.3	95.8

MS, mass spectrometry; EI, electrospray ionization.

^aRI_calc = Retention index calculated with respect to a homologous series of n-alkanes on a ZB-5ms column.

^bRI_db = Retention index from the databases.^20

-23

^cAverage of 3 measurements; SDs were small and for clarity are not shown.

^dMS (EI): 152 (3%), 134 (28%), 119 (17%), 109 (24%), 95 (21%), 92 (100%), 91 (86%), 81 (51%), 79 (40%), 77 (19%), 70 (14%), 67 (14%), 65 (14%), 55 (14%), 53 (18%), 43 (26%), 41 (34%).

^eMS (EI): 168 (5%), 153 (5%), 140 (13%), 139 (10%), 126 (100%), 98 (32%), 95 (16%), 81 (11%), 70 (16%), 67 (18%), 55 (15%), 53 (14%), 43 (46%), 41 (38%).

There was considerable variation in the leaf essential oil compositions of C. schweinfurthii. Monoterpene hydrocarbons (54.9%) were the principal class of compounds in the sample from Bukuru, Plateau State, with limonene (19.3%), α-pinene (17.4%), β-pinene (10.9% account for the observe), and p-cymene (5.2%), as the major monoterpene components. The Bukuru sample was also rich in juniper camphor (eudesm-7(11)-en-4α-ol, 16.1%). The leaf essential oil sample collected from Donga, Taraba State, on the other hand, showed a predominance of sesquiterpene hydrocarbons (56.1%), dominated by (E)-caryophyllene (14.6%), germacrene B (14.6%), and γ-elemene (7.1%). The essential oil from leaves collected from Azare, Bauchi State, had (E)-caryophyllene (18.7%), caryophyllene oxide (9.1%), limonene (7.2%), and phytol (6.3%) as the major components. As was observed for B. dalzielii leaf essential oils, the compositions of C. schweinfurthii leaf essential oils also show wide variation. The stem bark essential oils of C. schweinfurthii were dominated by monoterpene hydrocarbons (14.5%-22.7%) and oxygenated monoterpenoids (62.2%-77.0%). The major monoterpene was limonene (3.4%-18.3%), while α-terpineol (24.1%-38.1%) and terpinen-4-ol (3.6%-8.6%) were the main oxygenated monoterpenoids. To our knowledge, there have been no previous reports on the leaf or stem bark essential oils of C. schweinfurthii. Essential oils from the oleo-gum resins have been previously reported, however, and these materials are generally dominated by monoterpenes.^17
-19

Antibacterial and Antifungal Activity

The leaf essential oils of B. dalzielii (Zaria sample) and C. schweinfurthii (Bukuru sample) have been screened for antibacterial and antifungal activity (Table 4). The best activity was observed for C. schweinfurthii leaf essential oil against Aspergillus niger (minimum inhibitory concentration, MIC = 39.1 µg/mL). The major components in the Bukuru sample of C. schweinfurthii essential oil were limonene (19.3%), α-pinene (17.4%), juniper camphor (16.1%), β-pinene (10.9%), and p-cymene (5.2%). Several of the major essential oil components have been screened for antifungal and antibacterial activity (Table 5). The antifungal activities of α-pinene, β-pinene, as well as α-terpineol (MIC = 78.1 µg/mL) against A. niger (Table 5), may account for the observed activity of C. schweinfurthii leaf essential oil. The high concentration of juniper camphor may also be a factor but that compound was not available to us for screening. Note that juniper camphor was also relatively abundant in B. dalzielii leaf essential oil from Zaria (8.1%), but the essential oil did not exhibit a pronounced effect on A. niger (MIC = 156.3 µg/mL).

Table 4

Antibacterial and Antifungal Activities (MIC, μg/mL) of Burseraceae EOs from Nigeria.

Organism	Boswellia dalzielii leaf EO Zaria	Canarium schweinfurthii leaf EO Bukuru	Positive control^a
Bacteria
Bacillus cereus	312.5	312.5	1.2
Staphylococcus aureus	312.5	312.5	0.6
Staphylococcus epidermidis	312.5	312.5	<12.5
Molds
Aspergillus fumigatus	156.3	156.3	<12.5
Aspergillus niger	156.3	39.1	1.6
Cryptococcus neoformans	312.5	312.5	0.8
Microsporum canis	312.5	312.5	<12.5
Microsporum gypseum	312.5	312.5	<12.5
Trichophyton mentagrophytes	156.3	156.3	<12.5
Trichophyton rubrum	312.5	312.5	<12.5
Yeast
Candida albicans	156.3	156.3	1.6

MIC, minimum inhibitory concentration; EO, essential oil.

^aGentamicin for bacteria, amphotericin B for fungi.

Table 5

Antibacterial and Antifungal Activities (MIC, μg/mL) of Individual Chemical Components.

Organism	Compound
Organism	(+)-α-Pinene	(−)-α-Pinene	(−)-β-Pinene	p-Cymene	(+)-Limonene	(−)-Limonene	α-Terpineol	(E)-Caryophyllene	Caryophyllene oxide	Phytol
Bacteria
Bacillus cereus	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5
Staphylococcus aureus	625.0	312.5	156.3	625.0	312.5	312.5	312.5	312.5	78.1	312.5
Staphylococcus epidermidis	312.5	312.5	312.5	312.5	312.5	78.1	312.5	312.5	312.5	312.5
Molds
Aspergillus fumigatus	156.3	312.5	156.3	312.5	156.3	156.3	312.5	156.3	156.3	78.1
Aspergillus niger	78.1	156.3	78.1	156.3	156.3	156.3	78.1	1250	156.3	1250.0
Cryptococcus neoformans	312.5	312.5	625.0	312.5	312.5	312.5	312.5	312.5	78.1	312.5
Microsporum canis	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5
Microsporum gypseum	156.3	312.5	312.5	312.5	312.5	156.3	312.5	312.5	156.3	156.3
Trichophyton mentagrophytes	156.3	312.5	156.3	156.3	312.5	156.3	312.5	625.0	156.3	39.1
Trichophyton rubrum	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5	312.5
Yeast
Candida albicans	156.3	156.3	156.3	156.3	156.3	156.3	156.3	156.3	312.5	1250.0

MIC, minimum inhibitory concentration.

Conclusions

The leaf and stem bark essential oils of C. schweinfurthii are reported for the first time. The leaf essential oil of C. schweinfurthii showed pronounced antifungal activity against A. niger. The leaf essential oils of B. dalzielii have also been analyzed. The leaf essential oils of both B. dalzielii and C. schweinfurthii show a wide variation in chemical compositions, which may be attributed to geographical location and climatic conditions. The variations in essential oil compositions may have important consequences in the traditional uses of these members of the Burseraceae.

Materials and Methods

Plant Material

Leaves of B. dalzielii were collected directly from source trees from Kabanni Rock, Zaria (11°06′ 40.61″ N, 7°43′ 21.72″ E, 644 m elev., Zaria local government, Kaduna State, northern Nigeria, located some 82.3 km north-east of Kaduna town) during the dry season in the month of March 2019 (Figure 1A). Leaves of B. dalzielii were also collected from Bukuru (9°47′ 38.36″ N, 8°51′ 50.29″ E, 1277 m elev., Jos South Local Government, Plateau State) in the month of November 2019. The plants were taxonomically identified and authenticated by Muh’d Sule and Namadi Sunusi. A voucher specimen (Voucher number 0900121) has been deposited in the Department of Biological Sciences, Ahmadu Bello University, Nigeria. The leaves were manually removed, air-dried in the laboratory for 7 days, and then pulverized using an electric blender. Samples (450 g) of leaves of B. dalzielii from Kaduna and Plateau States (Jos) were subjected to hydrodistillation in an all-glass Clevenger-type apparatus. The B. dalzielii samples and water were mixed in a ratio of 2:6, and the mixtures were stirred constantly during hydrodistillation for 3-4 hours. The yields of the oils were 1.76% and 1.65% on a dry weight basis, respectively. The oils were dried over anhydrous sodium sulfate and stored in sealed vials under refrigeration (4 °C) prior to analysis.

Canarium schweinfurthii leaf and stem bark samples were taken directly from source trees in 3 states in northern Nigeria: Azare (11°40′ 29.21″N, 10°11′ 26.48″E, 644 m elev., Katagum Local Government, Bauchi State), Bukuru (9°47′ 38.36″N, 8°51′ 50.29″E, 1277 m elev., Jos South Local Government, Plateau State), and Donga (7°43′ 00″N, 10°03′ 00″E, 135 m elev., situated on Donga River in Donga Local Government, Taraba State) (Figure 1B). Both leaves and stem bark of C. schweinfurthii were obtained during the dry season in the month of March 2019. The plants were taxonomically identified and authenticated by Namadi Sunusi. A voucher specimen (voucher number 02639) has been deposited in the Department of Biological Sciences, Ahmadu Bello University, Nigeria. The leaves and stem bark were manually removed, air-dried in the laboratory for 7-10 days, and then pulverized using an electric blender. Samples (450 g each) of both leaves and stem bark of C. schweinfurthii, respectively, were subjected to hydrodistillation in an all-glass Clevenger-type apparatus. Each of the C. schweinfurthii samples and water were mixed in a ratio of 2:6, and the mixtures were stirred constantly during hydrodistillation for 3 hours until no more essential oil was apparent in the distillate. The yields of the leaf essential oils were 1.35%, 1.42%, and 1.82% yield, respectively, while the bark essential oils were obtained in 1.83%, 1.76%, and 1.85% yield, respectively, on a dry weight basis. The oils were dried over anhydrous sodium sulfate and stored in sealed vials under refrigeration (4 °C) prior to analysis.

Gas Chromatography-Mass Spectrometry

The essential oils from B. dalzielii and C. schweinfurthii were subjected to GC-MS analysis as previously reported⁴: Shimadzu GCMS-QP2010 Ultra, electron impact (EI) mode with electron energy = 70 eV, scan range = 40-400 atomic mass units, scan rate = 3.0 scans/seconds, and Shimadzu GC-MS solution software v. 4.45 (Shimadzu Scientific Instruments, Columbia, MD, USA); ZB-5ms fused silica capillary GC column (Phenomenex, Torrance, CA, USA); (5% phenyl)-polymethylsiloxane stationary phase, 0.25 µm film thickness; helium carrier gas, column head pressure = 552 kPa, flow rate = 1.37 mL/min; injector temperature = 260 °C, ion source temperature = 260 °C; GC oven temperature program: initial temperature = 50 °C, temperature increased 2 °C/minute to 260 °C. For each sample, a 5% w/v solution in dichloromethane was prepared, 0.1 µL was injected using a split ratio of 30:1. Each sample was injected 3 times. Identification of the individual components of the essential oils was determined by comparison of the retention indices, determined using a series of n-alkanes, in addition to the comparison of the mass spectral fragmentation patterns with those found in the MS databases^20

-23 using the LabSolutions GC-MS solution software v. 4.45 (Shimadzu Scientific Instruments, Columbia, MD, USA) and with matching factors >90%.

Antibacterial and Antifungal Screening

The essential oils were screened for antibacterial activity against bacteria (Bacillus cereus [ATCC No. 14579], Staphylococcus aureus [ATCC No. 29213], and Staphylococcus epidermidis [ATCC No. 12228]), and for antifungal activity against the molds (Aspergillus fumigatus [ATCC No. 96918], Aspergillus niger [ATCC No. 16888], Cryptococcus neoformans [ATCC No. 32045], Microsporum canis [ATCC No. 11621], Microsporum gypseum [ATCC No. 24102], Trichophyton mentagrophytes [ATCC No. 18748], and Trichophyton rubrum [ATCC No. 28188]), and 1 yeast (Candida albicans [ATCC No. 18804]) using the microbroth dilution technique^24,25 as previously reported.^26,27 Individual essential oil components ((E)-caryophyllene, (+)-α-pinene, (−)-α-pinene, (–)-β-pinene, p-cymene, (+)-limonene, (–)-limonene, α-terpineol, (E)-caryophyllene, caryophyllene oxide, and phytol were obtained from Sigma-Aldrich (St. Louis, MO, USA) and were used as received without additional purification.

All bacteria were cultured on tryptic soy agar (Sigma-Aldrich, St. Louis, MO, USA). All fungi were cultured on yeast malt agar (Sigma-Aldrich, St. Louis, MO, USA). For the bacteria and fungi, 50 µL of 1% (w/v) solution of the samples in dimethyl sulfoxide (DMSO) was diluted in 50 µL of cation-adjusted Mueller Hinton broth (CAMHB) (Sigma-Aldrich, St. Louis, MO, USA). The sample solutions were then serially diluted (1:1) in fresh CAMHB to obtain concentrations of 2500, 1250, 625, 313, 156, 78, 39, and 20 µg/mL. The microbes were harvested from a fresh culture and added to each well at a concentration of approximately 1.5 × 10⁸ colony-forming unit (CFU)/mL for bacteria and 7.5 × 10⁷ CFU/mL for fungi, and the 96-well microdilution plates for bacteria were incubated at 37 °C and the fungi were incubated at 35 °C for 24 hours. The minimum inhibitory concentration (MIC) was determined as the lowest concentration with no turbidity. Gentamicin (Sigma-Aldrich, St. Louis, MO, USA) was used as a positive antibiotic control and DMSO was used as the negative control (50 µL DMSO diluted in 50 µL broth medium, and then serially diluted as above). For fungi, the above-mentioned method was implemented using yeast-nitrogen base growth medium (Sigma-Aldrich, St. Louis, MO, USA) and Amphotericin B (Sigma-Aldrich, St. Louis, MO, USA) as a positive antifungal control.

Footnotes

Acknowledgments

This work was carried out as part of the activities of the Aromatic Plant Research Center (APRC, https://aromaticplant.org/).

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

William N. Setzer

References

Mabberley

. Mabberley’s Plant-Book. 3rd ed. Cambridge University Press; 2008:130.

Tucker

. Frankincense and myrrh. Econ Bot. 1986;40(4):425-433.doi:10.1007/BF02859654

DeCarlo

Dosoky

NS.

Satyal

Sorensen

Setzer

. The essential oils of the Burseraceae. In: Malik

, ed. Essential Oil Research: Trends in Biosynthesis, Analytics, Industrial Applications and Biotechnological Production. Springer Nature; 2019.

DeCarlo

Johnson

Okeke-Agulu

et al. Compositional analysis of the essential oil of Boswellia dalzielii frankincense from West Africa reveals two major chemotypes. Phytochemistry. 2019;164:24-32.doi:10.1016/j.phytochem.2019.04.015

http://www.ncbi.nlm.nih.gov/pubmed/31071599

Arbres

. Arbustes et Lianes Des Zones Sèches d’Afrique de l’Ouest. Troisième. Muséeum national d’histoire naturelle; 2009.

Jansen

Angenot

Tits

et al. Evaluation of 13 selected medicinal plants from Burkina Faso for their antiplasmodial properties. J Ethnopharmacol. 2010;130(1):143-150.doi:10.1016/j.jep.2010.04.032

http://www.ncbi.nlm.nih.gov/pubmed/20435124

Nadembega

Boussim

JI.

Nikiema

JB.

Poli

Antognoni

. Medicinal plants in Baskoure, Kourittenga Province, Burkina Faso: an ethnobotanical study. J Ethnopharmacol. 2011;133(2):378-395.doi:10.1016/j.jep.2010.10.010

http://www.ncbi.nlm.nih.gov/pubmed/20950680

Ouédraogo

Thiombiano

Hahn-Hadjali

Guinko

. Régénération sexuée de Boswellia dalzielii Hutch., un arbre médicinal de grande valeur Au Burkina Faso. Bois Forêts des Trop. 2006;289(3):41-48.

Tapsoba

Deschamps

J-P

. Use of medicinal plants for the treatment of oral diseases in Burkina Faso. J Ethnopharmacol. 2006;104(1-2):68-78.doi:10.1016/j.jep.2005.08.047

http://www.ncbi.nlm.nih.gov/pubmed/16214302

10.

Irvine

. West African insecticides. Colon Plant Anim Prod. 1955;5(1):34-38.

11.

Ngamo

TSL.

Ngassoum

MB.

Mapongmestsem

PM.

Noudjou

. Use of essential oils of plants as protectant of grains during storage. Agric J. 2007;2(2):204-209.

12.

Kubmarawa

Ogunwande

IA.

Okorie

DA.

Olawore

NO.

Kasali

. Constituents of the Essential Oils of Boswellia dalzielii Hutch. from Nigeria. J Essent Oil Res. 2006;18(2):119-120.doi:10.1080/10412905.2006.9699038

13.

Kohoude

MJ.

Gbaguidi

Agbani

Ayedoun

M-A.

Cazaux

Bouajila

. Chemical composition and biological activities of extracts and essential oil of Boswellia dalzielii leaves. Pharm Biol. 2017;55(1):33-42.doi:10.1080/13880209.2016.1226356

http://www.ncbi.nlm.nih.gov/pubmed/27650786

14.

Johnson

DeCarlo

Satyal

Dosoky

Sorensen

Setzer

. Organic certification is not enough: the case of the methoxydecane frankincense. Plants. 2019;8(4):88. doi:10.3390/plants8040088

15.

Harley

MM.

Clarkson

. Pollen morphology of the African Burseraceae and related genera. In: Heine

, ed. Palaeoecology of Africa and the Surrounding Islands-Volume 26. Routledge; 2018:225-242.

16.

Kuete

. Canarium schweinfurthii. In: Kuete

, ed. Medicinal Spices and Vegetables from Africa. Academic Press; 2017:379-384.

17.

Dongmo

PMJ.

Tchoumbougnang

Ndongson

et al. Chemical characterization, antiradical, antioxidant and anti-inflammatory potential of the essential oils of Canarium schweinfurthii and Aucoumea klaineana (Burseraceae) growing in Cameroon. Agric Biol J North Am. 2010;1(4):606-611.

18.

Engonga

PE.

Abdoul-Latif

FM.

Obame

LC.

Mewono

. Volatile constituents of Canarium schweinfurthii Engl. essential oil from Gabon. Int J AgriScience. 2012;2(3):200-203.

19.

Nagawa

Böhmdorfer

Rosenau

. Chemical composition and anti-termitic activity of essential oil from Canarium schweinfurthii Engl. Ind Crops Prod. 2015;71:75-79.doi:10.1016/j.indcrop.2015.03.078

20.

Adams

. Identification of Essential Oil Components by Gas Chromatography/Mass Spectrometry. 4th ed. Allured Publishing; 2007.

21.

Mondello

. FFNSC 3. Shimadzu Scientific Instruments; 2016.

22.

NIST17 . NIST17. National Institute of Standards and Technology; 2017.

23.

Satyal

. Development of GC-MS database of essential oil components by the analysis of natural essential oils and synthetic compounds and discovery of biologically active novel chemotypes in essential oils. [Ph.D. dissertation] University of Alabama in Huntsville; 2015.

24.

Sahm

DH.

Washington

. Antibacterial susceptibility tests: Dilution methods. In: Balows

Hausler

WJ.

Herrmann

KL.

Isenberg

HD.

Shamody

HJ.

, eds. Manual of Clinical Microbiology. Fifth Edit. American Society for Microbiology; 1991.

25.

EUCAST . Determination of minimum inhibitory concentrations (MICs) of antibacterial agents by broth dilution. Clin Microbiol Infect. 2003;9(8):ix-0.doi:10.1046/j.1469-0691.2003.00790.x

26.

Setzer

MC.

Setzer

WN.

Jackes

BR.

Gentry

GA.

Moriarity

. The medicinal value of tropical rainforest plants from Paluma, North Queensland, Australia. Pharm Biol. 2001;39(1):67-78.doi:10.1076/phbi.39.1.67.5944

27.

Satyal

Paudel

Poudel

Dosoky

NS.

Pokharel

KK.

Setzer

. Bioactivities and compositional analyses of Cinnamomum essential oils from Nepal: C. camphora, C. tamala, and C. glaucescens. Nat Prod Commun. 2013;8(12):1777-1784.doi:10.1177/1934578X1300801232

http://www.ncbi.nlm.nih.gov/pubmed/24555298

Essential Oil Compositions,Antibacterial and Antifungal Activities of Nigerian Members of the Burseraceae: Boswellia dalzielii and Canarium schweinfurthii

Abstract

Keywords

Results and Discussion

Essential Oil Compositions

Boswellia dalzielii

Canarium schweinfurthii

Antibacterial and Antifungal Activity

Conclusions

Materials and Methods

Plant Material

Gas Chromatography-Mass Spectrometry

Antibacterial and Antifungal Screening

Footnotes

Acknowledgments

Declaration of Conflicting Interests

Funding

ORCID iD

References