1.    Introduction

The genus Hedychium is part of the Zingiberaceae family and includes about 80 species distributed mainly in Asia. H. gardnerianum is a plant native to the Himalayas whose stem can be 2 meters long and its leaves 30 cm long. Its flowers can be pink or orange yellow [1-3]. It is considered an invasive plant in most of the Azores archipelago [1]. The rhizomes of the Hedychium species are known to be fleshy and aromatic. Some species are cultivated only to extract the fragrant essential oil from their rhizomes. Aerial parts of the Hedychium species can be used in the paper industry and its flowers as culinary ingredients [4]. The bloom of the Hedychium species is very brief and usually occurs during the monsoon. The chemical profile of Hedychium sp. EO is reported as complex and comprising monoterpene and sesquiterpene derivatives. The compounds α-pinene, β-pinene, eucalyptol, linalool and nerolidol, although quite ubiquitous, are described as markers of the genus Hedychium [4].

The genus Pittosporum belongs to the Pittosporaceae family and encompasses ca. 200 species [5]. Among these, Pittosporum senacia is a species found in the Indian Ocean Islands. The chemical composition of EO from the whole plant from Mauritius was described in 2020 and 2021 by Jugreet et al. [5, 6]. In their most recent article, the distillation yield for P. senacia was found to be 0.77%. The chemical composition mainly comprised monoterpene hydrocarbons (up to 71.9%), and particularly β-myrcene (62.2%). Other compounds found were germacrene D (7.8%), limonene (3.4%), and β-phellandrene (2.9%). In an earlier article from 1998, EO from the leaves of P. senacia coursii, endemic to Madagascar, was studied [7]. With a distillation yield of 0.67%, 95% of the chemical composition of the EO was determined by GC-FID and GC/MS. With monoterpene hydrocarbons accounting for only 20.4%, including β-myrcene (6.3%), α-terpinene (4.6%) and camphene (3%), the main compounds were found to be sesquiterpene hydrocarbons and derivatives (69.5%) such as α-cadinol (19%), α-muurolol (15.9%), and δ-cadinene (11.3%). In the same study, the antimicrobial activity of this EO against Staphylococcus aureus was shown to outperform streptomycin, while it was in the same order of magnitude as streptomycin against Streptococcus faecalis [7].

The genus Psidium belongs to the Myrtaceae family which contains ca. 5500 species [8, 9]. This genus is known for presenting rich essential oil bearing plants [9]. Psidium cattleianum is a species found in Oceania, Brazil, North America and the Caribbean [8]. The shrub is typically between 1 and 4 meters in height. The EO from the leaves of P. cattleianum has been described as having antifungal activities against Candida spp. and antibacterial activities against several strains such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa in qualitative analyses with the antibiotic ampicillin as control [8].

The chemical composition of EO from P. cattleianum leaves has been studied with plants coming mainly from Brazil [8-12]. Older studies describe P. cattleianum EO harvested in Hawaii [13], Cuba [14], and California [15].

As part of a project dedicated to the chemical and sensory evaluation of plants from Reunion Island for applications in perfumery, the chemical composition and olfactory properties of four essential oils (EOs) for which literature data are scarce or non-existent were studied. The four species, from the Zingiberaceae, Pittosporaceae, and Myrtaceae botanical families illustrated in Fig. 1 are listed hereafter:

- Longose (Hedychium gardnerianum Sheppard ex Ker-Gawl) – flowers,

- Yellow ginger (Hedychium flavescens Carey ex Roscoe) – leaves,

- Bois de joli coeur (Pittosporum senacia Putt.) – leaves,

- Chinese guava (Psidium cattleianum Afzel. Ex Sabine) – floral tops.

The aim of these studies was to determine the chemical composition of these essential oils and evaluate their olfactory profile for potential applications in perfumery.

2.    Materials and methods
2.1 Plant materials
H. gardnerianum, H. flavescens, P. senacia and P. cattleianum were collected in 2020 on Reunion Island, in the wild between 800 and 1300 meters of altitude and their essential oils were obtained from OLICA (19 Rue Fangourin, Saint-Leu 97424, La Réunion, FRANCE). The four pictures of the species in Fig. 1 are licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license without modification. Authors are (1) and (4) B. Navez, (2) Forest and Kim Starr, (3) Change-ecorce.

Figure 1. The four species studied: (1) H. gardnerianum, flowers; (2) H. flavescens, leaves; (3) P. senacia, leaves; (4) P. cattleianum, floral tops.

2.2 GC/MS-FID analyses
The analyses of the four EOs chemical compositions were performed on an Agilent GC 7820 chromatograph coupled to an Agilent 5977B electron ionization mass spectrometer and equipped with a flame ionization detector. The column used was Agilent HP5-MS capillary column (30 m x 0.25 mm i.d., film thickness 0.25 μm). The sample of EO was diluted to 1% v/v in ethyl acetate. One microliter of the sample was injected with a split ratio of 1/10. Carrier gas was helium with a flow rate of 1.2 mL/min. The temperatures of injector and source were 250 °C and 230 °C, respectively. The oven temperature was programmed to stay 4 min at 40°C, then to rise from 40 to 200°C with an increase of 2 °C/min and finally from 200 to 270 °C with an increase of 8 °C/min. For the MS, ionization energy was 70 eV and the range was from 35 to 350 m/z. The FID detector was set at 270 °C with an air flow of 400 mL/min and a hydrogen flow of 40 mL/min.

2.3 Characterization of the EOs
GC/MS was used for identification and GC-FID for quantification. The identification of EO constituents was carried out by matching the retention index (RI) determined against a series of C7-C40 alkanes as well as by matching the EI-MS mass spectra obtained with various databases (NIST20, Wiley6n and internal database).

2.4 GC/MS-O analyses
GC/MS-O analyses were performed on a Perkin Elmer Clarus 690 chromatograph coupled with a Perkin Elmer Clarus SQ8T mass selective detector and equipped with a Perkin Elmer sniffing port. The column was a Perkin Elmer Elite 5-MS (30m x 0.32mm i.d., film thickness 0.25μm). The sample of EO was diluted to 10% v/v in ethyl acetate. One microliter of the sample was injected with a split of 72 mL/min (inlet pressure: 23 psi). The split between the MS and the Olfactometry detector was 1:7 (v/v). The oven temperature was programmed to stay 2 min at 60 °C, to rise from 60 to 200 °C with an increase of 5 °C/min, then from 200 to 280 °C with an increase of 8 °C/min and finally held at 280 °C for 5 min. The solvent delay was 5.5 min. Four panelists carried out the GC/MS-O analysis in duplicate, on each of the four EOs. Compounds were annotated by matching the EI-MS mass spectra obtained with databases (NIST20).

3.    Results and discussion
3.1 Hedychium gardnerianum and Hedychium flavescens
Essential oils obtained from the rhizomes of the two species H. gardnerianum and H. flavescens have been described in the literature [2-4, 16-18]. For example, Ray et al. studied 10 species of Hedychium, including H. gardnerianum and H. flavescens, cultivated under the same conditions in India [4]. After harvesting, the EO of each plant was collected from the rhizomes and analyzed by GC/MS and GC-FID. The distillation yield of H. gardnerianum and H. flavescens species was about 0.20%, which is lower than other species of the genus such as H. thyrsiforme (0.75%) and H. gracile (0.65%), and higher than others such as H. flavum (0.10%) and H. greenii (0.05%). The EO of H. gardnerianum was described as dark yellow and that of H. flavescens as dark brown. The chemical compositions of the two EOs were determined, accounting for 75.9% and 92.8% of oils of H. gardnerianum and H. flavescens, respectively. Both were composed mainly of monoterpene derivatives, mostly β-pinene and α-pinene (28.03% and 21.15% for H. gardnerianum and 29.76% and 13.17% for H. flavescens, respectively). Eucalyptol, one of the main compounds of H. flavescens (12.80%), was found in a much smaller fraction in H. gardnerianum (0.42%) [4].

The EO of H. gardnerianum flowers has been very little studied; to the best of our knowledge, only two papers published in 2002 and 2003 described the EO obtained from this part of the plant [1, 2] and EO extracted from the leaves of H. flavescens has never been described. Medeiros et al. studied the chemical composition of EO from H. gardnerianum flowers from three locations on San Miguel Island in the Azores [1]. The composition of these was determined using GC/MS analysis alone, accounting for 87%, 94% and 91% of the total EO from the three locations, respectively. Although they came from the same island, significant differences in the relative percentages of compounds were observed, although GC/MS alone can hardly provide reliable quantitative information. The main compounds of the three EOs were monoterpene hydrocarbons with α-pinene (8.38-18.13%), β-pinene (5.06-11.99%), p-cymene (3.85-8.16%), γ-terpinene (3.15-14.43%) and the sesquiterpene derivatives α-cadinol (6.42-14.59%), β-caryophyllene (7.04-8.89%), δ-cadinene (4.89-8.76%) and τ-muurolol (2.64-5.86%). The chemical composition of EO from H. gardnerianum flowers from Fiji was studied by Smith et al. [2]. Up to 75% of its chemical composition was characterized by GC/MS-FID analyses. β-Caryophyllene (17.4%) and β-pinene (17.0%) were found to be the two main compounds.

3.2 Hedychium gardnerianum flowers EO analysis
The sample of H. gardnerianum flowers EO was found to be chemically very complex (Fig. 2). As shown in Table 1, a hundred compounds were detected by monodimensional gas chromatography and those identified accounted for more than 87% of the EO. The sample was mainly composed of sesquiterpene derivatives including β-farnesene (12.05%), α-cadinol (9.71%), α-farnesene (7.09%), τ-muurolol (5.89%) and δ-cadinene (5.83%). The monoterpene derivatives identified accounted for ca. 20% with α-pinene, β-pinene and humulene as main representatives (4.48%, 4.46% and 3.93%, respectively). The sample also contained diterpene derivatives including kaur-16-ene (2.42%).

Table 1. Chemical composition of Hedychium gardnerianum flowers essential oil. 

Peak #	RT (min)	Compound		Area %	Formula	RI	RI litt.
1	17.625	α-pinene		4.48	C10H16	931	937
2	18.563	camphene		0.08	C10H16	945	952
3	20.344	sabinene		0.15	C10H16	971	974
4	20.493	β-pinene		4.46	C10H16	973	979
5	21.682	β-myrcene		0.21	C10H16	991	991
6	22.460	α-phellandrene		0.39	C10H16	1002	1005
7	22.853	3-carene		0.04	C10H16	1008	1011
8	23.339	α-terpinene		0.24	C10H16	1015	1017
9	23.892	p-cymene		1.46	C10H14	1022	1025
10	24.175	limonene		0.52	C10H16	1026	1030
11	24.363	eucalyptol		0.08	C10H16O	1029	1032
12	25.000	(Z)-β-ocimene		0.23	C10H16	1038	1038
13	25.705	(E)-β-ocimene		2.97	C10H16	1048	1049
14	26.355	γ-terpinene		2.46	C10H16	1057	1060
15	28.431	terpinolene		0.09	C10H16	1086	1088
16	28.888	methyl benzoate		0.06	C8H8O2	1093	1094
17	29.371	linalool		2.22	C10H18O	1100	1099
18	30.504	(E)-4.8-Dimethyl-nona-1,3,7-triene		0.12	C11H18	1116	1116
19	31.954	sabinol		0.01	C10H16O	1137	1143
20	33.804	endo-borneol		0.09	C10H18O	1164	1167
21	34.654	terpinen-4-ol		0.10	C10H18O	1176	1177
22	35.662	methyl salicylate		0.11	C8H8O3	1191	1192
23	41.904	bornyl acetate		0.06	C12H20O2	1285	1285
24	41.921	2-undecanone		0.06	C11H20O2	1285	1294
25	43.170	indole		0.01	C8H7N	1304	1295
26	45.202	δ-elemene		0.05	C15H24	1336	1338
27	45.945	α-cubebene		0.16	C15H24	1348	1351
28	47.567	α-copaene		0.19	C15H24	1374	1376
29	48.614	β-elemene		0.21	C15H24	1391	1391
30	49.628	α-gurjunene		0.04	C15H24	1407	1409
31	50.219	β-caryophyllene		1.38	C15H24	1417	1419
32	51.67	guaia-6,9-diene		0.07	C15H24	1442	1443
33	52.281	humulene		3.93	C15H24	1452	1454
34	52.640	(6E)-β-farnesene		12.05	C15H24	1458	1457
35	52.848	allo-aromadendrene		0.01	C15H24	1462	1461
36	53.484	γ-gurjunene		0.18	C15H24	1472	1473
37	53.680	γ-muurolene		0.45	C15H24	1476	1477
38	53.914	germacrene D		0.96	C15H24	1480	1481
39	54.061	α-curcumene		0.21	C15H22	1482	1483
40	54.537	Bicyclosesqui-phellandrene		0.17	C15H24	1490	1489
41	54.822	bicyclogermacrene		1.67	C15H24	1495	1495
42	55.070	α-muurolene		1.05	C15H24	1499	1499
43	55.461	β-cadinene		0.43	C15H24	1506	1518
44	55.646	(3E,6E)α-farnesene		7.09	C15H24	1509	1508
45	55.848	γ-cadinene		1.03	C15H24	1513	1513
46	56.449	δ-cadinene		5.83	C15H24	1523	1524
47	56.891	cadina-1,4-diene		0.09	C15H24	1531	1532
48	57.186	α-cadinene		0.24	C15H24	1536	1538
49	57.476	α-calacorene		0.12	C15H20	1542	1542
50	57.897	elemol		3.00	C15H26O	1549	1549
51	58.246	204 161 121 105 93 69		0.18	-	1555	-
52	58.548	204 161 121 109 93 41		0.14	-	1561	-
53	58.767	(E)-nerolidol		2.11	C15H26O	1564	1564
54	59.140	202 69 41 79 93 109 55		0.59	-	1571	-
55	59.372	222 161 119 105 91 81		4.33	-	1575	-
56	59.444	spathulenol		0.55	C15H24O	1576	1576
57	59.735	caryophyllene oxide		0.75	C15H24O	1582	1581
58	60.000	204 161 119 105 91 81		0.19	-	1586	-
59	60.332	202 159 97 83 69 55		0.18	-	1592	-
60	60.622	220 121 107 93 88 67		1.41	-	1597	-
61	60.851	204 122 107 93 81 69		0.26	-	1602	-
62	61.179	humulene oxide		1.46	C15H24O	1608	1604
63	61.358	222 179 105 91 69 41		0.55	-	1611	-
64	62.25	220 119 93 81 67 41		1.35	-	1628	-
65	62.413	γ-eudesmol		0.97	C15H26O	1631	1631
66	63.024	τ-muurolol		5.89	C15H26O	1642	1642
67	63.225	204 161 119 105 95		0.84	-	1646	-
68	63.411	β-eudesmol		0.67	C15H26O	1649	1649
69	63.749	α-cadinol		9.71	C15H26O	1655	1653
70	64.460	200 157 142 123 93 69		0.16	-	1669	-
71	64.929	cadalene		0.10	C15H18	1677	1674
72	65.504	204 161 119 105 84 81		0.38	-	1688	-
73	66.212	220 177 159 131 117		0.12	-	1701	-
74	67.089	220 187 159 145 131		0.06	-	1719	-
75	68.005	oplopanone		0.21	C15H26O2	1736	1730
76	70.851	1-octadecene		0.06	C18H36	1792	1793
77	71.662	147 119 91 77 69 55		0.07	-	1808	-
78	72.253	187 159 119 107 93 77		0.10	-	1821	-
79	74.520	benzyl salicylate		0.79	C14H12O3	1867	1869
80	80.459	97 91 83 69 57 55		0.06	-	1993	-
81	81.149	(8β.13β)-kaur-16-ene		0.05	C20H32	2008	2012
82	82.173	kaur-16-ene		2.42	C20H32	2032	2041
83	85.762	Coronarin E		0.11	C20H28O	2123	2136
84	87.726	207 91 83 77 69 57		0.03	-	2194	-
85	89.042	298 146 123 91 77		0.04	-	2259	-
86	89.229	281 109 96 81 67 55		0.04	-	2269	-
87	89.325	9-tricosene		0.26	C23H46	2274	2278
88	89.806	324 99 85 71 57 43		0.15	-	2299	-
89	90.032	298 174 146 131 109		0.34	-	2313	-
90	90.719	207 151 81 69 55 40		0.03	-	2358	-
91	90.956	314 190 162 95 81 55		0.52	-	2373	-
92	92.293	283 109 95 82 67 55		0.05	-	2470	-
93	92.346	281 111 97 83 69 57		0.16	-	2475	-
94	92.402	290 108 95 79 67 55		0.19	-	2479	-
95	92.658	327 113 99 85 71 57		0.04	-	2498	-
Total identified				87.43 %
Monoterpenes /Monoterpenoids				20.28 %
Sesquiterpenes /Sequiterpenoids				63.21 %
RT: retention time; RI: retention indices; RI litt. from NIST 2020 database. NI: Not identified (12.55%). Bold: main compounds.

Our results are in agreement with the article by Medeiros et al. concerning the study of the Eos of longose leaves and flowers (H. gardnerianum) from the island of San Miguel (Azores) [1]. In their study, the main compounds were α-pinene, β-pinene, p-cymene, γ-terpinene, β-caryophyllene, β-cadinene and α-cadinol. These compounds were all present in the sample studied herein. However, β-farnesene, the main compound in our sample, was identified to a much lesser extent (ca. 3%) in the study by Medeiros et al. This could suggest a particular role of farnesene in plant defense particularly in the Reunion Island territory for a compound known to be associated with insect attraction [19].

Figure 2. Chromatogram of Hedychium gardnerianum flowers essential oil.

3.3 Hedychium flavescens leaves EO analysis
The EO sample of H. flavescens leaves was found to be relatively simple and to contain mainly three compounds: β-pinene (47.81%), α-pinene (18.74%) and β-caryophyllene (17.47%), which together accounted for 84.02% of the sample (Fig. 3). As shown in Table 2, in total, 96.26% of the EO was identified. In addition of these three compounds, monoterpene and sesquiterpene derivatives were found in smaller proportions such as the monoterpene hydrocarbons D-limonene (0.60%), β-myrcene (0.16%), γ-terpinene (0.05%) and sesquiterpene hydrocarbons bicyclogermacrene (2.65%), germacrene B (1.29%) and β-cadinene (1.14%).

Figure 3. Chromatogram of Hedychium flavescens leaves essential oil.

To our knowledge, the chemical composition of the EO obtained solely from the leaves of H. flavescens have not been published so far. In the most recent article on the EO of H. flavescens rhizomes, 78.05% of a sample obtained from a plant grown in India could be identified [4]. The main compounds described were β-pinene (24.77%) and α-pinene (11.17%), both present in large proportions in our sample (47.81 and 18.74%, respectively), together with β-caryophyllene and bicyclogermacrene.

Table 2. Chemical composition of Hedychium flavescens leaves essential oil. 

Peak #	RT (min)	Compound	Area %	Formula	RI	RI litt.
1	17.625	α-pinene	18.74	C10H16	931	937
2	18.553	camphene	0.04	C10H16	945	952
3	20.553	β-pinene	47.81	C10H16	974	979
4	21.715	β-myrcene	0.16	C10H16	991	991
5	23.562	α-terpinene	0.05	C10H16	1018	1017
6	24.093	p-cymene	0.02	C10H14	1025	1025
7	24.183	limonene	0.60	C10H16	1026	1030
8	24.352	eucalyptol	0.42	C10H18O	1029	1032
9	25.113	(Z)-β-ocimene	0.05	C10H16	1040	1038
10	25.799	(E)-β-ocimene	0.05	C10H16	1049	1049
11	26.391	γ-terpinene	0.05	C10H16	1058	1060
12	28.483	α-terpinolene	0.03	C10H16	1087	1088
13	29.398	linalool	0.02	C10H18O	1100	1099
14	31.920	pinocarveol	0.01	C10H16O	1137	1138
15	34.619	terpinen-4-ol	0.02	C10H18O	1176	1177
16	35.661	1-dodecene	0.03	C12H24	1191	1190
17	45.195	δ-elemene	0.90	C10H18O	1336	1338
18	47.567	α-copaene	0.02	C11H18	1374	1376
19	48.606	β-elemene	0.24	C15H24	1391	1391
20	49.650	β-maaliene	0.06	C15H24	1408	1398
21	50.269	β-caryophyllene	17.47	C15H24	1418	1419
22	51.215	γ-elemene	0.33	C15H24	1434	1434
23	51.673	guaia-6,9-diene	0.66	C15H24	1442	1443
24	51.996	204 161 133 119 105	1.19	-	1447	-
25	52.257	humulene	1.20	C15H24	1452	1454
26	52.658	(3E,6E)-α-farnesene	0.27	C15H24	1458	1457
27	52.683	allo-aromadendrene	0.27	C15H24	1459	1461
28	53.430	204 161 121 105 93 55	0.12	-	1471	-
29	53.659	204 161 133 119 105	0.08	-	1475	-
30	53.902	germacrene D	0.55	C15H24	1479	1481
31	54.202	204 189 147 122 108	0.02	-	1484	-
32	54.369	β-selinene	0.08	C15H24	1487	1486
33	54.521	204 189 161 104 91	0.14	-	1490	-
34	54.818	bicyclogermacrene	2.65	C15H24	1495	1495
35	55.057	161 136 105 95 91 53	0.02	-	1499	-
36	55.298	204 147 107 93 81 67	0.45	-	1503	-
37	55.454	β-cadinene	1.14	C15H24	1506	1518
38	56.277	204 161 136 121 105	0.89	-	1520	-
39	56.647	122 119 107 91 77	0.02	-	1527	-
40	57.524	α-calacorene	0.03	C15H20	1542	1542
41	58.010	106 91 79 41	0.02	-	1551	-
42	58.235	germacrene B	1.29	C15H24	1555	1557
43	59.428	spathulenol	0.07	C15H24O	1576	1576
44	59.706	caryophyllene oxyde	0.49	C15H24O	1581	1581
45	59.987	204 161 119 105 91 81	0.44	-	1586	-
46	60.843	161 105 93 81 77 67	0.08	-	1601	-
47	61.360	204 179 161 119 105	0.18	-	1610	-
48	62.099	204 161 119 105 91	0.07	-	1624	-
49	62.309	isospathulenol	0.43	C15H24O	1627	1638
50	63.668	204 161 121 91 81	0.01	-	1651	-
Total identified			96.26 %
Monoterpenes /Monoterpenoids			68.08 %
Sesquiterpenes /Sequiterpenoids			28.16 %
RT: retention time; RI: retention indices; RI litt. from NIST 2020 database. NI: Not identified (3.72%). Bold: main compounds.

 3.4 Pittosporum senacia leaves EO analysis
The relatively simple composition of the EO from Pittosporum senacia leaves was determined for more than 99% of the total EO (Fig. 4). As presented in Table 3, its chemical profile essentially contained four compounds: the C9 linear alkane hydrocarbon nonane (36.24%) and three monoterpene derivatives, β-pinene (25.11%), β-myrcene (19.19%) and α-pinene (7.36%), which together accounted for 87.9%. Moreover, the chemical profile included monoterpene derivatives such as limonene (1.46%), (Z)- and (E)-β-ocimene (0.01% and 0.09%, respectively), sesquiterpene derivatives like germacrene D (3.68%), humulene (0.40%), as well as other alkanes like decane (0.09%) and undecane (0.56%).

Figure 4. Chromatogram of Pittosporum senacia leaves essential oil.

Table 3. Chemical composition of Pittosporum senacia leaves essential oil. 

Peak #	RT (min)	Compound	Area %	Formula			RI	RI litt.
1	15.492	nonane	36.24	C9H20			900	900
2	17.233	α-thujene	0.03	C10H16			925	929
3	17.578	α-pinene	7.36	C10H16			930	937
4	18.984	camphene	0.06	C10H16			951	952
5	20.464	β-pinene	25.11	C10H16			973	979
6	21.675	β-myrcene	19.19	C10H16			991	991
7	22.628	decane	0.09	C10H22			1004	1000
8	22.843	α-phellandrene	0.05	C10H16			1008	1005
9	23.605	α-terpinene	0.07	C10H16			1018	1017
10	24.131	p-cymene	0.06	C10H14			1026	1025
11	24.183	limonene	1.46	C10H16			1026	1030
12	25.145	(Z)-β-ocimene	0.01	C10H16			1040	1038
13	25.818	(E)-β-ocimene	0.09	C10H16			1050	1049
14	26.414	γ-terpinene	0.22	C10H16			1058	1060
15	28.474	terpinolene	0.08	C10H16			1087	1088
16	29.383	undecane	0.56	C11H24			1100	1100
17	30.518	(E)-4,8-dimethyl-nona-1,3,7-triene	0.04	C11H18			1116	1116
18	35.662	1-dodecene	0.05	C12H24			1191	1190
19	36.632	decanal	0.05	C10H20O			1205	1206
20	45.180	δ-elemene	0.81	C15H24			1336	1338
21	45.941	α-cubebene	0.03	C15H24			1348	1351
22	47.279	α-ylangene	0.05	C15H24			1370	1372
23	47.557	α-copaene	0.12	C15H24			1374	1376
24	48.602	β-elemene	0.56	C15H24			1391	1391
25	50.222	β-caryophyllene	0.48	C15H24			1417	1419
26	50.795	β-copaene	0.15	C15H24			1427	1432
27	51.134	γ-elemene	0.15	C15H24			1433	1434
28	51.405	α-guaiene	0.05	C15H24			1437	1439
29	51.682	guaia-6,9-diene	0.10	C15H24			1442	1443
30	52.006	161 133 105 91 79 69	0.20	-			1447	-
31	52.242	humulene	0.40	C15H24			1451	1454
32	52.842	cis-muurola- 4(15),5-diene	0.03	C15H24			1461	1463
33	53.910	germacrene D	3.68	C15H24			1479	1481
34	54.213	β-selinene	0.03	C15H24			1485	1486
35	54.519	161 105 91 44	0.06	-			1490	-
36	54.720	161 105 91	0.07	-			1493	-
37	55.057	α-muurolene	0.06	C15H24			1499	1499
38	55.304	α-elemene	0.21	C15H24			1503	1462
39	55.834	γ-cadinene	0.11	C15H24			1512	1513
40	56.407	cadina-1(10),4-diene	0.39	C15H24			1523	1524
41	56.650	122 43	0.03	-			1527	-
42	58.244	germacrene B	0.65	C15H24			1555	1557
43	60.289	1-hexadecene	0.10	C16H32			1591	1592
44	61.085	rosifoliol	0.04	C15H26O			1606	1600
45	63.633	τ-muurolol	0.09	C15H26O			1653	1642
46	70.847	1-octadecene	0.03	C18H36			1792	1793
Total identified			99.09 %
Monoterpenes/Monoterpenoids			53.78 %
Sesquiterpenes/Sequiterpenoids			8.19 %
RT: retention time; RI: retention indices; RI litt. from NIST 2020 database. NI: Not identified (0.41%). Bold: main compounds.

Many of the metabolites present in the study by B. S. Jugreet et al. published in 2021 on the EO of P. senacia (whole plant) from Mauritius [5], were also identified in our samples such as β-myrcene, germacrene D, α-muurolene, limonene, α-pinene, α-thujene, p-cymene, β-ocimene, β-elemene, β-caryophyllene, and humulene. The alkanes nonane, decane, and undecane were not reported in the article by B. S. Jugreet et al. However, some alkanes, including nonane, have already been identified in the EO of the genus Pittosporum, such as in an endemic species of the Philippines, P. resiniferum [20]. Interestingly, nonane, a compound described as an insect attractant, [21] was found in 36.24% of our sample.

3.5 Psidium cattleianum floral tops EO analysis
In the most recent study, a distillation yield of 0.83% was reported for EO from P. cattleianum leaves [8]. A total of 68 compounds were observed within the oil, 60 of which could be identified. β-Caryophyllene was the main compound found in 14.7%, followed by eucalyptol (11.7%) and γ-muurolene (5.6%). The second most recent paper, published in 2019, describes the EO of the leaves of P. cattleianum. The EO was mainly composed of sesquiterpene and monoterpene derivatives (47.8% and 28.7%, respectively). A total of 46 compounds were identified with β-caryophyllene (23.4%), caryophyllene oxide (11.4%) and α-pinene (11.3%) as the main compounds [9]. Our results are in agreement with this study (Fig. 5), whose main compounds described were β-caryophyllene and α-pinene at 23.42% and 11.31%, respectively, caryophyllene oxide being present at 1.67%. Indeed, the chemical profile of the EO sample from P. cattleianum floral tops was identified at 88.41%. As shown in Table 4, nearly 70% of the composition consisted of sesquiterpene derivatives including the main compound, β-caryophyllene, present at 43.68% In addition, fifteen monoterpene derivatives have been observed and identified. The four main monoterpenes were β-myrcene (4.67%), α-pinene (4.50%), (Z)-β-ocimene (3.23%) and terpinolene (2.98%).

Figure 5. Chromatogram of Psidium cattleianum leaves essential oil.

Table 4. Chemical composition of Psidium cattleianum leaves essential oil.  

Peak #	RT (min)	Compound	Area %	Formula	RI	RI litt.
1	16.610	5,5-Dimethyl-1-vinylbicyclo[2,1,1]hexane	0.03	C10H16	916	921
2	17.214	α-thujene	0.15	C10H16	925	929
3	17.611	α-pinene	4.50	C10H16	931	937
4	18.920	camphene	0.01	C10H16	950	952
5	20.475	β-pinene	0.19	C10H16	973	979
6	21.677	β-myrcene	4.67	C10H16	991	991
7	22.467	α-phellandrene	0.24	C10H16	1002	1005
8	22.864	3-carene	0.14	C10H16	1008	1011
9	23.360	4-carene	0.12	C10H16	1015	1009
10	23.901	p-cymene	0.19	C10H14	1022	1025
11	24.181	limonene	1.07	C10H16	1026	1030
12	24.984	(Z)-β-ocimene	3.23	C10H16	1038	1038
13	25.710	(E)-β-ocimene	0.56	C10H16	1048	1049
14	26.346	γ-terpinene	0.63	C10H16	1057	1060
15	28.421	terpinolene	2.98	C10H16	1086	1088
16	40.039	linalyl acetate	0.23	C12H20O2	1257	1257
17	45.984	161 136 121 105 93 67	0.27	-	1349	-
18	47.293	α-ylangene	0.44	C15H24	1370	1372
19	47.581	α-copaene	1.18	C15H24	1374	1376
20	48.127	α-bourbornene	0.07	C15H24	1383	1384
21	48.598	204 121 108 93 81 55	0.12	-	1391
22	49.495	tetradecene	0.03	C14H28	1405	1392
23	49.641	204 189 161 119 105	0.03	-	1408	-
24	50.374	β-caryophyllene	43.68	C15H24	1420	1419
25	50.818	γ-elemene	0.42	C15H24	1427	1434
26	51.387	aromadendrene	0.07	C15H24	1437	1440
27	51.672	204 161 133 119 105 91	0.10	-	1442	-
28	52.009	204 161 119 105 91 79	0.16	-	1447	-
29	52.278	humulene	6.49	C15H24	1452	1454
30	52.709	9-epi-caryophyllene	0.18	C15H24	1459	1466
31	53.640	γ-muurolene	2.32	C15H24	1475	1477
32	53.874	α-amorphene	0.50	C15H24	1479	1482
33	54.197	β-selinene	1.27	C15H24	1484	1486
34	54.307	204 133 119 107 93 79	0.29	-	1486	-
35	54.517	204 189 161 133 91	0.25	-	1490	-
36	54.727	204 161 133 119 105 93	1.70	-	1493	-
37	55.059	α-muurolene	0.34	C15H24	1499	1499
38	55.454	204 161 134 119 105	0.51	-	1506	-
39	55.575	122 109 93 79 69	0.26	-	1508	-
40	55.837	β-bisabolene	0.87	C15H24	1513	1509
41	56.175	γ-cadinene	0.88	C15H24	1519	1513
42	56.401	cadina-1(10),4-diene	2.38	C15H24	1523	1524
43	57.015	204 189 161 133 105 91	2.35	-	1533	-
44	57.184	204 189 161 133 105	0.74	-	1536	-
45	57.385	selina-3,7(11)-diene	2.06	C15H24	1540	1542
46	57.987	161 109 95 91 79 69	0.11	-	1551	-
47	58.238	germacrene B	1.84	C15H24	1555	1557
48	58.604	204 189 133 119 105	0.17	-	1562	-
49	58.749	nerolidol	0.33	C15H26O	1564	1564
50	58.978	204 161 123 111 69 55	0.19	-	1568	-
51	59.701	caryophyllene oxyde	1.67	C15H24O	1581	1581
52	60.284	204 161 119 105 91 79	0.44	-	1591	-
53	60.593	204 161 119 107 93 79	0.07	-	1597	-
54	60.746	161 133 121 93 82 77	0.10	-	1600	-
55	60.956	204 161 133 119 105 95	0.09	-	1603	-
56	61.162	147 138 109 96 93 67	0.17	-	1607	-
57	61.623	202 187 131 123 91	0.29	-	1616	-
58	62.084	204 161 119 105 91	0.71	-	1624	-
59	62.221	204 161 119 105 91	0.78	-	1627	-
60	62.424	204 179 161 119 105	0.54	-	1631	-
61	62.642	159 136 107 91 79 69	0.14	-	1635	-
62	62.969	τ-cadinol	1.09	C15H26O	1641	1640
63	63.198	204 161 119 105 93	0.36	-	1645	-
64	63.489	202 187 121 105 91	0.41	-	1651	-
65	63.630	τ-muurolol	0.87	C15H26O	1653	1642
66	64.190	204 189 161 133 107	0.20	-	1664	-
67	65.113	126 119 111 77 55	0.06	-	1681	-
68	65.807	eudesm-7(11)-en-4-ol	0.49	C15H26O	1694	1692
Total identified			88.41 %
Monoterpenes /Monoterpenoids			18.70 %
Sesquiterpenes /Sequiterpenoids			69.99 %
RT: retention time; RI: retention indices; RI litt. from NIST 2020 database. NI: Not identified (11.61%). Bold: main compounds.

 3.6 Olfactory analysis
Olfactory evaluation of the four essential oils was performed by a panel of 4 persons by GC/MS-O analysis. The objective was to obtain an overview of the main contributors to the overall scent of each EO which was found to be generally woody, a family of olfactory properties highly priced in modern perfumery.

In Table 5, the main aroma-active compounds and their odor properties are presented.Hedychium gardnerianum flowers EO presented three characteristic areas, a woody area identified by 2 panelists out of 4, and two floral areas for 2 panelists out of 4. GC/MS-O analysis of EO from Hedychium flavescens leaves revealed a main contributor with a fresh, woody and green scent which was annotated as γ-elemene. The presence of woody, earthy, and green areas was highlighted by 5 panelists out of 5, floral and rose area by 4 panelists out of 5 and mint, herbal, and citrus areas by 2 panelists out of 5. The main aroma-active compounds of Pittosporum senacia leaves EO were annotated as β-myrcene with a green, woody and spicy scent and as terpinolene with a moss and woody scent. The GC/MS-O analysis revealed herbal, and pine tree area for 5 panelists out of 5 as well as floral and citrus area for 5 panelists out of 5.

Table 5. Overview of the main contributors of the four EOs. 

Samples	Annotated compound	Scent description	RT (min)	RIapolar
H. gardnerianum, flowers EO	Sabinol*	Floral	9.55	1144
	Unknown**	Woody	17.23	N.D.
	Unknown	Floral	22.48	16.94
H. flavescens, leaves, EO	Terpinolene	Woody	8.55	1093
	trans-a-bisabolene	Woody, rose	17.35	1512
P. senacia, leaves, EO	β-pinene	Pine, Green	6.61	N.D.
	Terpinolene	Woody	8.53	1092
P. cattleianum, floral tops, EO	β-pinene	Pine, Green	6.42	979
	Unknown**	Woody	8.26	1078
	Unknown	Citrus, spicy	11.80	1261

*Tentative assignation. **No peak detectable.

 Finally, Psidium cattleianum floral tops EO showed three characteristic scents with β-myrcene and two unknown compounds, eluting at 8.9 min and 13.25 min, respectively, both with floral scent. In addition of these markers, pine tree scent was found by 4 panelists out of 4, woody, and earthy area by 4 panelists out of 4, floral area by 2 panelists out of 4, and citrus with mossy/earthy area by 2 panelists out of 4. In addition to these main contributors, other smaller contributors as linalool, with floral and fresh scent, were detected in each of the four EOs GC/MS-O analyses.

In general, the chemical composition of an EO varies according to many factors such as the year of harvest, the geographical area, the climate, the storage of the raw material, the duration of storage of the plant before extraction, the extraction process [22]. Two EOs from the same species may therefore have a different chemical composition. Nevertheless, the chemical profile and chemical markers may be specific to a given plant or chemotype. The analysis and authentication tasks can be sometimes complicated by conformity or adulteration issues [23, 24]. Olfactory analysis is thus an useful addition to physico-chemical analysis.

4.    Conclusions

The main goal of our work was to characterize for the first time the EOs of the four species harvested on Reunion Island and to compare their chemical profiles with those described in the literature with samples collected in other locations. We used two complementary analyses, gas chromatography coupled with mass spectrometry (GC/MS) and flame ionization detector (GC-FID), to obtain the most complete description. Additionally, an olfactory analysis was performed on these four EOs by gas chromatography coupled with mass spectrometry and olfactometry (GC/MS-O). The chemical composition of each essential oil was identified in more than 87.43% for H. garderianum flowers, 96.26% for H. flavescens leaves, 99.09% for P. senacia leaves and 88.41% for P. cattleianum floral tops. The chemical composition of H. gardnerianum EO, mostly composed of mono- and sesquiterpene hydrocarbons of low complexity, was found to be consistent with other EOs within natural variability due to differences in their geographical origin (islands from the Atlantic, Pacific, and Indian oceans). The sample was mainly composed of sesquiterpene derivatives including β-farnesene (12.05%), α-cadinol (9.71%), α-farnesene (7.09%), τ-muurolol (5.89%) and δ-cadinene (5.83%). The monoterpene derivatives identified accounted for about 20% (mostly α-pinene, β-pinene and humulene). For the EO from H. flavescens leaves, our study provided the first description of its chemical composition, which appeared to be rather simple and to contain mostly hydrocarbons. The main compounds were found to be β-pinene (47.81%), α-pinene (18.74%) and β-caryophyllene (17.47%), which together accounted for 84.02% of the sample. For the P. senacia, while β-myrcene was found to be an important constituent of the EO, as was the case for material from Madagascar and Mauritius, which are geographically close to French Reunion, the composition was different but consistent, and the striking difference was the presence of nonane. The oil primarily contained nonane (36.24%), β-pinene (25.11%), β-myrcene (19.19%) and α-pinene (7.36%), together accounting for 87.9% of the composition. Lastly, the composition of the P. cattleianum EO was very consistent with other studies, with 70% sesquiterpene derivatives including the main compound, β-caryophyllene, present at 43.68%. With these compositions mostly based on mono- and sesquiterpene hydrocarbons, it came as no surprise that the panelists described the scent of these EOs as herbal, citrus, green, pine tree, and in some cases floral and woody. With these results in hand, these endemic essential oils from Reunion could receive in the future further attention for applications in fragrance and cosmetic products. Future work could include the determination of odor impact molecules by aroma extract dilution analysis based on the GC-O studies presented herein.

Authors’ contributions

Conceptualization, M.C and S.A.; Methodology, M.C and S.A.; Investigation, M.C, M.T. and S.A.; Resources, S.A.; Data Curation, M.C, M.T. and S.A.; Writing – original draft preparation, M.C and S.A.; Writing – review & editing, M.C, M.T. and S.A.; Supervision, S.A.; Project administration, M.C, M.T. and S.A.

Acknowledgements

This work was supported by Université Côte d’Azur, CNRS and Technopole de la Réunion in the framework of the Insola Scent project (Sophie Afchain). We are grateful to Charlotte Richard and Julie Abdalla for contributing to the olfactory evaluation during GC-O analyses and Dr. Catherine Buchanan for proofreading.

Funding
No specific funding to declare.

Availability of data and materials
All data will be made available on request according to the journal policy.

Conflicts of interest
The authors declare no conflict of interest.

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