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. 2022 Dec 14;27(24):8893. doi: 10.3390/molecules27248893

Analysis of Volatile Compounds from Different Parts of Houttuynia cordata Thunb.

Chen-Hsiang Lin 1, Louis Kuoping Chao 2, Li-Yun Lin 3, Chin-Sheng Wu 4, Lee-Ping Chu 5, Chien-Hsueh Huang 2,*, Hsin-Chun Chen 2,*
Editors: Francisco Pena-Pereira, Manuel A Coimbra, Antoni Szumny
PMCID: PMC9783048  PMID: 36558024

Abstract

Houttuynia cordata Thunb. is a medicinal and edible plant that has been commonly used in traditional Chinese medicine since ancient times. This study used headspace solid-phase microextraction (HS-SPME) and direct injection, combined with gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS), to identify the volatile compounds in H. cordata. Extraction from different parts of the plant using different extraction techniques for the identification of volatile compounds were determined. A total of 93 volatile components were analyzed in the leaves, stems, rhizomes, and whole plant samples of H. cordata. The leaves contained more (Z)-3-hexenal, β-myrcene, (Z)-β-ocimene, and (4E,6E)-allo-ocimene; the stems contained more geranyl acetate and nerolidol; and rhizomes contained more α-pinene, β-pinene, limonene, 2-undecanone, and decanoyl acetaldehyde. Among them, the essential oil extracted by HS-SPME could produce more monoterpenes, while direct injection could obtain higher contents of aliphatic ketones, terpene esters, sesquiterpenes, and was more conducive to the extraction of 2-undecanone and decanoyl acetaldehyde.

Keywords: Houttuynia cordata Thunb., essential oil, gas chromatography-mass spectrometry (GC-MS), headspace solid-phase microextraction (HS-SPME)

1. Introduction

Houttuynia cordata Thunb., belonging to Saururaceae, is a medicinal and edible perennial herb native to China, Japan, and Taiwan [1]. H. cordata is rich in nutrients and contains a variety of vitamins, amino acids, and trace elements, such as zinc, potassium, and copper [2]. The physiologically active substances of H. cordata include essential oils, steroids, and flavonoids [3], which have many pharmacological properties, including antibacterial, antiviral, anti-inflammatory, antioxidant, and anticancer effects. Many studies have been conducted on its active components and pharmacological properties [4,5,6,7,8].

Essential oils, secondary metabolites of plants, are industrially important natural products [9]. Essential oils were utilized in pharmaceutical and other related medical, and the amount of published evidence on aromatherapy and essential oils has gradually increased [10,11]. The essential oil components of H. cordata include decanoyl acetaldehyde, 2-undecanone, β-myrcene, decanal, and trans-caryophyllene [1]. Because the essential oil compounds of H. cordata will affect its pharmacological effects, analyses of the volatile components are also used to determine plant quality [12].

To date, there have been many studies on the volatile components of H. cordata. Kosuge [13] used steam distillation to extract essential oils from H. cordata and isolated decanoyl acetaldehyde, which has an antibacterial effect and is known to cause the unique stinking smell of H. cordata [14]. However, this component is easily oxidized into 2-undecanone during distillation and storage [15]. Both are important volatile components of H. cordata [14,16]. Yang et al. [17] analyzed 25 volatile compounds in H. cordata by GC-MS, including α-pinene, camphene, β-pinene, β-myrcene, (+)-limonene, γ-terpinene, decanal, linalool, β-caryophyllene, and 2-undecanone. Asakawa et al. [18] analyzed volatile compounds in different parts of the H. cordata plant. The study indicated that the main component of all parts analyzed was 4-tricancanone, and β-myrcene was the main monoterpene in the flowers, leaves, and stems, while the main monoterpene in the rhizomes and roots was β-pinene, and 1-decanal was the main polyketide in leaves and stems. Xu et al. [19] analyzed monoterpenes in the essential oils of three H. cordata accessions, and the results showed that the number and content of monoterpenes were different in different plant parts and different accessions.

In this study, extraction from different parts of the H. cordata plant, and different extraction methods on the volatile components. The results of this study can be used as a reference for the extraction and utilization of H. cordata in the future.

2. Results and Discussion

2.1. Analysis of Volatile Compounds from Different Parts of H. cordata

The leaves, stems, rhizomes, and whole plants of fresh H. cordata were analyzed for differences in volatile compounds (Figure 1, Figure 2 and Figure 3). Fresh plants and essential oils were analyzed using HS-SPME and direct injection. A total of 91 volatile components were identified in the H. cordata samples. The yield of essential oils was 0.09% (leaves), 0.02% (stems), 0.04% (rhizomes), and 0.04% (whole plants). Chen et al. [20] analyzed Angelica acutiloba essential oil and found that the highest content of essential oils was in the leaves. The main compounds from different parts were not the same, and the overall components and contents were different. In addition, the year-to-year yields of essential oil were slightly different, which may be due to differences in cultivation and climatic conditions [21].

Figure 1.

Figure 1

Figure 1

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Ion chromatogram of volatile compounds from different parts of fresh H. cordata analyzed by HS-SPME: (a) leaf; (b) stem; (c) rhizome; and (d) whole plant.

Figure 2.

Figure 2

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Ion chromatogram of volatile compounds in essential oil from different parts of fresh H. cordata analyzed by HS-SPME: (a) leaf; (b) stem; (c) rhizome; and (d) whole plant.

Figure 3.

Figure 3

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Ion chromatogram of volatile compounds in essential oil from different parts of fresh H. cordata analyzed by direct injection: (a) leaf; (b) stem; (c) rhizome; and (d) whole plant.

Analysis of fresh H. cordata samples using HS-SPME found that the main volatile compounds in the leaves were (Z)-3-hexenal, (Z)-3-hexenol, 1-hexenol, β-myrcene, (Z)-β-ocimene, (4E,6E)-allo-ocimene, (E)-β-caryophyllene, and decanoyl acetaldehyde. The main volatile compounds in the stem were α-pinene, β-pinene, β-myrcene, limonene, bornyl acetate, (E)-β-caryophyllene, and decanoyl acetaldehyde. The main volatile compounds in the rhizomes were α-pinene, sabinene, β-pinene, β-myrcene, limonene, bornyl acetate, (E)-β-caryophyllene, and decanoyl acetaldehyde. The main volatile compounds in the whole plant were α-pinene, β-pinene, β-myrcene, limonene, (Z)-β-ocimene, (4E,6E)-allo-ocimene, bornyl acetate, (E)-β-caryophyllene, and decanoyl acetaldehyde. β-myrcene had the highest content within all samples (Figure 4). Comparing the composition of leaves, stems, and rhizomes, the content of (Z)-3-hexenal, (Z)-3-hexenol, 1-hexenol, β-myrcene, (Z)-β-ocimene, and (4E,6E)-allo-ocimene in leaves was significantly higher than in the other parts of the plant. The rhizomes contained the highest content of α-pinene, sabinene, β-pinene, limonene, bornyl acetate, and decanoyl acetaldehyde. The stem had no components that were significantly higher than those of the leaves and rhizomes (Table 1).

Figure 4.

Figure 4

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Comparison of the contents of the major volatile compounds from different parts of fresh H. cordata analyzed by HS-SPME: (a) leaf; (b) stem; (c) rhizome; and (d) whole plant.

Table 1.

Comparison of the content of volatile compounds from different parts of H. cordata and their essential oils, analyzed by HS-SPME and direct injection.

Compound CAS Number Molecular Formula RI a RI b Relative Content (%) c
HS-SPME Essential Oil HS-SPME Essential Oil Direct Injection
Leaf Stem Rhizome Whole d Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole
Aliphatic Alcohols
prenol 556-82-1 C5H10O 751.5 745 0.04 ± 0.01
(Z)-3-hexenol 928-96-1 C6H12O 840 830 3.76 ± 0.45 0.47 ± 0.37 0.75 ± 0.07 0.08 ± 0.01 0.29 ± 0.06 0.08 ± 0.05 0.02 ± 0.01 0.07 ± 0.02
1-hexanol 111-27-3 C6H14O 854 849 1.38 ± 0.62 0.23 ± 0.09
(E)-p-menth-2-en-1-ol 29803-81-4 C10H18O 1112 1101 0.02 ± 0.01 0.03 ± 0.01 0.14 ± 0.03 0.14 ± 0.01 0.11 ± 0.01
1-nonanol 143-08-8 C9H20O 1157 1147 <0.01 0.05 ± 0.04 0.01 ± 0.001 0.27 ± 0.10 0.02 ± 0.004
1-decanol 112-30-1 C10H22O 1257 1256 0.01 ± 0.002 0.03 ± 0.004 0.08 ± 0.01
Aliphatic Aldehydes
(Z)-3-hexenal 6789-80-6 C6H10O 769.5 764 1.05 ± 0.12 0.16 ± 0.04 0.59 ± 0.31 0.09 ± 0.02 0.04 ± 0.01 0.02 ± 0.004
hexanal 66-25-1 C6H12O 776 766 0.01 ± 0.002 0.04 ± 0.01 0.01 ± 0.001
(E)-2-hexenal 6728-26-3 C6H10O 827 819 0.74 ± 0.24 0.30 ± 0.14 1.35 ± 0.51 0.10 ± 0.02 0.31 ± 0.06 0.55 ± 0.12 0.01 ± 0.01 0.09 ± 0.02
(2E,4E)-hexadienal 142-83-6 C6H8O 878 871 0.12 ± 0.08 <0.01 0.03 ± 0.01 0.01 ± 0.01 0.02 ± 0.003 0.01 ± 0.003
α-campholenal 4501-58-0 C10H16O 1105 1098 <0.01 0.01 ± 0.002
decanal 112-31-2 C10H20O 1185 1178 0.15 ± 0.05 0.40 ± 0.02 0.69 ± 0.13 0.29 ± 0.13 0.02 ± 0.002 0.04 ± 0.01 0.02 ± 0.01 0.13 ± 0.01 0.09 ± 0.002
decanoyl acetaldehyde 56505-80-7 C12H22O2 1367 1.59 ± 0.70 2.74 ± 1.23 6.55 ± 2.56 2.96 ± 0.86 0.04 ± 0.01 0.16 ± 0.09 0.33 ± 0.08 1.54 ± 0.33 0.62 ± 0.16
Aliphatic Ester
n-nonanyl acetate 143-13-5 C11H22O2 1292 1284 0.19 ± 0.19 0.05 ± 0.03
Aliphatic Ketones
sulcatone 110-93-0 C8H14O 964 956 0.03 ± 0.01 0.02 ± 0.01 0.01 ± 0.002
2-nonanone 821-55-6 C9H18O 1072 1063 <0.01 0.01 ± 0.003 0.01 ± 0.001
2-undecanone 112-12-9 C11H22O 1274 1272 0.17 ± 0.07 <0.01 5.51 ± 0.61 1.93 ± 0.56 2.67 ± 1.02 2.48 ± 0.47 22.89 ± 1.97 9.92 ± 1.02
3-dodecanone 1534-27-6 C12H24O 1370 1364 <0.01 0.02 ± 0.001
2-dodecanone 6175-49-1 C12H24O 1375 1367 <0.01 <0.01 <0.01 <0.01 0.08 ± 0.02 <0.01 0.06 ± 0.01 0.04 ± 0.004
Compound CAS Number Molecular Formula RI RI Relative Content (%)
HS-SPME Essential Oil HS-SPME Essential Oil Direct Injection
Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole
2-tridecanone 593-08-8 C13H26O 1477 1466 0.06 ± 0.02 0.12 ± 0.03 0.09 ± 0.01 0.17 ± 0.02 2.66 ± 0.76 1.70 ± 0.39 1.57 ± 0.17 2.93 ± 0.41
2-pentadecanone 2345-28-0 C15H30O 1681 1671 <0.01 0.14 ± 0.04 0.05 ± 0.03 0.14 ± 0.04
Aromatic Compounds
p-cymene 99-87-6 C10H14 1014 1010 0.03 ± 0.02 0.07 ± 0.002 0.06 ± 0.01 0.08 ± 0.04 0.03 ± 0.001 0.09 ± 0.01 0.15 ± 0.01 0.13 ± 0.02 0.04 ± 0.003 0.11 ± 0.01 0.06 ± 0.01 0.11 ± 0.003
p-cymenene 1195-32-0 C10H12 1073 1068 0.05 ± 0.01 0.06 ± 0.01 0.04 ± 0.01 0.02 ± 0.004
methyl salicylate 119-36-8 C8H8O3 1172 1169 <0.01 0.01 ± 0.002 0.01 ± 0.001 0.05 ± 0.01 0.03 ± 0.003
Hydrocarbon
nonane 111-84-2 C9H20 900 890 <0.01 0.01 ± 0.002 0.01 ± 0.002 0.01 ± 0.003 0.01 ± 0.002 0.01 ± 0.005 0.01 ± 0.001
Monoterpenes
tricyclene 508-32-7 C10H16 921 914 0.01 ± 0.001 <0.01 <0.01
α-thujene 2867-05-2 C10H16 924 917 0.13 ± 0.05 0.08 ± 0.02 0.19 ± 0.02 0.06 ± 0.01 0.01 ± 0.001 0.04 ± 0.01 0.02 ± 0.001
α-pinene 80-56-8 C10H16 933 925 0.26 ± 0.04 2.08 ± 0.11 9.45 ± 0.69 4.68 ± 0.92 0.52 ± 0.03 4.78 ± 0.41 14.74 ± 1.00 7.91 ± 0.72 0.44 ± 0.01 2.04 ± 0.59 7.28 ± 0.76 3.90 ± 0.51
α-fenchene 471-84-1 C10H16 944 938 <0.01
camphene 79-92-5 C10H16 946 940 0.13 ± 0.01 0.73 ± 0.03 0.78 ± 0.25 0.73 ± 0.10 0.31 ± 0.01 2.06 ± 0.25 1.53 ± 0.11 1.10 ± 0.07 0.22 ± 0.01 1.00 ± 0.31 0.77 ± 0.08 0.55 ± 0.06
sabinene 3387-41-5 C10H16 967 963 0.14 ± 0.02 2.07 ± 0.23 0.40 ± 0.09 0.02 ± 0.002 0.20 ± 0.34 0.19 ± 0.04
β-pinene 127-91-3 C10H16 972 965 0.13 ± 0.01 1.98 ± 0.33 21.01 ± 2.32 9.79 ± 2.11 0.05 ± 0.01 0.94 ± 0.12 37.61 ± 1.16 6.70 ± 0.46 0.16 ± 0.004 1.39 ± 0.17 19.16 ± 2.07 8.95 ± 0.57
β-myrcene 123-35-3 C10H16 983 983 70.39 ± 1.85 59.81 ± 2.25 34.34 ± 1.44 59.74 ± 5.65 76.68 ± 1.24 78.00 ± 1.15 23.32 ± 1.18 62.95 ± 1.03 64.03 ± 2.07 41.59 ± 12.01 20.08 ± 1.31 41.69 ± 2.87
α-phellandrene 99-83-2 C10H16 998 992 0.06 ± 0.01 0.19 ± 0.03 0.10 ± 0.02 0.03 ± 0.002 0.22 ± 0.02 0.16 ± 0.01 0.01 ± 0.001 0.03 ± 0.02 0.05 ± 0.01
δ-3-carene 13466-78-9 C10H16 1005 1001 <0.01
α-terpinene 99-86-5 C10H16 1010 1008 0.05 ± 0.01 0.13 ± 0.03 0.07 ± 0.01 0.03 ± 0.004 0.11 ± 0.003 0.14 ± 0.01 0.13 ± 0.01 <0.01 0.01 ± 0.01 0.04 ± 0.003 0.06 ± 0.01
limonene 138-86-3 C10H16 1023 1014 0.18 ± 0.01 1.73 ± 0.15 11.59 ± 1.01 5.12 ± 0.70 2.06 ± 0.16 3.07 ± 0.04 10.57 ± 1.18 6.13 ± 0.42 0.26 ± 0.01 2.00 ± 0.43 7.45 ± 0.61 5.48 ± 0.11
(Z)-β-ocimene 3338-55-4 C10H16 1028 1020 3.54 ± 0.29 0.61 ± 0.05 1.85 ± 0.25 3.99 ± 0.12 0.90 ± 0.01 1.40 ± 0.10 8.49 ± 1.21 1.71 ± 0.98 6.63 ± 0.15
(E)-β-ocimene 3779-61-1 C10H16 1038 1028 0.54 ± 0.10 0.41 ± 0.04 0.21 ± 0.03 0.36 ± 0.04 1.06 ± 0.25 0.48 ± 0.01 0.15 ± 0.01 0.74 ± 0.07 0.35 ± 0.09 0.16 ± 0.09 0.09 ± 0.003 0.58 ± 0.06
β-terpinene 99-84-3 C10H16 1049 1046 0.02 ± 0.001
Compound CAS Number Molecular Formula RI RI Relative Content (%)
HS-SPME Essential Oil HS-SPME Essential Oil Direct Injection
Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole
γ-terpinene 99-85-4 C10H16 1050 1047 0.12 ± 0.02 0.05 ± 0.01 0.01 ± 0.001 0.05 ± 0.01 0.29 ± 0.05 0.14 ± 0.02 0.02 ± 0.01 0.19 ± 0.02 0.07 ± 0.05
α-terpinolene 586-62-9 C10H16 1079 1072 0.19 ± 0.02 0.10 ± 0.01 0.43 ± 0.01 0.21 ± 0.07 0.10 ± 0.001 0.21 ± 0.01 0.42 ± 0.08 0.29 ± 0.04 0.15 ± 0.03 0.36 ± 0.03 0.22 ± 0.03
(4E,6Z)-allo-ocimene 7216-56-0 C10H16 1116 1107 4.22 ± 0.44 0.60 ± 0.03 0.18 ± 0.01 2.00 ± 0.30 9.32 ± 0.33 2.31 ± 0.08 0.13 ± 0.01 4.66 ± 0.12 0.14 ± 0.003 0.05 ± 0.01 0.01 ± 0.002 0.11 ± 0.01
(4E,6E)-allo-ocimene 3016-19-1 C10H16 1129 1123 0.33 ± 0.07 0.17 ± 0.05 0.03 ± 0.004 0.15 ± 0.03 0.39 ± 0.003 0.17 ± 0.002 0.02 ± 0.001 0.32 ± 0.02
Sesquiterpenes
α-cubebene 17699-14-8 C15H24 1351 1348 0.06 ± 0.03 0.01 ± 0.001 <0.01 <0.01 0.05 ± 0.004
α-copaene 3856-25-5 C15H24 1375 1377 <0.01 0.01 ± 0.001 0.04 ± 0.005 0.04 ± 0.01 0.01 ± 0.001
β-elemene 515-13-9 C15H24 1388 1386 0.19 ± 0.02 0.17 ± 0.02 0.17 ± 0.04 0.01 ± 0.001 0.02 ± 0.01 0.03 ± 0.003 0.03 ± 0.01 0.11 ± 0.01 0.14 ± 0.03 0.11 ± 0.01 0.13 ± 0.02
(Z)-β-caryophyllene 118-65-0 C15H24 1405 1402 <0.01 0.01 ± 0.001
(Z)-α-bergamotene 18252-46-5 C15H24 1413 1406 <0.01 <0.01
(E)-β-caryophyllene 87-44-5 C15H24 1419 1425 1.72 ± 0.34 1.89 ± 0.12 1.78 ± 0.27 1.70 ± 0.05 0.13 ± 0.02 0.41 ± 0.15 0.42 ± 0.04 0.32 ± 0.10 0.97 ± 0.04 2.22 ± 0.24 1.70 ± 0.22 1.56 ± 0.23
(E)-α-bergamotene 13474-59-4 C15H24 1432 1433 0.19 ± 0.04 0.30 ± 0.02 0.03 ± 0.002 0.08 ± 0.004 0.01 ± 0.001 0.02 ± 0.01 <0.01 0.01 ± 0.003 0.17 ± 0.02 0.18 ± 0.03 0.02 ± 0.003 0.10 ± 0.02
(Z)-β-farnesene 28973-97-9 C15H24 1446 1438 0.37 ± 0.05 0.34 ± 0.03 0.20 ± 0.02 0.29 ± 0.05 0.03 ± 0.001 0.08 ± 0.02 0.03 ± 0.01 0.06 ± 0.01 0.42 ± 0.01 0.77 ± 0.10 0.35 ± 0.06 0.45 ± 0.07
α-humulene 6753-98-6 C15H24 1451 1458 0.16 ± 0.03 0.29 ± 0.01 0.17 ± 0.003 0.01 ± 0.002 0.05 ± 0.02 0.04 ± 0.004 0.03 ± 0.01 0.11 ± 0.01 0.35 ± 0.06 0.27 ± 0.03 0.22 ± 0.03
alloaromadendrene 25246-27-9 C15H24 1460 1460 <0.01 0.01 ± 0.002
(Z,E)-α-farnesene 26560-14-5 C15H24 1480 1471 0.37 ± 0.06 0.02 ± 0.002
β-selinene 17066-67-0 C15H24 1482 1480 0.47 ± 0.04 0.83 ± 0.01 0.41 ± 0.05 0.16 ± 0.03 0.04 ± 0.003
valencene 4630-07-3 C15H24 1484 1490 0.10 ± 0.01 0.20 ± 0.003 0.08 ± 0.01 <0.01 0.01 ± 0.001 0.03 ± 0.01 0.01 ± 0.001 0.02 ± 0.003 0.20 ± 0.03 0.10 ± 0.01
α-selinene 473-13-2 C15H24 1490 1494 0.36 ± 0.03 0.52 ± 0.03 0.28 ± 0.02 0.03 ± 0.01 0.09 ± 0.02 0.04 ± 0.004 0.06 ± 0.01 0.44 ± 0.02 0.33 ± 0.04
β-bisabolene 495-61-4 C15H24 1500 1499 <0.01
γ-cadinene 39029-41-9 C15H24 1507 1508 0.05 ± 0.004 0.04 ± 0.02
(Z)-calamenene 72937-55-4 C15H22 1510 1510 0.08 ± 0.03 0.01 ± 0.001 0.01 ± 0.002 0.01 ± 0.001 0.19 ± 0.02 0.17 ± 0.05 0.11 ± 0.02
δ-cadinene 483-76-1 C15H24 1515 1513 0.04 ± 0.02 <0.01 0.01 ± 0.002 0.01 ± 0.001 0.04 ± 0.004 0.08 ± 0.01 0.06 ± 0.01
cadina-1,4-diene 16728-99-7 C15H24 1525 1524 <0.01 <0.01 0.04 ± 0.001 0.04 ± 0.01 0.04 ± 0.01
Compound CAS Number Molecular Formula RI RI Relative Content (%)
HS-SPME Essential Oil HS-SPME Essential Oil Direct Injection
Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole
Terpene Alcohols
linalool 78-70-6 C10H18O 1086 1074 0.10 ± 0.02 0.04 ± 0.003 0.11 ± 0.03 0.14 ± 0.02 0.08 ± 0.01 0.06 ± 0.01 0.23 ± 0.03 0.37 ± 0.02 0.11 ± 0.001 0.18 ± 0.01
borneol 507-70-0 C10H18O 1152 1144 0.01 ± 0.01 0.02 ± 0.004
terpinen-4-ol 562-74-3 C10H18O 1163.5 1162 0.03 ± 0.01 0.05 ± 0.01 <0.01 0.04 ± 0.01 0.24 ± 0.05 0.13 ± 0.02 0.43 ± 0.05 0.40 ± 0.03
α-terpineol 98-55-5 C10H18O 1175 1171 0.01 ± 0.003 0.08 ± 0.02 0.15 ± 0.03 0.13 ± 0.03 0.42 ± 0.12 0.38 ± 0.04 0.51 ± 0.09
(E)-geraniol 106-24-1 C10H18O 1237 1231 <0.01 <0.01 <0.01 <0.01 0.04 ± 0.01 0.03 ± 0.01 <0.01 0.02 ± 0.002
perilla alcohol 536-59-4 C10H18O 1281 1273 0.10 ± 0.03 <0.01
nerolidol 40716-66-3 C15H26O 1549 1540 0.15 ± 0.01 0.04 ± 0.001 <0.01 0.01 ± 0.001 0.01 ± 0.001 0.32 ± 0.01 1.22 ± 0.48 0.08 ± 0.01 0.26 ± 0.04
spathulenol 6750-60-3 C15H24O 1568 1569 <0.01 0.35 ± 0.02 0.66 ± 0.45 0.29 ± 0.02
globulol 51371-47-2 C15H26O 1579 1580 0.09 ± 0.01 0.19 ± 0.07 0.11 ± 0.02
veridiflorol 552-02-3 C15H26O 1580 1588 0.13 ± 0.01 0.18 ± 0.04 0.09 ± 0.02
isospathulenol 88395-46-4 C15H24O 1626 1625 0.08 ± 0.01 0.13 ± 0.05 0.05 ± 0.01
α-cadinol 481-34-5 C15H26O 1641 1642 0.09 ± 0.01 0.07 ± 0.03 0.05 ± 0.01
(2E,6E)-farnesol 106-28-5 C15H26O 1709 1700 0.04 ± 0.01 0.05 ± 0.02 0.03 ± 0.01
Terpene Aldehydes
β-cyclocitral 432-25-7 C10H16O 1196 1194 0.01 ± 0.001 0.01 ± 0.004 0.01 ± 0.004 0.01 ± 0.002 0.02 ± 0.004 0.04 ± 0.004 0.05 ± 0.003 0.03 ± 0.003
geranial 141-27-5 C10H16O 1247 1242 <0.01 0.11 ± 0.02
Terpene Esters
fenchyl acetate 13851-11-1 C12H20O2 1214 1205 0.01 ± 0.004 0.02 ± 0.01 0.01 ± 0.002 0.05 ± 0.004 0.05 ± 0.01
linalyl acetate 115-95-7 C12H20O2 1241 1235 0.08 ± 0.04
bornyl acetate 76-49-3 C12H20O2 1270 1271 0.60 ± 0.08 3.12 ± 0.05 3.37 ± 0.43 1.91 ± 0.39 0.49 ± 0.20 3.29 ± 0.96 2.62 ± 0.62 1.36 ± 0.29 1.79 ± 0.18 14.55 ± 1.61 5.56 ± 0.10 4.15 ± 0.18
α-terpinyl acetate 80-26-2 C12H20O2 1333 1330 0.31 ± 0.03 0.07 ± 0.02
neryl acetate 141-12-8 C12H20O2 1343 1333 0.13 ± 0.01 0.03 ± 0.01 0.09 ± 0.01 0.30 ± 0.04 0.15 ± 0.004 0.12 ± 0.01
geranyl acetate 105-87-3 C12H20O2 1361 1348 0.33 ± 0.05 0.46 ± 0.03 0.48 ± 0.03 0.27 ± 0.03 0.08 ± 0.02 0.18 ± 0.03 0.10 ± 0.03 0.18 ± 0.03 3.11 ± 0.19 0.96 ± 0.52
Compound CAS Number Molecular Formula RI RI Relative Content (%)
HS-SPME Essential Oil HS-SPME Essential Oil Direct Injection
Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole
(2E,6E)-farnesyl acetate 4128-17-0 C17H28O2 1816 1803 0.01 ± 0.01
Terpene Ketones
pinocarvone 30460-92-5 C10H14O 1140 1137 <0.01 0.02 ± 0.01 0.03 ± 0.01 0.03 ± 0.004 0.03 ± 0.001
carvone 99-49-0 C10H14O 1218 1215 <0.01 0.03 ± 0.003
piperitone 89-81-6 C10H16O 1232.5 1228 <0.01 <0.01 0.06 ± 0.03 0.02 ± 0.002
β-damascenone 23726-93-4 C13H18O 1361 1361 0.01 ± 0.001 0.01 ± 0.001 0.09 ± 0.02 0.64 ± 0.23
Terpene Oxides
(E)-limonene oxide 4959-35-7 C10H16O 1124 1115 <0.01 0.01 ± 0.001
caryophyllene oxide 1139-30-6 C15H24O 1573 1576 0.11 ± 0.005 0.03 ± 0.005 <0.01 0.27 ± 0.04 0.66 ± 0.42 0.27 ± 0.05 0.25 ± 0.02
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a The literature retention indices were obtained from [22,23,24,25,26]; b retention indices, using n-paraffin (C5–C25) as references; c values are mean ± SD of triplicates; and d references the whole plant.

The essential oils from different parts of H. cordata were extracted by steam distillation and then analyzed by HS-SPME and direct injections. The results showed that the main volatile components of essential oil from the leaves, as analyzed by HS-SPME, were (E)-2-hexenal, β-myrcene, limonene, (Z)-β-ocimene, (E)-β-ocimene, and (4E,6E)-allo-ocimene; in the stems were α-pinene, camphene, β-myrcene, limonene, (4E,6E)-allo-ocimene, and bornyl acetate; and in the rhizomes were α-pinene, camphene, β-pinene, β-myrcene, limonene, bornyl acetate, and 2-undecanone. In the whole plant were α-pinene, camphene, β-pinene, β-myrcene, limonene, (Z)-β-ocimene, (4E,6E)-allo-ocimene, bornyl acetate, and 2-undecanone (Figure 5). Among the three parts, the leaves contained the highest content of (Z)-3-hexenal, (E)-2-hexenal, (Z)-β-ocimene, (E)-β-ocimene, and (4E,6E)-allo-ocimene; the stem had the highest content of camphene, β-myrcene, and bornyl acetate, and the rhizome contained the highest content of α-pinene, β-pinene, limonene, and 2-undecanone.

Figure 5.

Figure 5

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Comparison of the contents of the major volatile compounds in essential oil from different parts of fresh H. cordata analyzed by HS-SPME: (a) leaf; (b) stem; (c) rhizome; and (d) whole plant.

The essential oils of leaves analyzed by direct injection were mainly composed of β-myrcene, (Z)-β-ocimene, bornyl acetate, 2-undecanone and 2-tridecanone; in the stems were α-pinene, β-pinene, β-myrcene, limonene, (Z)-β-ocimene, bornyl acetate, 2-undecanone, geranyl acetate, (E)-β-caryophyllene, nerolidol, and 2-tridecanone; in the rhizomes were α-pinene, β-pinene, β-myrcene, limonene, bornyl acetate, 2-undecanone, (E)-β-caryophyllene, decanoyl acetaldehyde, and 2-tridecanone; and in the whole plant were α-pinene, β-pinene, β-myrcene, limonene, (Z)-β-ocimene, bornyl acetate, 2-undecanone, (E)-β-caryophyllene, and 2-tridecanone (Figure 6). After comparing the components of leaves, stems, and rhizomes, the leaves contained the highest content of β-myrcene, (Z)-β-ocimene, and 2-tridecanone; the stems had the highest content of bornyl acetate, geranyl acetate, (E)-β-caryophyllene, and nerolidol; and the rhizomes contained the highest amounts of α-pinene, β-pinene, limonene, 2-undecanone, and decanoyl acetaldehyde.

Figure 6.

Figure 6

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Comparison of the contents of the major volatile compounds in essential oil from different parts of fresh H. cordata analyzed by direct injection: (a) leaf; (b) stem; (c) rhizome; and (d) whole plant.

Comparing the results from different parts of fresh plants with HS-SPME, there was more (Z)-3-hexenol, 1-hexanol, (E)-2-hexenal, (2E,4E)-hexadienal, α-cubebene, and (Z,E)-α-farnesene in the leaves than in other parts. Linalool, perilla alcohol, nerolidol, and caryophyllene oxide only appeared in the stems, and n-nonanyl acetate, p-cymenene, α-thujene, γ-terpinene, terpinene-4-ol, α-terpinyl acetate, and neryl acetate were only identified in rhizomes.

When comparing the results of the essential oils from the three parts analyzed by HS-SPME, the components that were only identified in the leaves included (Z)-3-hexenal, β-terpinene, 4-ethyl-1,2-dimethylbenzene, α-copaene, alloaromadendrene, (Z,E)-α-farnesene, β-selinene, β-bisabolene, cadina-1,4-diene, and β-damascenone. The only compound identified in the stems was borneol. The components that were only identified in rhizomes included 1-nonanol, 1-decanol, hexanal, α-campholenal, decanoyl acetaldehyde, 2-nonanone, 3-dodecanone, α-thujene, δ-3-carene, geranial, α-terpinyl acetate, neryl acetate, carvone, (E)-limonene oxide, and caryophyllene oxide.

The results of analyzing essential oils by direct injection showed that compounds only identified in the leaves included 3-methyl-2-buten-1-ol, (Z)-3-hexenal, hexanal, (2E,4E)-hexadienal, α-cubebene, and β-damascenone. The compounds only appearing in the stems were dodecanal, methyl salicylate, and borneol. The compounds only found in the rhizomes were 1-nonanol, 1-decanol, α-campholenal, decanal, 2-nonanone, 3-dodecanone, α-fenchene, terpinen-4-ol, geranial, fenchyl acetate, (2E,6E)-farnesyl acetate, carvone, and (E)-limonene oxide.

Asakawa et al. [18] analyzed the volatile components of different parts of H. cordata and showed that the main component of each part was 4-tricancanone. The main monoterpene in rhizomes and roots was β-pinene, while in flowers, leaves, and stems, it was β-myrcene. 1-decanal is the main polyketide compound in leaves and stems. Haghighi et al. [27] studied the effects of ecotypes and different plant parts (leaves, flowers, and fruits) on essential oil from Vitex pseudo-negundo. The results showed that there were significant differences in the yield and chemical characteristics of the essential oils in different plant parts. Zribi et al. [28] analyzed the volatile components and essential oils of Tunisian Borago officinalis L. and showed that the main components of different parts of this plant differed; octanal was the main component in the flowers, while in leaves, it was nonanal.

2.2. Comparison of Different Extractions

Comparing HS-SPME of fresh plants, HS-SPME of essential oil, and direct injection of essential oil, HS-SPME from fresh plants produced the smallest number of volatile compounds, followed by HS-SPME of essential oil, while direct injection of essential oil produced the most. Analysis of fresh plants by HS-SPME identified aliphatic alcohols and aliphatic aldehydes of low molecular weight, while analysis of essential oils by HS-SPME identified the highest content of monoterpenes. Direct injection of essential oils could identify more aliphatic ketones, sesquiterpenes, and terpene esters (Table 2).

Table 2.

Concentrations of chemical groups from different parts of H. cordata as analyzed by different extractions.

Compound Relative Content (%) a
HS-SPME Essential Oil HS-SPME Essential Oil Direct Injection
Leaf Stem Rhizome Whole b Leaf Stem Rhizome Whole Leaf Stem Rhizome Whole
Aliphatic alcohols 5.14 0.70 0.75 0.10 0.09 0.30 0.12 0.16 0.44 0.28
Aliphatic aldehydes 3.65 3.30 7.24 4.14 1.47 0.13 0.09 0.39 0.78 0.34 1.68 0.81
Aliphatic ester 0.19 0.05
Aliphatic ketones 0.23 0.12 5.60 2.10 5.58 4.25 24.55 13.05
Aromatic compounds 0.03 0.07 0.11 0.13 0.03 0.14 0.17 0.14 0.04 0.16 0.06 0.14
Hydrocarbon <0.01 0.01 0.01 0.01 0.01 0.01 0.01
Monoterpenes 79.91 68.47 80.66 85.33 94.57 93.30 89.11 92.69 74.10 50.19 55.67 68.50
Sesquiterpenes 4.27 4.69 2.79 3.00 0.32 0.78 0.59 0.59 3.09 4.65 3.10 2.95
Terpene alcohols 0.35 0.03 0.13 0.12 0.28 0.47 0.33 1.37 3.34 1.00 1.99
Terpene aldehydes 0.01 0.01 0.01 0.01 0.02 0.04 0.17 0.03
Terpene esters 1.01 3.58 4.29 2.18 0.57 3.48 2.84 1.55 1.88 17.96 6.73 4.32
Terpene ketones 0.01 0.02 0.01 0.09 0.09 0.08 0.67
Terpene oxides 0.11 0.03 <0.01 0.27 0.66 0.28 0.25
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a Values are the means of triplicates, and b references the whole plant.

Farag and Wessjohann [29] compared the volatile compound profiles of Glycyrrhiza glabra L. roots extracted by SPME and steam distillation. The results showed that SPME could easily extract several small molecular weight monoterpenes, while more compounds could be identified in the essential oils extracted by steam distillation, including the volatiles generated by chemical reactions during the heating process. Peng et al. [30] analyzed the volatile components of kumquat (Fortunella margarita Swingle) and showed that HS-SPME/GC could identify a higher proportion of monoterpenes but fewer sesquiterpenes than that by DI/GC. Gao et al. [31] compared different extractions to volatile components of Pu-erh ripe tea and observed that HS-SPME was beneficial for the extraction of highly volatile compounds, such as low molecular weight alcohols, aldehydes, ketones, and hydrocarbons.

Yang et al. [32] compared HS-SPME with conventional extraction in the analysis of Melia azedarach, and Kung et al. [33] analyzed Platostoma palustre (Blume) and pointed out that HS-SPME is a powerful analytical tool that can complement traditional methods. Overall, the results of these three methods showed all have high monoterpene content. Direct injection can be used to analyze more classes of volatile compounds, especially the larger molecular weight components, including important components of H. cordata such as 2-undecanone, and decanoyl acetaldehyde.

H. cordata has long been used as an edible vegetable and in traditional medicine [2]. Due to its pharmacological properties, it has been gradually applied in many fields, such as medicine, health food, preservatives and cosmetics, with great potential for development.

3. Materials and Methods

3.1. Plant Materials

H. cordata used in this study was provided by the Taoyuan District Agricultural Research and Extension Station, Council of Agriculture, Executive Yuan (24°57′09.3″ N 121°01′42.4″ E, altitude = 39 m). The experiment was designed with three replicates. Three parts (leaves, stems, and rhizomes) and fresh whole H. cordata plants were collected for experiments. Precisely 3 kg of voucher specimens for each batch were dried and deposited. A herbarium sample (No. TY 1406) was lodged at the Flavor and Fragrance Research Laboratory at China Medical University, Taiwan.

3.2. Analytical Methods

3.2.1. Extraction of Volatile Compounds from Fresh H. cordata by HS-SPME

After homogenizing (Electrolux, ECG120S) the samples for 15 s, 3 g were weighed and placed in a 22 mL cylindrical glass bottle (Supelco Co., No. 27170, Bellafonte, PA, USA) then sealed with Teflon rubber pad. The fiber was coated with 50/30 μm DVB/CAR/PDMS (Supelco) and extracted for 30 min. The extraction temperature was room temperature. After the extraction was complete, the fiber was inserted into the inlet of the GC or GC-MS and desorbed for 20 min. This experiment was repeated in triplicate.

3.2.2. Extraction of Essential Oil from H. cordata

A fresh H. cordata sample (600 g) was washed with clean water, and then 1800 mL of distilled water was added to homogenize (TATUNG, TJC-2200) for 30 s. The homogenate was then placed in a 5 L round-bottom flask for steam distillation. The extraction time was 3 h, and the extract was stored at 4 °C until analysis. The experiment was repeated in triplicates. The yields of essential oils from different parts of H. cordata were 0.09% (leaves), 0.02% (stems), 0.04% (rhizomes), and 0.04% (whole plants).

3.2.3. Gas Chromatography-Flame Ionization Detector (GC-FID)

GC was performed with an Agilent Model 7890A GC (Santa Clara, CA, USA), with a 60 m × 0.25 mm id Agilent DB-1 fused-silica capillary non-polar column with a film thickness of 0.25 μm; the HS-SPME injection mode was splitless, and the injection mode of direct injection was split. The GC heating conditions were as follows: the initial temperature was maintained at 40 °C for 1 min, then raised to 150 °C at 5 °C/min, maintained for 1 min, then raised to 200 °C at 10 °C/min and maintained for 11 min. The inlet temperature was 250 °C, the detector temperature was 300 °C, and a flame ionization detector (FID) was used for detection. The carrier gas was nitrogen at a flow rate of 1 mL/min.

3.2.4. Gas Chromatography-Mass Spectrometry (GC-MS)

GC-MS was conducted with an Agilent Model 5977A quadrupole mass spectrometer (Mass Selective Detector, MSD) coupled to an Agilent Model 7890B GC (Palo Alto, CA, USA). The operating conditions and column were the same as in Section 3.2.3. The carrier gas was helium, the ion source temperature of the MSD was 230 °C, and the electron energy was 70 eV. The transfer line was set at 250 °C. The mass range was 30–350 m/z. The quadrupole temperature was 150 °C. The mass spectra data were compared and judged using the Wiley 7N mass spectrum library.

3.2.5. Analysis of Essential Oil from H. cordata

For GC, 1 µL of essential oil was injected, while 0.5 µL was injected for GC-MS. For HS-SPME, 0.1 mL of the essential oil was added to a 4 mL cylindrical glass bottle (Supelco Co., No. 27136) with a Teflon rubber pad. Additionally, 50/30 μm DVB/CAR/PDMS fiber was used for extraction for 5 min, and the extraction temperature was room temperature. The fiber was then inserted into the inlet of the GC or GC-MS. All experiments were performed in triplicates.

3.2.6. Retention Index (RI) Comparison

The GC retention index of the volatile components in this experiment was based on a mixture of C5–C25 n-alkane standards (Sigma-Aldrich, St. Louis, MO, USA) and the GC retention time was used as a reference under the same conditions. The RI was calculated according to the method described by Curvers et al. in reference [34].

3.2.7. Relative Percentage Calculation

After volatile components were identified, the percentage composition was calculated using the peak area normalization measurements. The formula is as follows:

volatile component peak areatotal peak areas×100%

In addition to the volatile compounds of the sample, HS-SPME will also adsorb the impurity of the bottle or any silicon-containing coating. The total percentage in the above tables did not reach 100%, due to deducted from these impurities.

4. Conclusions

The volatile compounds of H. cordata leaves, stems, rhizomes, and whole plants were compared. The leaves of H. cordata had the highest essential oil content, but the rhizomes had higher 2-undecanone and decanoyl acetaldehyde content. Therefore, using rhizomes as raw materials is beneficial for extracting key components of H. cordata. Additionally, HS-SPME and direct injection of essential oil are highly complementary. Together, they cover the full range of volatilities and trace components and provide relatively complete data on the volatile components of H. cordata.

Acknowledgments

This study was granted financial support from the Council of Agriculture, Executive Yuan (Taiwan) 111AS-4.2.2-FD-Z1 (1), and Ministry of Education (Taiwan) (1038142*), and it is gratefully acknowledged.

Author Contributions

Conceptualization, C.-H.L., C.-H.H., and H.-C.C.; Formal analysis, L.-Y.L. and C.-S.W.; Investigation, C.-H.H. and H.-C.C.; Resources, C.-H.L. and L.K.C.; Data curation, L.-Y.L.; Writing—original draft, C.-H.L., L.K.C., C.-H.H., and H.-C.C.; Writing—review and editing, C.-H.L., L.K.C., L.-P.C., C.-H.H., and H.-C.C. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing not applicable. No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of the compounds are not available from the authors.

Funding Statement

This work was supported by a research grant from the China Medical University (Taiwan) (CMU110-S-04).

Footnotes

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

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Data Availability Statement

Data sharing not applicable. No new data were created or analyzed in this study. Data sharing is not applicable to this article.

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