Determination of Aroma Composition of Santalum album Linn by Solid-phase Microextraction-Gas Chromatography-Mass Spectrometry

Guotong CHEN, Meiqin LI, Chao HUANG, Na WEN, Aixia WANG

Xinjiang Academy of Analysis and Testing, Urumqi 830011, China

Abstract [Objectives]This study aimed to determine the volatile components in Santalum album Linn and gradually clarify the aroma composition of S.album Linn.[Methods]Solid-phase microextraction method was used to obtain the volatile components of S.album Linn.The aroma components were analyzed by gas chromatography-mass spectrometry and their relative contents were calculated using the area normalization method.[Results]In a dry state at room temperature, 39 chemical components were identified from S.album Linn, mainly olefins(91.15%), alkanes(3.00%), alcohols(2.56%), esters(2.19%), ketones(0.55%), aldehydes(0.41%)and heterocyclics(0.14%).[Conclusions]This method has the advantages of low sample consumption, easy operation, rapid identification of aroma components and high sensitivity, and can effectively separate and determine volatile components in S.album Linn, realizing the rapid identification of different S.album Linn varieties and providing technical support for further research on Chinese medicinal materials.

Key words Santalum album Linn, Solid-phase microextraction(SPME), Gas chromatography-mass spectrometry, Aroma component

1 Introduction

SantalumalbumLinn is also called Yuxiang.It is the heartwood ofSantalumspp.(Santalaceae)[1].The trunk ofS.albumLinn is white and tasteless.The yellow-brown pith has a strong scent of sandalwood and is non-toxic[2].S.albumLinn is native to Indonesia, Australia and other regions.The suitable temperature for growth is around 30 ℃.Tropical areas such as Taiwan(China), Guangdong and Hainan are the main planting areas.S.albumLinn is called the "tree of gold", and the broken wood of the trunk and roots can be used to extract essential oil[3].The pruned branches and leaves are the raw materials for making fragrant wood products, as well as high-quality wood for carving craftsmanship.The pith ofS.albumLinn is precious medicinal material, which has been regarded as treasure over the years.The volatile components ofS.albumLinn are dominated by santenes, which are refined into sandalols.According to theChinesePharmacopoeia, sandalols not only have good antioxidant activity but also have an outstanding calming effect on the human nervous system, and they are also an important indicator to identifyS.albumLinn[4-5].Sandalwood is commonly used to adjust the physiological functions of the spleen and stomach, improve appetite and relieve pain, and has a wide range of medicinal effects.Compared with other raw materials such as black tea that needs to be cooked to exude aroma substances[6], natural sandalwood itself has a strong aromatic smell.It has been gradually used to develop synthetic spices in depth, and has excellent development prospects[7-8].

In recent years,S.albumLinn has been widely planted in China.The trunk itself has a unique aroma, and its incense products have also been popular among people on the market.Currently, China’s main research onS.albumLinn is limited to content determination, refining essential oils, and extracting flavonoids[9-10].The main extraction method is organic reagent extraction, such as petroleum ether and ether repeated reflux and molecular distillation[11].The consumption is large and the yield is relatively low.In addition, only the camphenes in aroma ofS.albumLinn are used to synthesize sandalwood odorants[12], and many volatile components in sandalwood have not yet been identified.The research depth is not enough and the cost is high.Room-temperature solid phase microextraction technology[13]integrates adsorption, desorption and sampling, and it is simple, convenient and accurate to analyze volatile components in samples, and has been widely used in environment, medicine, traditional Chinese medicine, chemistry and other fields[14].In this study, solid-phase microextraction technology was used, and the conditions were optimized under different programmed heating conditions of gas chromatography-mass spectrometry; and the volatile components inS.albumLinn were determined, and the aroma composition were gradually clarified.This is of great significance to the research of Chinese herbal medicines.

2 Materials and methods

2.1 Materials

2.1.1Wood material.TheS.albumLinn used in the study came from Mysore, India and was commercially available.

2.1.2Instruments and equipment.The instruments and equipment used in this study mainly included solid-phase microextraction device equipped with 50/30 μm DVB/CAR/PDMS supelco and manual solid-phase microextraction sampling handle(SUPELCO, USA), GC-MS-QP2010Plus gas chromatography-mass spectrometer equipped with electron bombardment(EI)ion source and AOC-20i+s autosampler(Shimadzu, Japan)and high-speed universal crusher(Beijing Kaichuang Tonghe Technology Development Co., Ltd.).

2.2 Methods

2.2.1Determination conditions.(i)Headspace solid-phase microextraction.Under normal temperature, the adsorption time was 30 min; the desorption temperature was 250 ℃; and the desorption time was 5 min.(ii)Gas chromatography(GC).Carrier gas: He(helium); sampling method: split, split ratio 20∶1; DB-5MS capillary column(30 m × 0.25 mm × 0.25 μm); inlet temperature: 250 ℃; programmed heating: starting temperature 40 ℃, for 1 min, rising to 100 ℃ at 5 ℃/min, for 1 min, and rising to 260 ℃ at 15 ℃/min.(iii)Mass spectrometry(MS).Ion source: EI; ion source temperature: 230 ℃; ionization energy: 70 eV; interface temperature: 260 ℃; full scan range(m/z): 50-450; no solvent delay; acquisition time: 30 min.

2.2.2Pretreatment.(i)Supelco aging.Before the solid-phase microextraction handle was used for the first time, the supelco was inserted into the injection port and began to be used after aging at 270 ℃ for 1 h.Before subsequent use, the supelco still needed to be aged at this temperature for 5-10 min to ensure that the supelco desorbed the remaining volatile components at high temperature, avoiding interference with the sample to be tested.(ii)Sample treatment.An accurate amount(1.00 g)of the sample was placed into a 25 mL PTFE capped headspace bottle.After the sample was let standard for 5 min, the 50/30 μm DVB/CAR/PDMS supelco was inserted into the headspace bottle, pushed out, let absorb for 30 min at room temperature, and let desorb for 5 min at the inlet temperature of 250 ℃.After data collection is completed, the aroma components inS.albumLinn were determined.

3 Results and analysis

3.1 Total ion current of aromaUsing solid-phase microextraction-gas chromatography-mass spectrometry, the total ion current of aroma components ofS.albumLinn within 30 min was obtained(Fig.1).Fig.2 shows the partial enlarged chromatogram within 9-21 min.

Fig.1 Total ion current chromatogram of aroma components in Santalum album Linn by room-temperature solid-phase microextraction-gas chromatography-mass spectrometry

Fig.2 Total ion current chromatogram of aroma components in Santalum album Linn within 9-12 min

3.2 Composition of aromaUsing gas chromatography-mass spectrometry, valid data within 30 min was collected, and compounds with a similarity of over 85% were retained.The mass spectra corresponding to each chromatographic peak were analyzed manually by referring to the NIST14 library to identify the aroma components ofS.albumLinn, and using the area normalization method, the relative contents of the aroma components were calculated(Table 1).

As shown in Table 1, a total of 39 chemical components were identified through gas chromatography-mass spectrometry.Among them, olefins had the highest content, dominated by epi-beta-santalene(22.97%), santalene(21.47%), santene(20.16%)and β-santalene(17.35%).These ingredients make the medicinal material firm, not easy to break, and aroma stronger during the burning process.Organic reagents will destroy the tissue structure of the raw materials during the extraction process, interfering with the determination of volatile components.In addition, organic reagent extraction is mostly used for component screening[15].In contrast, solid-phase microextraction technology effectively avoids the influence of organic reagents, external conditions and other factors on the determination of aroma components inS.albumLinn[16-17].

Table 1 Aroma composition of Santalum album Linn by solid-phase microextraction-gas chromatography-mass spectrometry

4 Conclusions

The volatile aroma components ofS.albumLinn were identified by solid-phase microextraction-gas chromatography-mass spectrometry, and the relative content of each aroma component was determined by the area normalization method.The method for the determination of the aroma composition ofS.albumLinn has the advantages of small sample consumption, simple processing, easy operation and high sensitivity, and can quickly distinguishS.albumLinn varieties through the differences in aroma components, providing a scientific basis for the utilization ofS.albumLinn resources.