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The analysis and identication
of charred suspected tea remains
unearthed from Warring State
Period Tomb
Jianrong Jiang1, Guoquan Lu2*, Qing Wang2 & Shuya Wei1*
Recently, a bowl containing charred suspected tea remains unearthed from the early stage of Warring
States period tomb in Zoucheng City, Shandong Province, China. To identify the remains is signicant
for understanding the origin of tea and tea drinking culture. Scientic investigations of the remains
were carried out by using calcium phytoliths analysis, Fourier transform infrared spectroscopy (FTIR),
Gas Chromatograph Mass Spectrometer (GC/MS) and Thermally assisted hydrolysis—methylation
Pyrolysis Gas Chromatography Mass Spectrometry (THM-Py-GC/MS) techniques. Modern tea and
modern tea residue were used as reference samples. Through phytoliths analyses, calcium phytoliths
identiable from tea were determined in the archeological remains. The infrared spectra of the
archaeological remains was found similar as modern tea residue reference sample. In addition,
the biomarker compound of tea—caeine was determined in the archaeological remains by THM-
Py-GC/MS analysis. Furthermore, through GC/MS analysis, some compounds were found both in
the archeological remains and the modern tea residue reference samples. Putting the information
together, it can be concluded that the archaeological remains in the bowl are tea residue after boiling
or brewing by the ancient.
China is the rst country in the world to discover and cultivate tea. In Chinese legend, tea was rst discovered
as an antidote by Emperor Shen Nung in 2737 , according to the rst monograph on Chinese herbal medicine
Shennong’s Classic of Materia Medica (神农本草经)1. e rst mention of tea planting is believed to occur in
the Xiaxiaozheng (夏小正), a Chinese earliest almanac recording traditional agricultural aairs, probably writ-
ten in the Warring States Period (475–221 ). According to the literature, in the Spring and Autumn Period
(770–476 ), tea had been used as a sacrice and vegetable, in the Warring States period and the early Western
Han Dynasty, tea cultivation, tea making techniques and tea drinking custom in Sichuan province began to
spread to other places2.
e physical evidence of tea is very important to conrm the origin, development, function and culture of tea.
As archaeological plant leaves remains have been buried for many years, most of them have rotted or charred,
it is dicult to nd archaeological plant leaves remains in archeological excavation. e rst tea remains were
found in Northern Song tomb of Lu’an, Anhui Province3. e oldest physical evidence of tea remains are from
other two funerary sites: the Han Yangling Mausoleum in Xi’an, Sha’anxi Province, and the Gurgyam Cemetery
in Ngari district, western Tibet, revealing that tea was used by Han Dynasty emperors as early as 2100year BP
and had been introduced into the Tibetan Plateau by 1800year BP4, but whether the tea was used as beverage,
food, medicine is unclear. Recently, some charred suspected tea remains (CST) were found in a bowl unearthed
from tomb No. 1 at Xigang in the Ancient Capital City Site of the Zhu Kingdom in Zoucheng City (e early
stage of Warring States, approximately 2400years ago), Shandong Province (Fig.1)5. If the remains could be
determined as tea, that would be the direct evidence for tea drinking in the ancient time.
Previously, the researchers commonly used for the identication of plant remains were mainly based on
the morphology of the plant, however, most of archaeological plant remains have rotted or charred due to the
interference of various microorganisms, oxidation and other factors in the buried environment for many years,
the morphology of the plants also changed dramatically, therefore, to identify the plant species by morphology
is not applicable to the sample CST. Recently calcium phytoliths (calcium oxalate plant crystals), biomarkers
OPEN
Institute of Cultural Heritage and History of Science & Technology, University of Science and Technology Beijing,
*email:
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(caeine and theanine) were identied in archaeological tea remains by using Gas Chromatography/Mass
spectrometry (GC/MS) and Ultra-performance Lquid Chromatography and Mass Spectrometry (UPLC–MS)
techniques4. For modern tea study, Fourier transform infrared spectroscopy (FTIR)6–9, Spectrophotometry, er-
mospray–LC–MS10, Head space solids-phase microextraction in combination with gas chromatography–mass
spectrometry (HS-SPME/GC–MS)11, Gas chromatography–mass spectrometry (GC–MS)12,13 are the mainly
techniques applied.
In this study, methods of calcium phytoliths analysis, Fourier transform infrared spectroscopy (FTIR), Gas
Chromatography/Mass spectrometry (GC/MS) and thermally assisted hydrolysis–methylation Pyrolysis Gas
Chromatography/Mass Spectrometry (THM–Py–GC/MS) were chosen for the identication of the sample CST
found in the Warring State tomb. In the meantime, modern reference samples were studied by using the same
analytical methods as the archaeological sample for comparison.
Materials and methods
Archaeological sample: the Archaeological sample CST take from the residues which poured out from the bowl
unearthed from the Tomb No.1 at Xigang (Fig.2).
Reference samples: since the sample CST was unearthed in a bowl, therefore, it is not excluded that the sample
is tea residue le aer boiling or brewing by the ancient, so in this study, modern tea and modern tea residue
were used as reference samples. Modern tea residue was prepared from brewing tea with water for several times,
then dry thoroughly and nally grinded into powders. e modern tea samples were bought from tea shop in
Beijing, which are black tea produced from Shangdong Laoshan.
Analysis of calcium phytoliths. Calcium phytoliths experiment was performed according to the proce-
dure described in the literature4. Identication of calcium phytoliths was performed under a LEICA DM2700P
microscope.
Fourier transform infrared spectroscopy (FTIR). For FTIR analysis, Nicolet 6700 Advanced Fourier
transform infrared spectrometer (America ermo Fisher Scientic) was used. e spectra were collected over
Figure1. e map shows (a) Location of Shandong Province in China; (b) e Ancient Capital City Site of the
Zhu Kingdom in Zoucheng City; (c) e plan of the tomb; (d) e plan and prole of tomb No. 1 at Xigang.
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the 4000–500 cm−1 region, using attenuated total reectance (ATR) for the measurements, the spectral resolu-
tion is 4 cm−1 and the number of scans is 64. Each sample was scanned at 25℃ and the data acquisition system
used was OMNIC.
Gas chromatograph–mass spectrometer (GC/MS). GC–MS analysis was performed using Agilent
GC–MS-QP2010Ultra (Shimadzu, Japan). A capillary column Ultra-5MS (5% diphenyl/95% dimethyl silox-
ane), 0.25mm internal diameter, 0.25m lm thickness and 30m length [Frontier lab, Japan] was used for the
separation. Temperature programmed: initially keeping the column at 120°C for 2min, followed by a gradient
of 5°C/min to 270°C and hold for 10min. e injector temperature was set to 240°C. 30:1 split ratio. e car-
rier gas used was Helium (purity 99.999%). e electronic pressure control was set to a constant ow of 1ml/
min; Electron ionization (EI) temperature was at 280°C; Transmission lines temperature was at 220°C; Range
of Scanning: 35 ~ 510m/z.
Analysis procedure: A sample (20mg) was weighed, transferred into a sampling vial with ultrapure water,
boiled the sample for 10min in a water bath, extracted under sonication at 60°C for 30min and then centrifuged
for 10min. Aerwards, the supernatant was transferred to a sample vial, then it was evaporated and dried in a
stream of N2 at 60°C. Finally, the dried tea extract was dissolved in solvent acetonitrile (ACN) and derivatized
with N-(tert-Butyldimethylsilyl)-N-methyltriuoroacetamide (MTBSTFA, 1: 1 to ACN, v/v) at 110°C for 30min,
transfer the mixed uid into an auto sampling vial for GC/MS analysis.
Pyrolysis gas chromatography mass spectrometry (Py-GC/MS). For Py-GC/MS analysis, a Multi-
Shot pyrolyzer, type EGA/PY-3030D, made by Frontier Lab, Japan, and a gas chromatograph mass spectrometer,
GC–MS-QP2010 Ultra (Shimadzu, Japan). Shimadzu GC–MS real time analysis soware was used for GC–MS
control, peak integration and mass spectra evaluation.
e pyrolysis was performed at 550°C for 12s. e pyrolyser interface was set to 290°C and the injector was
set to 250°C. A capillary column SLB-5MS (5% diphenyl /95% dimethyl siloxane), 0.25mm internal diameter,
0.25m lm thickness and 30m length [Supelco] was used in order to provide an adequate separation of the
components. e chromatographic conditions were as follows: the oven initial temperature was set to 35°C for
5min, followed by a gradient of 60°C/min to 100°C, for 3min, 14°C/min to 240°C , then 6°C/min to 315°C
and hold for 1.5min, the carrier gas was Helium (He, purity 99.999%). e electronic pressure control was set to
a constant ow of 0.92ml/min, in split mode at 1:20 ratios. Ions were generated by electron ionization (145.3eV)
in the ionization chamber of the mass spectrometer. e mass spectrometer was set from m/z 35 to 750. EI mass
spectra were acquired by total ion monitoring mode. e temperatures of the interface and the source were
280°C and 200°C, respectively.
NIST14 and NIST14s Library of Mass Spectra were used for identifying the compounds.
Analysis procedure. About 50g sample was placed in a sample cup, 3 L of 25% aqueous TMAH (analytical
pure, Sinopharm Chemical Reagent Co., Ltd) solution were injected into the sample cup, the cup was placed
on top of the pyrolyzer at ambient temperature and then pyrolyzed immediately, aerwards the temperature
program for the GC/MS analysis was started. During the process of analysis, blank tests were conducted before
each sample.
Figure2. e map shows (a) Tomb No. 1 at Xigang; (b) Burial objects in the ware box; (c) e unearthed bowl;
(d) e residues which poured out from the bowl; (e) e sample CST take from the residues.
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Statement. e use of plants parts in the present study complies with National standards of the People’s
Republic of China on black tea (GB/T13738).
Results and discussion
Analysis of calcium phytoliths. Calcium phytolith analyses were carried out according to the procedure
described in the literature4. e morphology observation of sample CST under microscope is depicted in Fig.3,
which reveals that the sample contains abundant calcium phytoliths, including the crack, druses and trichome
base, these calcium phytoliths also match the genus Camellia, especially druse and trichome base are the most
distinctive crystals in tea plants4.
FTIR analysis. e infrared spectra of modern tea, modern tea residue and the sample CST are shown in
Fig.4. e vibrations of the functional groups of the compounds in tea and their corresponding infrared absorp-
tion characteristic peaks are consistent with the literatures2,6–8. Taking infrared spectrum of modern tea as an
example, the band assignment to chemical bonds for the vibrational FTIR spectra of modern tea is summarized
in Table1.
e peak shapes and the positions of main absorption peaks (1632, 1041 cm−1) of the archaeological sample
CST are consistent with the modern tea reference samples (Fig.4), so it is speculated that the sample CST is
most likely ancient tea.
e intensity of some absorption peaks in modern tea residue decreased signicantly in comparison with
modern tea, such as the peaks at 1516, 1454, 1237 cm−1, indicating some compounds in the tea may be dissolved
in water. Sample CST has been buried for hundreds of years, microorganisms and other factors in the burial
environment may cause chemical changes, resulting in the subtle dierences in infrared spectra between the
archaeological sample CST and reference samples. To conrm whether the sample CST is ancient tea or not,
further study by other techniques were carried out as following.
Biomarker analysis. THM‑Py‑GC/MS analysis. e chromatograms of modern tea, modern tea residue
and the sample CST obtained by THM-Py-GC/MS are shown in Fig.5. ree parallel analyses were conducted
for each sample, the analysis results are consistent with each other.
Figure3. Photographs under microscope of calcium phytoliths from sample CST. (a) crack-type calcium
phytoliths; (b) druse-type calcium phytoliths; (c) trichome-type calcium phytoliths.
Figure4. Infrared spectra of A—modern tea; B—modern tea residue; C—sample CST.
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Comparing retention time and mass spectrum of the main chromatographic peaks in the sample CST and
the reference samples (modern tea and modern tea residue), the main peaks found in the sample CST are also
present in the reference samples (peak No. 1–8), which are 1,3,5-trimethoxy-benzene, 2,4,6-trimethoxytoluene,
3,4-dimethoxy-benzoic acid methyl ester, 3,4,5-trimethoxy-benzoic acid methyl ester, caeine, hexadecanoic
acid methyl ester, 9-octadecenoic acid methyl ester, methyl stearate, the peak 1, 2, 3, 4 belong to methoxyben-
zene compounds which are the characteristic components of tea aroma14,15, and hexadecanoic acid methyl ester,
9-octadecenoic acid and methyl stearate are common fatty acids in tea16. Especially the biomarker compound
of tea—caeine was identied (peak No. 5, RT 10.5min) in CST sample, the mass spectra are shown in Fig.6.
Caeine is easily soluble in water, most of the caeine in tea was leached out in the process of brewing tea, there-
fore, the content of caeine in modern tea residue is signicantly lower than that in modern tea (Fig.5). Peak 3
is one of the most intense for CST but not signicant in the modern sample, probaly due to two reasons: rstly,
the relative contents of the chemical components in dierent tea are dierent; secondly, it is probably due to the
eect of the burial environment. In order to see the inuence of the burial environment, soil samples from the
area where the bowl was found were analyzed by Py-GC/MS, small amount of fatty acids were found, which will
not aect the conclusion for sample CST.
GC/MS analysis. e modern tea reference sample, modern tea residue reference sample and the sample CST
were pretreated according to the procedure described in a previous section in this document. e chromato-
grams of them obtained by GC/MS analyses are shown in Fig.7. ree parallel analyses were conducted for each
sample, the analysis results are consistent with each other.
e main amino acids contained in tea were detected in modern tea sample aer derivatized by MTBSTFA,
which is consistent with the literature17,18. Especially the tea marker compound-theanine, two derivatized peaks
of theanine were detected in modern tea reference sample (labeled as T1 and T2 in Fig.7). In the modern tea
Table 1. Band assignments for the FTIR spectra obtained from modern tea.
Wavenumber (cm−1) Vibrational mode assignment Absorption peak intensity: s (strong)/m
(medium)/w (weak)
3420 –OH stretching vibration of tea-polyphenols and tea-
polysaccharides s
2923, 2852 Saturated C–H stretching vibration m, w
1646 C=C stretching vibration peak of sugars and avonoids s
1516 –NO2 stretching vibration peak of aromatic compounds
in tea w
1454 saturated C–H deformation vibration w
1362 –NO2 stretching vibration peaks of aliphatic compounds w
1237 C–O stretchingvibrationpeak in amides w
1146 C–O–C antisymmetric stretching vibration w
1035 O–H in-plane deformation vibration s
Figure5. TIC chromatogram obtained by THM-Py-GC/MS of A—modern tea; B—modern tea
residue; C—sample CST; e peak numbers are corresponding to: (1): 1,3,5-trimethoxy-benzene; (2):
2,4,6-trimethoxytoluene; (3): 3,4-dimethoxy-benzoic acid, methyl ester; (4): 3,4,5-trimethoxy-benzoic acid,
methyl ester; (5): caeine; (6): hexadecanoic acid, methyl ester; (7): 9-octadecenoic acid, methyl ester; (8):
methyl stearate.
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residue sample, only a trace of theanine (T1) was found, but not found in the CST sample. eanine is the main
free amino acid in tea, its concentration is signicantly decreased aer tea was brewed due to its good solubility
in water, therefore, the content of theanine in modern tea residue and sample CST is so low that even cannot be
detected. However, there are some other compounds were detected both in modern tea residue and sample CST,
which are listed in Table2, most of these components are organic acids, which are the common components in
tea, and as a water-soluble substance, which can be also leached out in the process of brewing tea19. Although
some of the compounds were not identied what they were, but they were both present in modern tea residue
and sample CST (peak No. 1, 4, 10, 12, 13 in Fig.7), indicating those compounds origin from tea, which provide
additional evidence that the archaeological sample CST is most likely tea residue le aer boiling or brewing.
e relative intense of peak 4 is higher in CST sample in comparison with the reference samples, probably due
to ageing.
Conclusions
In this study, Calcium phytoliths analysis, Fourier transform infrared spectroscopy (FTIR), Gas Chromato-
graph Mass Spectrometer (GC/MS) and ermally assisted hydrolysis-methylation pyrolysis-gas chromatog-
raphy/mass spectrometry (THM–Py-GC/MS) techniques were applied for the identication of archaeological
remains–charred suspected tea (CST) excavated from the early stage of Warring State Period tomb in Shandong
Province. e experimental results show that the sample CST contains abundant calcium phytoliths identi-
able as tea, e FTIR spectra of CST sample are similar with that of the modern tea residue. Moreover, caf-
feine, methoxybenzene compounds, organic acids, 2-Amino[1,3]thiazolo[4,5-d]pyrimidine-5,7-diol and several
Figure6. e mass spectrum of caeine (peak 5 in Fig.5) of A—modern tea; B—modern tea residue; C—
sample CST by THM Py-GC/MS analysis.
Figure7. TIC chromatogram obtained by GC/MS of A—modern tea; B—modern tea residue; C—sample CST;
T1, T2: two derivatized peaks of theanine in modern tea sample (A); e peak numbers are corresponding to
the numbers in Table2.
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unidentied compounds were detected in both the sample CST and the reference sample (modern tea residue) by
THM–PY-GC/MS and GC/MS. By putting the information together, it can be concluded that the archaeological
remains in the bowl are tea residue aer boiling or brewing by the ancient.
Tea drinking is one of the most representative traditional cultures in China, since ancient times, the Chinese
people have always had the habit of drinking tea, but there is no physical evidence to prove when tea actually
appeared, until the discovery of tea in the Han Yangling Mausoleum, which proved that Chinese tea has a history
of at least 2150years, which has earned recognition from Guinness World Records as the oldest tea in 20164. e
identication of the tea remains at the Ancient Capital Site of the Zhu Kingdom in Zoucheng (the early stage of
Warring States, approximately 2400years ago) has advanced the origin of tea by nearly 300years. Furthermore,
the tea was found in a small bowl, providing additional evidence of the usage of tea. e results of this study
indicate that tea drinking culture may start as early as in Warring State period.
Received: 1 April 2021; Accepted: 20 July 2021
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Table 2. GC/MS analysis result of modern tea residue and sample CST.
Peak no. RT (min) Main ions (m/z) Compounds identied
1 18.04 115, 147, 173 Unidentied
259, 386
2 19.04 147, 189, 221 Boric acid, 3TMS derivative
263, 355
3 20.54 211, 269, 383, 425 Phosphoric acid, tris(tert-butyldimethylsilyl) ester
4 22.56 147, 221, 263, 337 Unidentied
5 27.53 117, 131, 313 Palmitic acid, TBDMS derivative
6 30.54 129, 337 Linoelaidic acid, tert.-butyldimerthylsilyl ester
7 30.59 129, 339, 381 Petroselinic acid, TBDMS derivative
8 30.68 129, 339 .alpha.-Linolenic acid, TBDMS derivative
9 31 117, 129, 341 Stearic acid, TBDMS derivative
10 32.92 117, 143, 237 Unidentied
252, 359
11 33.54 223, 339, 455, 469 2-Amino[1,3]thiazolo[4,5-d]pyrimidine-5,7-diol
12 34.15 185, 241, 256, 359 Unidentied
13 37.14 238, 323, 397 Unidentied
439, 495
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19. Liu, P. et al. Study on organic acids contents in tea leaves and its extracting characteristics. J. Tea Sci. 33, 405–410 (2013).
Acknowledgements
e authors gratefully acknowledge Professor Yan Wu (Key Laboratory of Vertebrate Evolution and Human
Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese
Academy of Sciences, Beijing) and Dr Xiumin Xia (National Museum of China) for the help of calcium phyto-
liths analysis.
Author contributions
J.J. performed all experiments, analyzed the data and produced gures. J.J. and S.W. draed the manuscript. G.L.
and Q.W. provided the archaeological data, materials and reviewed the manuscript.
Funding
Funding was provided by Scientic research and protection of ancient organic cultural relics (Grant No.
06102070) and the National Key Research and Development Program of China. No. 2020YFC1522402.
Competing interests
e authors declare no competing interests.
Additional information
Correspondence and requests for materials should be addressed to G.L.orS.W.
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