Characteristic of phenotype, amino acids and volatile compounds for fresh tea leaves of Korean tea cultivars ( Camellia sinensis (L.) O. Kuntze)

Tea ( Camellia sinensis (L.) O. Kuntze) is a popular beverage consumed worldwide. To establish fundamental scientific data, we analyzed the amino acids and volatile compounds in seven tea cultivars grown in Korea investigated phenotype also. Phenotypically, the leaf area and greenness index of young shoots and leaf blades were particularly different among the four Korean cultivars. Nine amino acids were detected from each cultivar, with the total amino acid and theanine contents being 9.08–41.42 and 2.81–24.60 mg/g, respectively. Moreover, 107 volatile compounds were identified as common components among tea cultivars using headspace solid-phase microextraction / gas chromatography–mass spectrometry (HS-SPME/GC-MS), and 38 key compounds were identified using partial least squares-discriminant analysis (PLS-DA) and hierarchical cluster analysis (HCA). The ( Z )-linalool oxide (furanoid) concentrations were significantly high in Korean tea plant cultivars, and linalool concentrations were also high or low, but had high relative contents. Linalool and its various oxides are the major compounds responsible for the tea aroma. In conclusion, Korean tea cultivars have distinct characteristics, and the results of this study will form the basis for identifying Korean tea plant cultivars that can produce high-value tea products.


Introduction
Tea, derived from tender leaves of tea plant (Camellia sinensis (L.) O. Kuntze), is one of the most popular beverages worldwide [1,2].Tea infusions offer unique flavors, aromas, and potential health benefits.Recently, extensive research on coronavirus disease (COVID-19) has revealed its health-promoting effects, such as enhancing the innate immune response [3], and the benefits of epigallocatechin gallate (EGCG) treatment in decreasing coronavirus RNA levels [4].Therefore, tea has garnered increasing attention, leading to active and sustained research.
The taste and aroma of tea are influenced by various compounds in the tea leaves [5].Amino acids constitute approximately 4% tea, with theanine being found exclusively in tea leaves, accounting for 70% amino acid content and typically comprising approximately 2% dried tea leaves [5,6].Amino acids play a crucial role in umami taste, with theanine being the major component [5,7].Specifically, theanine, the ethyl amide of glutamic acid, serves as a nitrogen storage [8] and enhances the taste of tea cultivars [9].Volatile compounds account for only 0.002-0.07%dry weight of fresh tea leaves [10], and more than 700 volatile compounds have been identified [11].These compounds are derived from secondary metabolites in tea leaves [12], primarily generated from various precursors, such as carotenoids, lipids, glycosides, primarily through the Maillard reaction pathway [13].
Amino acids are involved in aroma biosynthesis as direct precursors, producing many alcohols, aldehydes, acids, and esters in plants [14].The amino acid content of fresh tea leaves is influenced by different processing methods [15], including the ratio of bound to free forms in fresh tea leaves for optimal tea production [16], and amino acid-derived volatiles in white tea [17].The phenotype of tea leaves can serve as an easy indicator for assessing the quality of tea as it correlates with certain characteristics.Yellow tea leaves tend to contain more amino acids [18,19], whereas tea plants with larger leaves often have more linalool [20].These findings underscore the intricate interplay between various chemical compounds and amino acids in shaping the flavor and aroma of tea, highlighting the significance of the tea leaf phenotype as a pivotal indicator in assessing tea quality.
Korean tea is a traditional beverage that is being consumed since A.D. 828, as recorded in the book 'The Chronicles of the Three States' written in A.D. 1281.In Korea, tea has historically been used in important events such as memorial services, known as the 'tea ceremony, ' forming a unique cultural practice unlike that in any other country [21,22].Drinking tea was limited to temples or the royal family [23,24] primarily because of the scarcity of green tea made from tender leaves.However, these uncommon cultural practices began to change, and tea was introduced to the common people after the 14th century, driven by their medicinal effects as folk remedies [25,26].Based on these historical records, Korean tea is of significant cultural heritage and well-known as a functional food for health.However, very few studies have focused on the characteristics of tea plants in Korea despite the abundance of research on market product components in journals listed in the Korea Citation Index (KCI).
Twenty-two Korean tea cultivars were registered for plant variety protection with the Korea Seed and Variety Service until 2023.However, no comparative studies of cultivar characteristics have been conducted since their registration.Therefore, basic research is necessary to improve the tea quality and develop the Korean tea industry.In this study, we analyzed amino acids and volatiles, which are the major components of tea, and evaluated the phenotypes to identify the Korean tea cultivar characteristics.We aimed to enhance the value of domestic cultivars by utilizing their specific characteristics to process suitable teas, such as green tea.

Tea leaves collection and preparation
We used seven tea cultivars from tea germplasm maintained by the Research Institute of Climate Change and Agriculture, National Institute of Horticultural and Herbal Science, and Rural Development Administration.The Korean cultivars include 'Sangmok (SM), ' 'Keumsull (KS), ' 'Bohyang (BH), ' 'Chamnok (CN), ' and the native species (NS).For comparison, we included the Japanese cultivar 'Yabukita (YBKT)' and the Taiwanese cultivar 'Taicha12 (TC)' as control cultivars.
To evaluate phenotype, fresh tea leaves consisting of one bud and three leaves were harvested in May 2020 from 9 to 10 tea plants per cultivar.In addition, in August 2020, the mature leaves from brown branches of same tea plant were collected.To analyze amino acid and volatile compounds, fresh tea leaves consisting of one bud and one leaf were harvested on April 20, 2020, and promptly stored at − 80 °C.All fresh tea leaves were collected according to the picking standard.Based on data from the Korea Meteorological Administration, the average temperature in March and April 2020 was 11.5 and 13.2 °C, respectively (minimum: 2.5 and 6.0 °C, respectively; maximum: 23.2 and 24.8 °C, respectively).Development stage of young shoot and the list of detailed temperature conditions are shown in Supporting information, Fig. S1 and Table S1, respectively.The frozen samples were freeze-dried (LP20, Ilshin Biobase, Korea) at − 85 °C for 72 h.Prior to sample analysis, the tea samples were ground to a homogeneous particle using a mill (IKA Werke GmbH, Staufen, Germany) for 25 s at 24,000 rpm, and then stored at 4 °C until further analysis.

Phenotype evaluation
The phenotype of 12 young shoots and leaf blade of each cultivar were investigated in May and August 2020 respectively.Weight was measured using a precision electronic scale (AR3130, OHAUS, USA), length and width were measured using calipers (CD-10APX, Mitutoyo Corp., Japan), and thickness was measured using a QUICK mini (PK-1012CPX, Mitutoyo Corp., Japan).Leaf area and leaf type were calculated as length × width × 0.7 and length/width, respectively.The values of L, a, and b were measured using a color-difference meter (CR-400, KONICA MINOLTA, Japan) and calculated as |G| = |(a/b)×100| for greenness.The survey criteria were based on the Tea Guidelines of the Union for the Protection of New Varieties of Plants (UPOV) and the Korea Seed & Variety Service.After investigating the leaf phenotype, the mean values of each phenotype were carried out the Duncan's multiple range test (p < 0.05) using R software.

Amino acid analysis
A total of 250 mg tea leaf powder was taken in a 15 mL conical tube with 10 mL tertiary distilled water and heated in an autoclave (JAC ULTRASONIC-4020, KODO, Korea) at 95 ℃ for 20 min.Then, 1 mL supernatant filtered through a 0.45 μm nylon membrane (Whatman, Seoul, Korea) was dispensed in a 2 mL vial, and the amino acid content was quantified by HPLC (Agilent 1200 Series, Agilent, USA) system coupled to a diode array detector (DAD).

Volatile compound adsorption and analysis
The volatiles from tea leaves were adsorbed on a carboxen/polydimethylsiloxane (CAR/PDMS, 85 μm, 1 cm) coating fiber (Agilent Technologies, Bellefonte, PA, USA) using headspace solid-phase microextraction (HS-SPME), as reported previously [17,27,28].The parameters were: 1.0 g tea powder was first placed into a 20 mL sealed glass vial, and 6 mL boiling deionized water was added.Subsequently, the vial was immediately put into a thermostatic oscillator and incubated in a water bath at 60 °C.After stabilization for 1 min, the volatiles were adsorbed for 60 min using HS-SPME and separated using a gas chromatograph-mass spectrometry (GC-MS, GCMS-QP2010 Series, Shimadzu, Japan) equipped with a DB-5MS column (30 m × 0.25 mm × 0.25 μm, Agilent Technologies, Santa Clara, CA, USA).All samples were run in triplicate.
Gas chromatograph conditions were as follow: the temperature of the GC injector was set as 250 °C.The carrier gas was helium (> 99.99%) at 1.00 mL/min constant flow rate, and the injection mode was splitless.The programmed column temperature program was: initial temperature was 50 °C held for 2 min, increased to 80 °C (hold for 2 min) at 2 °C/min, then finally increased to 220 °C (hold for 1 min) at 4 °C/min; the total analyzing time was 55 min.
A total of 1.0 µL standard volatile (1000-fold dilution) was analyzed under same conditions for identifying the volatile compounds.

Volatile compound identification
The volatile compounds were tentatively identified by mass spectrometry from the NIST14MS data library, retention indices (RIs), and retention times with the data available in the published literature and online library (https://webbook.nist.gov/chemistry/cas-ser.html) and further positively identified with those of the available standard compounds.The RIs were calculated using n-alkanes (C7-C40) as external references under identical experimental conditions.
The volatile compounds were quantified using standard calibration curves as external standards, which were constructed using a series of solutions at 4-5 different concentrations containing the corresponding standards.The standard solutions were prepared from mixed aroma standards in the deodorized tea samples.The concentration of each compound was calculated as nanograms per gram (ng/g).

Multivariate statistical analysis
Volatile relative contents and concentration of the identified volatile compounds were calculated as mean values, and pie and bar charts were generated using Excel 2016 (Microsoft Corp., Redmond, WA, USA).Partial least-squares discriminant analysis (PLS-DA), hierarchical cluster analysis (HCA), correlation analysis, and nonparametric tests were performed using SIMCA-P + 12.0 software (Umetrics, Umea, Sweden).The heatmap of the main volatile compound contents was generated using MultiExperiment Viewer 4.9.0 (Oracle Corporation, Redwood Shores, USA), and non-parametric tests were carried out using SPSS Statistics 20.0 (IBM, USA).

Phenotype
We investigated 12 samples from nine to ten tea plants per cultivar, and all samples were in good condition (Fig. 1).Among the most important characteristics of young shoots and leaf blades in tea plants, phenotypes showing significant differences between cultivars were identified (Table 1).
Among the young shoots, the SM had the highest weight (14.67 ± 1.39 g), the BH was heavier than the YBKT, CN and NS were lighter than the YBKT, but they were judged similarly.KS had the lowest weight, similar to TC.The BH had the widest leaf area (10.77 ± 5.70 cm 2 ), similar to that of YBKT.The leaf area of CN and NS were similar to that of TC, whereas that of SM was in between that of BH and NS.Moreover, the leaf area of the KS plants, which had the lowest weight, was the smallest.The leaf type indices of SM, BH, and KS were 3.0 or higher because the leaf length of the shoot with one bud and three leaves was long.The leaf type indices of CN, TC, and NS were similar to those of YBKT.The greenness of SM was the highest (44.53 ± 5.10); KS had the next highest greenness, while the greenness of BH was similar like that of YBKT, and that of CN and NS were similar to that of TC.
The leaf blade phenotype also differed between cultivars.The SM leaves were the widest (20.24 ± 4.28 cm 2 ) and similar to BH leaves.The CN and NS leaves were narrower than YBKT leaves, and KS had the smallest leaves.Interestingly, the leaf type index of KS was the highest (3.4), while those of SM, BH, NS, and YBKT were similar and those of CN and TC were similar (the lowest).The CN leaves were the thickest (0.38 mm) and similar to BH leaves.The leaf thickness of SM and KS were similar to that of TC.The NS leaves were the thinnest and similar to YBKT leaves.The SM leaves was the darkest (56.19 ± 8.98) and similar to YBKT leaves.BH and NS leaves were darker than TC leaves, whereas KS and CN leaves were brighter than TC leaves.
The Korean tea cultivars were bred by selection from wild species as follows: SM was bred by the Rural Development Administration, KS was bred in the Jeju province, and BH and CN were bred in the Jeonnam province.These cultivars belong to Camellia sinensis var.sinensis and are suitable green tea varieties in Korea.Mahmood et al. [29] have reported the common morphology of Camellia sinensis var.sinensis.Leaf length and width were 5-30 and 4 cm, respectively, and the leaves were small, bright green, with abundant pubescence.However, the phenotype is particularly affected by the environment and can differ even in the same species depending on where and how it is grown [12].In this study, because SM is managed with periodic pruning, greenness, an important feature of tea leaves, was excellent.While KS had very small leaves with a certain lobular phenotype, BH had large and thick leaves, along with CN.The NS leaf phenotype largely varies among individuals and is similar to that of TC because the wild type was usually imported from China and Japan in the past and has survived by adapting to the domestic environment.

Amino acid contents
Analyzing the amino acid content of the tea leaf extract using HPLC revealed nine amino acids, and the remaining amino acid contents detected were markedly different among the cultivars (Fig. S2).The total amino acid and theanine contents of the control cultivars, YBKT and TC, were 14.25, 6.58, and 9.95, and 2.85 mg/g, respectively.The total amino acid and theanine contents of SM was 41.42 and 24.60 mg/g, respectively, which are significantly higher than those of the control cultivars (Fig. 2A).
The total amino acid and theanine contents of KS and BH were 25.83, 13.88, 21.58, and 12.43 mg/g, respectively, which were higher than those of the control cultivars.The total amino acid and theanine contents of CN were 11.69 and 3.57 mg/g, respectively, intermediate between those of YBKT and TC, while NS had the lowest the total amino acid and theanine content (9.08 mg/g total amino acids and 2.81 mg/g theanine).Among other amino acids, the L-histidine and L-glutamic acid contents were 1.63-3.54and 1.23-4.10mg/g, respectively (Fig. 2B).L-arginine was detected only in SM (5.83 mg/g), BH (0.54 mg/g), and KS (1.27 mg/g), whereas L-threonine content was the lowest (0-0.48 mg/g).The mean evaluation obtained from 9-10 plants (n = 9 or 10) ± SEM.Means in columns followed by the same letter are not significantly different at the p < 0.05 according to Duncan's multiple range test Currently, 26 amino acids have been identified in tea, which are involved in tea plant growth and tea taste [7].The umami taste of green tea is mostly related to L-glutamic acid and L-theanine, and the sweetness of green, oolong, and black teas is related to L-serine, L-alanine, L-proline, and glycine [5].Horanni and Engelhardt [22] analyzed 19 amino acids using HPLC.However, in this study, we analyzed 17 amino acids, which was sufficient to characterize Korean tea cultivars.The difference in amino acid content is influenced by various factors such as environment, cultivation, and cultivars.Tea leaves harvested in spring are distinguished from tea leaves harvested at other times because of their high theanine content [30].The mutant white tea leaves contain more total amino acid (mg/g), theanine, and glutamic acid (91.58, 45.31, and 10.86 mg/g, respectively) than ordinary tea leaves [19].This study confirmed that SM had a considerably high theanine and total amino acid content, and domestic cultivars, such as KS and BH, had higher total amino acid and theanine content than the control cultivars.When tea leaves are processed, their composition and content change owing to chemical reactions; however, the suitability of cultivars for processing into green and black tea can be determined depending upon the amino acids and polyphenol content of in the tea leaves [12].Comparing the amino acid content of raw leaves and six types of tea showed increased many amino acids, such as alanine and serine, content in white tea; however, green tea and yellow tea had higher contents of amino acids such as theanine, which is involved in the umami taste of tea [31].The amino acid analysis for each tea leaf part of the oolong tea variety showed that the total amino acid and theanine contents were high in the second (15.5 mg/g) and third (10.70 mg/g) leaves, respectively, which was considered a high-quality oolong tea [32].Therefore, high-quality tea leaves must be used to prepare tasty tea, and tea leaves with a high amino acid content are suitable for making unfermented or low-fermented tea to maintain their characteristics.Therefore, according to the results of this study, SM, KS, and BH, which have a high amino acid, such as theanine, content is suitable for preparing low-fermented tea.Further studies should identify suitable processing methods for analyzing the polyphenol, such as catechin, contents.

General characteristics of the common volatile distribution
The aroma components of seven different tea plant cultivars were analyzed using HS-SPME/GC-MS.Initially, approximately 340-400 peaks of the compounds in each sample were recognized through the NIST14MS data library (Fig. S3).Approximately 150-190 compounds in each sample were tentatively identified as aroma components after removing impurities from the column bleeding.The remaining compounds were verified by comparing the RIs and authentic standards; finally, 107 compounds were determined as common volatile compounds among all the tea leaves of seven tea plant cultivars (Table S2 in the Supporting Information).
The comparison of compounds among seven cultivars indicated that the alcohol (64.93%) and ketone (2.77%) Fig. 2 The amino acid contents of each cultivar.A) Total amino acid (Total AA) and theanine (Thea) contents.B) L-arginine (Arg), L-glutamic acid (Glu), L-aspartic acid (Asp), L-histidine hydrochloride monohydrate (His), L-serine (Ser), L-cystine (Cys), L-alanine (Ala), and L-threonine (Thr) contents contents were the highest, while the ester content (4.71%) was the lowest in SM (Fig. 3A).The aldehyde (27.64%) and alkane (2.37%) contents were the highest, whereas the alkene content (4.86%) was the lowest in KS (Fig. 3B).Alkenes (14.43%) and heterocyclic compounds (0.15%) were the most abundant, while the aldehydes (8.66%) were the least abundant in BH (Fig. 3C).The alcohol content (63.14%) of CN was the second highest, followed by that of SM, and the distribution profile of CN was similar to that of SM (Fig. 3D).The ester content (16.43%) was the highest in NS (Fig. 3E), whereas in YBKT, none of the compounds had the highest or lowest content (Fig. 3F).The distribution profiles of both NS and YBKT were in the same order as alcohols, esters, alkenes, aldehydes, ketones, acids, and alkanes; the ester content was the second highest, unlike in the other five cultivars.The acid content (0.41%) was the highest and the ketone (0.71%), alkane (0.08%), and heterocyclic compound (0.00%, trace) contents were the lowest in TC (Fig. 3G); the distribution profile was similar to that of BH in the order of alcohols, alkenes, esters, aldehydes, and ketones.The alcohol, aldehyde, ester, and alkene content distributions were higher than those of ketones, alkanes, acids, heterocyclic compounds, and other compound, which were < 1% relative contents.
In summary, the order of contents in each cultivar is as follows: and the number of compounds is given in parentheses for the seven cultivars.
The alcohol, aldehyde, ester, and alkene content distributions were higher than those of ketones, alkanes, acids, heterocyclic compounds, and other compounds were all under 1% relative contents.Highly related components of alcohols, aldehydes, esters, and alkenes cause green, fruity, or floral odors, but they can be lost due to their volatility or transformation during green tea processing.Heterocyclic compounds and ketones, with low relative contents, increased from fresh tea leaves to green tea products, which might be formed from L-theanine during the thermal reaction, being probably involved in producing volatiles by reacting with sugars during the roasting process, and are also responsible for the burned, nutty, and caramelized aroma of many famous green teas [33].
According to a previous study on high-grade Chinese green tea, the linalool and geraniol contents in final tea products were lower than those in fresh Jingshan cha green tea leaves [34].Based on these results, the four Korean tea plant cultivars are suitable for preparing green tea with fresh and tender chestnut aromas.In a slightly different trend, the most abundant compounds in KS were (Z)-3-hexen-1-ol and hexanal, which were volatilized and/or converted into other aroma components (such as (E)-3-hexen-1-ol, jasmone) owing to the high temperature during sterilization and drying [35].The content of hexanal, with a grassy odor, decline during withering, increase during fermentation, and retain its green aroma in green tea products [36].Based on the above results, we can conclude that Korean tea plants are suitable for preparing green tea, but also have a good scent, even for grassy black tea.

Multivariate analysis of GC-MS data and quantification
After comparing 108 compounds in nine categories in all seven tea leaf cultivars, PLS-DA [37,38] was used to investigate the concentration differences among the seven cultivars.PLS-DA is the most widely used discriminant analysis method and combines partial least squares regression and classification techniques [39].
The seven tea leaf samples were well distinguished by a dependable PLS-DA model (Fig. 4A and B), which presented satisfactory variance and cross-validated predictive capability (R 2 Y = 0.962, Q 2 = 0.802) without overfitting (200 repeats of calculations of the validation model; R 2 Y = 0.607, Q 2 =-0.869).Subsequently, 38 compounds with variable importance in the projection (VIP) values [28,40] > 1.0, and P < 0.05 according to the Kruskal-Wallis test [38,41] were identified as the key compounds with significant differences in concentration among the   [27,37] was used to determine the concentration distribution of key compounds among the seven cultivars.
The concentration distribution trends of the 38 key compounds were divided into seven classes: three aldehydes, 12 alcohols, five esters, four ketones, nine alkenes, two alkanes, two heterocyclics, and one acid (Fig. 4C).The two compounds in Class I with green aromas were present at high concentrations in the KS and TC cultivars.The five in Class II with herb and woody aroma had significantly high concentrations in CN; the three compounds in Class III with woody and floral aroma were present in KS, CN, and BH; the seven compounds in Class IV with floral and herb aroma had significantly high concentrations in BH and YBKT; the three compounds in Class V with citrus aroma had high concentrations in YBKT and TC; the four compounds in Class VI with green aroma were detected in NS and YBKT; and the 14 compounds in Class VII with sweet, herb, and woody aroma had significantly high concentrations in SM and partly in BH.In this heatmap, the amounts of four compounds in Class II, except α-cadinol, increased with floral and woody aroma, while the amounts of two compounds in Class VI, except (E)-3-nonen-1-ol, decreased with green aroma during withering, which is a key process in white tea processing [17].The fluctuation of compounds in other classes has not been specifically reported, but these results have been referred to in tea processing research, including withering.
Volatile compounds account for 0.002-0.07% of the dry weight [10] of fresh tea leaves and produce aroma components using different processing methods [11].The number and proportion of N-containing heterocyclic compounds and ketones were higher in green tea after roasting than those in fresh tea leaves, whereas those of linalool, geraniol, and (E)-linalool oxide (furanoid) were lower than those in fresh tea leaves.In addition, a high ratio of terpenoids to green leaf volatiles can be used as a reference index to screen tea cultivars suitable for making oolong tea [42].Alcohols constitute the largest portions of fresh tea leaf oil, and many compounds belonging to alcohols have a floral odor.Compounds with high boiling points, including aromatic alcohols and terpene alcohols, form tea aroma [43].Esters are known as the fruit odor and constitute 9.0% fresh tea leaf oil, 2.0% green tea, and trace levels of black tea [44].Aldehydes constitute 3.0% fresh tea leaf oil; the contents increase after processing and is higher in black tea than that in green tea.Aldehydes play an important role in the chestnut-like aroma because of their extremely low odor thresholds and similar odor characteristics [42].According to Zhu et al. [45], heptanal and (E,E)-3,5-octadien-2-one concentrations in fresh tea leaves were higher than those in green tea, while the compounds with high odor activity values, including linalool and nonanal, cause a chestnut-like aroma in green tea.Aldehydes were second highly distributed in SM, KS and CN, also among relative contents over 1% compounds, above mentioned four compounds which including heptanal, (E,E)-3,5-octadien-2-one, linalool and nonanal were all existed in SM, and three compounds except (E,E)-3,5-octadien-2-one were present in other six cultivars, considered be worth processing green tea with chestnut-like aroma.In BH, high methyl salicylate and jasmone concentrations formed the main aroma of black tea; therefore, it is worth processing.We speculate that NS and YBKT, with similar ester and other related compound contents, are suitable for preparing green tea.
Five tea plant cultivars From Korea were compared to YBKT from Japan and TC from Taiwan as the experimental control samples.The (Z)-linalool oxide (furanoid) concentrations were significantly higher, and the linalool concentrations were also higher in NS and CN, but low but high concentrations.Linalool and its various forms of oxides are the major compounds responsible for tea     aroma, and this result will be the basis for Korean tea plant cultivars that can produce high-value tea products.
In this study, we analyzed the volatile compounds in fresh tea leaves of Korean tea plant cultivars to determine the component content characteristics of each cultivar, evenly distributed throughout green, fresh, herbal, floral, and sweet odors.Although Korea mainly produces green tea, the results of this study indicate that Korean tea plants are suitable for producing not only green tea, but also black tea with a grassy and sweet aroma; therefore, this should be explored.Although we did not analyze the aroma compounds in green tea owing to the lack of fresh tea leaves, the results of our analysis and previous studies together can be used as basic data for developing novel tea processing methods and products for developing the Korean green tea industry.

Table 1
Evaluation of phenotype of young shoot and leaf blade

Table 2
Over 1% compounds with high relative contents seven groups.HCA

Table 3
The concentration of the identified volatile compounds with > 1.0 variable importance in the projection (VIP)