Hot-air full drying driven metabolome changes in white tea (Camellia sinensis L.)

ABSTRACT White tea (Camillia sinensis L.) is the least processed tea, and due to simpler processing steps involved, its flavor and nutritive compound composition is least disturbed. However, only a limited number of research has explored the key metabolomic changes during white tea processing (especially drying). The freshly harvested leaves of C. sinensis var. Tieguanyin were initially withered at room temperature for 72 h, and first-dried on fire at 70°C for 3 h. Then, they were spread at room temperature for 7 days and fully dried at 80°C for 4 h, followed by cooled at room temperature. The metabolome of the tea leaves before (CK) and after full drying (RO) were compared using UPLC-MS/MS. The LC-MS/MS analysis identified 1,253 compounds belonging to 11 classes. The highest number of accumulated compounds belonged to flavonoids, phenolic acids, and lipids. Of the 57 differentially accumulated metabolites (DAMs), 49 were up-accumulated in RO. These were classified as amino acids derivatives, lipids, organic acids, vitamins, alkaloids, nucleotides and derivatives, flavonoids, tannins, terpenoids, lignans and coumarins. We found that several health beneficial compounds showed up-accumulation in RO compared to CK. We concluded that Hot-air full drying alters white team metabolome composition.


Introduction
White tea (Camillia sinensis L.) is an important type of tea produced in China which involves simpler processing steps compared to the other five tea types, i.e., green, yellow, red, oolong, and dark tea.Its production in China reached 81,900 tons in 2021 [1] , mainly from Fujian province, whereas the global white tea market is expected to reach ~ 2.96 billion US$ by 2029 (https://www.databridgemarketresearch.com; accessed on March 20, 2023).The usage of white tea dates back to Shen Nong period, during which different tea processing methods evolved. [1,2]Since the processing of white tea do not involve fermentation or enzyme-deactivation, and only involve decolorization and drying, its health benefits are widely studied.It contains diversity of compounds such as alkaloids, polyphenols, vitamins, amino acids, flavonoids, organic acids, and polysaccharides. [1]Owing to the presence of such a diversity of compounds, white tea has several health benefits including modulation of cholesterol, reduction in blood glucose levels, improved glucose intolerance, [3] better insulin sensitivity, [4] improvement of cardiac glycolytic and oxidative profiles, [5] better bone health, [6] antibacterial and anti-inflammatory effects, [7] reduced depression risk, [8] and reduced oxidative damage in liver. [9][12] The average content of total polyphenols, catechins, and caffeine is higher in white tea compared to the green tea. [13]It is known that the chemical composition of white tea is different from green and black tea.For example, a study used same fresh tea leaves to manufacture white, green, and black teas, and reported that the content of amino acids, methylated catechins, theaflavins, kaempferol glycosides, galactosylated quercetins, myricetin and glycosides was highest in white. [10]The withering process causes significant changes in the metabolome profile such that major amino acids decrease with increase in time, whereas theasinensins and catechins increased. [10]Similarly, another study reported that the flavonoid and water-soluble saccharides displayed opposite accumulation trends when white tea was withered for 12 h.However, if the processing time was increased, the total flavonoid content reduced, whereas the watersoluble saccharides increased. [12]There are also reports which indicate that the content of specific metabolites may not necessarily follow either a decreasing or increasing trend. [14]oreover, the white tea samples grown in different regions may also differ in their metabolome profiles.For example, white tea samples from Yunnan and Fuding indicated that the later contains relatively higher contents of amino acids and alkaloids. [15]The Yunnan white tea samples were rich in flavonoids, polyphenols, phenolic and organic acids, and lipids.Similarly, Ma et al., [11] reported that white teas can be grouped based on their origin following a method based on principal component analysis, i.e., E-tongue. [16]However, limited knowledge is available on how individual stage affects the composition of white tea, indicating that continuous efforts are needed to explore the global metabolome profiles of white tea varieties processed at different temperatures.
The processing technology of the tea is directly associated with the taste, aroma, and health benefits of the tea. [17]Since white tea preparation method(s) involve minimal processing, it is considered a non-fermented tea.For white tea production, the buds and first leaves are picked, withered, and dried. [18]Among these steps, withering is the key step, which is a prolonged process that lasts up to 48 h.However, sometimes steam is used to produce nonfermented tea.Though researchers argue that the long withering process can initiate oxidation process and white tea can be partially-fermented. [19]Another method used in tea drying and roasting is the hot air-drying technology.In this method, the hot air is used as a heating medium, which exchanges the moisture and heat by convection circulation in such a way that the moisture is discharged from the tissue.[22] This method is considered as an important means for the white tea refining and roasting stage to enhance the fragrance.Its advantages are high drying efficiency, simple drying instrument structure and high productivity. [23,24]Hot-air drying is positively correlated with many tea characteristics, i.e., color index, color change, soluble sugars, and drying rate.Contrarily, it is negatively correlated with soluble protein contents, and radical scavenging capacity. [25]These positive and negative changes in response to hot-air drying have been associated with the degree of temperature in different teas.For example, in case of green tea drying at different temperatures yielded different aromas due to biosynthesis and conversion of volatiles. [26]Similar volatilome changes have also been reported in black tea, [27] indicating temperature-driven changes during drying are important for aroma and flavor.In order to provide recommendations for quality control of white tea, continued efforts are needed to explore changes in metabolome profile of white teas.To this regard, we employed hot air-drying method, and determined the changes in accumulation trends of different compounds through UPLC-MS /MS analysis.

Plant material
Fresh tea leaves of Camellia sinensis var.Tie Guanyin (white tea), were purchased from Fuzhou Migao Xian Tea Industry Co., Ltd.We bought the tea samples that were picked according to standard practices in China, which is the picking material should include a bud and a leaf.The picking date of the tea plants is 20, April 2022.The average temperature, humidity, and precipitation of the experimental location are 21°C, 77%, and 120.0 mm, respectively.During the growth period, all the standard irrigation, fertigation, and weeding practices were followed.Tea leaves were collected from uniform and healthy plants and further processed.

White tea processing
The white tea processing was done as reported earlier [19] and slightly modified.Briefly, fresh tea leaves were harvested and spread on frame for withering at 25°C for 72 h.Next, the tea leaves were dried on fire at 70°C for three hours, followed by spreading the leaves at room temperature, i.e., 20°C for 7 days.Finally, the leaves were then fully dried by tea drying oven (RL-1000) at 80°C for 4 h, and then cooled at the room temperature.The treated samples (RO) were compared with the samples before full drying, i.e., control (CK).

Metabolome analysis
Sample preparation, extraction, and UPLC-MS/MS analysis: Freeze-dried tea leaves before and after processing were turned to ground powder using zircona beads for 90 s at 30 Hz in a mixer mill (MM400, Retsch GmbH, Germany).We then added 70% 1.2 mL MeOH in the lyophilized grounded sample (100 mg).The mixing was repeated six times on a vortex for 30 s each.The dissolved samples were kept at 4°C overnight followed by centrifugation at 12,000 rpm for 10 min followed by filtration through a 0.22 μm filter (SCAA-104, ANPEL, Shanghai, China, http://www.anpel.com.cn/).The centrifugation and filtration steps were repeated thrice before UPLC-MS/MS analysis.The triplicate RO and CK extracts were analyzed using an UPLC-ESI-MS/MS system.The UPLC column, mobile phase, sampling measurement, and system operation were done according to the methods used in. [28]We recorded both types of ion modes.The system settings for ESI source operation were also according to the earlier report. [28]

Statistical analysis
We first scaled the data to unit variance and then used "prcomp" function in R for the unsupervised principal component analysis (PCA).Normalized signal intensities were used for heatmaps and Pearson Correlation Coefficient (PCA) computation using "pheatmap" and "cor" functions in R. The differentially accumulated metabolites (DAMs) in RO vs CK were screened based on criteria if the variable importance in projection (VIP) was ≥ 1 and the log2 fold-change (log2FC) ≥ 1 and ≤-1.An R package "MetaboAnalystR" was used for OPLS-DA analysis.Finally, the DAMs were annotated and mapped to pathways according to KEGG Compound database (http://www.kegg.jp/kegg/compound/) and mapped to KEGG Pathway database (http://www.kegg.jp/kegg/pathway.html).The significantly regulated metabolites' pathways were fed into metabolite sets enrichment analysis (MSEA), and their significance was determined by hypergeometric test p-values.

Metabolome analysis of the white tea leaves after hot-air full drying
The HPLC-MS/MS based metabolome profiling of white tea leaves before (CK) and after (RO) hot-air full drying resulted in the identification of 1,253 compounds.The PCA grouped the CK and RO replicates together (Figure 1a), and the PCC was higher than 0.98 (Figure 1b) indicating that the sampling was reliable.These metabolites belonged to 11 compound classes.Highest number of metabolites were classified as flavonoids (310) followed by phenolic acids (210), lipids (158), others (129), amino acids and derivatives (104), organic acids (101), alkaloids (80), nucleotides and derivatives (70), lignans and coumarins (38), tannins (33), and terpenoids (20) (Figure 1c).These results indicate that white tea is rich in multiple compound classes.

Global metabolome profile changes in white tea before and after hot air drying
Changes in Alkaloids: There were 80 compounds classified as alkaloids; 30 alkaloids, one isoquinoline alkaloid, 18 phenolamines, three piperdine alkaloids, 18 plumeranes, four pyridine alkaloids, five pyrrole alkaloids, and one quinoline alkaloid.Among these alkaloid classes, the total content of pyridine alkaloids and quinoline alkaloids increased by 51.44% and 28.71%, respectively, after hot air drying.The other alkaloid classes showed decreasing trend when considered the sum of all compounds classified in each of these classes (Figure 2; Table S1), which is consistent with the known fact that heat affects the alkaloid content as observed in Carica papaya leaves and Coptis japonica rhizomes. [29,30]However, individual compounds among these classes showed increasing trends.Different studies have shown that hot air drying can affect the alkaloid content.For example, hot air resulted in increased content of steroidal alkaloids in potato peels, shoots, and berries. [31]To this regard, 18 compounds classified as alkaloids, 15 phenolamines, one piperdine, 12 plumeranes, and two pyrrole alkaloids showed increasing accumulation trends.Notable increase in content was noted for 3-hydroxypyridine (30.16-fold), 1-acetyl-β-carboline (4.94-fold), N-acetylputrescine (2.77-fold), L-tyramine (1.83-fold), and theophylline (1.28-fold).The 30.16-fold increase in 3-hydroxypyridine is quite interesting since this compound or its derivatives have been reported to be used as pharmacological agents for the correction of ischemic brain injury [32] and induction of hepcidin expression in iron-overloaded β-thalassemic mice. [33]It has also been shown to have strong association with bone mineral density [34] through the consumption of coffee.Whereas, the 1-acetyl-β-carboline is an antimehicillin-resistant Staphylococcus aureus substance, which has been isolated from a marine bacterium. [35]Earlier studies on coffee brews have shown the occurrence of β-carbolines. [36]The βcarboline alkaloids have antitumor, antimicrobial, antiviral, as well as antiparasitic activities. [37]As far as N-acetylputrescine is concerned, limited studies have elaborated its role in humans.Nevertheless, it has been reported as an alternate substrate to glutamate for oxidation to gamma-aminobutryic acid. [38]t is also used as a biomarker to evaluate the efficacy of the anticancer drugs. [39]The L-tyramine is a trace amine derived from tyrosine, which benefits for the treatment of depression and drug abuse.It also acts as a precursor of catecholamines that are beneficial to health. [40]Finally, the theophylline has several health benefits ranging from improving steroid sensitivity in acute alcoholic hepatitis [41] to relieving of hypertension. [42]Overall, these results are consistent with the earlier findings that nonvolatile compounds, e.g., trans-catechins may increase after roasting. [43]Whereas the limited changes in the other alkaloids are understandable since earlier studies on different tea have shown that as a result of roasting, the contents of alkaloids are mostly stable. [44]hanges in amino acids and derivatives: There were 104 metabolites classified as amino acids and derivatives.The sum total of intensities of the compound class amino acids and derivatives decreased by 8.92% (Figure 2).The content of all the detected amino acids, i.e., L-serine, L-proline, L-valine, L-threonine, L-cysteine, L-leucine, L-Isoleucine, L-asparagine, L-aspartic acid, L-glutamine, L-lysine, L-glutamic acid, L-methionine, L-phenylalanine, L-theanine, L-arginine, L-citrulline, and L-tyrosine decreased after hot-air drying (Table S1).Free amino acids have significant role in tea flavor.During processing of tea types which involve fermentation, these amino acids are converted into other metabolic compounds. [45,46]Different tea processing methods have different effects on amino acid contents.For example, if coffee leaves are dried for a shorter time, i.e., 24 h at 160°C, the content of free amino acids increases. [25]A report on loquat flower tea indicated that amino acid content increases with temperature, [47] however, how the prolonged drying time effects the content is not known.In case of black tea, the hot-air drying had better sensory and chemical qualities when compared with hot roller drying method, [48] thus this method has some advantages over the others.This is evident from the increased contents of eight amino acid derivatives after hot air drying.The highly up-accumulated amino acid derivatives were N-ethylmaleimide (NEM), followed by L-glutamic acid-O-glycoside, L-glutamine-O-glycoside, 5-Oxo-L-proline, and L-tyrosine methyl ester.These results indicate that hot air drying can increase O-glycosides and esters but can decrease the amino acid content.The upaccumulation of the amino acid derivatives is consistent with the reduction in amino acids.Moreover, the increase in amino acid derivatives is consistent with an early report on white tea processing. [18]hese observations indicate that hot-air drying changes the amino acid profile of the white tea.
Changes in lignins and coumarins, and lipids: Dietary plants include a range of antioxidant compounds such as phenolics, flavonoids, coumarins, lignans, and other compounds. [50]The hot air drying caused an increase in lignans and coumarin content, however, this increase was mainly due to coumarins; coumarins showed a 12.16% increase (Figure 2).The most down-accumulated coumarins included isofraxidin-7-O-glucoside, 6,7-dihydroxy-4-methylcoumarin, and skimmin (7-hydroxycoumarin-7-O-glucoside).Whereas, 7,8-dihydroxy-4-phenylcoumarin showed the most increase in content after the hot air drying.Coumarins and benzeneacetaldehyde are phenylalanine derivatives and are produced as a result of oxidation in tea leaves. [51]Consistent reduction of phenylalanine in RO compared to CK is in accordance with this report.On the other hand, we observed a decrease in the contents of most of the lignans, e.g., epipinoresinol, pinoresinol, and isolariciresinol-9'-O-glucoside.Generally, the lignan substantially reduced (12.32%)after hot air drying (Figure 2).Earlier studies reported that lignans can be liberated as a result of processing in green tea but not in black tea. [52]This is possibly due to the degradation of lignans as heating up to 100°C has been shown to degrade lignans in sesame and rye seeds. [53]Coumarins are documented as anti-inflammatory, anti-coagulant, antihypertensive, and protects against viral, bacterial, fungal attacks, hyperglycemia, tuberculosis, and neurological disorder. [54]Thus, an overall increase in coumarins in white tea after the hot-air treatment is useful from the health perspective.
Contrastingly, the metabolites classified as lipids showed a decreased accumulation trend after hot air treatment.The content of the free fatty acids, sphingolipids, and lysophosphatidylethanolamine (LPE) decreased by 2.16%, 7.73%, and 13.96%, respectively.These results are consistent with the earlier work which reported that hot-air drying affects the lipid contents. [55]Another reason for reduced lipid content could be accumulation of catechins and flavonoid glycosides as they exert inhibitory activities on lipids in tea (Table S1). [56]Previously, it is known that withering and firing process in tea manufacturing causes considerable losses in fatty acid composition. [57]Whereas that of glycerol esters, LPC, and phosphatidylcholine (PC) increased by 4.85%, 3.13%, and 14.24%, respectively.The increase in glycerol esters indicates the hot-air drying increased the esterification reaction. [58]The glycerol esters can be health beneficial and can counteract diet-related disorders and have immune modulatory effects. [59]Whereas, the increase in other metabolite classes such as LPC and PC can also be beneficial for health based on the known benefits of these compounds. [60,61]hanges in nucleotides and derivatives, and organic acids: Earlier studies have reported the presence of nonvolatile metabolites, e.g., nucleotides and derivatives in teas. [62,63]The sum of intensities of compound class nucleotides and derivatives increased by ~ 5%.This observation is consistent with the results of an earlier study by Liu, Meng, [64] which concluded that hot-air drying increases nucleotide and their derivatives' content in Stropharia rugosoannulata.Overall, we detected 70 compounds classified as nucleotides and derivatives.Among these, the most up-accumulated compounds include 1-methylxanthine, uracil, N6-methyladenosine, and 1,7-dimethylxanthine, 8-azaguanine.On the contrary, we the hot air drying reduced the contents of nicotinic acid adenine dinucleotide, 5-methyl-2'-deoxycytidine, β-pseudouridine, and isocytosine.In living organisms, nucleotides are excellent candidates for vital nutrients, [65] hence their increased content in RO compared to CK can be useful upon consumption.
Interestingly, there was relatively less reduction in the content of organic acids as compared to the other metabolite classes (Figure 2).It is known that rolling, fermentation, and drying has no significant effect on some of the organic acids in black tea. [66]During green tea processing, similar reducing trend of organic acids was reported. [67]Notably, citraconic acid was not detected in CK whereas, its relative content in RO increased by 46,277-fold (Table S1).This is an interesting finding, and future research should concentrate on isolating citraconic acid from white tea or determining its health advantages.Currently, it is known that citraconate inhibits catalysis of itaconate and acts as an antioxidant and antiviral compound. [68]nother notable observation was the 7.29% and 36.85% increase in the content of compounds classified as others and vitamins, respectively.Whereas those classified as saccharides and alcohols decreased by 5.20% (Figure 2; Table S1).These observations are consistent with the previous work on garlic processing, which reported that high temperature processing accelerated the degradation of saccharides. [69]Among the amino acids, the increased accumulation of vitamin C is interesting since in other cases, e.g., green tea drying, the vitamin C content reduces with increase in temperature. [70]evertheless, the increased vitamin C and other vitamins, i.e., biotin, B2, and B3 is notable, especially from health perspective as they offer range of health benefits. [71]hanges in phenolic acids, tannins, and terpenoids: After flavonoids, the largest group of compounds detected was phenolic acids.The total phenolics content (sum of intensities of all compounds in this class) increased in RO by 8.27%.Earlier studies have shown that during white tea processing (including drying at 60°C for two hours), the phenolic acid content decreased during withering process. [19]Among the most up-accumulated compounds were pyrogallol, 3-O-p-coumaroylshikimic acid, hydroxytyrosol, and 2,3-dihydroxybenzoic acid, homogentisic acid, protocartechuic acid, gentisic acid, 3,4-dihydroxybeneacetic acid, sinapinaldehyde, tyrosol, salicylic acid, and methyl brevifolincarboxylate.The compounds classified as tannins decreased by 5.73%, whereas terpenoids increased by 4.5% in RO compared to CK.This decrease in tannin is consistent with earlier report related to the influence of drying temperature on chemical components of herbal tea. [72]Overall, our results highlight that hot-air drying changes the metabolome profile of white tea and most of the compounds are up-accumulated.These results provide the basis for future research related to the role of individual compounds as health beneficial metabolites.

Differential changes in metabolome profile of the white tea leaves after hot-air full drying
The screening criteria based on the VIP and absolute log2 foldchange resulted in the identification of 57 DAMs before and after hot air drying.Eight of the DAMs were down-accumulated and 49 were upaccumulated in RO compared to CK.Among the metabolite classes, the highest number of DAMs belonged to phenolic acids (12), followed by amino acids and derivatives (8), lipids (6), organic acids (6), others (5), alkaloids (4), nucleotides and derivatives (4), flavonoids (4), alkaloids (3), vitamins (2), tannins (1), terpenoids (1), and lignans and coumarins (1).Which is slightly different than global metabolite accumulation trend (Table S1).The most down-accumulated metabolites included alkaloids (stearamide and 3-indole acetamide), amino acids derivatives (l-homomethionine and S-adenosyl-L-methionine), lipids (2-linoleoylglycerol and 9-Oxo-10E,12z-octadecadienoic acid), and others (pantetheine and santalol).The highest down-accumulation of these compounds is consistent with the general accumulation trend (Table S1).Since it is known that heat can affect the alkaloid content in plants, [29,30] therefore, it is possible that processing of tea leaves at 80°C for four hours could have affected the alkaloids and lipids content.Nevertheless, the other DAMs classified as alkaloids were up-accumulated.Among these, the theophylline is a product of caffeine catabolism. [73]However, the results showed that the caffeine content increased (Table S1), this could be due to the reason that it is a slow process and the initial caffeine content in this variety could be higher. [73]Nevertheless, this is an important observation from health perspective since theophylline has long been used in the prevention of disease related to cell death in the nervous system (neurogenerative diseases). [42]We also observed up-accumulation of L-tyramine and N-acetylputrescine.These are also useful observations since processing of Zijuan tea resulted in decreased tyramine content. [74]L-tyramine is a trace amine and is a derivative of L-tyrosine.Tyrosine decarboxylase (TYDC) acts on L-tyrosine and converts it into L-tyramine. [75]Therefore, its biosynthesis during hot-air full drying indicates TYDC activity, which should further be explored in this and other tea types during drying process.Whereas N-acetylputrescine is a polyamine.The presence of both of these compounds should be carefully investigated since there are reports for their health impacts. [39,76]Overall, their production during hotair drying in white tea indicates that the processing technology adapted in this study promotes useful information from nutritional point of view.
In case of amino acids and derivatives, all the differentially up-accumulated compounds were derivatives (Table 1).Which is in association with the general metabolite accumulation trend (Table S1).This change is linked with the decrease in amino acids due to processing at high temperature, i.e., hot air drying at 80°C.An earlier study reported increase in amino acid derivative content in white tea after processing. [18]Moreover, the amino acid compositions of whey protein  isolates changed after glycation at temperatures 80°C and above. [77]Thus, such changes are expected when white tea is processed at this temperature for hours.Considering the role of amino acid derivatives in flavor, future studies will be required to understand the effect of the production of these derivatives on sensory and taste qualities of white tea. [78]imilarly, we observed that flavonoids such as kaempferol-3-O-(2''−acetyl)glucoside, morin, and herbacetin (Table 1) were up-accumulated in RO compared to CK.These results indicate hot air drying can result in increased flavonoid content, as noted in an earlier study. [12]The accumulation of flavonoids has also been reported in white teas of different origin in China. [79]The increased content of herbacetin and morin is interesting from health perspective since they have diverse pharmacological activities against a range of diseases. [80,81]Whereas kaempferol has already been reported in different plants include cruciferous vegetables, tea, berries, and grapes.It has been linked with reduced DNA damage and prevention of oxidative stress, cancer, and inflammatory symptoms. [82]he other up-accumulated metabolites included flavonols, lysophosphatidylcholines (LPCs), monoterpenoids, nucleotides and derivatives, organic acids, phenolic acids, alkaloids, and vitamins.The top-accumulated metabolites in RO compared to CK included citraconic acid, N-ethylmaleimide, 3-hydroxypyridine, N-benzoyl-2-aminoethyl-β-D-glucopyranoside, pyrrole-2-carboxylic acid, and L-glutamic acid-O-glycoside (Table 1).These compounds are known for their health beneficial effects.For example, N-ethylmaleimide plays role in redox regulation and cell survival. [83]Overall, these results present novel insights that hot air treatment (80°C) for four hours can significantly change the metabolite profile of the white tea.
The DAMs could be enriched on 30 KEGG pathways (Figure 3a).The significantly enriched KEGG pathways included tyrosine metabolism, caffeine metabolism, terpenoid backbone biosynthesis, glutathione metabolism, arginine and proline metabolism, biosynthesis of cofactors, and many other presented in Figure 3b.Overall, we observed that all the DAMs classified as phenolic acids, tannins, vitamins, organic acids, nucleic acids and derivatives, terpenoids, flavonoids, and lignans and coumarins showed up-accumulation.These results are consistent with earlier work and are discussed in below section in details.Whereas, the other classes included only one-to-two DAMs that were downaccumulated.These results clearly indicate that hot-air drying results in significant increase in most of the metabolite classes.

Conclusion
Our study provides a detailed description of global and differential metabolite changes in white tea during the drying step.We conclude that hot air drying at 80°C can alter compounds from several classes.In conclusion, hot air treatment results in increased contents of compounds classified as terpenoids, vitamins, phenolic acids, nucleotides and derivatives, coumarins, amino acid derivatives, glycerol esters, LPCs, PCs, flavonoids, pyridine alkaloids, and quinoline alkaloids.The differential screening results conclude that compounds of health beneficial effects are highly up-accumulated.Relatively lower number of metabolites are down-accumulated after hot air treatment.Thus, hot air treatment at 80°C for four hours induces useful chemical alterations.

Figure 2 .
Figure 2. Effect of hot air drying on the % change in relative intensities of metabolites of different compound classes.

Figure 3 .
Figure 3. KEGG pathway enrichment analysis.a) Graph representing the KEGG pathways to which the DAM could be enriched.b) KEGG pathways to which DAMs were significantly enriched.

Table 1 .
List of differentially accumulated metabolites in white tea after hot-air drying.

Table 1 .
(Continued).tea before processing, RO = white tea after hot-air drying, VIP = variable importance projection, p-value = p-value of significance test, FDR = false discovery rate after multiple hypothesis test verification, log2 foldchange = logarithm of foldchange with base 2.