Flavor Variations in Precious Tricholoma matsutake under Different Drying Processes as Detected with HS-SPME-GC-MS

By employing headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC-MS), this study displayed the compositional changes in volatile organic compounds (VOCs) in Tricholoma matsutake samples subjected to hot-air drying (HAD) and vacuum freeze-drying (VFD) processes from their fresh samples. A total of 99 VOCs were detected, including 2 acids, 10 aldehydes, 10 alcohols, 13 esters, 12 ketones, 24 alkanes, 14 olefins, 7 aromatic hydrocarbons, and 7 heterocyclic compounds. Notably, the drying process led to a decrease in most alcohols and aldehydes, but an increase in esters, ketones, acids, alkanes, olefins, aromatic, and heterocyclic compounds. Venn diagram (Venn), principal component analysis (PCA), and partial least squares-discriminant analysis (PLS-DA) analyses enabled an easy and rapid distinction between the VOC profiles of T. matsutake subjected to different drying methods. Among the identified VOCs, 30 were designated as marker VOCs indicative of the employed drying process. And the VFD method was more capable of preserving the VOCs of fresh T. matsutake samples than the HAD method. Benzaldehyde, 1-Octen-3-ol, 3-Octanol, and (E)-2-Octen-1-ol were identified as markers for FRESH T. matsutake. Conversely, (E)-3-Hexene, lavender lactone, and α-Pinene were associated with VFD T. matsutake. For HAD T. matsutake, olefins, pyrazine, and esters, particularly ocimene, 2,5-Dimethyl-pyrazine, and methyl cinnamate, significantly contributed to its particularities. The results from this present study can provide a practical guidance for the quality and flavor control of volatile organic compounds in preciously fungal fruiting bodies by using drying processes.

An important factor in determining the quality and flavor of dried T. matsutake is closely related to the drying method [9].Fresh T. matsutake has a high water content and Foods 2024, 13 is not resistant to storage, making it prone to various physiological changes after being picked.If no protection and anti-corrosion measures are carried out, T. matsutake is easily deteriorated, leading to the loss of nutritional components and a decrease in its edible and market value.Therefore, drying is usually an important storage method for T. matsutake to effectively control moisture and extend its food shelf life [7].During the drying and dehydration process, the concentration of C8 compounds is significantly reduced due to the Maillard reaction or the destruction of tissue cells [11].This process also leads to the formation of some volatile compounds, including hexaldehyde, heptal, 2(5H)-furanone, acetophenone, nonylaldehyde, phenacetaldehyde, etc., resulting in a partial loss of flavor and reduced quality of T. matsutake; thus, the selection of different drying methods is of great significance for preserving the flavor of T. matsutake.
Due to the limited research on the impact of various drying processes on volatile organic compounds of T. matsutake, in this present study, fresh T. matsutake was used as the raw material, and dried T. matsutake was prepared with hot-air drying (HAD) and vacuum freeze-drying (VFD) processes.Headspace solid-phase microextraction (HS-SPME) technology, known for its high selectivity, enrichment efficiency, and rapid analysis capabilities, was employed for extraction and analysis to assess the impact of various drying methods on T. matsutake flavor.The aim of this study is to provide a theoretical reference for the further process and utilization of T. matsutake and a practical basis for promoting its commercial application.

Fungal Materials and Sample Production
T. matsutake samples were obtained from the Diqing Tibetan Autonomous Prefecture, Yunnan, Southwest China.FRESH samples were stored at room temperature; VFD (vacuum freeze drying, FD-1A-50, BIOCOOL, Beijing, China) samples were frozen at −80 • C for 24 h, and then vacuum freeze-dried for 24 h at −40 to −50 • C, vacuum 10 Pa; HAD (hot air drying, GZX-GF 101-3 BS, Yuejin Medical Co., Shanghai, China) samples were weighed at a certain quantity, cut into uniform slices, dried for 4 h at 60 to 70 • C, and then dried for 2 h at 70 to 100 • C (Figure 1).
Foods 2024, 13, x FOR PEER REVIEW 2 of 14 An important factor in determining the quality and flavor of dried T. matsutake is closely related to the drying method [9].Fresh T. matsutake has a high water content and is not resistant to storage, making it prone to various physiological changes after being picked.If no protection and anti-corrosion measures are carried out, T. matsutake is easily deteriorated, leading to the loss of nutritional components and a decrease in its edible and market value.Therefore, drying is usually an important storage method for T. matsutake to effectively control moisture and extend its food shelf life [7].During the drying and dehydration process, the concentration of C8 compounds is significantly reduced due to the Maillard reaction or the destruction of tissue cells [11].This process also leads to the formation of some volatile compounds, including hexaldehyde, heptal, 2(5H)-furanone, acetophenone, nonylaldehyde, phenacetaldehyde, etc., resulting in a partial loss of flavor and reduced quality of T. matsutake; thus, the selection of different drying methods is of great significance for preserving the flavor of T. matsutake.
Due to the limited research on the impact of various drying processes on volatile organic compounds of T. matsutake, in this present study, fresh T. matsutake was used as the raw material, and dried T. matsutake was prepared with hot-air drying (HAD) and vacuum freeze-drying (VFD) processes.Headspace solid-phase microextraction (HS-SPME) technology, known for its high selectivity, enrichment efficiency, and rapid analysis capabilities, was employed for extraction and analysis to assess the impact of various drying methods on T. matsutake flavor.The aim of this study is to provide a theoretical reference for the further process and utilization of T. matsutake and a practical basis for promoting its commercial application.

Fungal Materials and Sample Production
T. matsutake samples were obtained from the Diqing Tibetan Autonomous Prefecture, Yunnan, Southwest China.FRESH samples were stored at room temperature; VFD (vacuum freeze drying, FD-1A-50, BIOCOOL, Beijing, China) samples were frozen at −80 °C for 24 h, and then vacuum freeze-dried for 24 h at −40 to −50 °C, vacuum 10 Pa; HAD (hot air drying, GZX-GF 101-3 BS, Yuejin Medical Co., Shanghai, China) samples were weighed at a certain quantity, cut into uniform slices, dried for 4 h at 60 to 70 °C, and then dried for 2 h at 70 to 100 °C (Figure 1).

Headspace Solid-Phase Microextraction (HS-SPME)
Samples were extracted using a manual headspace sampling system, equipped with a 50/30 µm DVB/CAR/PDM fiber (Supelco, Bellefonte, PA, USA).Fresh samples were chopped and weighed at 5.0 g.The samples were placed in 40 mL headspace vials, preequilibrated at 45 °C for 5 min, and then extracted for 40 min at the same temperature.After extraction, the fiber was immediately inserted into the injection port of GC-MS for thermal desorption at 250 °C for 10 min.

Headspace Solid-Phase Microextraction (HS-SPME)
Samples were extracted using a manual headspace sampling system, equipped with a 50/30 µm DVB/CAR/PDM fiber (Supelco, Bellefonte, PA, USA).Fresh samples were chopped and weighed at 5.0 g.The samples were placed in 40 mL headspace vials, pre-equilibrated at 45 • C for 5 min, and then extracted for 40 min at the same temperature.After extraction, the fiber was immediately inserted into the injection port of GC-MS for thermal desorption at 250 • C for 10 min.

Gas Chromatography-Mass Spectrometry (GC-MS) Analysis
Gas chromatography-mass spectrometry (7890A-5975C, Agilent, Santa Clara, CA, USA) with a capillary column DB-5MS (30 m × 0.25 mm, 0.25 µm, Agilent, USA) was utilized.The injection port was operated in splitless mode at 250 • C. The following chromatographic separations were performed: 40 • C held for 5 min, increased to 180 • C at a rate of 5 • C/min and held for 2 min, and then to 260 • C at a rate of 10 • C/min.Helium was used as the carrier gas with a flow rate of 1.0 mL/min.The operating conditions for the MS system were as follows: the ion source was set at 230 • C, and the electron ionization mode was at 70 eV with mass ranges from 35 to 500 m/z.

Statistical Analysis
Each component underwent NIST11 library search, and data were analyzed using MSD ChemStation software (Agilent Technologies, version G1701EA E. 02.02.1431).For each analyte, its relative mass fraction was calculated by the peak area normalization method.
Data were reported as means ± standard deviation (SD).There were three replicates for each treatment, and p-values for differences between different treatments within the same species were examined using Student's t-test (p ≤ 0.05).Principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) were performed using Simca-p 14.1 software, while Origin 2021 was utilized for correlation analysis and visualization of any differences between samples.

Changes in HS-SPME-GC-MS of T. matsutake with Differing Drying Processes
The varying VOCs in T. matsutake with differing drying processes were analyzed using HS-SPME-GC-MS.The signals in the 20-25 min retention time were rapidly increased in VFD and HAD while remaining consistent among the ion chromatograms of the other samples (Figure 2).A mass of VOCs was indicated to be released during the drying processes.Herein, a total of 99 different volatile compounds were identified by the HS-SPME-GC-MS analysis, including 2 acids, 10 aldehydes, 10 alcohols, 13 esters, 12 ketones, 24 alkanes, 14 olefins, 7 aromatic hydrocarbons, and 7 heterocyclic compounds (Table 1).The relative amount of each compound was obtained by its peak area normalization.

Gas Chromatography-Mass Spectrometry (GC-MS) Analysis
Gas chromatography-mass spectrometry (7890A-5975C, Agilent, Santa Clara, CA, USA) with a capillary column DB-5MS (30 m × 0.25 mm, 0.25 µm, Agilent, USA) was utilized.The injection port was operated in splitless mode at 250 °C.The following chromatographic separations were performed: 40 °C held for 5 min, increased to 180 °C at a rate of 5 °C/min and held for 2 min, and then to 260 °C at a rate of 10 °C/min.Helium was used as the carrier gas with a flow rate of 1.0 mL/min.The operating conditions for the MS system were as follows: the ion source was set at 230 °C, and the electron ionization mode was at 70 eV with mass ranges from 35 to 500 m/z.

Statistical Analysis
Each component underwent NIST11 library search, and data were analyzed using MSD ChemStation software (Agilent Technologies, version G1701EA E. 02.02.1431).For each analyte, its relative mass fraction was calculated by the peak area normalization method.
Data were reported as means ± standard deviation (SD).There were three replicates for each treatment, and p-values for differences between different treatments within the same species were examined using Student's t-test (p ≤ 0.05).Principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) were performed using Simca-p 14.1 software, while Origin 2021 was utilized for correlation analysis and visualization of any differences between samples.

Changes in HS-SPME-GC-MS of T. matsutake with Differing Drying Processes
The varying VOCs in T. matsutake with differing drying processes were analyzed using HS-SPME-GC-MS.The signals in the 20-25 min retention time were rapidly increased in VFD and HAD while remaining consistent among the ion chromatograms of the other samples (Figure 2).A mass of VOCs was indicated to be released during the drying processes.Herein, a total of 99 different volatile compounds were identified by the HS-SPME-GC-MS analysis, including 2 acids, 10 aldehydes, 10 alcohols, 13 esters, 12 ketones, 24 alkanes, 14 olefins, 7 aromatic hydrocarbons, and 7 heterocyclic compounds (Table 1).The relative amount of each compound was obtained by its peak area normalization.A total of 66 VOCs were detected in the VFD group, with a high relative content of 36.82%hydrocarbons (alkanes and olefins), 32.38% alcohols, and 21.01%esters, respectively.In the HAD group, a total of 65 volatile components were detected, with 54.60% esters, 23.67% hydrocarbons, and 10.89% ketones, respectively.In the FRESH group, a total of 44 VOCs were detected, with 89.47% alcohols, but without acid substances (Table 1 and Figure 3).Different drying methods had a significant effect on the VOCs in T. matsutake.After drying, the relative contents of volatile components in T. matsutake increased, while both alcohols and aldehydes were decreased.However, the relative content of other components, such as esters, increased.Esters were formed by the interaction of alcohols and free fatty acids resulting from fat oxidation [12].

Changes in the Types and Relative Contents of VOCs
A total of 66 VOCs were detected in the VFD group, with a high relative content of 36.82%hydrocarbons (alkanes and olefins), 32.38% alcohols, and 21.01%esters, respectively.In the HAD group, a total of 65 volatile components were detected, with 54.60% esters, 23.67% hydrocarbons, and 10.89% ketones, respectively.In the FRESH group, a total of 44 VOCs were detected, with 89.47% alcohols, but without acid substances (Table 1 and Figure 3).Different drying methods had a significant effect on the VOCs in T. matsutake.After drying, the relative contents of volatile components in T. matsutake increased, while both alcohols and aldehydes were decreased.However, the relative content of other components, such as esters, increased.Esters were formed by the interaction of alcohols and free fatty acids resulting from fat oxidation [12].

Analysis of the Unique and Common VOCs in Different Drying Processes of T. matsutake
From Table 2 and Figure 4, the VFD, HAD, and FRESH groups of T. matsutake contained 17, 18, and 7 unique components, with respective relative contents of 7.2%, 4.49%, and 0.58%.The VFD group was divided into seven alkanes, four aromatics, two heterocyclics, and one of each acid, aldehyde, ester and olefin.The HAD group was divided into five alkanes, three heterocytypes, two kinds of alcohol, ketone and olefin, and one kind of acid, aldehyde, ester and aromatic.And the FRESH group was divided into three aldehydes and one of alcohol, ester, ketone and alkanes.These three groups had 19 common components, with relative contents of 73.53% (VFD), 69.19% (HAD), and 80.95% (FRESH).

Characteristic VOCs via PCA and PLS-DA
To further understand the differences in the VOCs under three key T. matsutake processing points, a total of 99 significantly different volatiles among samples were used to run the PCA (Figure 5A).PC1 and PC2 were the qualitative and quantitative analysis of VOCs in the spectrum, with contribution rates of 47.1% and 29.9%, respectively.There was no overlap among the three sample groups in Figure 5A, thereby indicating significant differences in the VOCs among the sample groups.The samples with different drying methods can thus be well distinguished by PCA.The value of PC2 was increased in the following order: HAD < VFD < FRESH.A large separation between HAD and the other drying groups implied significant changes in the VOCs caused by the HAD method.Conversely, the smaller separation between FRESH and VFD indicated that the effects of drying treatments on their chemical profiles were similar.Therefore, the results revealed that HS-SPME-GC-MS coupled with PCA can rapidly distinguish T. matsutake via different drying treatments, and thus be a promising quality control method of the three processes.In Figure 5B, the differentiation among the T. matsutake samples from three drying methods was more clearly demonstrated through score plots combined with loading plots, effectively illustrating the correlations between the 99 VOCs and the samples.

Discussion
Differences were found in the types and contents of VOCs of T. matsutake compared with a previous study.These variances could be attributed to differences in the fried heating/pan-frying temperatures and times [2,3], cold storage times [7], and geographical origins [4,5,13], etc.
The VOCs mostly originate from the chemical or enzymatic oxidation of unsaturated fatty acids, followed by interactions with proteins, peptides, and free amino acids.Other volatile compounds result from the Strecker degradation of free amino acids and Maillard reactions [14].
The contents of C8 compounds, especially 1-octen-3-ol, 3-octanone, 1-octanol, 3-octanol, and (E)-2-octen-1-ol, were significantly decreased after the drying process.Yang et al. [15] reported the degradation of C8 components during heat treatment.Due to the destruction of the cell wall and cytoplasm, more various intracellular components are released from cells and participate in the reaction during drying while some VOCs might be formed.
Aldehydes significantly contribute to the formation of flavors in edible fungi, characterized by their abundant presence and relatively low odor thresholds [16].Our analysis revealed that aldehydes varied in quantity across the samples, with five compounds identified in both VFD and HAD samples, and eight compounds in the FRESH samples.Notably, aldehydes constituted the highest proportion of volatile compounds in the FRESH sample, accounting for up to 4.90% of the relative content.Similarly, substantial quantities of aldehydes were detected in the other two mushroom samples.All identified aldehyde compounds were classified as unsaturated aldehydes, commonly recognized as the oxidation products of unsaturated fatty acids [17].The variation in aldehyde content and composition across samples was primarily attributed to the different drying methods employed.In the context of actual production, processing conditions, particularly drying methods, significantly influence the concentration of aldehydes [18].Contrary to expectations, the quantity of aldehydes in our study exhibited a decrease, highlighting the impact of processing techniques on aldehyde profiles.1).

Discussion
Differences were found in the types and contents of VOCs of T. matsutake compared with a previous study.These variances could be attributed to differences in the fried heating/pan-frying temperatures and times [2,3], cold storage times [7], and geographical origins [4,5,13], etc.
The VOCs mostly originate from the chemical or enzymatic oxidation of unsaturated fatty acids, followed by interactions with proteins, peptides, and free amino acids.Other volatile compounds result from the Strecker degradation of free amino acids and Maillard reactions [14].
The contents of C8 compounds, especially 1-octen-3-ol, 3-octanone, 1-octanol, 3-octanol, and (E)-2-octen-1-ol, were significantly decreased after the drying process.Yang et al. [15] reported the degradation of C8 components during heat treatment.Due to the destruction of the cell wall and cytoplasm, more various intracellular components are released from cells and participate in the reaction during drying while some VOCs might be formed.
Aldehydes significantly contribute to the formation of flavors in edible fungi, characterized by their abundant presence and relatively low odor thresholds [16].Our analysis revealed that aldehydes varied in quantity across the samples, with five compounds identified in both VFD and HAD samples, and eight compounds in the FRESH samples.Notably, aldehydes constituted the highest proportion of volatile compounds in the FRESH sample, accounting for up to 4.90% of the relative content.Similarly, substantial quantities of aldehydes were detected in the other two mushroom samples.All identified aldehyde compounds were classified as unsaturated aldehydes, commonly recognized as the oxidation products of unsaturated fatty acids [17].The variation in aldehyde content and composition across samples was primarily attributed to the different drying methods employed.In the context of actual production, processing conditions, particularly drying methods, significantly influence the concentration of aldehydes [18].Contrary to expectations, the quantity of aldehydes in our study exhibited a decrease, highlighting the impact of processing techniques on aldehyde profiles.
Alcohols are primarily formed through the lipid oxidation of polyunsaturated fatty acids, which typically have a higher threshold and contribute to a soft and sweet aroma [13].In the VFD, HAD, and FRESH samples, 7, 8, and 5 alcohols were observed, respectively.Simultaneously, alcohols were the most abundant group in the FRESH sample, occupying 89.47% of the total peak area.In addition to fatty alcohols, terpenes such as linalool and nerolidol were also included, which were detected in the samples.Among these samples, the sample from the FRESH group contained the highest alcohol content (89.47% at room temperature), which decreased with increasing drying temperatures: VFD (32.38% at −40 • C to −50 • C for 24 h) and HAD (4.13% at 60 • C to 70 • C for 4 h; 70 • C to 100 • C for 2 h).These results were in accordance with other reports that focused on the change in alcohols in edible fungi at different heating temperatures.Additionally, (E)-2-octen-1ol, 1-octene-3-ol, and 1-octanol were detected in all the three T. matsutake samples.The alcohol content was decreased after the drying processes.It could contribute to the development of matsutake mushroom flavor.The 1-octene-3-ol alcohol group was identified as the major volatile compound found in raw mature T. matsutake.This aliphatic unsaturated alcohol is beneficial for enhancing the manifestation of mushroom flavor.1-Octen-3-ol, with a typical odor reminiscent of mushrooms, lavender, rose and hay, has been detected and reported in most edible fungi [6,19].1-octen-3-ol is the product of autoxidation and/or the enzymatic oxidation and cleavage of linoleic acid in mushroom [20].Alcohols are a class of VOCs that have been detected in raw mushroom and mushroom products like Volvariella volvacea, shiitake mushrooms, and Agaricus bisporus [21].
Esters mainly exist in fruits and exhibit a sweet and fruity flavor, which is associated with the oxidation of unsaturated fatty acids [22].The content of esters varied greatly in T. matsutake samples at different drying temperatures.The total content of esters was increased with the increased in drying temperature, ranging from 3.85% to 54.60% in samples dried using FRESH, VFD, and HAD methods.Processing methods, such as drying, could lead to an increase in esters [18].Among these esters, the contents of tetrahydrofurfuryl propionate and methyl cinnamate in dried samples (VFD and HAD) was higher than these in the FRESH sample.Tetrahydrofurfuryl propionate imparts a fruit aroma, while methyl cinnamate impacts a strawberry aroma.
A lower content of ketones was found in T. matsutake, accounting for 0.40-10.89% of the total VOCs.The content of ketones showed a relative increasing trend with the increase in drying temperature.Several ketones were generated during the drying process as a result of the thermal degradation of amino acids or the thermal oxidation of polyunsaturated fatty acids, such as leucine, phenylalanine, and threonine [23,24].Different amounts of ketones were detected, with 7, 11, and 5 compounds identified in the VFD, HAD, and FRESH samples, respectively.Ketones were observed to be the most abundant compounds in HAD samples, accounting for 10.89% of the peak area, while in other samples, they were relatively low.Ketones are products of the decomposition of esters or the oxidation of alcohols [25].
Hydrocarbons (alkanes and olefins) are generally not considered to have an aroma contribution due to their relatively high odor threshold.However, alkanes could help en-hance the flavor of food [15].The hydrocarbons content was increased at both low and high drying temperatures.The VFD samples (low temperature) showed a more significant increase compared to the HAD samples (high temperature), with contents of 36.82% and 23.67% of hydrocarbons, respectively.This phenomenon can be attributed to the dynamic equilibrium between the cracking reaction of alkoxyl radicals and the loss of volatile components at higher temperatures [25].Some alkanes and olefins were also detected in the samples, accounting for 15, 26, and 25 compounds in the FRESH, VFD, and HAD samples, respectively.
All samples also contained a very small number of aromatic hydrocarbons, which were identified as six compounds in VFD, two compounds in HAD, and one compound in FRESH samples.A minimal number of acid compounds was only detected in VFD (1 compound, 0.23%) and HAD (1 compound, 0.18%) samples, but not detectable in the FRESH samples.These acid compounds and aromatic hydrocarbons have not been reported in T. matsutake by other references [8].Eleven acids were identified from different geographical origins of T. matsutake [24], which differed from our results.
Heterocyclic compounds, especially pyrazine, are an important source of the unique VOCs of T. matsutake, which has a strong odor intensity with nutty and roasted flavors [10].It was observed that 2,5-Dimethyl pyrazine changed with the increase in drying temperature for the VFD (0.11%) and HAD (2.63%) samples.
By analyzing the relative contents of common VOCs in different drying methods (FRESH (80.95%) > VFD (73.53%) > HAD (69.19%), we can see that the VFD samples were relatively close to the FRESH samples.As seen from the Venn diagram of the VOCs, the VFD samples had a greater amount of common VOCs with the FRESH samples compared to the HAD samples.(E)-2-octenal, 1-Octen-3-ol, 1-Octen-3-one, 3-Octanol and 3-Octen-2-one had a characteristic mushroom-like odor and were recognized as a key odorant in forming the distinctive mushroom aroma, playing a role in the reconciliation and complementation of the flavor of T. matsutake samples [24].And they were much better retained in the VFD than the HAD sample.Especially, the relative amount of 1-Octen-3-ol and 1-Octen-3-one in VFD samples (31.41%, 1.95%) were much more abundant than HAD samples (0.77%, 0.72%).Moreover, the smaller separation between the FRESH and VFD samples indicated that the effects of drying treatments on their chemical profiles were similar.Thus, the VFD method was more capable of preserving the VOCs of fresh T. matsutake samples than the HAD method.

Conclusions
This study focused on the diversity of the VOCs in T. matsutake samples under fresh, hot-air-drying, and vacuum freeze-drying treatments.SPME-GC-MS was successfully employed to identify flavor compounds formed after different drying treatments of T. matsutake.A total of 99 flavor substances were identified across these three treatments of T. matsutake, including acids, aldehydes, alcohols, ketones, esters, alkanes, olefins, aromatic hydrocarbons and heterocycle compounds.In addition, the PCA analysis from GC-MS showed that samples from different drying processes could be distinguished by their VOCs, and the VFD method was more capable of preserving the VOCs of fresh T. matsutake samples than the HAD method.Based on the VIP score diagram of the PLS-DA model on VOCs in these samples, 30 VOCs were identified as potentially contributing to the aroma of T. matsutake.Benzaldehyde, 1-Octen-3-ol, 3-Octanol, and (E)-2-Octen-1-ol were identified as the primary compounds responsible for the mushroom aromas of fresh T. matsutake before the drying process.This study demonstrated the potential of HS-SPME-GC-IMS in combination with PCA and PLS-DA as a reliable analytical screening technique to quickly and sensitively identify and classify the VOCs of T. matsutake.Results from this present study can provide a theoretical and practical basis for the quality control of flavor in the processing of preciously edible fungal products.

Figure 2 .
Figure 2. Total ion chromatograms of T. matsutake during the drying process.(Number of peaks is shown in Table1).

Figure 2 .
Figure 2. Total ion chromatograms of T. matsutake during the drying process.(Number of peaks is shown in Table1).

Figure 3 .
Figure 3. Classification analysis of VOCs in dry T. matsutake after different drying processes.

Figure 3 .
Figure 3. Classification analysis of VOCs in dry T. matsutake after different drying processes.

Figure 5 .
Figure 5. PCA and PLS-DA analysis of VOCs of dry T. matsutake after in different drying methods.(A) PCA analysis of VOCs of T. matsutake after different drying treatments.(B) PCA loading diagram.(Numbers in the figure are the same as those in Table 1).(C) VIP score diagram of PLS-DA model.(Numbers in the figure are the same as those in Table1).

Table 1 .
The relative amounts of volatile compounds in different-drying T. matsutake.

Table 1 .
Cont.Variation in VOCs of T. matsutake 3.2.1.Changes in the Types and Relative Contents of VOCs Notes: nd = not detected.

Table 2 .
The unique and common VOCs in dry T. matsutake after different drying treatments.