Taxonomy, phytochemical and bioactive compounds and potential use as material with different drying methods of Alpinia latilabris Ridl. new record from Thailand

Alpinia latilabris Ridl., a new record from Thailand, has great potential for use as a material for food and traditional medicine. Dried samples preserve the quality and avoid the degradation of phytochemicals. The aim here was to determine the taxonomy and changes in the phytochemical and bioactive compounds when using different drying methods as well as the antioxidant properties in this first report for this species. The results show that freeze-dried samples had greater quality volatile compounds, bioactive compounds, organic acid, phenolic acid, flavonoids and antioxidants compared with a fresh sample while having a microstructure similar to that of the fresh sample. The major volatile compounds were 1,8-cineole in fresh and dried samples, as confirmed by FTIR spectra. The bioactive chemicals are sensitive to thermal drying and sunlight due to degradation of the phytochemicals. This result can be useful information and be applied to the preparation of material for further development of functional foods, medicinal plants or cosmetics. found that the main organic acid in a of study describes the first report of organic acids in A. latilabris . The result shows that we have found total organic acid contents for all samples with different drying methods for A. latilabris in the following order shown


Introduction
Alpinia Roxb. is the largest genus in the tribe Alpinieae with more than 250 species belonging to subfamily Alpinoideae, family Zingiberaceae or ginger family (Kress et al., 2002;Leong-Škorničková et al., 2 168), and this species matched with Alpinia latilabris. This species is accepted, and its native range is Borneo, Malaya, Myanmar and Vietnam (Kew Science, 2021). Therefore, this species is a new record for Thailand. The local people used the young inflorescence, young psuedostem and young rhizomes of this species as vegetables. The microstructure, phytochemical (volatile compounds and organic acids), bioactive compounds (phenolic acids and flavonoid compounds) along with the antioxidant properties (DPPH radical scavenging activity: DPPH and Ferric Reducing Antioxidant Power: FRAP) have never been reported in Thailand. Even more, dried samples are used as material in food or traditional medicine, which have never been studied previously.
Alpinia latilabris Ridl. is a medicinal plant and species that is widely used. Both in food, herbs, spices, for aesthetics and active substances. The few reported chemical compounds in A. latilabris were 1,8-cineole and βpinene (19.0%) as the most abundant components in the fruit oil (unripe and ripe) found in Malaysia (Ibrahim et al., 2014). Most have been reported in galangal (Alpinia galanga), A. conchigera, A. zerumbet and A. malaccensis (Chumroenphat et al., 2019;Zhou et al., 2021). The main substances found in genus Alpinia were essential oils, which comprise most of the active ingredients at more than 70% (terpene alcohols, ketone esters, aldehydes and their derivatives) found in the rhizome, about 0.2-1.5% (dry weight). The most active ingredients in the rhizome essential oil were 1,8-Cineole (64.2%) followed by limonene 3.7%, which has antioxidant activity (DPPH and FRAP). Galangal is a yellow crystal spicy and pungent smelling agent, which is generally a component of essential oils. Many reports found phenolic compounds in many plants. Phenolic compounds collectively known as simple polyphenols are predominantly found in tubers or root crops. This substance performs a role as an antioxidant. Almost all parts are used (leaves, stems, flowers and rhizomes), especially the rhizomes that are widely used in both for food, medicine and cosmetics.
Each of the various drying procedures has its own set of benefits and disadvantages. Freeze drying (FD) is good for preserving quality, but it needs a long time for the drying period, high energy usage and expensive capital costs. Hot air drying (HD) is the most common method of drying. However, the low temperature for drying with HD takes a long time to remove moisture from the material. Instead, at high temperatures, there is a possibility of color, flavor and bioactive chemicals being degraded. Sun drying (SD) is a conventional method at a low temperature due to the long time required for drying the sample and may possibly result in product quality and bioactive ingredients (Prathapan et al., 2009;Chumroenphat et al., 2021). In this research, we reported different drying methods for Alpinia.
Consequently, we aimed to find the taxonomy, volatile compounds, organic acids, phenolic acids, flavonoids and antioxidants with DPPH and FRAP of A. latilabris and compared drying methods as potential usage for food and traditional medicine. This research will mainly provide useful information for a wider application of these plants. This study effort should provide a reliable framework for development studies on the usage as a material for functional foods and traditional medicines.

Taxonomy
Specimens for research were collected form Sakon Nakhon Province. Voucher specimens were deposited at Mahasarakham University Herbarium and Khon Kaen University Herbarium (KKU). The morphological 3 characteristics of specimens were described using a stereo microscope. Identification and classification of this species was based on morphological data and available literature. Distribution data and ecological data were also provided. Utilization data of the Kha-Khom was obtained through interviewing local villagers who were living in Phu Phan District, Sakon Nakhon Province. The conservation status of this plant in Thailand was based on the evaluation criteria of the distribution area and author during a survey for collection of specimens.

Plant material and sample preparation for drying
The fresh samples were collected during April-May 2021 in the northeastern region of Thailand. The voucher specimen number was AZCT021 deposited in the herbarium. The rhizomes were cleaned of all physical contaminants (gravel and soil) and washed with water. Then samples were cut into slices before drying with different drying methods and compared between fresh and dried samples maintained at 4 o C. Rhizome drying: each 1000 g of A. latilabris sliced sample were dried with different drying test methods (freeze drying (FD), sun drying (SD) and hot air drying with 40, 60 and 80 o C (HD40, HD60 and HD80, respectively). The final dried samples must have a lower moisture content than 7% by each drying method. For FD, A. latilabris rhizome slices were freeze dried (Scanvac Cool Safe; 100-9 Pro, Labo Gene ApS, Denmark) and cooled to −100 °C and the vacuum was under 20 Pa absolute pressure. HD involved a hot-air oven dryer that was electric thermo-static drying (model FED 115,WTB Binder,Germany) for drying at 40, 60 and 80 °C. For SD, sample slices were revealed to the sun at 35-45 °C for 2-3 days. The samples were ground after each drying process and then sieved through a 60-mesh wire sieve. The samples were kept at -20 °C before analysis.
Microstructure of fresh and dried Alpinia latilabris Ridl.
The microstructure was observed by scanning electron microscope (SEM) (Hitachi, TM-4000plus, Japan) with the TM 4000plus program used to examine section slides of fresh and dried samples. For SEM analysis in vacuum mode, samples were coated with gold (Hitachi, MC1000, Japan).
Identification of volatile compounds using gas chromatography/mass spectrometry (GCMS) with headspace solid-phase microextraction (HS-SPME) Extraction of rhizome volatile constituents used a HS-SPME coupled to GC/MS instrument with methods according to Chen et al. (2018) with some modified. The SPME fibre uses divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS/10, Agilent Technologies; Switzerland), which was prepared at 200 °C for 1 h. The finely powdered rhizome (1.0 g) was placed in a 10 mL bottle and equilibrated for 10 minutes at 80 °C. The samples were extracted for 40 min with an agitator (speed 250 rpm) and then the SPME fibre was inserted into the GC injector for desorption at 250 °C for 5 min.
The volatile components of the rhizome were measured using a GC ⁄ MS series QP2010 of Shimadzu (Tokyo, Japan). The GC/MS analysis used a fused silica capillary column (Rtx-5MS; Restek Co., Bellefonte, PA, USA) with 30 m x 0.25 mm id x 0.25 µm film thickness. The temperature of the injection port was 250 °C and transfer line at 280 °C, and the ion source was 230 °C. The oven temperature of the GC program followed the method of Chen et al. (2018) with some modification of initially 50 o C for 5 min, then to 100 °C (3 °C/min) hold for 5 min, then to 250 °C (5 °C/min) constant for 3 min and a final ramp to 280 °C (50 °C/min) hold time 5 min. The MS condition was operated in the full-scan range: m/z 40-550 amu with electron ionisation mode, 70 eV. The blank control was run without sample using the same procedure. The peaks were identified by comparing their mass fragmentation pattern to data available in the spectral with NIST14 libraries (NIST). The n-alkanes standard solution (C7-C23, Sigma-Aldrich) was analysed using the same procedure to obtain the retention index (RI). The relative content of each compound was displayed as a percent peak area.

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Total phenolic contents (TPC) and Total flavonoid contents (TFC) The TPC and TFC methods were done according to Chumroenphat et al. (2019). The reaction of the experiment was measured using a Varioskan Lux Multimode microplate reader (Thermo Fisher Scientific, USA) at 725 nm and results were expressed in gallic acid equivalents (mg GAE/g db) with dry basis. For TFC absorbance measured at 510 nm, the results were shown in rutin equivalents (mg RE/g db) with a dry basis.

Vitamin C by HPLC
The method of extraction and analysis for vitamin C followed Siriamornpun and Kaewseejan (2017). The identified used a Shimadzu LC-20AC series HPLC system (Shimadzu, Tokyo, Japan) with diode array detector at 280 nm, and the result was shown on a dry basis.
Organic acid by HPLC The extraction of organic acid follows Moreno-Ortega et al. (2020). The identification method was determined previously and described by Zhang et al. (2022) with some modifications using a HPLC system including an anion exchange column, Aminex HPX-87H (300 mm × 7.8 mm, Bio-Rad, Richmond CA, USA), at 65 °C and detected with a photodiode array at 210 nm. The concentrations were calculated using calibration curves constructed previously with appropriate chromatographic standards. The result was expressed on a dry basis.
Phenolic acids and flavonoid compounds by HPLC The extraction method for phenolic acid and flavonoid compounds follows Chumroenphat et al. (2021). Identification used HPLC apparatus (Shimadzu, Tokyo, Japan) and analysis conditions were according to Chumroenphat et al. (2019). The phenolic acids and flavonoids in the extracts were identified by comparing their relative retention times with external standards. The result was expressed on a dry basis.

FTIR measurements
The measured spectrum was applied by a FTIR instrument (Frontier) with a UATR accessory (Perkin Elmer, USA) and a Diamond/ KRS-5 crystal composite were used to get the FTIR spectra of A. latilabris samples (one bounce). The examination of A. latilabris powders was possible without any special preparation due to the direct use of UATR-FTIR spectra. Thirty-two scans with a spectral resolution of 4 cm -1 were used to generate the spectral data, which covered the spectral range 4000-400 cm -1 . A force gauge of 110 units was used to measure all A. latilabris powders. The software also recorded a background spectrum, which was automatically removed by the software Antioxidant activities DPPH free radical scavenging assay The scavenging DPPH radials of the extracts were studied using a previously published method by Chumroenphat et al. (2019). Results were expressed as mg Trolox equivalents (TE) per one gram on a dried basis (mg TE/g db).

Ferric reducing/antioxidant power assay (FRAP)
The procedures used for this assay were according to Chumroenphat et al. (2019), which were measured using a Varioskan Lux Multimode microplate reader (Thermo Fisher Scientific, USA) at 593 nm, and reported as mg FeSO4 in 1 g on a dry basis (mg FeSO4/g db).
Ecology. -Dry evergreen forests, 50-500 m alt. Phenology. -Flowering February -March and fruiting March -June. Conservation status: This species is reported in a few localities in Thailand. Therefore, it is reported to be a rare species.
Change in microstructure of Alpinia latilabris Ridl. with different drying methods The microstructures of fresh and dried A. latilabris Ridl. were determined by scanning electron microscope (SEM) as shown in Figure 2. The results show that the microstructure of the freeze dried (FD), hot air dried at 40 °C (HD40) and 60 °C tissues were comparable to that of the fresh samples. This is because water is sublimated via the direct transfer of water from the frozen substance to vapour in the freeze-drying process, which maintains the shape of the microstructure , also the hot air drying at 40 °C and 60 °C has a stable temperature and water transfer. Whereas the sun dried (SD) and 80 °C dried samples (HD80) had more damaged microstructure compared with FD, HD40 and HD60. The microstructure of the parenchyma cell was seriously affected, and starch grains were dispersed throughout the tissue, as shown in Figure 2. In addition, the SD and HD80 samples demonstrated different microstructures due to temperature and moisture gradients that produced cell-wall rupture, folding and deformation throughout the drying process. The SD has 6 a more damaged microstructure due to variations in sun-induced temperatures during the drying process (Deng and Zhao, 2008;Chumroenphat et al., 2021). Effect of drying method on volatile compounds of Alpinia latilabris In the fresh and dried rhizomes of A. latilabris, numerous volatile compounds were found. Total compounds identified were 44 as presented in Table 1. The number of compounds found in A. latilabris rhizome samples, fresh and dried, ordered by SD, HD60, FD, HD40, HD80 and fresh was 36, 30, 29, 28, 24 and 14 compounds, respectively. The relatively high contents were 1,8-cineole, (-)-β-pinene and α-pinene.
These data support previous studies of predominant volatile compounds found in Alpinia spices, which were 1,8-cineole by more than 60% (Rana et al., 2010;Victório et al., 2011;Raj et al., 2013). However, Raj et al. (2013) reported that the major compounds of A. calcarata gown in India were 1,8-cineole, β-fenchyl acetate, βpinene, camphene and α-terpineol, and A. malaccensis had different compounds, which were α-phellandrene, β-pinene and p-cymene. The main volatile component discrepancies can be attributable to the diverse origins of ginger, extraction processes and solvent types applied (Ding et al., 2012). In the case of different drying methods, all drying methods decreased the levels of all 1,8-cineole contents, compared with the fresh sample. The loss of 1,8-cineole content was in the following decreasing order: HD40>HD60>SD>HD80>FD. However, FD was greater and maintained 1,8-cineole due to not using temperature in the dying process. Whereas, the thermal drying methods drastically decreased after hot-air dried in HD40 (72%), HD60 (71%), HD80 (43%) and sun-dried (66%). In the case of low temperature (HD40, HD60 and SD) there was a decreased content of 1,8-cineole, indicating that chemical component degradation, such as curcumin degradation to vanillin, vanillic acid by direct oxidative and/or through the action of an oxidizing enzyme such as polyphenoloxidase (PPO), causes more degraded smaller molecules (Chumroenphat et al., 2021).
Particularly in the case of SD, when UV and light are also implicated, the losses of volatile compounds in the HD80 sample were due to higher drying temperatures. In more detail, several volatiles in plant samples have a higher affinity for the water fraction and were lost along with the evaporating water during the drying process (Sellami et al., 2011).
Moreover, the variability of the relative content in different drying methods may be explained by transformation of terpinotene, limonene, a-terpinene, 7-terpinene, ~-terpineol and 1,8-cineole in the drying processes with reaction of ring expansion and ring opening of pinenes and their metabolic pathways (Narushima et al., 1982). Comparable findings were reported by Mohammed et al. 2020, who found chemical transformations occurring during the drying processes in rosemary (Rosmarinus Officinalis L.) resulted in a significant decrease in major components (1,8-cineole and camphor). Whereas, other constituents were either at par or at increased levels due to the chemical content depending on the drying periods and other factors like temperature, mode of heating, condensation apparatus, cooling gradient, duration of extraction and the presence of water in the extraction assembly, which were kept constant. Finally, different drying methods resulted in varying volatile components. FD, on the other hand, considerably preserved the volatile compounds, whereas drying with heat resulted in volatile compound losses.   Table 2. Comparing all samples, the concentration of TPC decreased in all dried samples (p < 0.05). The highest TPC content was found in the fresh sample followed by FD, SD, HD40, HD60 and HD80, respectively. According to Chumroenphat et al. (2021), TPC in fresh samples was decreased by freeze-drying, sun-drying and hot air-drying. In terms of TFC, the fresh sample had the highest contents compared with all drying methods. The lowest was found in hot drying methods (HD40, HD60 and HD80) with no significant 9 differences (p < 0.05). Similar for vitamin c content, the highest level was found in fresh, while other drying methods significantly decreased it (p < 0.05). Vitamin c was decreased most by SD (88%), followed by HD80 (81%), HD40/HD60 (79%) and FD (76%). This supports the findings of a previous study, reporting that FD preserved more TPC, TFC and vitamin c contents than other drying methods (Chumroenphat et al., 2021).
These findings may be explained by decreases of TPC, TFC and vitamin c due to polyphenol oxidase (PPO) activity at low temperature. Sun-drying was apparently unable to inhibit PPO activity as much, as the enzyme was activated at the temperature of sun drying (35-40 °C). While heat drying at HD40 was a low temperature for PPO activity combined with oxygen that is overflowing in hot air oven which is too low for TPC, TFC and vitamin c. In addition, the high temperature 60 and 80 °C had degradation of the polyphenol in the sample, leading to a lower level of TPC, TFC and vitamin c. On the other hand, FD had the highest level compared with the other drying methods due to the low temperature used for freeze drying, polyphenol oxidase was inhibited, supporting previous studies Lakshmi et al., 2018;Chumronephat et al., 2021). The findings of this study should be valuable in understanding the A. latilabris rhizome drying process, which will help to preserve food quality and bioactivity by avoiding phytochemical degradation.

Effects of drying method on phenolic acids and flavonoid compounds of Alpinia latilabris
The identification of the phenolic compounds was by comparing their retention times with individual standards, as shown in Table 3. For the dried sample, FD drying had the highest total phenolic acids (553 µg/ g db) (losses 51% compared to fresh sample) followed by SD (280 µg/ g db), HD80 (257 µg/ g db), HD40 (248 µg/ g db) and HD60 (206 µg/ g db). The highest individual phenolic acids in A. latilabris were caffeic acid (fresh), vanillin (FD, HD40 and HD80) and gentisic acid (SD and HD60). In these studies, vanillin was at highest levels in dried samples caused by the metabolic pathways that reduced ferulic acid production to vanillic acid, while vanillic acid can be reduced to vanillin, causing an increase in the level of vanillin. According to a previous study of dried turmeric (Zingiberaceae family), at low temperatures from both HD samples (50 °C) and SD sample (35-40 °C), vanillin levels increased, whereas curcumin levels declined dramatically, particularly when UV and light were present (Suresh et al., 2009;Agnihotri and Mishra, 2011;Chumroenphat et al., 2021) as shown in the pathway supported by Gallage and Møller (2015). Elzaawely et al. (2007) found that vanillin and cinnamic acid were significantly higher in chloroform and ethyl acetate extracts of A. zerumbet following exposure to copper. It was observed that other phenolic acids were found to be significantly less sensitive to low temperatures when FD and HD40 were used, but highly sensitive when SD was used. Thermal dried samples (HD60 and HD80), similar to a previous report, may not be the major cause of these effects; other factors, such as polyphenol oxidases (PPO), may also play a role in the degradation of phenolic acids during the preparation process prior to drying (Prathapan et al., 2009). Our results suggest that the fresh sample of A. latilabris mostly had total phenolic acid rather than the whole sample with drying methods. As a conclusion, we suggest that depending on the type of compound regarded as the most important, each drying method may be appropriate for different products.
The identified flavonoid compounds in A. latilabris with different drying methods are show in Table 3.
Four flavonoids, namely rutin, catechin, quercetin and apigenin, were identified and quantified by HPLC. The overall and individual quantities of flavonoid compounds differed significantly. In general, catechin and apigenin were found to be the most predominant flavonoid compounds in all A. latilabris samples studied. In addition, we found significant differences in total and individual contents of flavonoids, comparing jujube varieties and various tissues. When comparing the amount of total and individual contents of flavonoids with different drying methods, it was found that the fresh sample had the highest level of flavonoids. While, FD and SD had higher levels of total flavonoids than HD40, HD60 and HD80, respectively. Means with different letters (a, b, c, d) are significantly different at p < 0.05 within the same column with drying method. While total phenolic acid and total flavonoid compounds compared within the same row (p < 0.05). Values are expressed as mean ± SD of triplicate measurements (n = 3). ND: Not detected; FD: Freeze dried; HD: Hot air dried; SD: Sun dried Effects of drying method on organic acids of A. latilabris with HPLC Organic acids have a variety of beneficial effects on human health and metabolism, including fumaric acid that has effectiveness in the prevention of cardiovascular disease, citric acid that has potential for diabetic protection and malic acid that has potential as an antimicrobial agent against a variety of harmful microorganisms (Gao et al., 2012;Delgado et al., 2018). Several studies have also found that the main organic acid in fruits, and that fruits contain a lot of organic acid. This study describes the first report of organic acids in A. latilabris. The result shows that we have found total organic acid contents for all samples with different drying methods for A. latilabris in the following order -HD80 > SD > HD60 > Fresh > FD >HD40, as shown 11 in Table 4. Oxalic acid was found to be the main organic acid in all dried samples, which ranged from 13 to 50 mg/g db. However, contents of citric acid (0.3-1.7 mg/g db), malic acid (0.6-15.0 mg/g db), quinic acid (1.3-8.6 mg/g db), sucinic acid (1.3-3.6 mg/g db) and furmaric acid (0.1-0.6 mg/g db) were far lower than oxalic acid in our study. In the case of an increase in the amount of all organic acids (oxalic acid, citric acid, malic acid, quinic acid, succinic acid and furmaric acid) due to different drying methods, the dehydration, decarboxylation and Maillard reactions may be responsible for the increase in most of the organic acids. On the other hand, a thermal treatment for the fruit resulted in a decrease in the organic acids (Barretto et al., 2013;Sarkar et al., 2020). Table 4. Contents of organic acid analyses in Alpinia latilabris with different drying methods Means with different letters (a, b, c, d) are significantly different at p < 0.05 within the same row. Values are expressed as mean ± SD of triplicate measurements (n = 3). ND: Not detected; FD: Freeze dried; HD: Hot air dried; SD: Sun dried Relationship of chemical compounds degradation by FTIR analysis Figure 3 shows FTIR spectra of A. latilabris from different drying methods. Each peak comes from the absorption of functional groups in A. latilabris with different drying methods. Several previous studies reported the main compounds found in rhizome of Apinia galnaga (Mallavarapu et al., 2002) and other species in the genus Alpinia, for example, Alpinia calcarata K. Schum (Padalia et al., 2010), Alpinia zerumbet (Murakami et al., 2009), Alpinia species K. Schum (Indrayan et al., 2011) and A. officinarum Hance (Rana et al., 2010;Wu et al., 2012). Nevertheless, the volatile compounds found in Alpinia sp. contained camphor, pinene and thujone as well. The spectrum of signature peaks for 1,8-cineole were 1016-1080 cm −1 (C-O stretching vibrations), 1164-1042 cm -1 (C-O-C) and 2854-2968 cm −1 (C-H stretching vibrations) (Ciko et al., 2016;Rashed et al., 2019;Yin et al., 2021). β-pinene was 817 -828 cm -1 , Camphor, α-and β-thujone were both present, resulting in a distinctive stretch vibration for the C═O bond at around 1740 cm -1 , present in all samples. Interestingly, the variability in the relative content from different drying methods transformed the chemical constitutes in the samples as described by a previous study (Mohammed et al. 2020). The deformation of 1,8-cineole was present in the spectral peaks present at 1016-1080 cm −1 and 2854-2968 cm −1 , which are at different intensities. In the comparison with fresh and dried samples, we found that the relative contents of 1,8-cineole decreased as shown in Table 1. While β, α-Pinene and camphene increased significantly in the dry compared to the fresh sample. This supports the previous study of Shen et al. (2020) who reported the amount of released α-pinene, β-pinene, myrcene, camphene and limonene increased after samples were dried. The spectra shown in the band as 817 -828 cm -1 had significantly increased intensity in the HD60 samples.
For the relationship of phenolic compounds, as previously reported (Staurt, 2004;Chumroenphat et al., 2021), ferulic acid can be degraded into smaller molecules with different functional groups, such as vanillic acid and vanillin, as shown in Figure 3 with FTIR spectra of aldehyde group (C-O stretching) peaks at 1724 cm -1 and 1725 cm -1 , which could indicate that vanillic acid and vanillin were the predominant compounds found in fresh and dried samples, as shown in Table 3  The results of antioxidant capacity with different drying methods are shown in Table 5. The antioxidant activities were to determine DPPH radical scavenging activity shown by trolox equivalents on centration (TE) and FRAP value as mg FeSO4/ g db. DPPH is a free-radical molecule. The free-radical scavenging ability has long been measured using the color of DPPH. Antioxidants produce a color change from purple to yellow and a decrease in absorbance at 517 nm when they interact with the DPPH radical measured using a microplate reader. There were significant decreases, compared with fresh samples. DPPH radical-scavenging activity was found to be highest in the fresh sample (33 mg TE /g db) and lowest found in HD80 (0.93 mg TE/g db). The DPPH radical-scavenging activity of the HD80 sample was 33 times lower than the fresh sample. Moreover, all samples that were dried lost activity for DPPH radical-scavenging due to the temperature of the SD and HD40, which was 35-40 °C; this is the temperature at which PPO will be stable while performing at maximum capacity (Prathapan et al., 2009). While, the temperatures of HD60 and HD80 degraded the bioactive compounds and gave color losses (Summen and Erge, 2014). This study supports the previous report that found that FD preserved more bioactive compounds than other drying methods . Additionally, to analyze the anti-oxidation capabilities, the FRAP assay was used to evaluate the reducing properties of compounds that function by breaking the free-radical chain by donating a hydrogen atom (Benzie and Strain, 1996). Results shown in Table 5 have similar values for DPPH antioxidant activity to the highest FRAP value found in the fresh sample (24 mg FeSO4/ g db) and lowest found in HD80 (7 mg FeSO4/ g db). When compared to the dried samples, it was found that FD (16 mg FeSO4/g db) had a high FRAP value and losses in the FRAP value of 33% from the fresh sample were caused by PPO activity, which occurs during preparation prior to drying and is inhibited in the freeze-dried process due to the low temperature. These results followed a similar trend as TPC and TFC. Based on the findings of previous research, the relationship between bioactive content (TPC and TFC) and antioxidant activity (DPPH and FRAP activity) has a strong positive correlation (Wan-Ibrahim et al., 2010;Chumroenphat et al., 2019;Kainama et al., 2020). northearten Thailand) was reported as a new record for Thailand. The local people used this species for food and in traditional medicine due to several phytochemical and bioactive compounds and biologic activities. Our present study on the effects of different dying methods differed in the conditions that affect the microstructure, volatile compounds, bioactives and antioxidant activities. Freeze-dried samples had a microstructure that was similar to that of the fresh sample. Furthermore, when compared to all other samples dried by different methods, the freeze-dried sample had a higher amount of bioactive compounds and antioxidant activity. 1,8cineole was the predominant volatile compound found in Alpinia spices. Thermal drying can lead to deformation and decreased the 1,8-cineole relative contents. On the other hand, (-)-β-pinene and α-pinene were increased with thermal drying, as confirmed by FTIR spectra. All these bioactive chemicals are sensitive to thermal drying and sunlight (the combination of UV, visible light and air being especially damaging). This justifies freeze drying providing the highest amounts of TPC, TFC and vitamin C. The organic acids were increased by drying samples. Alternatively, there were losses in the phenolic compounds in dried compared to fresh samples. The predominant phenolic acid and flavonoid were vanillin and catechin, respectively. Each drying method could be appropriate for certain products depending on the targeted compounds, such as volatiles, phenolics, flavonoids or organic acids. This study should provide useful information about the design of the drying method for producing A. latilabris Ridl rhizome dried material, thus preserving the food quality, great bioactivity and high antioxidants by avoiding the degradation of the phytochemicals.

Authors' Contributions
The study was conceptualized and designed by TC and SS. TC: designed the research study and/or evaluation. TC and SS drafted the manuscript and reviewed it before submitting it to the journal. Both authors read and approved the final manuscript.
Ethical approval (for researches involving animals or humans) Not applicable.