The Influence of Drying Temperature and Extraction Methods on α-Mangostin in Mangosteen Pericarp

W. Satong-aun1， R. Assawarachan2 and A. Noomhorm1

1. Food Engineering and Bioprocess Technology， School of Environment， Resources and Development， Asian Institute of Technology， Klong Luang Pathumthani 12120， Thailand

2. Faculty of Engineering and Agro-Industry， Maejo University， Sansai， Chiang Mai 50290， Thailand

Received: March 7， 2011 / Published: July 20， 2011.

Abstract: The effects of drying temperature and extraction methods on α-mangostin content in mangosteen pericarp (Garcinia mangostana L.) powder were investigated. In the first part of experiment suitable drying temperature for retention α-mangostin content was determined. Three levels of drying temperatures (55， 65 and 75 °C) were used in this study. The drying rates were increased with drying temperature. Room temperature extraction method was performed to investigate the effect of drying temperature on retention α-mangostin content in mangosteen pericarp. The α-mangostin content extracted at three different drying temperatures (55， 65 and 75 °C) was 35.98 ± 0.49%， 40.32 ± 0.24%， and 37.79 ± 0.34% w/w， respectively. The results showed that the suitable temperature for drying mangosteen pericarp was 65 °C that gave the highest of α-mangostin content. The second part of experiment was the comparison between extraction methods， such as shaking water bath extraction (SWE)， soxhlet extraction (SE) and microwave-assisted extraction (MAE). The results show that MAE gave the highest extraction rate and α-mangostin content as compare to SWE and SE. The α-mangostin content extraction from SWE， SE and MAE are 45.83 ± 0.02， 34.82 ± 0.17 and 49.79 ± 0.15% w/w of crude extract， respectively.

Key words: Mangosteen pericarp， alpha-mangostin， hot air drying， room temperature extraction， water bath extraction， soxhlet extraction， microwave-assisted extraction.

1. Introduction

The mangosteen (Garcinia mangostana Linn.) fruit is also known as the “Queen of fruits” because of its excellent flavor [1]. The fruit is round with a smooth， thick and tough pericarp. The color of the pericarp is dark purple when fully ripe. The edible pulp of mangosteen fruit is white， soft and juicy with a slightly acid， sweet flavor and a pleasant aroma. Mangosteen is native to Malaysia. The main producing countries of mangosteen are Thailand and Malaysia [2]. In Thai traditional medicine， the pericarp of mangosteen fruit has been used to treat skin infections and wounds and for relieving from diarrhea [3]. The values of mangosteen have two important components which are antioxidant properties and other medicinal properties of xanthones such as alpha (α)-， beta (β)- and gamma(γ)-mangostins. Xanthones are phenolic compounds which possess medicinal benefits [4]. The antioxidant and anticancer preventive activities of the extract of the pericarp of mangosteen have been reported [5]. The major xanthone in pericarp of mangosteen fruit isα-mangostin that is proven to be a strong antioxidant capability. The pericarp of mangosteen at mature stage contained highest amount of α-mangostin [6].

Drying is the most common method of medicinal plant preservation. Drying represents 30% to 50% of the total costs in medicinal plant production [7]. Optimal drying temperature should be considered because the degradation of the dried product quality occured at higher temperatures [8]. Furthermore， different drying temperatures may also influence the yield of extractedα-mangostin contents from the pericarp of mangosteen. Normally， the conventional extraction methods are widely used to extract the desire substance from plant materials. Xanthones are commonly obtained by extraction with organic solvents such as ethanol， acetone， dichloromethane and hexane [9]. The main advantages of room temperature extraction method were less of solvent loss and less degradation of heat-sensitive compounds because the heat process was not required. Room temperature extraction was used in the extraction of phenolic compounds， flavonoid， tannin andα-mangostin from fruit rinds of Garcinia mangostana by 95% ethanol solution [6].

Soxhlet extraction method is widely used as a conventional standard extraction method against other extraction methods such as normal stirring extraction， ultrasonic extraction and microwave-assisted extraction [10]. The main disadvantage of soxhlet extraction method is that it requires large solvent volumes， and take long extraction time at high temperature that cause degradation of heat sensitive compounds. According to Pothitirat et al. [6]， the required time to extract the fruit rind of mangosteen with 95% ethanol using soxhlet apparatus was 15 hours. Shaking water bath extraction has been used mostly to extract antioxidant compounds such as phenolic compounds from canola meal [11]， carnosic acid from dried rosemary [12]， tanshinones from red sage root [13] and total phenolic compounds from barley [14]. The main advantages were to elevate in temperature that help to decrease the viscosity of solvent. Therefore， the solvent had more ability to wet the matrix of sample and solubilize the target compound and also help to break the matrix bond of sample. Moreover， the agitation of the solvent during shaking water bath extraction process helped to increase the eddy diffusion and increased the transfer of material from the sample surface to the solvent， and also helped to prevent sedimentation of fine particle of sample. At present， microwave-assisted extraction(MAE) which is the innovative extraction method is widely used to extract the antioxidant compounds from plants namely extraction of artemisnin from Artemisia annua L. [10]， silymarin from milk thistle seeds [15]， glycyrrhizic acid from licorice root， vitamin E from rice bran [16] and phenol compound from black tea[17]. Microwave-assisted extraction gave some advantages over conventional extraction method including reducing extraction time and solvent consumption [17].

Therefore， the objectives of this work were: to determine the suitable drying temperature for the retention of α-mangostin content in mangosteen pericarp powder; to compare the efficiency of three different extraction methods， such as shaking water bath extraction (SWE)， soxhlet extraction (SE) and microwave-assisted extraction (MVE) for the extraction of α-mangostin content from the powder of mangosteen pericarp.

2. Materials and Methods

2.1 Chemical and Reagents

Alpha-mangostin (purity 97%) was purchased from Chroma Dex Inc.， USA， while methanol (analytical grade) and 95% ethanol (commercial grade) were obtained from Mallinckrodt Co.， USA.

2.2 Preparation of Mangosteen Pericarp Samples

The mature fruits of Garcinia mangostana L. were procured from Talad Thai market， Thailand. The fruits were cleaned and the fresh mangosteen pericarp was manually separated from the fruits. Mangosteen pericarp samples were cut into small pieces and roughly ground with blending machine. The initial moisture content of fresh mangosteen pericarp was 176.99 ± 2.41% dry basis， as determined by hot air drying at 105 °C for 24 hours [18]. The roughly ground mangosteen pericarp was dried at air temperature of 55， 65 and 75 °C by using hot air oven until the moisture content of mangosteen pericarp was reached to about 15.93 ± 1.15% dry basis. The dried mangosteen pericarp was ground into a powder by using blending machine and passed through a sieve(20 mesh). The dried mangosteen pericarp powder was packed in a zip lock polyethylene bag and covered with aluminum foil bag before sealing by using vacuum pack machine， then kept in room temperature until use. 2.3 Experiment Setup

Roughly ground mangosteen pericarp samples were dried in a laboratory hot-air dryer (Fig. 1)， a tangential air-flow tunnel equipped with automatic temperature and air moisture control devices. The laboratory scale hot-air dryer was developed at Food Engineering workshop， Asian Institute of Technology and consisted of a fin coil heater (4 kW)， drying chamber with tray feeder， temperature controller， weight measuring sensor and other measuring instruments with interface facility to record data. The loss weight of sample was recorded using a computer software data logger through balance connected to a PC during drying operation. A sample of 30 g of roughly ground mangosteen pericarp was spread in a single layer on the tray and hot-air dried at three different drying air temperatures of 55， 65 and 75 °C from initial moisture content of 176.99 ± 2.41% dry basis until the final moisture content was about 15.93 ± 1.15% dry basis. During air drying， weight and temperature of the sample were recorded automatically by the data logger every 2 min.

2.4 Moisture Analysis

Mangosteen pericarp samples of approximately 30 g were placed in hot-air oven dryer at three different drying air temperatures of 55， 65 and 75 °C. The moisture content of mangosteen pericarp during the hot air drying process was determined by standard method. The loss in weight was calculated in term of percent moisture as follow Eq. (1) [19].

Moisture content (% dry basis)

(1)

The moisture ratio (MR) of mangosteen pericarp sample during the hot air drying process was estimated using the following Eq. (2) [20].

Where M， Me and Mi are moisture content (kg water/ kg dry matter) at any time， equilibrium moisture content and initial moisture content， respectively.

2.5 Room Temperature Extraction (RTE)

To investigate the effect of drying temperature on the alpha-mangostin content in the powder of mangosteen pericarp， the dried sample of manogsteen pericarp powder which dried at three different drying temperatures was extracted by room temperature extraction method. Ten grams of dried mangosteen pericarp powder was macerated with 95% ethanol at room temperature (25 ± 1.08 °C) by shaking continuously at 150 rpm for 3 days. After that， each ethanolic extract was combined. The extraction was done in triplicate.

2.6 Soxhlet Extraction (SE)

Ten grams of dried powder of mature fruit pericarp of Garcinia mangostana L. were placed into a thimble and were extracted with 400 mL of 95% ethanol in a soxhlet apparatus. Extraction was carried out for 15 hours with approximately 5 cycles/hour (65-70 °C) [4]. The extraction was done in triplication.

2.7 Shaking Water Bath Extraction (SWE)

Ten grams of dried powder of mature fruit pericarp of Garcinia mangostana were weighed in 500 mL Erlenmeyer flask， and extracted with 400 mL of 95% ethanol. The extraction process was done in water bath shaking to maintain temperature at 55 °C for 2 hours. 2.8 Microwave-Assisted Extraction (MAE)

Household microwave oven (B602-KOR-Daewoo) was modified to use in this study with the addition of a digital temperature control and rotavapor. An experimental stand for microwave extracting is shown in Fig. 2. The temperature during extraction process was controlled by connecting a copper wire with digital temperature control to measure the temperature at the center of the mixture. Ten grams of dried mangosteen pericarp powder was placed in round bottom flask and 400 mL of 95% ethanol was added. A round bottom flask was placed inside the microwave oven. The mixture was exposed to microwave irradiation at 55 °C for 13 min. The super boiling of the mixture did not occur during irradiation. Then， the round bottom flask was allowed to cool in ice water bath until the temperature reached to room temperature. 2.9 Sample Preparation

After extraction， the ethanolic extract was filtered through a Whatman No.1 filter paper under suction. The rotary vacuum evaporator was used to concentrate the filtrate under reduced pressure (90 mbar) at 50 °C. The yield of mangosteen pericarp crude extract (MPE) and α-mangostin contents were calculated as mean ±SD (n = 3) and expressed as gram per 100 g of dried mangosteen pericarp powder (% w/w of dried powder) and gram per 100 g of the mangosteen pericarp crude extract (% w/w of crude extract)， respectively.

2.10 Determination of α-Mangostin Content

The UV-spectrophotometry was performed using UV-Vis spectrophotometer using a 1.0 quartz cell. The wavelength at 320 nm was used for all measurements due to no interference from solvent absorbance [11]. 2.11 Preparation of Standard Solution

To prepare a stock solution of α-mangostin reference standard， 2.5 mg of α-mangostin were accurately weighed and dissolved with methanol in a 25 mL volumetric flask. From this solution， various concentrations of the standard solution were diluted with methanol in a volumetric flask to obtain final concentration at 20， 16， 12， 8， 4 and 2 μg/mL. The absorbance of standard solutions was measured at 320 nm. The standard curve of α-mangostin was determined by plotting the absorbance of standard solution against eth concentration of standard solution using linear regression method.

2.12 Preparation of Sample Solution

To prepare sample solution， 10 mg of dried mangosteen pericarp extract were accurately weighed and dissolved with methanol in a 10 mL volumetric flask. Methanol was added to volume (final concentration 1，000 μg/mL). Aliquot of the solution(500 μL) was diluted with methanol in a 10 mL volumetric flask to make a concentration of 50 μg/mL[6]. The absorbance of sample solutions was measured at 320 nm. The absorbance was compared with standard curve to obtain α-mangostin content in mangosteen pericarp crude extract.

3. Results and Discussion

3.1 Drying Characteristic of Mangosteen Pericarp

Mangosteen pericarp was dried at three different drying temperatures (55， 65 and 75 °C) from initial moisture content using hot air drying method. The required time of drying mangosteen pericarp at 55， 65 and 75 °C was achieved in 52， 40 and 26 minutes， respectively. The relationships between moisture ratios versus drying time at different drying temperatures of mangosteen pericarp during hot air drying are shown in Fig. 3. The drying rate went along with the temperature of drying because the higher air drying temperature used， the more moisture removed from the mangosteen pericarp to the air. These results were in accordance with the results reported by Kavak et al. [21]， Wang et al. [22]， Doymaz [23] and Roberts et al. [24] who studied the drying characteristics of red pepper， apple pomace， leek slices and grape seeds using hot air convective drying method.

3.2 Effect of Drying Temperature on α-Mangostin Content in Mangosteen Pericarp Powder

The pericarp of mangosteen (Garcinai mangostana L.) at mature stage contains high a mounts of α-mangostin and acts as a powerful antioxidants [6]. To extent the storage time of mangosteen pericarp for further utilization， the fresh mangosteen pericarp was dried by using hot air drying method. However， the heat during drying process might result the degradation ofα-mangostin in mangosteen pericarp. In this research， three different drying temperatures， 55， 65 and 75 °C， were used to study the effect of drying temperature on the stability of α-mangostin in mangosteen pericarp powder. The effect of drying temperature on yields of MPE and α-mangostin content from dried mangosteen pericarp powder using room temperature extraction method are shown in Fig. 4. For statistic analysis， the mangosteen pericarp powder dried at different drying temperature had the significantly difference ofα-mangostin content at 95% confident level.

The suitable temperature for dying mangosteen pericarp powder was 65 °C because of the highest retention yield of MPE and α-mangostin content that were 40.32 (% w/w of crude extract). Pothitirat and Gritsanapan [4] used UV-spectrophotometric method to measure total mangostins in ethanolic extract of the fruit rinds of G. mangostana. The mangosteen pericarp obtained from this drying condition was selected in this study. The degradation of α-mangostin content in mangosteen pericarp occurred at high drying temperature. However， the mangosteen pericarp dried at 75 °C gave higher α-mangostin content than that of 55 °C. It can be explained that the longer drying temperature might cause the degradation of α-mangostin content in mangosteen pericarp during drying process. Garau et al. [25] studied the effect of drying temperature on antioxidant capability of orange peel using room temperature extraction. They reported that the high drying temperature and long drying times destroyed the antioxidant compounds from orange peel samples.

3.3 Comparison of the Effect of Different Extraction Methods on α-Mangostin in Mangosteen Pericarp Powder

Soxhlet extraction (SE) was used as the conventional standard extraction method for extracting α-mangostin from mangosteen pericarp in order to comparing with the shaking water bath extraction (SWE) and microwave-assisted extraction (MAE). Before extraction， the mangosteen pericarp was dried at 65 °C using hot air drying method because this drying condition gave the highest of α-mangostin content. For all extraction methods， 95% (v/v) ethanol was used as solvent and the dried mangosteen pericarp powder to solvent ratio of 10 to 400 g/mL. The results of different extraction methods on the yield of MPE andα-mangostin content were illustrated in Figs. 5 and 6， respectively. It was indicated that the classical extraction method， soxhlet extraction， is given the highest yield of MPE (25.45 ± 0.22% w/w of dried powder)， but the lowest α-mangostin content when comparing with shaking water bath extraction and MAE. It might be caused the effect of temperature during the extraction because soxhlet extraction used longer extraction time with higher temperature than other extraction methods. In addition， long extraction time gave more yield of MPE， while the high temperature caused the degradation of α-mangostin content during extraction process. MAE took a shorter extraction time， and the higherα-mangostin content (49.79 ± 0.15% w/w of crude extract) than SWE (45.83 ± 0.02% w/w of crude extract) and SE (34.82 ± 0.17% w/w of crude extract)， respectively. In MAE process， the dipole rotation of polar solvent in the microwave field was the main mechanism to enhance the yield of α-mangostin content. The target compound could adequately absorb microwave energy and be quickly transferred into the extraction solvent. It shows the similar results as obtained by Hao et al. [10]， Grigonis et al. [26]， Shu et al. [27] and Bimakr et al. [28] who studied about the comparison of extraction methods on antioxidant compounds from Artemisia annua L.， sweet grass， ginseng root and spearmint leaves.

4. Conclusion

In this study， the effect of different drying temperature on retention α-mangostin content in mangosteen (G. mangostana L.) pericarp by using hot air drying method was investigated. The room temperature extraction was performed to extract dried mangosteen pericarp powder which dried at three different temperatures. The results showed that the optimum temperature for drying mangosteen pericarp powder was 65 °C because it achieved the highest maintenance α-mangostin content that was 40.32 ± 0.24(% w/w of crude extract). Because mangosteen pericarp contained the antioxidant substance which easily degraded at high temperature， the suitable drying condition for mangosteen pericarp before extraction should be considered for utilization in food systems. In comparison of conventional standard extraction method， soxhlet extraction， with MAE and shaking water bath extraction， MAE was showed the best method for mangosteen pericarp extraction due to less extraction time and highest yield of α-mangostin content.

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