Role of virgin coconut oil (VCO) as co-extractant for obtaining xanthones from mangosteen (Garcinia mangostana) pericarp with supercritical carbon dioxide extraction
Graphical Abstract
Introduction
Mangosteen (Garcinia mangostana) is a common tropical evergreen tree found in Southeast Asia and has fruits containing a sweet edible juicy white flesh surrounded by an inedible rind. For industrial use, the edible part can be processed into wine, jam, puree and fresh cut [1]. The inedible mangosteen pericarp (MP) has twice the mass of the edible part [2] and is commonly discarded even though it is rich in biologically active compounds, such as xanthones [3], which could be used as a functional ingredient for herbal cosmetic, food or pharmaceutical applications [1]. Highly desirable xanthones contained in MP are mainly α-mangostin and γ-mangostin [4], as they have been shown to increase oxygen radical absorbance capacity within healthy human volunteers [5], inhibit colon tumors [6], or stabilize vegetable oils under accelerated storage conditions [7]. Recovery of xanthones from MP has been studied with liquefied dimethyl ether extraction [8], aqueous micellar biphasic systems [9], microwave assisted extraction (MAE) [10], maceration [11] and macroporous resins [12], wherein it has been concluded that polar solvents are necessary for isolating xanthones.
Extraction of xanthones from MP with supercritical carbon dioxide (scCO2) is attractive from the point of view of food processing, since scCO2 does not leave a harmful residue in foods and scCO2 can be used to further process extracts into particles or food ingredients [13]. Zarena et al [14], [15] demonstrated that scCO2 could be used to recover xanthones from MP samples that had been dried and powdered (500 μm) using a 4 L extraction apparatus and identified many of the xanthones present in MP. Zarena and Udaya [16] concluded that the use of ethanol co-solvent with scCO2 allowed 200 times the concentration of xanthones to be obtained at 30 MPa and 50 °C compared with extractions made using scCO2 alone.
The use of food oils as co-solvents with scCO2 was proposed early by researchers seeking to avoid organic solvents for extraction of foods and natural products [17], [18], [19]. In the separation of lycopene from tomato with scCO2 extraction, Vasapollo et al. [19] considered vegetable oils (hazelnut, almond, peanut, sunflower seed) and found that hazelnut oil greatly enhanced lycopene separation and that it was the only oil compatible with lycopene due to degradation. In the separation of carotenoids from carrot with scCO2 extraction, Sun and Temelli [18] found that use of canola oil as co-solvent with scCO2 could double carotenoid yields and quadruple lutein yields. In the separation of astaxanthin from Haematococcus pluvialis, Krichnavaruk et al. [17] proposed the use of soybean oil as co-solvent with scCO2 as it could enhance extraction of astaxanthin by 30%. The use of vegetable oils as co-solvents continues to be an active area of research as shown by works on scCO2 extraction that use tomato oil for lycopene [20], avocado oil with tomato pomace [21], or vegetable oils for microalgae [22].
In the separation of lycopene from tomatoes with scCO2, Ciurlia et al. [23] showed that there are striking differences between lycopene yields obtained for the case when vegetable oil is fed simultaneously with scCO2 (i.e. as co-solvent) or when the vegetable oil (roasted oily almonds) is mixed with the solid substrate (i.e. as co-extractant), with co-extraction yields being 40% higher than co-solvent yields. Vegetable oils used as co-extractant provided higher lycopene yields than when they were used as co-solvent in the scCO2 extraction process that was attributed by those authors to a diffusion-controlled mechanism that made the extraction more efficient [23].
In previous work [24], vegetable oils (rice bran, sunflower, olive, red palm, grape seed, canola, palm kernel, virgin coconut oil (VCO)) were assessed at temperatures from 60 °C to 98 °C and at atmospheric conditions according to their ability to dissolve mangosteen pericarp extract, which was obtained from ethanol extraction of MP. In that work [24], it was concluded that scCO2 extraction with VCO as co-extractant could provide higher α-mangostin bio-accessibility (91%) than α-mangostin obtained with liquid solvent extractions (bio-accessibility values of 47% for ethanol, 5% for n-hexane, 67% for ethanol-VCO and 11% for n-hexane-VCO) with VCO being inferred as the reason for the mangostin selectivity differences in the extractions, where bio-accessibility is α-mangostin concentration in the micellar fraction and non-digested MPE. Sungpud et al. [1] reported that 9.2 mg of xanthone per 100 g of extract could be obtained when VCO was used.
In this work, separation of xanthones from MP with scCO2 using VCO as co-extractant is studied with the focus being to determine the role of VCO in the extraction mechanism. Namely, experimental conditions were chosen to explore xanthone mass transfer in CO2-saturated VCO and results were analyzed with theoretical, statistical and empirical models. The theoretical model chosen to use was that proposed by Pardo-Castaño model I (PC-I) [25], because it is based on desorption and it has three parameters with physical meaning. The statistical model used was a full quadratic model with ten constants. The empirical model chosen to study was that of Naik et al. [26] that is referred to as the Lentz model. The Lentz model contains two parameters and its mathematical form makes it easier to generalize than complicated relationships.
Section snippets
Materials
Dried mangosteen (Garcinia mangostana) pericarps packed in aluminum bags were supplied by Cadeau, Malaysia. Virgin coconut oil (VCO) was obtained from Orifera, Malaysia. Food grade carbon dioxide, CO2 of 99.9% purity was supplied by Alpha Gas Solution (Selangor, Malaysia). All HPLC grade reagents, namely methanol (99.9%) (Friendemann Schmidt, Malaysia) and acetonitrile (99.9%) (JT Baker-Fisher, Pittsburgh, PA, USA), analytical grade ethanol (95%) (HmbG Chemicals, Germany), ortho-phosphoric acid
Mangosteen pericarp (MP) characterization
The MP had a moisture content of 10.4% (w/w) with particle sizes ranging from 0.04 mm to 1.90 mm with a median size of 0.85 mm. Initial oil content of the MP was 0.8% (w/w) and the MP had a high affinity for VCO as assessed qualitatively by contact photographs (Fig. S5). There were no apparent changes in particle size of MP after mixing with VCO.
Material balance and experimental reproducibility
Detailed material balances can be found in the Supplemental Materials (Table S1). Reproducibility of experiment data was confirmed at the center point
Conclusion
In this study, virgin coconut oil (VCO) was used as a co-extractant to mangosteen pericarp (MP) for separating xanthones from MP with supercritical carbon dioxide (scCO2) extraction. The role of VCO in the extraction mechanism was studied by variation of conditions (temperature, pressure, %VCO) and analysis of extraction yields with phenomenological, statistical and empirical theories based on Pardo-Castaño model I (PC-I), RSM full quadratic model and the Lentz model, respectively. At all
CRediT authorship contribution statement
Siew Lee Kok: Data curation, Investigation, Methodology, Formal analysis, Writing - original draft, Visualization. Wan Jun Lee: Data curation, Investigation, Methodology. Richard Lee Smith Jr: Conceptualization, Formal analysis, Methodology, Writing - review & editing. Norhidayah Suleiman: Supervision, Methodology. Kriskamol Na Jom: Supervision, Methodology. Kanithaporn Vangnai: Supervision, Methodology. Amir Hamzah Bin Sharaai: Supervision, Methodology. Gun Hean Chong: Conceptualization,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was a part of dual MSc program co-funded by Erasmus+573957-EPP-2016-TH-EPPKA2-CBHE-JP (2016–3771) project and was conducted under the financial support of research grant (UPM/800/3/3/1/GP-IPS/2018/9655100) from Universiti Putra Malaysia.
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