Extraction of anti-cancer damnacanthal from roots of Morinda citrifolia by subcritical water

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Abstract

Roots of Morinda citrifolia (Noni or Yor in Thai) are the source of important compounds, anthraquinones, which have been proven to have anti-viral, anti-bacterial, anti-cancer activities. The most medicinally valuable anthraquinones in the roots of this plant is damnacanthal, which has been used for treatment of chronic diseases such as cancer and heart disease. In this study, subcritical water extraction was investigated as a benign alternative for solvent extraction of damnacanthal from the dried root of Morinda citrifolia. The experiments were conducted in a continuous flow system at a pressure of 4 MPa at different temperature between 150 and 220 °C and water flow rates of 1.6, 2.4, 3.2 and 4 ml/min. The quantitative analysis of damnacanthal was performed using RP-HPLC with UV detection at 250 nm. The results of the study revealed that the highest amount of damnacanthal extracted with subcritical water was obtained at 170 °C. In addition to the effect of temperature, extractions were conducted at various flow rates and the data were fitted with mathematic models to determine the extraction mechanism. The results suggested that the overall extraction mechanism was influenced by solute partitioning equilibrium with external mass transfer through liquid film. Nevertheless, the desorption model could describe the extraction behavior of Morinda citrifolia reasonably at high flow rates.

Introduction

For centuries, scientists and medical professionals have been investigating chemical constituents in all parts of Morinda critifolia (Noni or Yor), including leaf, fruit, bark, and root. The plants contain several medicinally active components that exhibit various therapeutic effects. These include anti-bacterial [1], [2], anti-viral [3], [4], and anti-cancer [5], [6] activities as well as analgesic effects. Critical reviews of the therapeutic properties of the plants are given by Chan-Blanco et al. [8] and Wang et al. [7]. A group of compound in Morinda citrifolia that were shown to be responsible for the plant's therapeutic properties is anthraquinones and among the different anthraquinones, damnacanthal which is present mainly in the root is of particular interest, due to its important activity in fighting against cancers [6].

Nowadays, the desire to reduce the use of the organic solvent in food and medicine processing has led to new extraction methods including supercritical fluid extraction (SFE) and subcritical water extraction (SWE). For extraction of slightly polar compounds such as anthraquinones, subcritical water is more preferred over supercritical carbon dioxide. Water at subcritical condition refers to liquid water whose temperature lies between boiling (100 °C) and critical temperature (374 °C). At such condition, the intermolecular hydrogen bonds of water break down, causing water polarity to decrease. As a result, water becomes a more effective solvent for several organic compounds. The review on extraction of medical botanicals with subcritical has recently been available [9].

In our previous study, we have shown the feasibility of extracting anthraquinones from noni roots with subcritical water [10]. The subsequent study on antioxidant activity of the root extracts showed that subcritical water extraction yields the extract with high antioxidant activity compared with that obtained by conventional solvent extraction techniques [11]. In the previous study, spectrophotometric analysis was used for the quick determination of the total amount of anthraquinones according to the method described by Zenk et al. [12]. In this work however, the target anti-cancer compound, damnacanthal, in the extracts was quantified using reversed-phase high performance liquid chromatography (RP-HPLC). The effects of various factors such as temperature and flow rate on extraction efficiency of this compound were determined. In addition, the experimental data were fitted with four simple models: thermodynamic partition model, one-site and two-site kinetic desorption models, and thermodynamic partitioning with external mass transfer resistance model, in order to determine which of these models could best describe the behavior of subcritical water extraction of damnacanthal. This will provide useful information for the initial sizing and the economic evaluation of the system in a commercial scale.

Section snippets

Plant material and chemicals

Morinda citrifolia used in this study were grown locally in Thailand. The roots of these plants were harvested, washed, and then oven dried at 50 °C for 2 days. The dried sample was then ground to small size using mortar and pestle with liquid nitrogen. The ground samples were oven dried at 50 °C for 1 day, and then stored in a dry place until use.

Standard damnacanthal (99% purity) was purchased from Merck, Germany. Ethyl alcohol was purchased from Fisher Scientific, UK and dimethyl sulfoxide

Extraction mechanism

In general, extraction of any compound from a single plant particle involves the following steps: (a) transport of the compound through the matrix or down its pores (intra-particle diffusion), (b) diffusion through stagnant liquid film around the solid plant particles (external diffusion), and (c) elution or removal of the compound from a solid matrix by thermodynamic partitioning into the flowing solvents.

The plots of the amount of compound extracted versus solvent flow rates and versus

RP-HPLC chromatograms of extract

In this study RP-HPLC was chosen as a means to quantitatively determine the amount of damnacanthal target compound. It was necessary to concentrate the water extract and this could be achieved by first evaporating off water under vacuum to dryness. The dried extract was redissolved in dimethyl sulfoxide (DMSO) and analyzed. The chromatograms of damnacanthal standard and the extract are shown in Fig. 2. The retention time of the target compound was approximately 12 min.

Effect of subcritical water temperature

The effect of subcritical

Conclusions

In summary, subcritical water provides a promising alternative for extraction of the anti-cancer damnacanthal from roots of Morinda citrifolia. The most suitable condition for subcritical water extraction of damnacanthal was at the temperature of 170 °C and the water flow rate of 2.4–4 ml/min. At higher temperature than 170 °C, the decomposition of damnacanthal occurred. Overall, a mathematical model base on the combination of partition coefficient (KD) and external mass transfer gave a good

Acknowledgements

The author thanks Thailand Japan Technology Transfer Program, Thailand Research Funds, and the Commission of Higher Education for financial support.

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