Elsevier

Fluid Phase Equilibria

Volume 498, 15 October 2019, Pages 51-58
Fluid Phase Equilibria

Efficient separation of curcumin using tetra butyl phosphonium bromide / carbohydrates (sorbitol, fructose) aqueous two-phase system

https://doi.org/10.1016/j.fluid.2019.06.015Get rights and content

Abstract

Curcumin, a natural polyphenol, is a main constituent of turmeric, which is frequently used in food industries as well as pharmaceutical and medicine fields. This bioactive compound is sensitive to high temperature, light, high concentrations of salt, organic solvents, and pH. An economical benign method to extract this precious polyphenol is what seems to be required especially for industrial applications. Aqueous two-phase systems (ATPSs) have demonstrated their potentials for the extraction and separation of bioactive agents. In recent years, researchers have taken a keen interest in the use of green biocompatible components capable of forming biphasic systems. In this study, the ATPSs consisting of carbohydrates (sorbitol, fructose) and tetra butyl phosphonium bromide (IL) were chosen to extract curcumin. To evaluate the efficiency of the system, the partition coefficient and recovery of curcumin were calculated. Furthermore, some factors affecting the curcumin partitioning such as temperature, pH and weight percent of carbohydrates and IL were taken into account. The results indicate that curcumin has a tendency to migrate towards the IL-rich phase. The highest values of the curcumin recovery (≈99%) and partitions coefficient suggest the ability of our proposed ATPS to meaningfully enhance the extraction of curcumin.

Introduction

Curcumin, which is classified as a polyphenol, is obtained from the root of turmeric plant [1]. Thanks to its unique characteristics, curcumin is in great demand as a functional biomolecule in chemical, food, and pharmaceuticals industries as well as medicine [2]. For instance, food manufacturers make use of it as a permitted color additive, preservative (antibacterial and antifungal properties), functional compound (strong antioxidant). In recent years, a considerable amount of scientific research has focused on curcumin capabilities for combating such chronic diseases as liver fibrosis, neurogenic, hypocholesteremic, alzheimer, heart protector, diabetic wounds, and stomach ulcer. This natural polyphenol can be exploited as an anti-cancer, anti-tumor, anti-inflammatory, lower blood pressure, anti-viral, anti-bacteria, anti-carcinogenic, anti-venom, anti-oxidant and anti-HIV agent [[3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]].

Since curcumin is a bioactive compound, it can be degraded when exposed to light or in harsh conditions like high temperature, salinity, or pH. Therefore, in order to extract curcumin, a benign technique in which the curcumin structure is preserved should be implemented. A whole range of methods has been utilized to extract curcumin so far including:soxhlet extraction with conventional solvent, high-performance liquid chromatography (HPLC), ultrasonication, microwave, ultrasonic, and super-critical fluid (SCF) [5]. Each of these useful methods have their own drawbacks and limitations, making them inappropriate for curcumin extraction. To name a few, the soxhlet extraction utilizing inefficient organic or traditional solvents decomposes biomolecule and harms the environment. The HPLC cannot be applied to large-scale systems and economically justified. Also, the operational safety of SFCs are not reliable enough. Accordingly, the development of an economical, eco-friendly method for the extraction of valuable polyphenols like curcumin appears necessary. Besides, the replacement of hazardous traditional techniques by green sustainable technologies was emphasized by FAO (Food and Agriculture Organization) in the 44th and 51th meetings of JECFA [15].

In this work, with the aim of attainment the curcumin partitioning, we took advantage of a novel green ATPS (containing carbohydrate and tetra butyl ammonium bromide) introduced first by Quental et al., [16].

Despite the fact that curcumin is a polyphenol capable of being dissolved in organic solvents, it shows little solubility in water. The pivotal point of our research was to use a proper green ATPS whose components were able to dissolve curcumin. This can open up a new horizon for bioresearches dealing with the extraction of low-soluble biomolecules using ATPS.

IL-based ATPS has drawn particular attention in recent years [17]; however, to the best of our knowledge, there has been little study on the ATPS with phosphonium-based ILs [17], bearing in mind that this group of ionic liquids are more industrially practical thanks to their cheaper price. These systems have been shown to be successful in alkaloids [18]. The IL tetra butyl phosphonium bromide (TBPB) with its unique characteristics can be utilized to form a biphasic system capable of enhancing the extraction efficiency. Its symmetric cations and short-length chains grant TBPB such properties as high melting point and favorable thermal stability [19]. Since the mononuclear anions and cations of TBPB are smaller compared to those of other conventional ILs (like imidazolium-based ILs), it exhibits higher polarity, which makes it easier to perform the separation process and gain greater IL recovery. It is worth noting that the IL solubility depends on its hydrophilicity, which is, in turn, affected by the length of alkyl chains [20,21].

Although there has been so much work on ATPS comprising ILs and mineral salts, the time has come for the salts to be superseded by suitable alternatives owing to the fact that the application of salts in aqueous biphasic systems complicates the IL recovery process. Furthermore, salts alkalize the ATPS, damaging the structures of pH-sensitive biomolecules [22]. The usage of carbohydrate along with ILs boosts both the efficiency and solubility of the system, resulting in a greener process [23].

Sorbitol and fructose are carbohydrates whose applications in food and pharmaceuticals industries are widespread [24]. These compounds are suitable carbohydrates, which is chemically stable and enjoys high solubility in water and ILs.

In this work, taking into consideration such parameters as high efficiency, selectivity, ease of biomolecule recovery, low cost, and rapid mass transfer, we made use of sorbitol/fructose + TBPB ATPS and analyzed its potential for separating curcumin through the determination of partition coefficient. Aimed at specifying the optimal conditions for curcumin partitioning, this study investigates the effects of carbohydrate weight percent, IL weight percent, temperature and pH on the partition coefficient.

Section snippets

Materials

All the detailed properties of chemicals and materials used in this study are provided in Table 1. The distilled water used in all experiments was produced in RO Lab with crossing through a reverse osmosis system by a water distiller (model 2102 GFL, Germany). Distilled deionized water with the conductivity of 0.054 μs/cm was used to prepare the solutions in all of the experiments. The molecular structure of curcumin, sorbitol, fructose and tetra butyl phosphonium bromide has been presented in

Phase diagram, tie lines

With the aim of examining the ATPS behavior as well as specifying the concentration of components in each phase, we used the phases diagrams featuring tie-lines and binodal curves at 298 K (Fig. 2, Fig. 3). The concentrations on the phase diagrams are presented as weight percent(w/w). The empirical binodal data obtained from the cloud point method and tie-line data were fitted using a regression analysis.

To determine the relationship between the weight percent of the IL and carbohydrate (based

Conclusions

Aqueous biphasic systems based on ILs are currently being studied. In this piece of research, with the purpose of devising a powerful biocompatible technique for the separation of curcumin, the green ATPS comprising TBPB and two different types of carbohydrates were analyzed. The system's working points were specified with the help of the phase diagram at 298 K and atmospheric pressure. Subsequently, the partition coefficient and the recovery of curcumin were calculated. Moreover, the impacts

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