Abstract
Solubility, extraction and stabilization of curcumin extracted from Curcuma longa are still a challenge. Either the solubility power of the extracting solvent mixture is not at its optimum or non-sustainable solvents are used or the curcumin instability against oxidation is a problem. In order to tackle these problems, we consider here a promising alternative solvent medium, which is a ternary ...
Abstract
Solubility, extraction and stabilization of curcumin extracted from Curcuma longa are still a challenge. Either the solubility power of the extracting solvent mixture is not at its optimum or non-sustainable solvents are used or the curcumin instability against oxidation is a problem. In order to tackle these problems, we consider here a promising alternative solvent medium, which is a ternary system composed of water/sodium salicylate (an anionic, preservative hydrotrope)/ethyl acetate. The effects of the structuring of the system are also studied. The position of the new critical point and the orientation of tie-lines in the liquid/liquid area were determined and further examined via interfacial tension and diffusion ordered spectroscopy (DOSY NMR) measurements. The critical point between the mono-phasic region and the liquid/liquid area is a classical one, around which no special nano-structuring is found, in contrast to some other ternary mixtures with hydrotropes. The system was investigated in terms of its curcumin solubility and its extraction power thereof. Good extraction yields (~90% of the Soxhlet reference) could be achieved in the area of best solubility. Surprisingly, the hydrophobic curcumin shows a significant solubility in systems that contain a significant amount of water in presence of sodium salicylate. These mixtures are far from the critical point but show significant structuring. The solubility is even higher than in pure ethyl acetate. At the point of highest solubility (water/sodium salicylate/ethyl acetate 7/13/80 w/w/w) 15.48 mg of curcuminoids per g Curcuma longa are successfully extracted.
The partition coefficient in the lower liquid/liquid two-phasic region was determined for a subsequent purification of curcumin by precipitation. Surprisingly, curcumin accumulates at the “oil-water” interface in the more polar phase. Sodium salicylate could be removed from the precipitated curcumin by washing it with water (no trace of sodium salicylate has been detected with NMR after the washing process).
The preservative effect of salicylate against the oxidative effect of light on curcumin was found to be significant. A better stabilization of curcumin was observed far away from the critical point and was most efficient in the region, where aggregates could be detected. So, extraction, solubilization, and chemical stabilization of a light sensitive substance could be performed using an anti-oxidative hydrotrope.
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