The solubility of curcumin in the pure water subcritical and water–ethanol solution (water + (5–10) % (v/v) ethanol) subcritical is investigated for the first time. The design approach taken from this study is the response surface methodology due to the Box Behnken. The experiments were performed in the temperature range of (90–150) °C, (0–10) volumetric percent of ethanol and the flow rate of (0.2–0.8) ml/min. As the pressure effect is ignored in the subcritical conditions, the pressure is constant in 2 MP in the experiments. All analyses were carried out employing the high-performance liquid chromatography apparatus. The curcumin solubility data were correlated with the dielectric constant of solvent mixture. Curcumin solubility modeling in subcritical conditions was done due to cubic-plus-association equation of state. The present study indicated that the rise in temperature and ethanol percentage cause an increase in curcumin solubility. Other important finding was by increasing the flow rate, curcumin solubility rate increased with a very mild slope. The optimum conditions for the curcumin solubility were in the water flow rate of 0.8 ml/min, 10% (v/v) of ethanol, and the temperature of 150 °C.

中文翻译：

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姜黄素在亚临界水（水/乙醇）中溶解度的实验、相关性和建模

首次研究了姜黄素在亚临界纯水和水-乙醇溶液（水 + (5–10) % (v/v) 乙醇）亚临界中的溶解度。本研究采用的设计方法是 Box Behnken 的响应面方法。实验在 (90–150) °C 的温度范围、(0–10) 体积百分比的乙醇和 (0.2–0.8) ml/min 的流速下进行。由于在亚临界条件下忽略压力效应，实验中压力恒定为 2 MP。所有分析均采用高效液相色谱仪进行。姜黄素溶解度数据与溶剂混合物的介电常数相关。由于立方加缔合状态方程，在亚临界条件下进行姜黄素溶解度建模。目前的研究表明，温度和乙醇百分比的升高会导致姜黄素溶解度增加。另一个重要发现是通过增加流速，姜黄素溶解率以非常温和的斜率增加。姜黄素溶解度的最佳条件是水流速为0.8 ml/min，乙醇浓度为10% (v/v)，温度为150 °C。