Optimization of the extraction process of hydroxytyrosol

Hydroxytyrosol is a natural phenolic compound with multiple biological activities and has broad application prospects in the fields of food, medicine, cosmetics, etc. Supercritical CO₂ extraction and green solvent extraction are currently the extraction methods of hydroxytyrosol that have been studied more. The following are the progress in the optimization of the extraction process of hydroxytyrosol from supercritical CO₂ to green solvent technology:

I. Supercritical CO₂ Extraction Technology

Basic Principle: Supercritical CO₂ extraction utilizes the characteristics of CO₂ in the supercritical state, such as high diffusivity and low viscosity, as well as its dissolving ability for solutes like hydroxytyrosol. By adjusting parameters such as temperature and pressure, the extraction and separation of hydroxytyrosol can be achieved.

II. Progress in Process Optimization

Application of Entrainer: When initially extracting hydroxytyrosol by supercritical CO₂, due to the limited solubility of CO₂ for hydroxytyrosol, the extraction efficiency is not high. Later studies found that adding an appropriate amount of entrainers such as ethanol and methanol can significantly increase the solubility of hydroxytyrosol in CO₂. For example, under certain extraction conditions, adding 10% (volume fraction) of ethanol as an entrainer can increase the extraction rate of hydroxytyrosol by 30%-50%.

Optimization of Extraction Parameters: Through optimization methods such as the response surface method, a systematic study is carried out on parameters such as extraction temperature, pressure, time, and CO₂ flow rate. Studies have shown that under the conditions of an extraction temperature of 40-60°C, a pressure of 20-40MPa, an extraction time of 1-3h, and a CO₂ flow rate of 1-3L/h, a higher extraction rate of hydroxytyrosol can be obtained.

III. Green Solvent Extraction Technology

Basic Principle: The green solvent extraction technology uses environmentally friendly solvents, such as ionic liquids, deep eutectic solvents, water, etc., to extract hydroxytyrosol, reducing the environmental pollution caused by traditional organic solvents.

IV. Progress in Process Optimization

Extraction with Ionic Liquids: Ionic liquids have the advantages of strong designability, good solubility, and low vapor pressure. By screening ionic liquids with different combinations of cations and anions, researchers have found that certain imidazole-based ionic liquids have good solubility and selectivity for hydroxytyrosol. For example, the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) can achieve an extraction rate of hydroxytyrosol of more than 80% under the conditions of a mass ratio of the ionic liquid to the raw material of 1:10-1:20, an extraction temperature of 40-60°C, and an extraction time of 1-2h. Moreover, the ionic liquid can be recycled by simple methods such as distillation or extraction, reducing costs and the environmental impact.

Extraction with Deep Eutectic Solvents: Deep eutectic solvents are low eutectic mixtures formed by hydrogen bond donors and hydrogen bond acceptors through hydrogen bond interactions. They have the characteristics of simple preparation, low cost, and good biocompatibility. Taking the choline chloride-ethylene glycol deep eutectic solvent as an example, under the conditions of a molar ratio of choline chloride to ethylene glycol of 1:2-1:4, a mass ratio of the solvent to the raw material of 1:5-1:10, an extraction temperature of 50-70°C, and an extraction time of 30-60min, a higher extraction rate of hydroxytyrosol can be obtained. At the end of the day, deep eutectic solvents also have a certain selective extraction effect on other components in the raw materials, which is beneficial for subsequent separation and purification.

Extraction with Water: Water is a greenest solvent. When extracting hydroxytyrosol with hot water, a certain extraction effect can be achieved by optimizing parameters such as extraction temperature, time, and the solid-liquid ratio. For example, under the conditions of an extraction temperature of 80-100°C, an extraction time of 1-3h, and a solid-liquid ratio of 1:10-1:20 (g/mL), the extraction rate of hydroxytyrosol can reach 60%-80%. To further improve the extraction efficiency of water extraction, auxiliary extraction technologies such as ultrasound and microwave can also be combined. Ultrasound-assisted water extraction can destroy the plant cell wall through ultrasonic cavitation, promoting the dissolution of hydroxytyrosol; microwave-assisted water extraction utilizes the thermal effect and non-thermal effect of microwaves to accelerate the extraction process of hydroxytyrosol.

From the development of supercritical CO₂ extraction to green solvent technology, the extraction process of hydroxytyrosol is constantly optimized, and it is developing towards a more efficient, environmentally friendly, and economical direction. Green solvent technology, due to its unique advantages, is expected to be more widely applied in the industrial production of hydroxytyrosol in the future.