The Application of deep eutectic Solvents in the Extraction Process of Hydroxytyrosol

Deep eutectic solvents (DESs) are low-eutectic mixtures formed by hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) through hydrogen bond interactions. They exhibit significant advantages in the extraction process of hydroxytyrosol, and their applications are described in detail as follows:

I. Advantages of Deep Eutectic Solvents for Hydroxytyrosol Extraction

Good Solubility

DESs interact with hydroxytyrosol through intermolecular hydrogen bonds and van der Waals forces, effectively dissolving the target component. Additionally, they can disrupt plant cell walls to some extent, increasing cell membrane permeability and facilitating the dissolution of hydroxytyrosol, thereby improving extraction efficiency.

Green and Environmentally Friendly

Most DESs are derived from natural products such as amino acids and sugars, featuring good biocompatibility and degradability. They are environmentally friendly and align with the development philosophy of green chemistry.

Strong Designability

By changing the types and proportions of HBAs and HBDs, the physicochemical properties of DESs (e.g., melting point, viscosity, polarity) can be precisely regulated, enabling accurate control of the hydroxytyrosol extraction process.

Low Cost

DESs are prepared from widely available raw materials, some of which are inexpensive, and their preparation processes are relatively simple, effectively reducing extraction costs.

II. Specific Application Methods of DESs in Hydroxytyrosol Extraction

1. Single Extraction

Mix an appropriate amount of DES with raw materials containing hydroxytyrosol (e.g., olive leaves, olive pomace), and stir or perform ultrasonic treatment at a certain temperature for a period to fully dissolve hydroxytyrosol in the DES. Then, separate the extract through filtration or centrifugation, and purify hydroxytyrosol from the DES via methods such as vacuum distillation or liquid-liquid extraction.

2. Combined with Other Techniques

Ultrasound-Assisted Extraction

Utilizing the cavitation and mechanical effects of ultrasound, the extraction process of hydroxytyrosol by DESs is accelerated. During ultrasound-assisted extraction, cavitation allows DESs to penetrate more easily into the interior of raw material cells, disrupting cell wall structures and improving extraction efficiency. Compared with single DES extraction, ultrasound assistance significantly shortens extraction time and increases hydroxytyrosol yield.

Microwave-Assisted Extraction

Microwaves rapidly heat DESs and raw materials, causing a rapid temperature rise inside the materials and generating vapor pressure to promote hydroxytyrosol dissolution. Microwave-assisted extraction features fast heating and good selectivity, effectively improving extraction efficiency and reducing extraction time. Meanwhile, microwave radiation can inactivate enzymes in raw materials, preventing oxidative degradation of hydroxytyrosol during extraction.

III. Application Case of DESs in Hydroxytyrosol Extraction

A study used a DES formed by proline and ethylene glycol to extract hydroxytyrosol from olive leaves. The results showed that this DES achieved a higher extraction rate of hydroxytyrosol compared to the traditional organic solvent ethanol, and required a shorter extraction time under the same conditions. Additionally, the DES exhibited good biocompatibility and environmental friendliness, providing a new green method for hydroxytyrosol extraction from olive leaves.

IV. Challenges and Solutions

Challenges

High viscosity of DESs may affect mass transfer efficiency during extraction, prolonging extraction time.

The preparation process for some DESs is relatively complex and costly, limiting large-scale applications.

The interaction mechanism between DESs and hydroxytyrosol is not fully understood, making precise formulation design and process optimization difficult.

Solutions

Reduce DES viscosity by adding appropriate diluents or surfactants to improve mass transfer efficiency.

Further optimize DES preparation processes, explore cheaper raw materials, and reduce production costs.

Strengthen research on the interaction mechanisms between DESs and hydroxytyrosol, and use advanced characterization techniques and theoretical calculations to deeply understand their working principles, providing theoretical support for DES design and application.