Plant extracts are obtained from plants through physical and chemical extraction and separation processes, according to the intended use and requirements of the final extracted product. They involve the targeted acquisition or concentration of one or more active components in plants, and can be used in the food, pharmaceutical, and daily chemical industries.

With the continued growth in global demand for natural health products, the plant extract industry shows tremendous development potential. In 2023, the global plant extract market size exceeded 50 billion USD, with an annual growth rate exceeding 15%, demonstrating a strong development trend.

Common methods currently used to extract plant extracts include solvent extraction, microwave extraction, ultrasonic extraction, and enzymatic extraction. Among these, microwave-assisted extraction and supercritical fluid extraction, as new extraction technologies, have been widely used.

01. Solvent Extraction Method

Solvent extraction uses a solvent to extract active ingredients from solid raw materials. The solvent used must be miscible with the solute being extracted. After the plant material is pulverized, it is placed in a suitable container, and several times the amount of solvent is added. Extraction can be carried out using methods such as maceration, percolation, decoction, reflux, and continuous extraction.

In the solvent extraction process, the concentration of the solvent, the solid-liquid ratio, the extraction temperature, and the extraction time directly affect the extraction rate of the active ingredients.

02. Ultrasonic Extraction Method

Ultrasonic extraction utilizes the strong vibrations and cavitation effects generated by ultrasound to accelerate the release and diffusion of substances within plant cells and their dissolution into the solvent. Simultaneously, it maintains the structure and biological activity of the extracted substances. The principle of ultrasonic extraction is primarily a physical process, and it is a relatively new extraction method that has gradually gained attention in recent years. For most components, the ultrasonic extraction method significantly shortens the extraction time compared to conventional solvent extraction methods, consumes less solvent, has a high extraction rate, and exhibits high extraction efficiency.

In the ultrasonic extraction process, the choice and concentration of the solvent, the solid-liquid ratio, the extraction temperature, and the extraction time directly affect the extraction rate. Experimental results show that the extraction rate increases with increasing temperature and increasing power. The ultrasonic extraction method is 6 times faster than the enzymatic extraction method, and the extraction rate is 2-3 times that of the enzymatic extraction method. Compared with the commonly used organic solvent extraction method, the ultrasonic extraction method not only has a high extraction rate, fast speed, and high efficiency, but it is also a room-temperature extraction that does not require heating, saving energy.

03. Supercritical Fluid Extraction Method

Supercritical fluid extraction (SFE) is a relatively new extraction and separation technology, generally using CO2 as the extractant. The principle of supercritical fluid extraction is to utilize the unique solubility of supercritical fluids and the fact that the solubility of substances in supercritical fluids is very sensitive to changes in pressure and temperature. By means of increasing temperature and decreasing pressure (or both), the dissolved substances in the supercritical fluid are separated, achieving the purpose of separation and purification. It combines both distillation and extraction, with advantages such as the prevention of active ingredient inactivation, high product quality, and simultaneous completion of the extraction and separation process. It is considered a green and environmentally friendly high-tech separation technology, particularly suitable for the separation and purification of unstable natural products and physiologically active substances.

04. Microwave-Assisted Extraction Method

Microwave-assisted extraction (MAE) is a new technology that uses microwave energy to improve extraction efficiency. Microwave-assisted extraction is a method that uses the characteristics of microwave heating to selectively extract target components from materials. By adjusting the microwave parameters, the target components can be effectively heated to facilitate their extraction and separation. The principle of microwave-assisted extraction of plants is that the plant sample absorbs a large amount of energy in the microwave field, while the surrounding solvent absorbs less, thus generating thermal stress inside the cells. The plant cells rupture due to the internal thermal stress, causing the substances inside the cells to directly contact the relatively cold extraction solvent, thereby accelerating the transfer of the target product from the inside of the cells to the extraction solvent, thus enhancing the extraction process. Microwave-assisted extraction uses thermal energy, similar in principle to soaking and filtration, but the speed of extracting plant extracts is much faster than traditional methods, reducing extraction time while preventing the destruction and degradation of valuable plant extracts.

Currently, microwave-assisted extraction, with its fast extraction speed and good extract quality, has become a powerful tool for extracting natural plant active ingredients. However, microwave-assisted extraction is selective internal heating and requires the material being processed to have good water absorption. In other words, the location of the product to be separated must easily absorb water; otherwise, the cells will not be able to absorb enough microwaves to break themselves, and the product will not be able to be released quickly. For liquid extraction systems, the solvent must be polar; non-polar solvents are not sensitive to microwaves.

05. Microwave-Ultrasonic Synergistic Extraction Method

Microwaves are non-ionizing electromagnetic radiation. The polar molecules of the irradiated substance rapidly rotate and align in the microwave electromagnetic field, causing tearing and friction, resulting in heat generation. This ensures rapid energy transfer and efficient utilization, with advantages such as energy saving and no industrial pollution. However, the penetration depth of microwaves is limited (on the same order of magnitude as its wavelength), and its mass transfer function is not obvious in the enhanced extraction process. Ultrasound is a high-frequency mechanical wave with turbulent effects, micro-perturbation effects, interface effects, and energy focusing effects, but the thermal effect produced by ultrasound is not obvious and is limited to a very small area around the cavitation bubbles. Combining the two, the synergistic effect is beneficial for the release of cell wall components, i.e., microwave-ultrasound synergistic enhanced extraction technology can obtain a low-cost and pollution-free method for extracting bioactive substances.

06. Enzymatic Extraction Method

Plant cell walls are composed of cellulose, and the active ingredients of plants are often enclosed within the cell walls. Enzymatic extraction uses cellulase, pectinase, protease, etc. (mainly cellulase) to break down the plant cell walls, promoting the maximum dissolution and separation of plant active ingredients. In the enzymatic extraction process, the choice of enzyme, enzyme concentration, pH value, enzymatic hydrolysis temperature, and enzymatic hydrolysis time all affect the extraction rate of plant extracts. Enzymatic extraction is often used in the preparation of plant extracts, especially in cases where cell walls need to be broken down to release active ingredients.

The plant extract industry is showing a trend toward personalization and customization, with innovative compound extracts becoming an important trend. By 2025, China is expected to become the world's largest producer and exporter of plant extracts, further enhancing industry concentration and international competitiveness.