Plant extracts are products formed by using plants as raw materials and undergoing physical and chemical extraction and separation processes according to the needs of the final product's use, targeting and concentrating one or more active ingredients in the plant without altering their structure.

1. Classification by extraction purpose:

① Ratio extracts: These are extracts, tinctures, or powders made by extracting and concentrating plant or animal materials. The mathematical ratio between the amount of raw material before extraction and the product after extraction and concentration is fixed. These extracts generally do not have clearly defined components and contents. For example, 10 kilograms of Scutellaria baicalensis herb is extracted and concentrated into 1 kilogram of powdery product, which we call a 10:1 ratio extract of Scutellaria baicalensis. The important indicators such as baicalin and baicalein in this extract do not have clear standards. Ratio extracts are usually qualitatively tested using thin-layer scanning (reflection method). The concept is relatively vague, which is not conducive to the development of the extract industry. Therefore, establishing a quality control system and standards for ratio extracts has been a consistent call from the industry for many years.

② Standard extracts: These are herbal, plant, or animal extracts with consistent standards.

③ Standard extracts of traditional Chinese medicine refer to extracts obtained by using modern scientific and technological methods to extract and process traditional Chinese medicinal materials, with relatively clearly defined content and quality (quantitative).

1. Classification by extracted components:

① Alkaloids: These are a class of complex nitrogen-containing organic compounds with special physiological activity and therapeutic effects. For example, Ephedra contains ephedrine, which treats asthma, and Datura contains scopolamine, which has antispasmodic and analgesic effects.

② Glycosides, also known as glycosides: These are formed by the combination of sugar and non-sugar substances. The commonality of glycosides lies in the sugar part, while different types of aglycones have different physiological activities and multiple functions. For example, Digitalis leaves contain cardiotonic glycosides, and Ginseng contains ginsenosides, which have the effects of invigorating qi, promoting body fluid production, and calming the nerves.

③ Volatile oils: Also known as essential oils, these are fragrant, volatile oily liquids, mixtures of various compounds with physiological activity and various medical uses, such as cough suppression, asthma relief, diaphoresis, diaphoresis, expectoration, wind-dispelling, analgesia, and antibacterial effects. Medicinal plants with relatively high volatile oil content include Thuja orientalis, Magnolia officinalis, Magnolia liliiflora, Cinnamomum camphora, Cinnamomum cassia, Evodia rutaecarpa, Angelica dahurica, Ligusticum chuanxiong, Angelica sinensis, and Mentha haplocalyx.

④ Tannins: Mixtures of polyphenols. They exist in many plants, especially in plants of the Salicaceae, Fagaceae, Polygonaceae, Rosaceae, Leguminosae, Myrtaceae, and Rubiaceae families. The galls produced on the medicinal plant Rhus chinensis are called Chinese galls, which contain Chinese gall tannins and have astringent, antidiarrheal, and antiperspirant effects.

⑤ Other components: Such as sugars, amino acids, proteins, enzymes, organic acids, oils, waxes, resins, pigments, and inorganic substances, each with special physiological functions, many of which are important clinical drugs. Current extraction methods for plant extracts commonly used methods for extracting plant extracts include solvent extraction, ultrasonic extraction, and microwave extraction, while supercritical fluid extraction and microwave-assisted extraction are widely used as new extraction technologies. Solvent extraction generally refers to the method of extracting effective parts from traditional Chinese medicine. According to the solubility of various components in traditional Chinese medicine in solvents, a solvent with high solubility for active ingredients and low solubility for unnecessary components is selected, and the method of dissolving the active ingredients from the medicinal material tissue is called solvent extraction. When the solvent is added to the raw material of traditional Chinese medicine, the solvent penetrates into the cells through diffusion and osmosis, dissolving soluble substances, causing a concentration difference between the inside and outside of the cells, and the concentrated solution inside the cells continuously diffuses outward, while the solvent continuously enters the cells of the medicinal material tissue. This process is repeated many times until the concentration of the solution inside and outside the cells reaches dynamic equilibrium. The saturated solution is filtered out, and a new solvent is added to dissolve most of the required components.

Ultrasonic extraction Ultrasonic extraction uses the strong vibration and cavitation effect produced by ultrasound to accelerate the release and diffusion of substances within plant cells and dissolve them into the solvent, while maintaining the structure and biological activity of the extracted substances. The principle of ultrasonic extraction is mainly a physical process, and it is a relatively new extraction method that has gradually received attention in recent years. For most components, the ultrasonic extraction method can significantly shorten the extraction time, consume less solvent, and have a high extraction rate compared with conventional solvent extraction, thus having higher extraction efficiency. In the ultrasonic extraction process, the choice and concentration of solvent, the ratio of material to liquid, the extraction temperature, and the extraction time will directly affect the extraction rate.

Supercritical fluid extraction Supercritical fluid extraction is the most advanced physical extraction technology internationally, abbreviated as SFE (supercritical fluid extraction). At a lower temperature, when the pressure of a gas is continuously increased, the gas will be converted into a liquid. When the pressure increases, the volume of the liquid increases. For a specific substance, there is always a critical temperature (Tc) and critical pressure (Pc). Above the critical temperature and critical pressure, the substance will not become a liquid or gas. This point is the critical point. In the range above the critical point, the state of the substance is between gas and liquid. The fluid in this range is called supercritical fluid (SF). Supercritical fluids have a strong penetration force similar to that of gases and a large density and solubility similar to that of liquids, and have good solvent properties. They can be used as solvents for extraction and separation of monomers.

Microwave-assisted extraction 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 the extraction and separation of the target components.