Herbal medicine has been an important part of traditional medicine in many cultures for thousands of years. In East Asia, in particular, it has played a vital role in treating diseases. The bioactive components in herbs and plants form the basis of many treatments, and their relative safety and low side effects compared to chemically synthesized drugs make them an attractive alternative. However, the traditional herbal decoction (THD) method of extracting these bioactive compounds has some drawbacks, such as a long extraction time and decomposition of active pharmaceutical ingredients (APIs).

To address these issues, researchers have developed new green extraction and separation technologies, with subcritical water extraction (SBWE) being the most promising. Subcritical water refers to liquid water at a temperature and pressure below its critical point, and it can extract a wide range of compounds from natural products by adjusting the temperature and pressure conditions. Since water is nontoxic, it is an ideal extraction fluid for herbs, plants, fruits, vegetables, and the like.

SBWE has many applications, including environmental remediation, hydrolysis, degradation, and synthesis reactions, and extraction of active ingredients from natural products. Research has focused on the extraction of flavonoids, carbohydrates, glycosides, organic acids, polyphenolics, alkaloids, essential oils, quinones, terpenes, lignans, and steroids. Subcritical water can simultaneously extract several active ingredients from natural products, and separation, identification, and quantification of each natural product compound in the subcritical water extracts are achieved by liquid chromatography.

In conclusion, SBWE is a promising technology for the extraction of bioactive compounds from natural products. It is a green and safe extraction method that is cost-effective and efficient. With more research and development, SBWE has the potential to become the standard method of extraction for natural products in the future.