**3.1 Solvent method**

*Phytochemicals in Human Health*

**2.2 Steam distillation method**

substances of small molecules from plants.

often low, and it is not suitable for large-scale production.

**3. Isolation and purification of phytochemicals**

**2.3 Sublimation method**

**2.4 Pressing method**

Steam distillation is suitable for the extraction of volatile components which can be distilled with steam without being destroyed and are insoluble in water. These compounds' boiling points of are mostly higher than 100°C, and they possess certain vapor pressures at about 100°C. The principle of steam distillation is that the vapor pressure of each component is equal to that of their pure state, while the existence of another liquid does not affect their vapor pressure. The total vapor pressure of the mixing system is equal to the sum of the vapor pressures of the two components. Because the total vapor pressure of the system is higher than that of any single component, so the boiling point of the mixture is lower than that of any component. It is mainly used to extract volatile oils, some alkaloids, and phenolic

The process that solid material converts into steam directly without melting after heating is called sublimation. The phenomenon that steam condenses into solid after cooling is called deposition. Some natural chemicals have sublimation properties, which can be extracted directly with the sublimation method, for example, the extraction of camphor from camphor wood and caffeine from tea. In addition, some small molecular alkaloids, coumarins, organic acids, and other components also have sublimation properties, such as aesculetin and benzoic acid. However, it is easy to carbonize natural products because of long heating time. The volatile tar-like substances often adhere to sublimates, which are difficult to remove and often accompanied with thermal decomposition. The yield of this method is

When the content of active ingredients is relatively high and exists in the juice of plants, the juice can be extracted directly from fresh raw materials. Volatile oils can also be extracted from plant tissues by mechanical pressing, such as orange peel oil and lemon oil. It is performed at room temperature, so its components will not be decomposed by heat. However, the products obtained are impure and often contain impurities such as water, mucoid substances, and cell tissues, so they are often turbid, and it is not easy to press the volatile oil in plants entirely. Therefore, the crushed residue is often distilled by steam to extract volatile oils completely. For example, the black soybean oil from black soybean is often extracted with the low-temperature pressing method.

The separation of phytochemicals is a process of isolating the constituents of plant extracts or effective parts one by one and purifying them into monomer compounds by physical and chemical methods. Classical isolation methods, including solvent extraction, precipitation, crystallization, fractional distillation, saltingout, and dialysis, are still used commonly at present. On the other hand, modern separation technologies such as column chromatography, high performance liquid chromatography, ultrafiltration, and high performance liquid drop countercurrent chromatography also play an important role in the separation of phytochemicals. This section describes the common methods and their specific applications in isola-

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tion of phytochemicals.
