Volatile aromatic substances are secondary products transformed from some plants through a series of enzymatic reactions, which may protect the plants themselves to prevent the invasion of pathogenic bacteria, repel pests and attract insects to pollinate. They exist in roots, stems, leaves or flowers, fruits, seeds and other organs and are secreted by glands. However, the existence of aromatic substances in some plants is limited to one organ, while others exist in several organs or even all organs. Most of them are free, and a few of them combine with sugar to form glycosides. Aromatic substances in glycoside state can only be decomposed and released under the action of acid, alkali or enzyme under appropriate temperature conditions.

The main methods of extracting volatile aromatic substances are: ① steam distillation. Uniformly loading the raw materials into a porous steaming pad in a steamer, adding water under the steaming pad, boiling or introducing steam, when the boiling point is reached, aromatic substances escape from oil cells in plant tissues, evaporate with water into mixed steam, and enter the condenser through a conduit. Steam condenses into a mixture of water and oil, and then flows into the oil-water separator. Because the specific gravity of oil and water is different, they can be separated automatically. The obtained products are essential oils, such as peppermint oil and geranium oil.

② Volatile solvent extraction. Some raw materials, such as some flowers, are easy to deteriorate the aromatic components because of the high temperature during distillation, or it is difficult to evaporate because of its high boiling point, so this method is needed. In operation, the raw materials are first soaked in a certain volume of volatile solvent (such as petroleum ether). After the solvent permeates the cell wall, the essential oil in the protoplasm is selectively dissolved, then diffused outside the cell and transferred to the solvent. After filtration, the solvent was distilled from the leaching solution under normal pressure, and then a semi-solid extract was obtained under vacuum. Such as jasmine extract and magnolia extract. The extract can be extracted with ethanol to obtain pure oil.

③ Grinding and pressing method. Mainly used for extracting citrus essential oil. Puncture the oil sac on the outer layer of the peel with a sharp thorn of a fruit mill or a press to make the essential oil flow out, and then clarify, filter and centrifuge the oil-water mixture to obtain the essential oil. The residue after pressing can be distilled to recover the residual essential oil. Such as orange peel oil.

Uses: Aromatic products extracted from plants are mainly used for:

(1) Food flavoring agents and seasonings, such as essence added to candy and drinks;

(2) Daily chemicals, cosmetics and sanitary products, such as soap, toothpaste, perfume and health incense. ;

(3) preparation of drugs, such as peppermint oil and menthol used to make cool oil;

(4) extracting separated spices, such as separating anethole from fennel oil;

⑤ As the raw material of some synthetic spices, such as Litsea cubeba oil (mainly containing citral) can be used to synthesize ionone series products;

⑥ Flavoring of tobacco and stationery.

Focus on cultivating new varieties of important aromatic crops; Exploitation, utilization and protection of wild aromatic plant resources; Improvement of processing equipment and technology; To explore the chemical composition and biosynthesis process of plant essential oil, and provide clues for the chemical synthesis of some new spices.