Comparative Study on Five Methods for Extracting Volatile Oil from Ginger
Zingiber officinale Roscoe is a fresh rhizome of the perennial herbaceous plant ginger in the ginger family, native to tropical Asia and widely cultivated in most tropical countries of the Americas. The “Shennong Bencao Jing” states, “Living beings are of good quality. Long term consumption can eliminate foul odors and promote the well-being of the gods.” The “Newly Compiled Materia Medica” states, “Smooth the minds of the gods, ward off epidemics, and aid in the generation of qi, which can dispel wind and evil spirits.” Ancient books record that regularly consuming ginger can dispel wind and evil spirits, strengthen the brain, and clear the mind. The volatile oil of ginger mainly contains two types of compounds: monoterpenes and sesquiterpenes. The compounds with higher content include α – gingerene, α – pinene, β – carvacene, camphene, laurene, citronellol, etc. Modern pharmacological research has shown that ginger has pharmacological effects such as anti-inflammatory, analgesic, antioxidant, antibacterial, antiemetic, and can also treat cardiovascular and immune system diseases. The research team has previously confirmed through network pharmacology that ginger volatile oil has a multi-component, multi-target, and multi pathway mechanism of action in treating head wind disease, indicating that it has a certain protective effect on the nervous system.
The commonly used extraction methods for ginger essential oil include steam distillation, ultrasound, microwave, enzyme assisted distillation, etc. Supercritical CO2 extraction is commonly used in industry. Li et al. used steam distillation to extract volatile oils from ginger from different regions, with oil yields ranging from 0.14% to 0.41%, and identified 23 to 39 compounds. Xie et al. used flash assisted steam distillation to extract ginger volatile oil with an oil yield of up to 0.665%. Chen et al. found that the extraction rate of volatile oil from ginger varies in different regions, with Sichuan producing ginger having a higher extraction rate and Shandong producing ginger having a lower extraction rate; The types of components in the volatile oil of ginger in different regions are similar, with the main difference being the varying levels of each component. However, there are few reports on the differences in the main components of volatile oils obtained from different extraction methods of ginger produced in Shaanxi. This study used GC-MS to detect the chemical components of ginger volatile oil obtained by five extraction methods. Principal component analysis (PCA) and cluster heatmap analysis were used to compare the differences in chemical components and relative peak areas. The microstructure of the medicinal residue was visually compared, in order to provide reference for the selection of ginger volatile oil extraction methods and further development and utilization of ginger in practical applications.

The extraction of ginger volatile oil in the Chinese Pharmacopoeia (2020 edition) is carried out according to the volatile oil determination method (General Rule 2204A method). Currently, laboratory extraction of ginger volatile oil usually uses the current pharmacopoeia’s steam distillation method. Literature research has shown that the volatile oil components of ginger obtained by supercritical CO2 extraction in industry are more complex than those obtained by steam distillation, with significant differences in composition, and are prone to mixing with other non-volatile components such as phenols. Therefore, this study mainly used three types of assisted steam distillation methods, namely enzymatic hydrolysis, ultrasound, and microwave, to compare with steam distillation, and also added the simple operation of pressing method to compare with the above four methods.
The oil yields of ginger volatile oil extracted by five methods, namely steam distillation, enzyme assisted steam distillation, ultrasound assisted steam distillation, microwave-assisted steam distillation, and pressing, were 0.18%, 0.19%, 0.21%, 0.18%, and 0.10%, respectively. Among them, ultrasound assisted steam distillation had the highest oil yield and identified the most types of chemical components. The volatile oil components detected by GC-MS in this study were similar to those detected by Li et al. and Gunasena et al., but there were also differences, which may be due to differences in the origin and extraction methods of ginger.
When using traditional methods such as steam distillation and solvent extraction to extract volatile oils from medicinal herbs, there are usually problems such as excessive energy and time consumption, residual organic solvents, and low yield of volatile oils, which are gradually replaced by emerging technologies. Enzyme assisted steam distillation is a newly developed method for extracting essential oils from natural plants. By applying appropriate enzymes for enzymatic pretreatment of plants, the cell wall is completely hydrolyzed, thereby enhancing the release of secondary metabolites within the cell and increasing the yield of volatile oils. Ultrasonic assisted steam distillation mainly utilizes mechanical effects, cavitation effects, thermal effects, and chemical effects to promote the rapid separation of target molecules from the carrier, that is, to promote the destruction of plant cell structure, and effectively promote the outflow of cell contents such as volatile oils. Microwave is an electromagnetic wave that can promote the rapid rotation of polar molecules in an electric field through dipole dipole interactions, thereby achieving rapid heating. The introduction of microwaves greatly improves the heating rate of the system by changing the heating method in essential oil distillation. Through the synergistic effect of heat and mass transfer, the separation rate of volatile oils is effectively improved. However, excessive microwave irradiation power can easily lead to the loss of volatile components and thermal degradation of plant materials. Compared with the steam distillation method, the three auxiliary steam distillation methods may undergo changes due to the thermal instability of volatile components, which may be affected by microwave, ultrasound, and enzyme effects, resulting in differences in components and relative peak areas.
In this study, the extraction method of ginger volatile oil from the reference literature was used for juice extraction and further processing to obtain fat soluble components. When using GCMS to determine the volatile oils (lipophilic components) obtained by different extraction methods, the threshold was uniformly adjusted to 20, and three compounds were identified by pressing method. Compared with other methods, it is speculated that the extraction of ginger volatile oil by pressing method is not incomplete. However, the relative peak areas of α – gingerene and β – sesquiterpene obtained were significantly higher than the other four methods, and relatively more 6-gingerol could be obtained. From this, it can be seen that the pressing method can easily and quickly extract α – gingerene, β – sesquiterpene, and 6-gingerol from fresh ginger, with low energy consumption and minimal pollution. 6-gingerol is an alkyl phenolic compound formed by dehydration of 6-gingerol, belonging to gingerol. The molecular structure of gingerol contains 3-methoxy-4-hydroxyphenyl functional group. According to the different hydrocarbon chains connected by this functional group, gingerol can be divided into different types such as gingerol, gingerol, gingerol, gingerol diketone, gingerol diol, etc. The concentration of gingerol is lower than gingerol, but it has higher biological activity.
When observing ginger residue obtained by different extraction methods under microscope, manual slicing is difficult to ensure uniform sample thickness standards, and the sample contains a large number of bubbles. Therefore, microscopic observation is only a simple and intuitive method to verify the effect of various methods on volatile oil extraction. Compared with the oil yield, ginger has strong fibrous properties, and ultrasound and enzymatic hydrolysis are more conducive to the rupture of oil cells and the outflow of volatile oil during steam distillation, thereby improving extraction efficiency. Although microwave has a certain impact on the structure of ginger cells, it may lead to the loss of volatile components and thermal degradation of fresh plants.

This study compared the chemical composition, relative peak area, and microstructure of ginger volatile oil obtained by different extraction methods, and analyzed the characteristic components of ginger volatile oil obtained by different methods, in order to provide reference for the selection of ginger volatile oil extraction methods and further development and utilization of raw ginger in practical applications.