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Extraction and composition analysis of essential oil from Chinese fir by superheated steam

Chinese fir essential oil is an important natural fragrance, can be used in perfume, incense, cosmetics and other daily chemical products, in addition, it also has antibacterial immunity and other effects. The aroma and chemical composition of Chinese fir essential oil are similar to those of Chinese cedar essential oil, and the main components are terpenoids such as cedryl alcohol, cedryl ene and arham-cedryl ene.


At present, the main extraction methods of Chinese fir essential oil are steam distillation (SD), solvent extraction and dry distillation. The quality of the essential oil extracted by steam distillation is the best, clear and transparent, pure aroma, the most suitable for aroma, but because the method is usually atmospheric distillation, low temperature, the extraction of aromatic components is incomplete, so the yield of essential oil is low.


The solvent extraction method has a high extraction rate and complete extraction of aromatic components, but the product has many impurities, poor fluidity and deep color. 

The yield of fir essential oil obtained by dry distillation method is high, but the high temperature during the extraction process will produce local overheating, resulting in high content of acids and phenols in the obtained fir essential oil, heavy scorch odor, affecting product quality, and complicated follow-up treatment, so some people have studied the method of superheated steam distillation to extract cedar essential oil.

Effect of superheated water vapor temperature on the yield of essential oil

Through the same G-tree, the same distillation time, but different temperatures, 100 degrees Celsius, 130 degrees Celsius, 160 degrees Celsius, 190 degrees Celsius, 220 degrees Celsius, 250 degrees Celsius and 280 degrees Celsius, the obtained fir essential oil is detected by GC-MC, and the superheated vapor temperature has a great impact on the yield of essential oil. High temperature, high boiling point components can also be steamed with steam, extraction is relatively complete, so the yield of essential oils increases. However, when the temperature is too high, the aromatic components are prone to pyrolysis and the low boiling point components are also easy to lose, which leads to the decrease of the yield of Chinese fir essential oil. As the temperature rises, the crystallization of the distilled essential oil decreases significantly, and the color of the essential oil increases from light yellow to light reddish brown.

Chemical composition analysis

With the increase of temperature, the aroma of wood and balm decreased, the taste of sweetness and sour increased, the relative content of cedryl alcohol decreased from 49.99% at 100℃ to 25.41% at 280℃, and the relative content of α-cedryl increased from 16.61% to 30.14%. The relative content of β-cedrene increased from 4.10% to 11.92%. At 280℃, the relative content of cypresene was 42.06%.

Chemical composition analysis

Comparison of extraction of essential oil from Chinese fir by atmospheric steam distillation and superheated steam distillation

The composition and relative content of essential oil obtained by atmospheric steam distillation and superheated steam distillation are different. The fir essential oil obtained by atmospheric steam distillation contains moniterpenoids such as camphor and fenisol, which mainly provide camphor and pine fragrance [15]. At high temperature, moniterpenoids are not detected in the essential oil, and the relative content of cedarwood decreased by 70% to 80%. This explains why the temperature rises and the characteristic aroma of wood drops.


A total of 38 compounds were identified from the essential oil extracted by atmospheric steam distillation, and the detection rate was 99.00%. There were 3 monoterpenoids (relative content 0.47%), 28 sesquiterpenoids (relative content 93.61%), 5 diterpenoids (relative content 3.08%), and the relative content of other compounds accounted for 1.84%. Compared with the oil extracted by steam distillation, the relative content of sesquiterpene compounds was significantly higher, and the types and relative content of diterpenes were reduced.

Comparison of extraction of essential oil from Chinese fir by superheated steam distillation at different temperatures

The main difference of extraction of essential oil from Chinese fir by superheated steam distillation at different temperatures is the relative content of essential oil. Cedryl and cedryl alcohol are the main components of Chinese fir essential oil, and cedryl alcohol is a sesquiterpene alcohol, which is widely used in xylem, spice and Oriental flavor. It is also widely used in disinfectants and hygiene products as a fixed aroma agent, modifier, can be well integrated with sandalwood oil, guaiac oil, salicylate and other raw materials, improve the chemical flavor of some raw materials in the flavor and make the aroma round and sweet alcohol, widely used in daily chemical flavor; It is widely used in medicine for antibacterial and anticancer purposes. α-cedrene is mainly used as a synthetic series of cedarwood oil derivatives, such as cedrone, acetyl cedrene, cedrenal, cedrenol, epoxy cedrene and other spices.

With the change of extraction temperature, the relative content of the two changes significantly. Cedryl alcohol is dehydrated at high temperature to produce cedryl ene. Due to the partial pyrolysis reaction of wood in superheated water vapor, acidic substances are released to produce wood vinegar. Under high heat and acidic conditions, cedryl alcohol is protonated and dehydrogenated by carbocation. The higher the extraction temperature, the easier the dehydration of cedryl alcohol, and the more obvious the relative content of cedryl in essential oil.

In addition to cedrylene and cedryl alcohol, ylangolene, β-serinene, α-aphene and other compounds also change linearly with the increase of superheated water vapor temperature. When the extraction temperature was 130℃, the relative contents of ylangylene, β-serinene and α-aphene were 0.76%, 0.79% and 1.33%, respectively. When the temperature of superheated water vapor is 280℃, the relative content increases to 1.00%, 1.17% and 2.20%, respectively. Equivalent temperature > At 220℃, the relative content of these compounds increased significantly, indicating that increasing the high temperature was conducive to increasing the relative content of these compounds. As shown in Figure 5b, when the temperature > After 190℃, cedryl acetate, lignin alcohol and rhodoconol have strong woody, cedar and vetilant-like aroma. With the increase of temperature, the relative content of these compounds decreases. The reduction in the relative content of these substances may reduce the pharmacological effects of the essential oil and reduce the woody aroma in the odor.

The relative content of some compounds is independent of extraction temperature, but has a higher relative content at a specific temperature. For example, the relative content of elemol at 280℃ is 1.3~4.3 times that of other extraction temperatures. Therefore, it can be considered that after high temperature extraction of essential oil, separation of refined elemol monomer flavor. The relative contents of cipreene and perillyl alcohol were higher in the essential oil extracted at 190℃. Therefore, the appropriate temperature can be selected to increase the relative content of some compounds.

Fragrance

The aroma intensity of wood and resin aroma of Chinese fir essential oil decreases with the increase of temperature, because the extraction temperature is too high, the content of compounds with low boiling point is reduced (borneol, armanthia, etc.), such substances are the main aroma components, with the reduction of the content of these substances, resulting in the reduction of wood and resin aroma of essential oil. 

The main reason for the production of burnt sweet aroma is the sugar substance produced by wood pyrolysis, so the extracted essential oil is not sweet enough at low temperature, but obvious at high temperature. The cooling sensation mainly comes from the increase of the content of alcohol substances.

 The higher the temperature, the less substances with low boiling point, the more types of alcohol substances, the more obvious the cooling sensation odor. With the increase of temperature, partial pyrolysis of wood occurs, producing acid substances, resulting in an increase in sour taste and irritation.

Conclusion

By using superheated steam to extract the essential oil of Chinese fir, it was found that there were differences in yield, odor and composition of the essential oil obtained by steam distillation and steam distillation. The yield of essential oil obtained by superheated steam distillation method is higher than that by steam distillation method. When the steam temperature is 190℃, the yield of essential oil is the highest, which is 4.89%, about 3.2 times of that by atmospheric steam distillation (SD) method.

 With the increase of superheated water vapor temperature, the crystallization amount of distilled Chinese fir essential oil decreases, the color of essential oil deepens, the aroma of wood and resin decreases, and the taste of burnt sweet and sour increases.

 The relative content of cedryl alcohol decreased, the relative content of cedryl ene increased, when the temperature reached 280℃, the relative content of cedryl ene was 42.06%, and the relative content of cedryl alcohol was 25.41%. 

Superheated steam distillation method greatly improved the yield of essential oil, and obtained the structure-activity relationship between the temperature change of different superheated steam and the chemical composition and aroma of essential oil, which could meet the different needs of Chinese fir essential oil products. This method has a good industrial application prospect and can be used as reference and demonstration for other aromatic essential oil extraction.

 

Noted:The above content is from Fine Chemical Industry Journal, volume 39, Issue 12, by Ma Shouxiao, Duan Haoyuan, Zhu Kai

 

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