What Are Supercritical CO2 Extraction Of Chamomile Essential Oil?

Chamomile (chamomile) is a genus of chamomile in the family of Asteraceae, native to Europe, China, Xinjiang, and other places and also cultivated in large quantities. Because of the calming effect of chamomile, it is widely used in herbal tea. In addition, chamomile extract is also commonly used in the cosmetic industry as a fragrance for care products. Chamomile contains terpenes, flavonoids, choline, coumarin, malic acid, proteins, sugars, oils, and minerals. Chamomile essential oil has 116 kinds of chemical substances that have been identified [1-2], including 28 types of terpenes (the most important is α-sweet myrrh terpene alcohol, orchid oil azulene, α-sweet myrrh terpene alcohol oxides, etc.), 36 kinds of flavonoids and other 52 types of substances, including organic acids, coumarins, choline and so on.

At present, there are not many domestic and foreign reports on the extraction process of chamomile essential oil and related products, among which, Zhu Dongliang et al [3] used water vapor distillation and simultaneous distillation extraction method to prepare the Roman chamomile oil produced in Xinjiang and compare the compositions; Kaiser et al [4] used supercritical CO2 extraction of chamomile flowers and stabilized with β-cyclodextrin; Lan Wei et al [5] used response surface method to optimize the total flavonoids extraction process of chamomile in Germany, and the extraction rate could be up to 34.5 %, and the extraction rate could reach up to 34.4%. Lan Wei et al.[5] used the response surface method to optimize the extraction process of total flavonoids from German chamomile, and the extraction rate could reach 34.792 mg/g. 792 mg/g; Chen Lichun et al.[6] optimized the extraction of apigenin from chamomile by reflux method with organic solvent using response surface analysis, and the extraction rate of apigenin under the optimal conditions was 2.14%; Fu Chunxue et al.[7] optimized the extraction of apigenin from chamomile by using β-cyclodextrin stabilization. 14%; Fu Chunxue et al[7] conducted GC-MS analysis on the volatile oil of Roman chamomile from Heilongjiang and Xinjiang and found that the volatile oil of chamomile was similar, but the content of the constituents varied greatly; Wang Jinbiao et al[8] provided a supercritical CO2 extraction of chamomile extracts, and ethanol was used as the entraining agent, with an extraction rate of 2.8%.

The use of supercritical CO2 extraction of volatile components of chamomile has the advantages of no solvent residue in the product, high aroma intensity, and realistic aroma[9-10] , but due to the wax in the product, the separation of essential oils and waxes is difficult, and it is difficult to obtain high-quality essential oils. Molecular distillation makes use of the different molecular free processes in high vacuum to separate the materials, which has the advantages of low distillation temperature, low oxidation of the materials, high heat transfer efficiency, no pollution, no residue, and pure and safe products[11-13] , and is widely used in the purification of essential oils because of its ability to separate the materials that are difficult to be separated by conventional distillation.

For example, Song Wangdi et al.[14] used molecular distillation to purify lavender essential oil, and the purities of aryl acetate, camphorated alcohol, and lavender acetate were 45.11%, 25.3%, 25.3%, and 25.3%, respectively, under the optimal conditions. 11%, 25 . 52%, 14.27%; Hu et al. 27%; Hu Anfu et al.[15] investigated the molecular distillation technique for the separation and purification of essential oil of Buddha's hand, and the content of α-pinene and main limonene increased from 44.2% to 75.3% under the optimal conditions.Hu Xuefang et al.[16] used supercritical combined molecular distillation to extract and purify cumin essential oil, and the content of cumin aldehyde, the main component of cumin essential oil, increased from 11.48% to 30.4% before purification. The content of cumin aldehyde, the main component of cumin essential oil, increased from 11.48% before purification to 30.30%. The main component of cumin essential oil, cumin aldehyde, was increased from 11.48% before purification to 30.30%, and the purification results were satisfactory. Hu Xuefang et al.[17] used supercritical CO2 extraction and molecular distillation to purify the essential oil of primary Eucalyptus megacephalus leaves, and the mass fractions of 1,8-eucalyptol and α-pinene were increased by 77.62% and 56.72%.

In this study, supercritical CO2 extraction of chamomile was used, and the essential oil of chamomile was separated and purified by molecular distillation. The effects of extraction pressure, extraction temperature, extraction time and other major factors on the extraction rate of the essential oil were selected for the study, and a three-factor, three-level orthogonal test was designed based on a one-factor test, to optimize the parameters of the extraction process. Since the addition of an entrainer would increase the difficulty of subsequent solvent separation, no entrainer was added in this process.

1 Materials and Methods

1.1 Materials and Instruments

Chamomile originated from Yili, Xinjiang, Zhejiang Tiancao Bio-technology Co. CO2 gas, food grade, purity greater than 99.5%, Hangzhou Jin Gong Gas Co., Ltd; supercritical fluid extraction device SFE130-50-02C, Jiangsu Nantong Huaxing Petroleum Co.

1.2 Test Methods

1.2.1 Process Flow

The process of semi-continuous supercritical CO2 extraction of chamomile essential oil includes fluid compression, extraction, depressurization, and separation, etc., in which the CO2 in Separator 3 is purified and then compressed, and then returned to the CO2 compressor to realize recycling, and the flow of the device is shown in Figure 1. The CO2 flow rate in this test is 24L/h, and the pressure of separator 1 is set at 8 MPa and the temperature is 30 ℃; the pressure of separator 2 is set at 6 MPa and the temperature is 25 ℃; the pressure of separator 3 is set below 4.5 MPa and the temperature is 15 ℃; the pressure of separator 3 is set at 4.5 MPa and the temperature is 15 ℃. The pressure of separator 3 is below 4.5 MPa and the temperature is 15 ℃.

Fig.1    Diagram of semi-continuous  supercritical CO2    extraction unit for chamomile essential oil

1.2.2 Chamomile Pretreatment

The dry head of chamomile is placed in the oven to dry for 24h, and pulverized, through a 40-mesh sieve, the powder is accurately weighed, and spare.

1.2.3 Chamomile Extract Supercritical CO2 Extraction

Weigh the above dried chamomile powder 500 g into the extractor sealed, the extraction pressure, temperature, time, and other factors that may affect the test.

1.2.4 Purification of Chamomile Extract by Molecular Distillation

1.2.4.1 Wax Removal of Chamomile Extracts

Dissolve the extract obtained from supercritical extraction in 10 times the volume of anhydrous ethanol at 50 ℃, then filter it through a 1 μm filter to remove most of the waxes after cooling.

1.2.4.2 Concentration

The ethanol concentrate is obtained by vacuum distillation at 70 ℃.

1.2.4.3 Solvent Removal

Fixed feed flow rate of 1 mL/min, scraping film speed of 150r/min, evaporation temperature of 80 ℃ and distillation pressure of 100Pa, condensing surface temperature of 5 ℃, with molecular evaporation of ethanol and water in the concentrate is completely removed.

1.2.4.4 Refinement of Essential Oils

Remove ethanol and water after the concentrate into the molecular distillation of the material bottle, the separation process parameters for the distillation temperature of 120 ℃, vacuum degree of 3. 0Pa, rotational speed of 350r/min, feed flow rate of 1mL/min, condensing surface temperature of 5 ℃, to get the essential oil.

2 Results and Analysis

2.1 Supercritical CO2 extraction of chamomile essential oil single factor effects

2.1.1 Extraction Pressure

Under the conditions of extraction temperature of 40 ℃, CO2 flow rate of 24L/h, and extraction time of 120min, the extraction pressures of 15, 20, 25, 30, 35, and 40MPa were selected to examine the effect of extraction pressure on the extraction rate of essential oils (Figure 2). As the extraction pressure increased, the density of CO2 increased, and the solubility increased. However, when the pressure was increased to a certain extent, the density of CO2 increased slowly, and the increase in solubility also slowed down. Moreover, when the pressure increased to 35 MPa and above, the wax dissolution in chamomile increased significantly, and the subsequent separation was more difficult. It was found that the extraction pressures of 25, 30 and 35 MPa were more suitable by one-way test.

Fig.2    Effect of extraction pressure on extraction rate of chamomile essential oil

2.1.2 Extraction Temperature

Under the conditions of CO2 flow rate of 24 L/h, extraction time of 120 min, and extraction pressure of 25 MPa, temperatures of 35, 40, 45, 50, 55, and 60 ℃ were selected to examine the effect of extraction temperature on the extraction rate of essential oils (Figure 3). At lower supercritical CO2 pressures, the increase in extraction temperature would reduce the fluid density and the solubility would be weakened, but the product would contain less waxes and the post-treatment would be simpler. At higher supercritical CO2 pressures, an increase in extraction temperature increases the diffusion coefficient of the extractant, which greatly increases the solubility of weakly polar organic substances, while at the same time the extracted by-products are greatly increased, with a significant increase in the wax content. When the temperature rises from 35 ℃ to 45 ℃, the extraction rate of essential oil gradually increases; however, the extraction rate tends to decrease after exceeding 45 ℃. Therefore, it is more appropriate to choose the extraction temperature in the range of 40, 45 and 50 ℃.

Fig.3    Effect of extraction temperature on extraction rate of chamomile essential oil

2.1.3 Extraction Time

Under the conditions of CO2 flow rate of 24 L/h, extraction pressure of 25 MPa, and extraction temperature of 40 ℃, the effect of extraction time on the extraction rate of chamomile essential oil was examined (Figure 4). At the early stage of extraction, the yield of chamomile extract increased rapidly with the increase of time, and under this condition, the extraction rate of the extract slowed down after 120 min of extraction, and the operating cost would increase if the extraction time was prolonged. Moreover, at the early stage of extraction, the quality of the extracted product was better judging from the sensory, and the color of the extracted product was dark blue with a strong aroma; at the later stage of extraction, the color of the extract was slightly yellowish, and the liquidity was relatively poor, which was probably due to the long extraction time, increasing the relative amount of waxes in the product, and the decrease of the texture of the first extract. Therefore, the extraction times of 90, 120 and 150 min were chosen as the appropriate ranges.

Fig.4    Effect of extraction time on extraction rate of chamomile essential oil

2.2 Orthogonal Test Design and Analysis

2.2.1 Orthogonal Test Design

The range of the levels of each factor was obtained through the one-way test, and the extraction rate of essential oil was taken as the main index to design the L9 (3 3 ) orthogonal test table and carry out the experiment, and the factors and levels are shown in Table 1.

Table 1     Horizontal table of orthogonal experimental factors

2.2.2 Orthogonal Test Results and Analysis

An orthogonal test was conducted according to the factors and levels in Table 1 to obtain the extraction rate of chamomile essential oil under different conditions, and the test results were analyzed by extreme deviation, and the results are shown in Table 2.

Table 2    Results  and analysis  of orthogonal experiment

From the results of the analysis of variance, it can be seen that the influence of the factors on the extraction rate of chamomile essential oil in the following order: extraction pressure > extraction time > extraction temperature, extraction pressure of 30 MPa, extraction time of 120min, extraction temperature of 50 ℃, chamomile essential oil extraction rate is the highest. Under these conditions, the extraction rate of chamomile essential oil was 4.13%.

3 Conclusion

Chamomile was extracted by supercritical CO2 extraction, and the essential oil was separated and purified by molecular distillation. The extraction rate of chamomile essential oil was taken as an index, and the effects of extraction pressure, time, temperature, and other factors were examined, and the optimal process parameters were obtained through a three-factor, three-level orthogonal test. The results showed that the optimal process parameters were: extraction pressure 30MPa, extraction time 120min, extraction temperature 50 ℃, and the extraction rate of chamomile essential oil after separation by molecular distillation was 4.13%. 13%. The obtained chamomile essential oil has the advantages of no solvent residue, high aroma intensity and realistic aroma, and has a promising application prospect.

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