Study on Co2 Extracted Ginger Essential Oil

Ginger is the fresh rhizome of the perennial herb Zingiber officinale Roscoe (family Zingiberaceae), which is widely cultivated in central, southeastern, and southwestern China. As one of China's traditional condiments, ginger is used in cooking for its unique aroma and pungent flavor to enhance the fragrance, remove fishy smells, and enrich the flavor of foods. Ginger also has a place in traditional Chinese medicine history, and has been used in many prescriptions for activating blood circulation and removing blood stasis to treat gynecological, internal medicine, and orthopedic diseases in past dynasties. Modern pharmacological studies and clinical trials have proven that ginger and its active ingredients can lower triglycerides and cholesterol, reduce the synthesis of body fat; they can also inhibit platelet aggregation, anticoagulate, prevent thrombosis, and prevent the formation and development of atherosclerosis [1]. Ginger's unique fragrance and its medicinal value as a food and medicine are playing an increasingly important role in industrial applications such as food, medicine, and cosmetics.

Currently reported ginger extracts mainly include flavor substances (ginger essential oil, ginger oleoresin), ginger dietary fiber, ginger polysaccharides, and ginger protease. This article mainly introduces the current research status of ginger extracts, providing a theoretical basis for the comprehensive utilization of ginger and the improvement of economic added value.

1 Flavor substances

1.1 Extraction of ginger essential oil

Ginger essential oil and ginger oleoresin are currently the main flavor extracts studied at home and abroad, and they contain the main active substances in ginger. Ginger essential oil is a general term for a class of ginger that contains almost no high-boiling volatile substances. It is a yellow, transparent, oily liquid with a strong, characteristic, aromatic ginger smell, and it is the basic source of the aroma and flavor of ginger. The traditional extraction method has always been based on steam distillation, which is easy to operate and requires low investment. However, the disadvantages are long distillation times and low oil yields. Liu Jiangwei et al. [2] determined that the factors affecting the ginger essential oil extraction process are the distillation time, ginger powder soaking time, ginger powder drying temperature, and liquid-to-material ratio, and orthogonal optimization was used to obtain the optimal process conditions, with a ginger essential oil yield of 1.6%. Other technical aids can improve the efficiency of ginger essential oil extraction. Liu Hongxia et al. [3] optimized the conditions for extracting ginger essential oil by distillation, and the essential oil extraction rate could reach 1.44%. After that, microwave-assisted water distillation was used to extract ginger essential oil, which improved the extraction efficiency to a certain extent. Under the same extraction rate, the extraction time was shortened by nearly 1 times.

With the development of extraction technology, Lin Lijing [4] and others used supercritical CO2 technology to obtain high-quality ginger essential oil, with an extraction rate of 1.77%. Lei Hong et al. [5] optimized the process conditions of supercritical CO2 extraction by response surface methodology, using 6-gingerol, an active substance in ginger essential oil, as the index for investigation. The optimal ginger essential oil extraction conditions were obtained: a carbon dioxide flow rate of 25 L·h-1, ginger powder sieved to 80 mesh, the addition of 92.46 mL of anhydrous ethanol, and an optimal 6-gingerol yield of 3.21%.

With the development of extraction technology, the extraction rate of ginger essential oil has basically stabilized at 2%, but the extraction efficiency has been greatly improved, which is of certain reference value for reducing production costs in industrial production.

1.2 Analysis of the composition of ginger essential oil

The composition of ginger essential oil obtained by different extraction methods and from different origins will also differ to a certain extent. This has a certain guiding significance for industrial production, and the specific effects of different ginger essential oil products need to take the extraction method and origin into account.

Pei Yaping [6] used gas chromatography-mass spectrometry (GC-MS) to compare and analyze the volatile components of Shandong rhubarb ginger essential oil extracted by supercritical CO2 extraction (SFE) and water steam distillation (SD). supercritical CO2 extraction of rhubarb ginger essential oil detected 126 volatile components; while water vapor distillation extracted rhubarb ginger essential oil, 107 volatile components were detected. The two essential oils contain the same 80 ingredients, but in different proportions.

Gao Liang Jiang is a medicinal herb used for both food and medicine, and it has a high content of volatile oil. Its main growing area is Xuwen, Guangdong. In order to expand its planting area, Hainan, with similar climatic conditions, was selected for expansion. Zhai Hongli et al. [7] studied the differences in the composition of the volatile oil of two growing bases. The volatile oil of Hainan-grown Gao Liang Jiang contains 8.23% α-terpineol, while the content of β-pinene and camphene can reach more than 10%. The α-terpineol content in the volatile oil of galangal produced in Xuwen is only 1.67%, and the content of β-pinene and camphene is only 0.13%, but the content of τ-juniperol is higher, at 6.83%.

The main components of the volatile oil of Hainan-produced galangal are very different from those of Xuwen-produced galangal, which can provide a reference for its use as medicine and as a spice.

1.3 Extraction of ginger oleoresin

Ginger oleoresin contains non-volatile fatty components that are not found in ginger essential oil, and it retains the characteristic spicy and bitter smell of ginger. It is mainly extracted from the rhizome of ginger using an organic solvent to obtain a relatively viscous liquid that is dark amber to dark brown in color. After standing, there will be a granular precipitate. Zingerone is the main spicy compound in it. It is the general term for the ginger-related spicy substances of gingerol, shogaol, and zingerone. The traditional method of extracting ginger oleoresin mainly involves extracting with organic solvents such as ethanol, acetone, and petroleum ether. With the development of extraction technology, there are new technologies and methods such as supercritical CO2 extraction and double-water phase extraction. Due to the different origins of the raw materials and extraction methods, the composition and content of ginger oleoresin can vary significantly.

Zhou Lingguo[8] and others conducted experiments on the extraction of ginger oleoresin using a two-phase solvent system. Using β-cyclodextrin, or β-cyclodextrin in combination with sodium carbonate or table salt, mixed with ginger juice and water, a two-phase solvent system with clear phases can be formed. The target component in ginger oleoresin, shogaol, is distributed in the lower phase, and the extraction rate can reach more than 70%.

The optimal process conditions for ethanol extraction are: extraction temperature of 60 °C, extraction time of 5 h, mass ratio of 1:10, particle size of 40 mesh, and vacuum degree of -0.07 MPa. The chemical composition of ginger oleoresin extracted with ethanol at different temperatures is basically the same. As the extraction temperature increases, more chemical components are detected in ginger oleoresin [9].

Based on traditional organic solvent extraction, the use of ultrasonic-assisted ethanol extraction can significantly improve the extraction rate of ginger oleoresin, which can reach 5.29% [10]. Some experiments have also pretreated ginger powder with enzymes to make the physiologically active substances in ginger oleoresin more easily released. Supercritical CO2 technology can also be used for the extraction of ginger oleoresin [11]. Compared with the reflux method with ethanol, it was found that supercritical CO2 technology is significantly superior to ethanol extraction, but there are certain differences in the extracted components.

Through technological research and development and technological integration, the core technologies for the extraction and conversion of ginger oleoresin have been matured and integrated to form a highly efficient and standardized technical specification for ginger oleoresin extraction. Using Laiwu ginger as raw material and through an integrated extraction process, the yield of dried ginger can reach 20%, the extraction rate of ginger oleoresin can reach more than 97%, and the solvent residue can reach an undetectable level [12].

1.4 Analysis of the composition of ginger oleoresin

Fingerprinting is a technique that was born with the development of modern analytical technology to study complex material systems as a whole. This model is based on various spectroscopic, spectrometric, chromatographic and other techniques, and has the characteristics of fingerprint characteristic analysis and macroscopic inference analysis.

At present, the composition analysis of ginger oleoresin is mainly focused on establishing the basis of mass spectrometry analysis. The composition of ginger oleoresin is analyzed using solid-phase microextraction (SPME) technology combined with gas chromatography-mass spectrometry. The establishment of a fingerprint map of ginger oleoresin can provide a simpler, faster and more effective method for quality evaluation, provide new ideas for the intrinsic quality of ginger oleoresin, provide a basis for the quality control and identification of raw materials, and provide a solid guarantee for the quality and application of ginger oleoresin [13].

2. Ginger protease

Ginger protease is considered to be another member of the papain family, and has certain homology in structure and properties with plant proteases such as papain and bromelain. The main methods of extracting ginger protease are the organic solvent method, the salt method combined with an organic solvent, the tannin method, and the ultrafiltration method. The tannin method is not commonly used because the tannin is toxic. The precipitation method is mostly used to prepare ginger protease as an acetone powder by acetone precipitation, and this is used as the enzyme source for further separation and purification. Fresh ginger is cut into pieces, a phosphate buffer solution with a pH of 6.5 is added, the mixture is homogenized, the buffer solution is diluted, sodium chloride is added and stirred, the mixture is filtered, the residue is extracted with the buffer solution, the filtrate is collected, filtered through a microporous filter membrane, and then ultrafiltered [14].

3 Ginger polysaccharides

Ginger polysaccharides mainly refer to the dietary fiber that can be extracted from ginger and polysaccharides with certain physiological functions.

3.1 Extraction of dietary fiber

Dietary fiber is one of the seven essential nutrients for the human body. It cannot be absorbed or digested by the intestines and does not produce energy, but it is closely related to human nutritional health. Dietary fiber can be divided into two main categories: soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). The main methods of extracting dietary fiber are enzymatic, alkaline, ultrasound-assisted, membrane separation, fermentation, and shear emulsification-assisted enzymatic hydrolysis. The enzymatic method is easy to operate, saves energy, and is environmentally friendly. Song Rongzhen [15] et al. used the enzymatic method to extract soluble dietary fiber from ginger, and optimized the process conditions for the extraction of soluble dietary fiber from ginger by plant protease: the amount of plant protease was 6%, the enzymatic temperature was 55 °C, and the enzymatic time was 5 h. At this time, the extraction rate of soluble dietary fiber was 13.24%.

3.2 Extraction of ginger polysaccharides

Studies have reported that the main extraction methods for ginger polysaccharides are hot water extraction, microwave-assisted extraction, ultrasound-assisted extraction, and synergistic extraction using multiple extraction techniques. Liao Dengwei et al. [16] determined the optimal process conditions for hot water extraction of ginger polysaccharides, with an extraction yield of (11.74±0.23)%.

Wang Yun et al. [17] used a complex enzyme (cellulase, pectinase, papain and α-amylase) to extract ginger polysaccharides. The determined ratio of the complex enzyme was 1.5%, 1.0%, 2.0% and 2.5% for cellulase, pectinase, papain and α-amylase, respectively, and the polysaccharide extraction rate can reach 22. 18%. Wang Ying et al. [18] studied the microwave-assisted extraction of ginger polysaccharides and optimized the optimal process conditions using response surface methodology, with an extraction rate of 18.93%. At present, there is relatively more research on the ultrasonic-assisted extraction of ginger polysaccharides in China. Xia Shulin et al. [19] used ginger powder as the raw material to study the ultrasonic-assisted extraction of ginger polysaccharides, and used orthogonal test methods to optimize the best extraction process, with an extraction rate of 11.32%. Different extraction methods have certain advantages. Innovative technical methods based on experimental optimization methods can lay the foundation for the future industrial production of ginger polysaccharides.

4 Conclusion

Ginger's unique flavoring effect, high nutritional value, potential health benefits and not to be ignored medicinal value make it an economic crop with great development and utilization value. This paper summarizes the current research progress on ginger extract, with a view to providing a reference for the comprehensive utilization of ginger.

References

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