Extraction of Essential Oil from Citrus junos Peel using Supercritical Carbon Dioxide

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1 Extraction of Essential Oil from Citrus junos Peel using Supercritical Carbon Dioxide Munehiro Hoshino 1,2, Masahiro Tanaka 2, Mitsuru Sasaki 1, Motonobu Goto 1 1 Graduate School of Science and Technology, Kumamoto University, Japan 2 Maruboshi Vinegar Co., Ltd., Fukuoka, Japan Correspondence: mgoto@kumamoto-u.ac.jp ABSTRACT Citrus essential oil was extracted from peel of Citrus junos (yuzu) that is typical citrus fruit in Japan with supercritical carbon dioxide in a semi-continuous flow extractor. Extraction was carried out at 333K and 10-30MPa with supercritical carbon dioxide in order to optimize the extraction conditions. Oil was also extracted by using soxhlet apparatus with hexane and ethanol as a solvent for 4 hours, steam distillation for 24 hours, and cold-pressing for 3 days to compare the efficiency of supercritical carbon dioxide extraction. GC-MS was used to analyze the contents of essential oil, and GC-FID was used to analyze quantitatively. Among the conditions studied, the highest extraction efficiency was observed at pressure of 20MPa and temperature of 333K that was about 1.278% of feed material. As determined by GC-MS, the extracted oil contained 79.76% of monoterpenes, 4.42% of sesquiterpenes and 13.5% of oxygenated compounds. Oxygenated compounds consist of the aldehyde, alcohol, and the ketone, and these contribute to the smell greatly. The other oils extracted from steam distillation and cold-pressing contained 3.02% and 1.05% of oxygenated compounds respectively. As determined by GC-FID, the major compound of oil extracted was limonene, and it was found to be 9.28mg / g feed material. For comparison with soxhlet extraction and steam distillation, the extraction efficiency of soxhlet extraction was higher than supercritical carbon dioxide extraction and steam distillation. 1. INTRODUCTION Keywords: supercritical carbon dioxide, Essential oil Citrus Junos, called yuzu, an evergreen tree that is harvested mainly in Kochi Prefecture in Japan. Yuzu is a very well-known citrus fruit in the south part of Japan. Annual production of the fruit is tons (2004). About 65-75% of those are utilized for juice processing, leaving 25-35% handled in the fresh-fruit market. Since yuzu has a particular flavor smell, for its essential oils are widely used in food, beverage, pharmaceutical, perfume, and cosmetic industries. The essential oil is usually extracted from waste of juice processing residue by cold pressing. The cold-pressing process is not suitable for yuzu because of its thick peel. The essential oil of citruses exists in the oil gland in the peel, and can be obtained by pressing. However, it is difficult for the peel of yuzu to obtain the essential oil in pressing because it is thick, and the interaction with oil gland with albedo is strong. Citrus oils from Colombian lemon and orange have been extracted by steam distillation and/or cold pressing and the compositions also have been compared at different stages of maturity of the fruits by Tirado et al. (1) The conventional production methods of oils such as steam distillation or solvent extraction can lead to degradation of heat sensible compounds and partial hydrolysis of water sensible compounds. Supercritical fluid extraction is an effective alternative process to the conventional methods. Supercritical fluid extraction has received increasing attention in a variety of fields due to the following factors: (i) supercritical fluids provide superior solubility and mass transfer rates; (ii) fluid property can be turned by the pressure or temperature. CO2 is mostly used as supercritical fluid for the extraction of citrus oils from natural materials because of its low critical temperature that prevents the thermal degradation of volatile components of the citrus oils, no residual problem, odorless and colorless properties. It is also non-toxic and is generally accepted as a harmless ingredient of foods and beverages, and easily available. The physical properties of CO2 that make it widely used in extraction process are low surface tension and viscosity, and high diffusivity. The diffusivity of supercritical fluids is one to two orders of magnitude than those of other liquids, which permits rapid mass transfer, resulting in a larger extraction rate than that obtained by conventional methods. By the supercritical CO2 with such a high diffusive, it is expected that essential oil is efficiently extracted from the thick peel of yuzu. The extraction of flavoring materials from fruit juice and many other natural products with supercritical CO2 has been carried out by a number of workers as Shutlz et al. (2), Caragay et al. (3), and Moyler et al. (4). This method shows a

2 great potential in replacing conventional methods such as liquid solvent extraction and steam distillation by Meyer-Warnod (5). There are monoterpene, sesquiterpene, and oxygenated compounds in the aroma composition contained in the essential oil of citruses. It is known that the monoterpene that centers on limonene doesn't contribute to the aroma so much. On the other hand, the sesquiterpene and the oxygenated compound with few contents are a lot of one with a strong aroma comparatively, and characterize a peculiar smell to the citrus. The odorant of feature yuzu is identified in the cold-press oil obtained from the yuzu peel. (6) In this work, the extraction of the essential oil was tried by using the supercritical carbon dioxide from the peel of yuzu. And, the optimum extraction condition was examined, and the element ratio and amount of the aroma composition of the extracted essential oil with the essential oil that had been obtained by conventional production methods were compared. 2. MATERIALS AND METHODS Materials. Yuzu fruit samples were cultivated at farm in Fukuoka Prefecture, Japan. Samples were harvested before it matured in green, in October The peel on the surface was shaved off during freshness, and peel was stored at 253K until extraction. And the peel was carved small immediately before extraction. Supercritical CO 2 Extraction. An apparatus for supercritical CO 2 extraction (AKICO Co., Ltd., Tokyo) was a semi-continuous flow extractor. A schematic diagram of the supercritical CO 2 apparatus is shown in Figure 1. Initially, about 40g of carved yuzu peel was placed in the extractor of 20cm height, 7cm inside diameter and 500ml capacity. Liquid CO 2 from a cylinder with siphon attachment was passed through a chiller kept at 262K and compressed CO2 was flowed into the extractor placed in the heating bath that was maintained at the operating temperature. The exit fluid from the extractor was expanded to a pressurized separator at 2-2.5MPa and 273K by back-pressure regulator (BPR)1 and then expanded to ambient pressure by BPR 2. The pressure in the extractor was controlled by BPR 1, while the pressure in the separator was controlled by BPR 2. CO 2 flow rate was measured by flow meter and dry gas meter. Oil extracted was collected from the pressurized separator at every 60mins for 300min and weighted immediately after collection. Extraction was carried out at temperature of 333K, pressure of 10,20 and 30 MPa, CO 2 flow rate of m 3 /s based on CO 2 exiting the separator at room temperature and 0.1MPa. Back pressure valve 1 Back pressure valve 2 Flow meter CO 2 Extractor Dry gas meter CO 2 cylinder Chiller High pressure pump Heating bath Extract Water bath Pressurized separator Figure 1. Schematic diagram of the experimental apparatus GC-MS Analysis. The oil samples diluted to 20 times by ethanol and the samples obtained by the solvent extraction that uses hexane and ethanol were analyzed with GC-MS (Hewlett-Packard-5890 series, Palo Alto, CA), coupled with a mass selective detector (HP 5972). The column used was a HP-5MS phenyl methyl siloxane capillary (30m x 0.25mm i.d.; film thickness, 0.25 m). The GC conditions were as follows: oven temperature 323K for 2min, then programmed from 323 to 533K at 3K min -1 and then 533K for 3min; injector temperature, 523K; injection volume, 0.2 l; injector and detector temperature, 523K; the split ratio, 99:1; total carrier gas (helium) flow rate, 24ml/min; and ionizing energy, 70eV. As for the main components limonene and linalool were identified by comparison of mass spectra and retention times with those of pure standards. For other components, the probability-based matching algorithm was employed for finding the most probable match in the reference library (NIST library of mass spectra and subsets, HPG 1033A). The weight composition was calculated from the GC peak area. GC-FID Analysis. quantity of each samples were analyzed with GC (Shimadzu GC-14A FID), coupled with

3 Abundance Oil yield ( g oil / g sample ) SECRETARIAT USE; Header should be blank. a flame ionization detector (FID). Peak area were integrated with Shimadzu C-R6A Chromatopack integrator. The column used was a HP-5MS phenyl methyl siloxane capillary (30m x 0.25mm i.d.; film thickness, 0.25 m). The GC conditions were as follows: oven temperature 343K for 2min, then programmed 343 to 453K at 5K min-1; injection volume, 0.2 l; injector and detector temperature, 523K. Authentic compound of dodecane (WAKO) was used as internal standard. The weight composition was calculated from the GC peak area. 3. RESULTS AND DISCUSSION Effect of Pressure on the Supercritical CO 2 Extraction. Yuzu peel was used as feed materials for the extraction of citrus oil with supercritical CO 2 at 333K and 10-30MPa. The extracts consist of oil layer and the water layer. The yield was defined as the weight of extracted oils per 100g of feed materials. Figure 2 shows the change in the extraction efficiency of the extracted yuzu oil for the consumption of CO 2 under the pressure of 10-30MPa. Oil was extracted for five hours. The plot shows the yield of the oil that had been collected every 60min. The extraction of oil ended until almost three 180min later at each condition. The extraction efficiency of oil became the maximum at the pressure of 20MPa. On the other hand, the extraction efficiency has decreased when pressure was increased. Yield of oil at the pressure of 20MPa was 1.278% MPa 20MPa 30MPa CO 2 consumed ( g CO 2 / g sample ) Figure 2. Extraction efficiency at 333K GC-MS. Components in the extract that had been obtained by the solvent extraction, the cold-press method, the steam-distillation method, and the supercritical CO 2 extraction method were compared with GC-MS analysis. Figure 3 showed each of the chromatograms. As for the extract obtained by the solvent extraction (Figure 3, a, and b), compared with other extraction methods, content of limonene that was the monoterpene compound, was large and the ratio of the oxygenated compound and the sesquiterpene was low. Especially, the oil obtained by the supercritical CO 2 extraction was comparatively low content of limonene, and high content of the sesquiterpenes and the oxygenated compound named linalool. a. Extraction with ethanol b. Extraction with hexane Time (min) Figure 3. GC-MS analysis of extract from yuzu peel of each extraction method

4 Abundance SECRETARIAT USE; Header should be blank. c. Cold-press d. Steam distillation e. Supercritical CO 2 Monoterpenes Sesquiterpenes, Oxygenated compounds Nonevolatile compounds Time (min) Figure 3. GC-MS analysis of extract from yuzu peel of each extraction method Table 1 shows the aroma components in the supercritical extraction oil. The contents of sesquiterpenes and the oxygenated compound of the aroma composition detected later than linalool were considerably higher than that obtained by the other extraction methods. Table 1. Composition of supercritical CO2 extraction oil Peak NO. Retention Time (min.) Component Peak % (w /w ) Thujene tr α-pinene Sabinene tr (-)-β-pinene β-myrcene α-phellandrene α-terpinene tr α-ocimene γ-terpinene Carene tr (+)-2-Carene p-cymenene tr p-mentha-1,5,8-triene tr Terpinene-4-ol Linalyl propanoate Decanal tr (+)-Carvone tr Piperitone tr Thymol Carvacrol tr Terpinolene (+)-Camphene α-cubebene tr Copaene (1-Methylethylidene)bicyclo[4.1.0]heptan tr β-cubebene tr (1,1-Diethylpropyl)benzene Zingiberene tr Caryophyllene Calarene tr Elixene α-caryophyllene tr cis-β-farnesene γ-muurolene tr β-cubebene ,5-Dimethyl-3-methylene-1,5-heptadiene δ-cadinene Elemol tr Elixene Camphene tr Fenchone Geraniol formate 0.29

5 Table 2 shows the comparison of the content aroma for the various extraction methods. As the content of the sesquiterpenes and the oxygenated compound thought to be a greatly related to the feature of the flavor the citrus oil, flavor the oil that had been obtained by the supercritical CO 2 extraction may be the highest quality. Table 2. Comparison of aroma composition percentage contents of extract Extraction method Monoterpene (%) Sesquiterpene (%)Oxygenated compounds (%) Extraction with ethano 91.5 tr 1.24 Extraction with hexane 95.1 tr 2.99 Cold-press Steam distillation Supercritical CO GC-FID. Table 3 shows the yield of limonene and yield of oil obtained by the various extraction methods. The quantity of limonene in the extracted material that had been obtained by the solvent extraction was numerous. Yield of limonene obtained by the supercritical fluid extraction is about 15% when of the yield of obtained by the solvent extraction. But extract with solvent has some problems. The first of all, the influence on the environment of removed solvent. Secondary, yield of the aroma composition decreases along with the removal of the solvent and safety as commodity after solvent removal. Moreover, Table 3 shows yield of the oil obtained by the cold- press method, the steam-distillation method, and the supercritical CO 2 extraction method. Yield of the oil that had been obtained by the supercritical CO 2 extraction was about 30 times larger than the cold-press oil. Though yield of the steam distillation was higher than that of supercritical CO 2 extraction, the smell of oil was quite different from the aroma of the fresh yuzu. This might originate the fact that the oil that adheres to the piping of the extractor and the part of BPR cannot be collected. It is thought that there is room for the improvement also in the collection of the essential oil component with the separator. In conclusion, it succeeded in obtaining a near essential oil by the high-yield by the smell of nature even if there was a problem in yield. Table 3. Yield of limonene by GC-FID analysis and Yield of oil. Extraction method (g) Materials (g) Yield of limonene (%) Yield of oil (%) Extraction with ethanol Extraction with hexane Cold-press Steam distillation Supercritical CO REFERENCES (1) C. B. Tirado, E.F Stashenko, M.Y. Combariza, J.R. Martinez, Comparative Study of Colombian Citrus Oils by High-Resolution Gas Chromatography and Gas Chromatography-Mass Spectrometry. J.of Chromatography A, 1995, 697, (2) W. G. Shutlz, J.N. Randall, Liquid Carbon Dioxide for Selective Aroma Extraction. Food Technol, 1970, 24, (3) A. B. Caragay, Supercritical Fluids for Extraction of Flavor and Fragrance from Natural Products. Perfum and Flavor, 1981, 6, (4) D. A. Moyler, Carbon Dioxide Extracted Ingredients for Fragrance. Perfum and Flavor, 1984, 9, 109 (5) B. Meyer-Warnod, Natural essential oils. Perfum and Flavor, 1984, 9, 93. (6) H. S. Song, M. Sawamura, T. Ito, K. Kawashimo and H. Ukeda, Quantitative Determination and Characteristic Flavor of Citrus junos (yuzu) Peel Oil. Flavor and Fragrance J, 2000, 15, ACKNOWLEDGMET This work was partly supported by Kumamoto University 21 st century COE Program Pulsed Power Science.