Considerable effect of dimethylimidazolium dimethylphosphate in cinnamon essential oil extraction by hydrodistillation

Abstract

The effect of addition of dimethylimidazolium dimethylphosphate in the maceration step, which precedes hydrodistillation, on yield and composition of the essential oil of cinnamon dried bark and cortex has been evaluated. The use of a 1 : 1 ionic liquid (IL)–water mixture permitted the improvement of the essential oil yield by about 200%. Moreover, an appreciable change in the composition of the essential oils when the IL was added was observed. Noteworthy, an enrichment in (E)-cinnamaldehyde, the active metabolite of cinnamon essential oil, attributable to the degradation of lignin by the IL accompanied the impressive increase in essential oil yield.

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Introduction

Essential oils (EOs), commonly known as volatile oils, are complex mixtures of terpenes, phenylpropanoids and other hydrocarbon constituents, all with a low molecular weight.¹ They can contain more than one hundred compounds in different concentration, although generally only two or three species are present as major constituents at fairly high concentrations (20–70%).² Today, approximately three thousand EOs are known, three hundred of which are commercially important for their industrial applications, especially in the pharmaceutical, agronomic, food, cosmetic and perfume industries.³ Well-known for their fragrance and antiseptic properties, EOs are indeed used to preserve food and as antimicrobial, analgesic, sedative, anti-inflammatory, spasmolytic and locally anesthetic remedies. In particular, Cinnamomum zeylanicum Blume (sin. Cinnamomum verum J. Presl) is a tropical small evergreen tree belonging to the Lauraceae family, which grows wild in Sri Lanka, Madagascar, India and Indonesia, but has been introduced in many tropical countries.³ The cinnamon spice, having the classic look of a small and brown scroll, derives from the inner bark of about three years old branches and is widely applied in Mediterranean and tropical countries in perfumery, flavouring and pharmaceutical industry.⁴ However, cinnamon is also regarded as an effective phytomedicine having anti-inflammatory, antioxidant, antimicrobial, and antidiabetic effects. Much interest is currently focused on proanthocyanidins, one of the main active groups of constituents, due to their promising pharmacological effects against the development of atherosclerotic lesions and different forms of cancer. Many in vitro tests proved that proanthocyanidins are powerful radical-scavengers and have high antioxidant capacity.⁵ The cinnamon bark essential oil (CZEO) is an amber liquid, with a pungent aroma, characterized mainly by the presence of (E)-cinnamaldehyde (from 44% to about 90%).³ It is widely used as flavouring in cola-type drinks, and, to a lesser extent, in bakery goods, sauces, confectionery products and liquors. Moreover, it is used together with nitrite as meat preservative, allowing reduction in nitrite content.^5,6 Traditional used against bacteria, virus and parasites, CZEO has been recently object of investigations showing important therapeutic properties:^7–13 in particular, as antiparasitic,⁸ fungicidal,^9–11 insecticidal,⁸ antioxidant¹³ and antimicrobic,^3,4,11,12 especially due to its content in benzaldehyde, (E)-cinnamaldehyde and linalool.⁹

EOs are volatile liquids, soluble in lipids and organic solvents generally with a lower density than that of water. They are usually extracted at hobbyist and industrial level by steam or hydrodistillation. The relatively simple process of distillation has however as main drawback the very low product yield: in particular, in the case of CZEO it is less than 1% (0.93% ± 0.23 v/w dried weight).³ The low yields and the high market demand make these substances high added-value products and, therefore, it is extremely challenging to improve the process yield.

In a recent work, we have shown that in the case of Rosmarinus officinalis L the addition of specific ionic liquids (ILs) during hydrodistillation improves the EO yield by about 25%.¹ Today, the term ILs defines an extremely large class of compounds, constituted exclusively by ions (generally, organic cations associated to polyatomic anions), which exhibit important properties,¹⁴ such as a negligible vapour pressure, low flammability, high thermal and chemical stabilities and high solvation ability for organic, inorganic and polymeric compounds, including biopolymers such as cellulose, chitine, keratin and lignin.¹⁵ For these unique properties, which can be tailored through an appropriate cation and anion selection, ILs have been proposed as efficient and “greener” solvents in the most diverse applications,¹⁶ including as (co)solvents for the extraction of value-added compounds from natural sources. An exhaustive review about this latter topic has been recently published.¹⁷

In the present work we report the use of 1,3-dimethylimidazolium dimethylphosphate as solvent or co-solvent in the cinnamon dried bark maceration showing its positive effect on the subsequent essential oil extraction process by hydrodistillation.

1,3-Dimethylimidazolium dimethylphosphate has been selected due to the high hydrogen-bond basicity of its anion that represents a conditio sine qua non to have a good dissolution of lignocellulosic materials.¹⁸ Anions able to act as hydrogen bond acceptors favor indeed the dissolution process due to their ability to intercalate themselves between the polysaccharide chains, through the formation of hydrogen bonds with the hydroxyl groups of biopolymers (cellulose and hemi-cellulose). Since cinnamon bark is composed by cellulose, hemi-cellulose and lignin in variable percentage, the selected IL could favor essential oil recover increasing permeation of the bark matrix through a partial dissolution of the structural biopolymers. Moreover, this class of ILs presents also other attracting features: dimethylphosphate-based IL are indeed obtained by a simple one-step synthetic procedure, have low viscosity and high thermal and hydrolytic stability¹⁹ and a relatively low-cost.

During this investigation we have tested the capability of this IL to affect essential oil extraction comparing four different maceration media: deionized water, aqueous solution of NaCl 5%, pure 1,3-dimethylimidazolium dimethylphosphate, aqueous solution of 1,3-dimethylimidazolium dimethylphosphate, 50%. Furthermore, the possible additional effect of ultrasound during maceration in IL was also evaluated.

Experimental

Ionic liquid preparation

Methylimidazole (99%, Sigma-Aldrich) and trimethylphosphate (99%, Sigma-Aldrich) were used without any purification. 1,3-Dimethylimidazolium dimethylphosphate (Fig. 1) was prepared by addition of trimethylphosphate (1.1 eq.) to 1-methylimidazole (1 eq.) and the mixture was heated at 100 °C for 36 h. After cooling, the unreacted trimethylphosphate was extracted with diethyl ether and the resulting liquid was further purified by hydrodistillation. The structure and purity of the recovered yellowish IL (95.2%) was confirmed by NMR analysis. The IL was dried under vacuum.

Fig. 1 Employed IL: 1,3-dimethylimidazolium dimethylphosphate.

Samples pre-treatment

The cinnamon cortex was purchased on a Jordan market in 2012. Crushed dried barks (not rolled) of Cinnamomum zeylanicum Blume were used to prepare 5 identical samples (15 g), which were inserted into a 2 L spherical flask and treated separately as follows:

- [Sample A]: 500 mL of water were added and macerated under agitation for 24 hours; then other 500 mL of water were added and the mixture was hydrodistilled;

- [Sample B]: 500 mL of NaCl (5%) water solution were added and macerated under agitation for 24 hours; then other 500 mL of water were added and the mixture was hydrodistilled;

- [Sample C]: 45 g of IL were added and macerated under agitation for 24 hours; then 1000 mL of water were added and the mixture was hydrodistilled;

- [Sample D]: 25 g of IL and 25 mL of water were added and macerated under agitation for 24 hours; then other 950 mL of water were added and the mixture was hydrodistilled;

- [Sample E]: 45 g of IL were added, then the mixture was sonicated for 1 hour (40 °C, 59 kHz, 70% power), macerated for 24 hours, sonicated again, then 1000 mL of water were added and finally hydrodistilled.

Analogously, crushed dried rolled bark of cinnamon were used to prepare 5 identical samples (15 g), which were put into a spherical flask treated as below:

- [Sample F]: see procedure sample A;

- [Sample G]: see procedure sample B;

- [Sample H]: see procedure sample C;

- [Sample I]: see procedure sample D;

- [Sample J]: see procedure sample E.

Hydrodistillation

Hydrodistillation was performed using a water-recycling Clevenger-type apparatus accordingly to the European Pharmacopoeia. All the different samples were put separately in a 2000 mL spherical flask and heated with a heating mantle to the boiling point for two hours. The essential oil was recovered from the lateral arm of the apparatus and stored in a glass vials at 5 °C until analysis.

GC-FID and GC-MS analyses

The GC analyses were accomplished with a HP-5890 Series II instrument equipped with HP-WAX and HP-5 capillary columns (30 m × 0.25 mm, 0.25 mm film thickness), and with the following conditions: temperature program of 60 °C for 10 min, followed by an increase of 5 °C min⁻¹ to 220 °C; injector and detector temperatures at 250 °C; carrier gas helium (2 mL min⁻¹); detector dual FID; split ratio 1 : 30; injection of 0.5 mL of a 10% hexane solution of the essential oil. For both the columns, identification of the chemicals was performed by comparison of their retention times with those of pure authentic samples and by means of their Linear Retention Indices (LRI) relative to the series of n-hydrocarbons.

GC-EIMS analyses were performed with a Varian CP-3800 gas-chromatograph equipped with a HP-5 capillary column (30 m × 0.25 mm), GC-EIMS analyses were performed with a Varian CP-3800 gas-chromatograph equipped with a HP-5 capillary column (30 m × 0.25 mm; coating thickness 0.25 mm) and a Varian Saturn 2000 ion trap mass detector. Analytical conditions: injector and transfer line temperatures at 220 and 240 °C respectively; oven temperature was programmed from 60 °C to 240 °C at 3 °C min⁻¹; carrier gas helium at 1 mL min⁻¹; injection of 0.2 mL (10% hexane solution); split ratio 1: 30. Identification of the constituents was based on the comparison of the retention times with those of authentic samples, comparing their linear retention indices relative to the series of n-hydrocarbons, and by computer matching against commercial (NIST 98 and ADAMS 95) and home-made library mass spectra built up from pure substances and components of known essential oils. The compositions and the yields of the essential oils obtained with the different methods are reported in Table 1.

Table 1 Composition and relative percentages of volatile compounds in the different C. zeylanicum essential oils (CZEOs)^a

Compound	LRI	Not rolled cinnamon bark					Rolled cinnamon cortex
		Sample A	Sample B	Sample C	Sample D	Sample E	Sample F	Sample G	Sample H	Sample I	Sample J
a LRI, linear retention index. Compounds with relative percentages smaller or equal to 0.1% are considered as traces (tr.). The components are listed in order of their elution on the DB-5 column. Chemical compounds showed relative percentages smaller than 0.01% and lacking LRI (lit.) were excluded from the table and from the analysis.
α-Thujene	932	tr		tr	tr	tr	tr	tr	tr	tr	tr
Tricyclene	932	0.2	0.1	0.4	0.4	0.5	0.3	0.4	0.8	0.8	0.6
Camphene	955	0.2	0.2	0.2	tr	0.2	0.1	tr	0.3	0.3	0.1
Benzaldehyde	963	0.2	0.2	3.5	1.3	0.8	0.2	0.2	1.8	2.9	0.2
Sabinene	978	tr	tr	tr	tr	tr	tr	tr	tr	tr	0.1
β-Pinene	981	tr	tr	tr	tr	0.2	tr	tr	0.2	0.2
6-Methyl-5-hepten-2-one	987	tr	tr				tr	tr			tr
Myrcene	993	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
δ-3-Carene	1001					tr
δ-2-Carene	1012				tr	tr	tr	tr
α-Terpinene	1019										tr
o-Cymene	1024	tr	tr	0.1	tr	0.2	tr	tr	0.2	0.2	tr
Limonene	1032	0.2	0.1	0.3	0.2	0.4	0.3	0.3	0.6	0.6	0.3
1,8-Cineole	1036	0.2	0.2	0.7	tr	1.3	0.1	0.1	2.1	1.6	0.2
(Z)-β-Ocimene	1042	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
Benzene acetaldehyde	1047			0.2	tr	tr			tr	tr	tr
γ-Terpinene	1062	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
Acetophenone	1068	tr	tr	0.3	tr	tr	tr	tr	0.5	0.4	tr
Terpinolene	1090			tr		tr			tr	tr	tr
Linalool	1100	tr	tr	tr	tr	0.2	tr	tr	0.2	0.2	tr
n-Nonanal	1104						tr	tr			tr
endo-Fenchol	1117					tr	tr	tr	0.1	tr	tr
α-Campholenal	1127			tr		tr
cis-Limonene oxide	1137								tr	tr
trans-Limonene oxide	1142			tr					tr	tr
Camphor	1145	7.2	7.3	tr	tr	tr	tr	tr	0.3	tr	0.7
Camphene hydrate	1150	tr	tr	0.1					0.2	0.1	tr
Isoborneol	1156			tr		tr			tr		1.5
Hydroxycinnamaldehyde	1167	tr	tr	0.2	0.2	0.4	tr	tr	0.3	0.1
Borneol	1169	4.3	4.4	0.7	0.2	0.6	0.2	0.2	0.9	0.5
4-Terpineol	1180	0.2	0.2	tr	tr	0.7	tr	tr	0.6	0.2	tr
para-Cymen-8-ol	1185					tr				tr
para-Methyl acetophenone	1186			tr	tr	tr	tr	tr	tr		tr
α-Terpineol	1192	0.4	0.3	0.5	tr	0.8	tr	tr	2.2	0.8	0.1
Estragole	1196					tr	tr	tr			tr
(Z)-Cinnamaldehyde	1218	1.1	1.1	3.4	1.6	1.3	1.0	1.0	1.5	2.0	1.1
Cumin aldehyde	1242			0.1	tr	tr	tr	tr	0.1	0.1	tr
Carvone	1246					tr	tr	tr		tr	tr
trans-Ascaridol glycol	1269					tr			0.5	0.1
(E)-Cinnameldehyde	1270	67.8	68.6	84.4	91.1	91.1	77.4	77.9	76.2	86.2	89.1
Isobornyl acetate	1287	0.8	0.6	0.9		0.7			2.4	0.9
(Z)-Methyl cinnamate	1300								0.4	0.1
δ-Elemene	1340	0.2	0.1		tr					tr
α-Terpinyl acetate	1352								tr
Cyclosativene	1371						0.2	0.2			tr
α-Ylangene	1372	tr	tr				tr	tr
α-copaene	1376	2.7	2.6	tr	0.5	0.1	3.7	3.6	0.3	0.2	1.1
iso-Longifolene	1385	tr	tr		tr						tr
β-Elemene	1392	tr	tr		tr		tr	tr			tr
Sativene	1395	tr	0.1		tr		0.1	0.1			tr
Longifolene	1404	tr	tr				tr	tr			tr
Sesquithujene	1417					tr	tr	tr		tr
β-Caryophyllene	1418	0.2	0.2			tr	tr	tr			tr
4,8-β-Epoxy-caryophyllane	1425						tr	tr			tr
β-Copaene	1429						tr	tr			tr
trans-β-Bergamotene	1437	0.1	tr				tr	tr		0.5	tr
Coumarin	1435			1.3					0.2
(E)-Cinnamyl acetate	1446			1.6	0.1	0.3	0.2	0.1	4.1	0.9
α-Humulene	1456	0.3	0.2				0.2	0.2			tr
γ-Muurolene	1477	0.5	0.5	tr	0.1	tr	0.7	0.8		tr	0.3
α-Amorphene	1480	tr	tr				tr	tr			tr
ar-Curcumene	1484	0.2	0.2		tr		0.2	0.3			tr
10,11-Epoxy-calamenene	1492	tr	tr		tr		tr	tr			tr
Viridiflorene	1495	0.1	0.2			tr	0.3	0.2			tr
α-Muurolene	1499	1.9	1.8	tr	0.3	tr	1.9	1.9	0.4	0.2	0.5
β-Bisabolene	1509	tr	0.1				0.1	0.2	0.2		tr
γ-Cadinene	1512	0.2	0.2		0.1		0.3	0.3			0.1
trans-Calamenene	1529			tr	0.3	tr				tr	0.8
δ-Cadinene	1523	3.0	3.0				4.9	5.0	0.2
trans-Cadina-1(2),4-diene	1533	0.6	0.7		1.2		0.3	0.3			0.5
(E)-ortho-Methoxy cinnamaldehyde	1536	0.7	0.7				0.2	0.2			0.3
α-Calacorene	1542	0.8	0.8				0.6	0.6
Caryolan-8-ol	1573						tr	tr		tr	0.1
Caryophyllenyl alcohol	1571	0.2	0.2	tr	0.1		0.1	0.2	tr
Caryophyllene oxide	1582	0.2	0.2	tr	0.2	0.3			0.3	0.2
Gleenol	1586	0.1	0.1		tr		0.3	0.3			0.1
Humulene epoxide II	1607	0.1	0.1		0.1	tr
1,10-di-epi-Cubenol	1614	0.2	0.2		0.3		0.2	0.2			0.1
10-epi-γ-Eudesmol	1623	tr	0.1				tr	tr			tr
1-epi-Cubenol	1630	0.5	0.4	tr		tr	0.6	0.6	0.2	tr	0.4
γ-Eudesmol	1634	tr	tr				tr	tr
τ-Cadinol	1640										0.7
epi-α-Muurolol	1645	1.1	1.2	tr	0.6	tr	1.7	1.7	0.2	tr	0.5
α-Muurolol	1651	0.8	0.8	tr	0.6	tr	1.0	1.1	0.1	tr
α-Cadinol	1655	0.2	0.3		0.2	tr	0.4	0.4	0.1	tr	0.2
β-Bisabolol	1672						0.2	0.2
Cadalene	1676	0.2		0.1			0.4	0.2			tr
epi-α-Bisabolol	1685		0.2		tr		0.2	0.4			0.1
Not terpenic compounds (NT)		0.2	0.2	5.2	1.3	0.8	0.2	0.2	2.5	3.2	0.2
Hydrogenated monoterpenes (MH)		0.5	0.5	0.9	0.6	1.4	0.7	0.6	2.0	2.0	1.1
Oxygenated monoterpene (OM)		13.0	13.0	3.0	0.2	4.3	0.3	0.3	9.5	4.4	2.4
Hydrogenated sesquiterpenes (SH)		11.0	10.7	0.1	2.6	0.1	13.9	13.7	1.1	0.9	3.2
Oxygenated sesquiterpenes (OS)		3.5	3.8	0.0	2.1	0.3	4.7	5.0	0.9	0.2	2.2
Phenylpropanoids (PP)		69.6	70.4	89.6	93.0	93.1	78.7	79.2	82.3	89.3	90.5
Total (%) identified		97.7	98.5	98.9	99.8	100.0	98.6	99.0	98.4	100.0	99.7
EO yields (% w/w)		0.89	0.97	1.90	2.63	0.89	1.05	1.26	1.79	1.76	1.02

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Results and discussion

Cinnamomum zeylanicum Blume was selected for its commercial availability, also considering the important task that its essential oil is extensively used in cosmetics and food and has important therapeutic properties. Moreover CZEO can be obtained in reasonable yield for easy laboratory tests and the lignocellulosic nature of the matrix containing the essential oil could give us the opportunity to evaluate the effect of ILs when used as solvents or co-solvents in the predistillation step, i.e. maceration phase.

Composition and yield of CZEO, obtained by hydrodistillation of samples arising from different maceration procedures, i.e. carried out using pure water, aqueous solution of NaCl (5%), pure 1,3-dimethylimidazolium dimethylphosphate and an 1 : 1 aqueous solution of 1,3-dimethylimidazolium dimethylphosphate, are reported in Table 1 and Fig. 2. Altogether, 88 constituents were identified in the different examined samples, accounting for 98.4–100% of the whole essential oil compositions.

Fig. 2 C. zeylanicum essential oil yield (% w/w) in samples A–J.

CZEO yield and composition strongly depended on pre-treatment procedure. The classic hydrodistillation method gave a 1.02–1.05% essential oil yield (Table 1). Contrary to previously reported data for other essential oils, no significant differences were obtained by preventive 24 h maceration in the presence of inorganic salts that should increase the ionic strength. The use of a 5% aqueous solution of NaCl for maceration (samples B and G) was indeed unable to affect CZEO yield (0.97 and 1.05%, respectively) and EO composition. On the contrary, the yield increased significantly when cinnamon was pre-treated with IL before hydrodistillation (samples C and H, with a yields of 1.90 and 1.79%, respectively). However it is interesting to note that the most relevant result was obtained when a 1 : 1 IL–water mixture was employed for cinnamon maceration; in fact the EO yield reached indeed the significant value of 2.63% in sample D. This increase in the yield (around 200%) is very important in the case of essential oils being of high value added products. Furthermore, the fact that the IL exerts its positive action also in the presence of relevant amounts of water, actually water appears to increase IL activity, strongly suggest a selective effect of this IL on lignin component. Although the presence of water generally has a negative effect on the ability of ILs to dissolve cellulose, it has been recently shown that the addition of an appropriate amount of water to some dialkylimidazolium ILs having methanesulfonate, acetate, bromide and dibutylphosphate as counteranions facilitates lignin dissolution.²⁰

Finally, it is noteworthy that attempts to further increase EO yield coupling the IL pretreatment with ultrasound failed. Samples E and J gave a EO yield comparable to those obtained by conventional procedures (samples A, B, F, G): surprising, ultrasound appears to dissolve any IL effect in terms of productivity. However, a more in deep analysis of oil composition shows a product distribution of samples E and J similar to the other samples arising from maceration in IL or in the presence of IL, suggesting a negative effect exerted by ultrasound on some specific classes of compound.

Related to the chemical composition, it is to remark that all the essential oils obtained by hydrodistillation were almost exclusively formed by phenylpropanoids, accompanied by small amounts of oxygenated monoterpenes and sesquiterpene hydrocarbons (Table 1). However, the amounts of oxygenated monoterpenes and sesquiterpene hydrocarbons decreased in the hydrodistilled samples arising from maceration procedures carried out in the presence of IL (samples C, D, E, H, I, J). Actually, these samples were characterized by a significant increase in phenylpropanoid components (from 69.6 to 93.1%). In particular, (E)-cinnamaldehyde, the principal CZEO compound, was present in significantly lower amount in samples A, B, F and G (67.8, 68.6, 77.4 and 77.9%, respectively) with respect those treated with the IL during the maceration process, samples D and E, where (E)-cinnamaldehyde is 91.1%. Analogously, (Z)-cinnamaldehyde (1.0–3.4%), tricyclene (0.1–0.8%), benzaldehyde (0.2–3.5%), limonene (0.2–0.6%) and 1,8-cineole (0.1–2.1%) increased in the sample pretreated with IL whereas camphor (7.3–<0.1%), borneol (4.4–0.1%) and α-copaene (3.7–0.1%) were present in lower amounts in these samples.

Related to the mechanism determining the IL effect on the maceration-hydrodistillation process, it is noteworthy that the inability of NaCl to increase significantly essential oils yield allows to conclude that the ionic strength is a not relevant factor in this EO extraction process. Furthermore, EO yields and chemical composition strongly suggest that the presence of the IL in the maceration phase favours the CZEO release probably determining a partial dissolution of the lignin constituting the cinnamon barks and cortex. Actually, the highest EO yield was obtained when the cinnamon samples were macerated in a 1 : 1 mixture, IL–water before hydrodistillation. As previously observed for lignin dissolution,²⁰ the presence of water, with its inflating power, probably favours the action of the ionic liquid, which become more “available” to penetrate inside the plant material. The diffusion constants of IL cations and anions increase indeed substantially as the water content increases.²¹ Furthermore, the addition of a proper amount of water reduces the strength of the cationic stacking as well as of the electrostatic anion–cation interactions.²²

Strictly related to the ability of the IL to favour dissolution of the lignocellulosic material is the observed increase in (E)-cinnamaldehyde which can be rationalized considering a partial degradation of the lignin, which is actually a phenylpropanoid polymer, operated by the IL.

Related to the presence of camphor in a relatively high amount in samples A and B, this is attributable to the “quality” of the phytomaterial available on the market, which is probably contaminated by the cheaper root bark. As reported by Senanayake et al.,²³ a high percentage of camphor should be found only in CZEO arising from root barks: stem barks contain indeed camphor in traces.

Finally, it is necessary to stress that the negligible vapour pressure of the employed IL and its chemical and thermal stability are fundamental properties that can improve CZEO isolation/separation. The stability of dimethylimidazolium dimethylphosphate under the process conditions (i.e. in the presence of water for a long time and under prolonged hydrodistillation conditions) has been verify: determination of physical constants and spectroscopic measurements on the recovered IL evidenced no appreciable degradation. Furthermore, the non-flammability of the employed IL is another useful property in particular in this kind of application considering that small and medium-sized craft enterprises often use open flame to heat the still apparatus.

Conclusions

In conclusion, the use of dimethylmidazolium dimethylphosphate together with water in the treatment of cinnamon bark and cortex, before hydrodistillation, gave a surprising increase in EO yield (around 200%) and contemporaneously assured a high quality of the recovered essential oil, due to the non-volatility of the used IL. Furthermore, the enrichment in (E)-cinnamaldehyde observed in the samples treated with IL during maceration, probably due to a partial dissolution of lignin, could be considered an additional positive effect of the ionic liquid since this compound is considered the active metabolite of cinnamon essential oil.²⁴

Notes and references

1. G. Flamini, B. Melai, L. Pistelli and C. Chiappe, RSC Adv., 2015, 5, 69894–69898.
2. F. Bakkali, S. Averbeck, D. Averbeck and M. Idaomar, Food Chem. Toxicol., 2008, 46, 446–475.
3. M. Unlu, E. Ergene, G. V. Unlu, H. S. Zeytinoglu and N. Vural, Food Chem. Toxicol., 2010, 48, 3274–3280.
4. G. Singh, S. Maurya, M. P. de Lampasona and C. A. N. Catalan, Food Chem. Toxicol., 2007, 45, 1650–1661.
5. Y. Liu, L. Yang, Y. Zu, C. Zhao, L. Zhang, Y. Zhang, Z. Zhang and W. Wang, Food Chem., 2012, 135, 2514–2521.
6. M. Moarefiani, M. Barzegari and M. Sattari, J. Food Biochem., 2013, 37, 62–69.
7. G. Fico, G. Flamini, L. J. Zaralli and S. Perrucci, Phytomedicine, 2007, 14, 227–231.
8. Y.-C. Yang, H.-S. Lee, S. H. Lee, J. M. Clark and Y.-J. Ahn, Int. J. Parasitol., 2005, 35, 1595–1600.
9. L. Ranasinghe, B. Jayawardena and K. Abeywickrama, Lett. Appl. Microbiol., 2002, 35, 208–211.
10. A. Simić, M. D. Soković, M. Ristić, S. Grujić-Jovanović, J. Vukojević and P. D. Marin, Phytother. Res., 2004, 18, 713–717.
11. M. T. Baratta, H. J. D. Dorman, S. G. Deans, A. C. Figueiredo, J. Â. G. Barroso and G. Ruberto, Flavour Fragrance J., 1998, 13, 235–244.
12. A. R. Shahverdi, H. R. Monsef-Esfahani, F. Travasoli, A. Zaheri and R. Mirjani, J. Food Sci., 2007, 72, 5055–5058.
13. J. V. Kamath, A. C. Rana and A. R. Chowdhury, Phytother. Res., 2003, 17, 970–972.
14. (a) P. Wasserscheid and T. Welton, Ionic Liquids in Synthesis, Wiley-VCH, Weinheim, 2nd edn, 2008; (b) J. P. Hallett and T. Welton, Chem. Rev., 2011, 111, 3508; (c) H. Ohno, Electrochemical Aspects of Ionic Liquids, John Wiley &Sons, Hoboken, NJ, 2nd edn, 2011; (d) C. Chiappe and D. Pieraccini, J. Phys. Org. Chem., 2005, 18, 275.
15. G. Cevasco and C. Chiappe, Green Chem., 2014, 16, 2375.
16. N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123.
17. H. Passos, M. G. Freire and J. A. P. Coutinho, Green Chem., 2014, 16, 4786.
18. (a) T. Vancov, A. S. Alston, T. Brown and S. McIntosh, Renewable Energy, 2012, 45, 1–6; (b) C. Froschauer, M. Hummel, G. Laus, H. Schottenberger, H. Sixta, H. K. Weber and G. Zuckerstätter, Biomacromolecules, 2012, 13, 1973–1980.
19. E. Kuhlmann, S. Himmler, H. Giebelhaus and P. Wasserscheid, Green Chem., 2007, 9, 233–242.
20. Y. Wang, L. Wei, K. Li, Y. Ma, N. Ma, S. Ding, L. Wang, D. Zhao, B. Yan, W. Wan, Q. Zhang, X. Wang, J. Wang and H. Li, Bioresour. Technol., 2014, 170, 499–505.
21. (a) S. Stevanovic, A. Podgorsek, A. A. H. Padua and M. F. Costa Gomes, J. Phys. Chem. B, 2012, 116, 14416–14425; (b) A. A. Niazi, B. D. Rabideau and A. E. Ismail, J. Phys. Chem. B, 2013, 117, 1378–1388.
22. T. Mendez-Morales, J. Carrete, O. Cabeza, L. J. Gallego and L. M. Varela, J. Phys. Chem. B, 2011, 115, 6995–7008.
23. U. M. Senanayake, T. H. Lee and R. B. H. Wills, J. Agric. Food Chem., 1978, 26, 822–824.
24. E. A. Monu, C. Techathuvanan, A. Wallis, F. J. Critzer and P. M. Davidson, Food Control, 2016, 65, 73–77.

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