Guanghui Chen,Fengrui Sun,Shougui Wang,Weiwen Wang,Jipeng Dong,Fei Gao,*

1 Key Laboratory of Mutiphase Flow Reaction and Separation Engineering of Shandong Province,College of Chemical Engineering,Qingdao University of Science and Technology,Qingdao 266042,China

2 Fundamental Chemistry Experiment Center(Gaomi),Qingdao University of Science and Technology,Gaomi 261500,China

Keywords:Cinnamon oil Extraction Ultrasound Distillation Optimization Chemical composition

ABSTRACT Cinnamon essential oil with many bioactivities is an important raw material for the production of various chemicals,and the conventional hydrodistillation(HD)for cinnamon oil extraction always require a longer extraction time.In this work,ultrasound-assisted hydrodistillation extraction(UAHDE)technique was employed to enhance the extraction efficiency of essential oils from cinnamon barks.The parameters with significant effects on the essential oil extraction efficiency(ultrasound time,ultrasound power,extraction time,liquid–solid ratio)were optimized,and the proposed UAHDE was compared with the conventional HD extraction in terms of the extraction time,extraction yield,and physicochemical properties of extracted oils.Compared to the HD extraction,the UAHDE resulted in a shorter extraction time and a higher extraction yield.Using GC–MS analysis,the UAHDE provided more valuable essential oil with a high content of the vital trans-cinnamaldehyde compounds compared with the HD.Scanning electron micrograph(SEM) confirmed the efficiency of ultrasound irradiation for cinnamon oil extraction.In addition,the analysis of electric consumption and CO2 emission shows that the UAHDE process is a more economic and environment-friendly approach.Thus,UAHDE is an efficient and green technology for the cinnamon essential oil extraction,which could improve the quantity and quality of cinnamon oils.

1.Introduction

Essential oil,generally defined as volatile oils containing different organic components extracted from the aromatic plants,has been widely used in foods,drinks,cosmetics,cleaning products,fragrances,pesticides and medicines industries[1–3].Among the essential oil-producing plants,Cinnamomum cassia(also called cinnamon)belonging to the Lauraceae family is an important spices and traditional medicinal materials extensively distributed in China,India,Vietnam,Seychelles,Madagascar and SriLanka,and China is the major cultivating country of cinnamon distributed in the southern provinces[4,5].

The essential oil extracted from the cinnamon plant contains some vital bioactive components of terpenes and aromatic compounds,making cinnamon oil exhibits remarkable antimicrobial,antibacterial,anti-inflammatory,antiallergy and anticancer activities [6,7].Thus,cinnamon oil has been widely used in medicine industry as an important raw material for the production of various pharmaceuticals.In addition,recently,for human health,extensive efforts have been devoted to the elimination of synthetic chemical additives from the food production,and cinnamon oil has been used in food industry as the natural additives,condiments and flavoring agents due to their excellent carminative,antioxidant and preservative activities [8,9].Cinnamon oil can be extracted from different parts of cinnamon plants including barks,leaves,twigs,calyxs,seeds,etc.Among them,the bark of cinnamon is regarded as the most ideal commercial source of cinnamon raw materials owing to its higher contents of essential oils and trans-cinnamaldehyde than other parts of cinnamon which is a major and important bioactive ingredient for cinnamon oils[10,11].

The traditional technologies for the essential oil extraction from plant materials mostly rely on expression,organic solvent extraction,hydrodistillation(HD)and steam distillation[12–14].The traditional technologies have some inherent disadvantages,such as the lower extraction yield of the expression method and the toxic solvent residue in essential oils of the organic solvent extraction.HD is currently the most widely used commercial technology for the essential oil extraction from the medicinal herbs/plants due to low costs and easy operations.However,it also suffers from some disadvantages of the longer extraction time,resulting in the loss of the volatile and thermally sensitive components of essential oils during the extraction process,which seriously affect the quantity and quality of essential oils [15,16].Recently,several novel techniques have been developed for the essential oil extraction from plants,including supercritical fluid extraction[17],microwave-assisted extraction (MAE) [18],and ultrasound-assisted extraction(UAE)[19].Among them,UAE has the remarkable advantages of time-and energy-savings,higher extraction yield and better quality of essential oils owing to its cavitation,mechanical and thermal effects accelerating the extraction process[20–22].Consequently,ultrasound-assisted hydrodistillation extraction(UAHDE),as a complementary extraction method with both advantages of UAE and HD,has been widely used for extracting essential oils from several plant materials[23].There are two types of UAHDE approaches for the essential oil extraction including ultrasound pretreatment followed by hydrodistillation and simultaneous ultrasound-assisted hydrodistillation extraction,e.g.,Hashemi et al.[24]and Morsy[25]extracted essential oils from Aloysia citriodora Palau leaves and cardamom seeds using ultrasound pre-treatment with a ultrasound probe followed by the conventional HD,Damyeh et al.[26]extracted essential oils from Prangos ferulacea Lindl.and Satureja macrosiphonia Bornm.Leaves using ultrasonic pretreatment in an ultrasonic water bath prior to HD,and Liu et al.[27]and Solanki et al.[15]extracted essential oils from Iberis amara seeds and java citronella grass by simultaneous HD and sonication performed in a Clevenger HD apparatus equipped with a ultrasound probe.Compared with the conventional HD,both of the above two different UAHDE approaches were obvious characterized by faster extraction rate,less extraction time and energy consumption and better product quality,and could be regarded as green techniques for extracting essential oils from natural plants.

For the essential oil extraction process,the extraction efficiency can be significantly affected by the extraction parameters,so it is valuable to explore and optimize the extraction parameters.The conventional optimization of keeping one parameter variable and all other constant is a time consuming,expensive and arduous task.In addition,the conventional approach does not provide any information about the interactive effects between various process variables on the process output.Hence,it is imperative to use the statistical design of experimental(DOE)approach for the optimization of technological processes,and the most commonly used DOE methods for the optimization of operational variables are the orthogonal array design,Central Composite Design and Box–Behnken design(BBD)[28–30].Among them,the orthogonal experimental design has become an easier,cheaper and faster DOE methodology since it allows optimization with a minimum number of experiments based on a fractional factorial design.Numerous factors can be simultaneously optimized,resulting in a fast estimation of the individual factors with main effects and easy determination of the optimal combination of process factors.In addition,the orthogonal design methodology optimizes the process by minimizing the variation in process output caused by uncontrollable factors like ambient temperature.The above distinct features make it a robust design solution,and widely used to optimize operating parameters for improving the essential oil extraction processes.

Herein,the aim of this work is to evaluate the influence of the ultrasound pretreatment prior to hydrodistillation on the essential oil extraction from cinnamon barks.The extraction parameters significant affecting the extraction process were optimized by the single-factor experiments and orthogonal test design.In addition,the proposed extraction method was compared with traditional HD in terms of the extraction time,extraction yield and environmental impact.Moreover,the extraction mechanism was elucidated with the microscopic structural changes of cinnamon barks before and after the ultrasound treatment,and the physicochemical properties of the obtained cinnamon oil were analyzed.

2.Materials and Methods

2.1.Materials

Cinnamomum cassia(cinnamon)bark supplied by Luoding Rongxing Perfumery Co.,Ltd.of Guangdong Province in China was used as experimental raw material in this work.The fresh cinnamon barks were contaminated by some sand particles,so the raw material was cleaned to remove these substances as much as possible.Firstly,the fresh sample was washed with the flowing deionized water for 30 min,and then dried naturally at ambient temperature of 25–30°C for 2 days,making the relative humidity of raw material reaches about 35%.After that,the samples were crushed and grinded physically,and sieved using a sieve with the mesh size of 0.25 mm.And then the cinnamon bark powders were dried at 105°C until the weight did not change.The dried cinnamon bark powder sample was kept in a desiccator for the utilization of UAHDE and HD extraction studies.

2.2.Extraction procedures

2.2.1.Conventional hydrodistillation

Hydrodistillation was carried out using a Clevenger-type apparatus,and a schematic of the apparatus is shown in Fig.1.Forty grams of the dried cinnamon bark powder was added into a 1 L round bottom flask with a ratio of solid(g):water(ml)of 1:7,and then the mixture was subjected to the hydrodistillation with an electric heating mantle at 500 W power.On the basis of our preliminary research results,the optimal extraction time for HD was determined to be 2 h.The extracted essential oils were dried over anhydrous sodium sulfate.And then the collected yellow oils were weighed and stored in sealed vials at 4°C for the further analysis.The essential oil yields were reported as grams of essential oils per 100 g of dried cinnamon bark powders.Each extraction was repeated for three times and the mean values of the extraction yields were reported.

2.2.2.Ultrasound-assisted hydrodistillation extraction(UAHDE)

Forty grams of the dried cinnamon bark powder sample was accurately weighed and added into a 1 L round bottom flask containing a certain amount of distilled water,and then the mixtures of(cinnamon bark+H2O)were subjected to the ultrasonic treatment using a ultrasonic cell pulverizer(JY92-IIN,25 kHz,Ningbo xinzhi biotechnology Co.,Ltd.,China) at different power levels for different time.Consequently,the various cinnamon bark samples treated with ultrasound irradiation at different power levels for different time were obtained to investigate the effects of the ultrasound power and time on the cinnamon oil extraction.After the ultrasonic treatment,the resulting mixture was immediately submitted to the hydrodistillation for the cinnamon oil extraction using a Clevenger-type apparatus as previously described in the conventional hydrodistillation part.The different extraction time and solid–liquid ratios were conducted to investigate the effects of these factors on the essential oil yield for the UAHDE method.

2.3.Optimization of UAHDE conditions

In the present work,the single-factor experiments and orthogonal test design were conducted to optimize the UAHDE conditions(ultrasound time,ultrasound power,extraction time,liquid–solid ratio).Before the orthogonal experiment,the single-factor experiments were conducted to evaluate the effects of four factors on the essential oil extraction yield and determine the range of each parameter.On the basis of single-factor test result,four parameters were investigated at three levels using a standard orthogonal array L9as shown in Table 1,and the cinnamon oil yield was taken as responses.Minitab 18.0 software(Minitab Inc.,PA,U.S.A.)was used for planning the experiments,analyzing the influence of individual factors and determining the optimal conditions.

Table1 Orthogonal test design L9(34)and essential oil yields

2.4.Scanning electron microscopy(SEM)

Morphological changes of the dried cinnamon bark powder before and after the ultrasound treatment were observed by a JSM-6700F scanning electron microscopy(JEOL,Japan),operating at an accelerating voltage of 8.0 kV and at a working distance of 8 mm.Prior to the SEM observation,the samples were fixed on a specimen holder with conductive tape and then sputtered with gold.

Fig.1.Schematic of experimental apparatus for essential oil extraction from cinnamon barks:(a),Conventional hydrodistillation;(b),Ultrasound-assisted hydrodistillation.

2.5.Gas chromatography–mass spectrometry(GC–MS)

The components of the cinnamon oil were analyzed using a 7890B-7000C gas chromatography–mass spectrometry (GC–MS) (Agilent,American)equipped with a mass selective detector operating in the electron impact mode with the ionization energy of 70 eV(source temperature 230°C).The GC part(Agilent 7890B)was fitted with an Agilent HP-5MS capillary column(30 m×0.25 mm,film thickness 0.25 μm).The temperature program of the oven was as follows:initially keeping 60°C for 3 min,and then heating to 280°C at 20°C·min?1and holding for 10 min.The test samples were diluted with dichloromethane at a ratio (1/10,V/V),and 1 μl sample was injected at 310 °C to GC with the injector in split mode at a split ratio of 1/100.Helium was used as the carrier gas at a rate of 15 ml·min?1.The components of the extracted oil were identified by comparing their recorded mass spectra with the standard mass spectra from the National Institute of Standard and Technology(NIST)libraries database.

2.6.Environmental impact

Regarding the environmental impact,the electric consumption and CO2emission of different extraction methods were calculated.The electric consumption per gram of obtained essential oil(EO)was calculated using the following equation[31]:

where ECis the electric consumption per gram of EO(kW?h·g?1),P is the power consumption(kW),t is time(h),and m is the mass of obtained essential oil(g).

The process of generating 1 kWh electricity by burning fossil fuels will release 800 g of CO2into the atmosphere[32].Based on this calculation,the CO2emission per gram of EO was estimated using the following equation:

3.Results and Discussion

3.1.Influence of the ultrasound time,power,extraction time and liquid–solid ratio on essential oil yield

Fig.2.Effect of ultrasound time on essential oil yield.

Some operation factors can potentially affect the extraction process,so the extraction conditions of cinnamon oils were investigated.Fig.2 shows the influence of the ultrasound time on essential oil yield.The cinnamon bark powders treated with different ultrasound time of 10,20,30,40,50 and 60 min at the ultrasound power level of 300 W were subjected to the essential oil extractions for 2 h.It can be seen that the cinnamon oil yield increases with increasing the ultrasound time from 10 to 30 min,and decrease gradually with further increasing the ultrasound time.The increase of the ultrasound time would improve the cell disruption degree of the cinnamon bark sample,conducive to the release of essential oils to the solution,resulting in an increase of the cinnamon oil yield.However,the longer the ultrasound time,the more oil compounds were degraded into small molecule species[33].In addition,the localized temperatures would increase with the increase of ultrasound time,leading to the loss of easy volatile components and the degraded components [34],causing the decrease of essential oil yield at the ultrasound time of longer than 30 min.Hence,ultrasound time of 30 min was chosen for the subsequent optimization.

Fig.3 illustrates the effect of the ultrasound power on essential oil yield.The ultrasound treated samples with different ultrasound powers of 100,200,300,400 and 500 W for 30 min were subjected to the essential oil extractions for 2 h.It can be seen that at ultrasonic powers of lower than 300 W,the extraction yield increases steadily with the increase in the ultrasonic power,while it decreases with further increasing the ultrasonic power of higher than 300 W.During the ultrasonic irradiation,the shear forces and localized pressures generated with the cavitation bubbles collapse around the cinnamon bark surfaces would lead to the destruction of the plant tissue and consequently accelerate the release of intracellular substances into the solution,resulting in the essential oil yields increase[35].However,at too higher ultrasonic powers,the superheated localized temperatures and more free radicals generated as more cavitation bubble collapse would lead to the degradation of targeted compounds,resulting in a decrease of essential oil yield[36].A similar behavior was observed in the ultrasound-assisted extraction of the essential oil from chickpea[37].Thus,300 W was regarded as the appropriate ultrasound power for the subsequent experiment.

Fig.3.Effect of ultrasound power on essential oil yield.

Extraction time is also an important factor for the essential oil extraction process,and it is necessary to determine the appropriate extraction time to avoid the excessive use of energy.Thereby,the effect of the extraction time on essential oil yield was investigated.The cinnamon bark samples were treated with ultrasound at the power of 300 W for 30 min,and subjected to the essential oil extractions for the different time of 15,30,60,90 and 120 min.From Fig.4,it can be seen that the extraction yield increases steadily with the increasing the extraction time to 60 min,and then decreases slightly with further increasing the extraction time.The decrease may be due to the loss of some volatile components during the longer time of extraction.Liu et al.[27]reported the similar result in the ultrasound-assisted extraction of essential oil from Iberis amara seeds.Hence,60 min was selected as the extraction time for the subsequent optimization.

Fig.4.Effect of extraction time on essential oil yield.

Fig.5.Effect of liquid–solid ratio on essential oil yield.

The liquid–solid ratio is another crucial factor and was also investigated to optimize the extraction yields.Generally,within a certain range,a higher liquid-to-solid ratio could dissolve the target constituents more effectively,and resulting in a better extraction yield[38].However,the use of excess solvent,apart from the energy consumptions for the solvent separation,will cause unnecessary waste and decrease the ultrasound adsorption of materials.Thus,a series of extraction experiments were carried out with different liquid–solid ratios of 4,6,8,10 and 12(V/m,ml·g?1)to evaluate the effect of the liquid-to-solid ratio on the essential oil yield,and the results are illustrated in Fig.5.It can be seen that the extraction yield increases with increasing the moisture content for liquid–solid ratios up to 6,but decreases slightly with the corresponding rise in moisture content.The higher liquid–solid ratios would lead to the decrease of the ultrasound adsorption of the cinnamon bark material,resulting in the insufficient energy in facilitating the cell wall breakage for the release of the essential oil compounds.A similar observation was reported by Zhao et al.[39] in the extraction of saikosaponins from Radix Bupleuri.Therefore,liquid–solid ratio of 6 was chosen as the suitable moisture content for further optimization.

3.2.Optimisation of extraction conditions of cinnamon oils

From the preliminary single-factor analysis,the various factors can potentially affect the extraction process,so the extraction conditions of cinnamon oils by UAHDE were further optimized utilizing an orthogonal L9(34) test.As shown in Table 1,based on the results of preliminary single-factor analysis,nine extraction tests were conducted with four factors and three levels as follows:ultrasound time (25,30,35 min),ultrasound power(250,300,350 W),extraction time(45,60,75 min)and liquid–solid ratio(5,6,7 ml·g?1).The cinnamon oil yield was selected as the responses and required to be maximized.The above nine tests were carried out randomly to minimize the effects of unexpected variability.From Table 1,based on the analysis of R values,the order of impact of the three factors on the cinnamon oil yield is ultrasound time>extraction time>ultrasound power>liquid–solid ratio.Moreover,the optimum extraction condition was determined as A3B2C2D3,meaning that the combination of the ultrasound time of 35 min,the ultrasound power of 300 W,the extraction time of 60 min,and the liquid–solid ratio of 7 is the optimum condition for the cinnamon oil extraction.The extraction experiments under the above optimal extraction were conducted with three repetitions,and the average yield was 2.14%.

3.3.Comparison of UAHDE and HD

3.3.1.Comparison of extraction time,yield,and physicochemical properties of essential oil

In this work,UAHDE was compared with the HD extraction in accordance with the extraction time,the extraction yield,and the chemical composition of the extracted essential oil,and the comparison results are demonstrated in Fig.6 and Table 2.

From Table 2,a significant saving in the extraction time was clearly observed in the UAHDE process,and HD required 120 min to complete the extraction process whereas UAHDE required only half of the time(60 min),indicating that the UAHDE is a faster extraction process.Moreover,it can be seen that the cinnamon oil yield extracted by UAHDE(2.14%)is about 27%higher than that extracted by HD(1.68%).This 27%enhancement is higher than the 6.4%enhancement of ultrasound auxiliary extraction reported by Jadhav et al.[40],and slightly lower than the 34% enhancement of microwave auxiliary extraction reported by Jeyaratnam et al.[41],which may be due to the stronger thermal effect of microwave irradiation than ultrasonic irradiation[42].

The chemical compositions of essential oils extracted from cinnamon barks by UAHDE and HD were analyzed by GC–MS(Fig.6 and Supplemental Material),and the analysis results are listed in Table 2.The relative percent contents were calculated by peak areas using normalization method.It can been seen from Table 2 that,22 components were identified in the essential oil obtained by UAHDE representing 98.53%of the total oil content,and 15 components were identified in the essential oil obtained by HD representing 96.05%of the total oil content.Transcinnamaldehyde is a major and vital component in cinnamon oils owing to its great medicinal and curative properties.It can be obviously observed that trans-cinnamaldehyde is the primary compound in the extracted cinnamon oil with UAHDE and HD,suggesting that the results obtained herein are consistent with the results of previous studies[10,11,43].However,the content of trans-cinnamaldehyde was found to be different in the two cinnamon oils obtained by different methods,and 81.9%and 78.3%were obtained from UAHDE and HD respectively,indicating that UAHDE is a promising technique for obtaining the cinnamon oil with a higher content of trans-cinnamaldehyde from cinnamon barks.In addition,from Fig.6 and Table 2,the other main compounds in HD cinnamon oil,such as 2-methoxycinnamaldehyde and copaene,can also be observed in UAHDE oil,and some monoterpenes and sesquiterpene hydrocarbons in UAHDE oil are absents in the essential oil obtained by HD.The above results prove that ultrasound irradiation would not alter the main effective components in cinnamon essential oils,but improve the content of effective compositions.This may be attributed to more effective liberation of certain components from the secretory structures of cinnamon bark tissues undergo ultrasound irradiation and the shorter extraction time with UAHDE preventing the labile components from thermal degradation which is common with HD[44].

Table2 Chemical compositions of cinnamon essential oils obtained by UAHDE compared to HD

To determine the quality of the cinnamon oils extracted by HD and UAHDE methods,the usual physical constants defining the essential oil(specific gravity,refractive index,optical rotation)were measured according to the standard method suggested by ISO 3126:1977(E) and ISO 3524:2003 (E),and the analysis result was compared with quality standards data.As shown in Table 3,there is no significant difference in physical constants of essential oils extracted by UAHDE and HD methods.In addition,it can be seen that the physical properties of obtained cinnamon oils meet the requirements of quality standards.

Fig.6.GC–MS chromatograms of cinnamon essential oils extracted by HD technique(a),UAHDE(b).

Table3 Physical properties of cinnamon oils obtained by UAHDE and HD from cinnamon barks

3.3.2.Mechanism analysis with morphological characterization

To elucidate the mechanism of UAHDE for the essential oil extraction from cinnamon barks,the morphological changes in surface structure of the cinnamon bark samples before and after the ultrasonic pretreatment,HD extraction and UAHD extraction were observed by SEM.As shown in Fig.7a,the external structure of the sample without any treatment is intact and smooth,and no significant disruption is observed.It can be seen from Fig.7b,after the ultrasonic pretreatment,the cinnamon bark samples are crushed into some small granules,and many cracks and gaps on these particle surfaces are clearly visible.In addition,the sample particles are dispersed more evenly after ultrasonic treatment.From Fig.7c and d,after the extraction,the cinnamon bark tissues are ruptured,and the obvious porosity with many irregular cavities are observed on the sample surfaces.Moreover,obviously,the surface structures of the sample extracted by UAHDE are disrupted more severely than those of the sample extracted by HD,which is attributed to the cracks and gaps on the sample surfaces generated by the ultrasonic pretreatment.

Based on the SEM results,the extraction mechanism for UAHDE process was elucidated as shown in Fig.8.During the ultrasonic irradiation,cavitation bubbles are produced near the plant substrate surfaces,and the bubbles grow in successive cycles.When reaching the critical value,the bubbles will collapse violently,generating a localized high pressure (200 MPa) of the micro-jets with a very high speed(>400 km·h?1)to the cinnamon bark tissue surfaces[45–47].Consequently,on the one hand,sonication broke up the large particles and homogenized the cinnamon bark particles,promoting the contact of cinnamon bark tissues with water.On the other hand,the cell walls of cinnamon bark tissues were destroyed during the ultrasonic irradiation,and a direct contact was established between the intracellular active components and the external water,facilitating the penetration of water into the inner cells and the release of active components.Compared with the conventional HD,UAHDE destroyed the cinnamon bark tissues more seriously,which could enhance the mass transfer,leading to a more and faster release of active components along with water in vapor state for the UAHDE process,resulting in a higher essential oil yield,shorter extraction time and better essential oil quality.

Fig.7.SEM images of cinnamon bark samples before(a)and after ultrasonic pretreatment(b),HD(c)and UAHDE(d).

3.3.3.Comparison of energy and environmental impact

Fig.8.Schematic representation of possible mechanism for UAHDE process.

Fig.9.Electric consumption and CO2 emission of HD and UAHDE for the extraction of cinnamon oil.

In order to highlight the vantage of the UAHDE method,the energy consumption and CO2emissions resulted from this extraction process with the optimum extraction condition were also compared with the traditional HD method,and the result was summarized in Fig.9.A significant energy saving was clearly observed in the UAHDE method.The required electrical energy consumption to obtain one gram of cinnamon oil is 1.49 kWh for HD,while is only 0.79 kWh for UAHDE,which was ascribed to the breakage of cinnamon bark tissues by the ultrasonic irradiation,resulting in a fast and efficient extraction for UAHDE.Regarding the environmental impact of pollution,the calculated amount of CO2rejected into the atmosphere per gram of cinnamon oil extracted by HD(1.19 kg)is much higher than that of UAHDE(0.63 kg).Therefore,UAHDE can be suggested as an economic and environment-friendly approach for the extraction of essential oil from the cinnamon plants.

4.Conclusions

UAHDE technique was successfully applied for the extraction of essential oil from cinnamon barks.The optimum extraction conditions for the UAHDE are:ultrasound time of 35 min,ultrasound power of 300 W,extraction time of 60 min,and liquid–solid ratio of 7.Under the optimum condition,the cinnamon oil yield of UAHDE is 2.14%,which is about 27% higher than that of HD(1.68%).Meanwhile,the extraction time of UAHDE (60 min) is significantly lower than that of HD (120 min),indicating that the UAHDE is a faster extraction approach.From GC–MS analysis,22 and 15 components were identified in the essential oil obtained by UAHDE and HD,respectively,and UAHDE would not alter the types of main effective components in cinnamon essential oils like trans-cinnamaldehyde,2-methoxycinnamaldehyde and copaene.Furthermore,the cinnamon oil extracted by the UAHDE could obtain a higher content of the vital trans-cinnamaldehyde compound (81.9%)than that of HD(78.3%).The physical constants analysis suggests that the physical properties of the obtained cinnamon oil meet the requirements of quality standards.The SEM analysis confirms that the primary driving force for the efficient extraction by UAHDE is the structure destruction of the cinnamon bark tissues generated by the ultrasonic irradiation.In addition,using UAHDE could reduce the energy consumption and CO2emission compared with the HD.In summary,UAHDE is a promising technique for the cinnamon essential oil extraction,and thus can be used for the essential oil extractions from other plant materials.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Natural Science Foundation of Shandong Province(No.ZR2018BB071),Qingdao Science and Technology Plan Application Foundation Research Project(No.19-6-2-28-cg)and Key Research and Development Project of Shandong Province (No.2019GSF109038).

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2020.08.007.