The extraction of essential oils is generally carried out by two main techniques: azeotropic distillation (hydrodistillation, hydrodiffusion, and steam distillation) and extraction with solvents. However, these traditional methods are a bit expensive, especially since they are extremely energy and solvent consuming. This work consists in studying two methods of extraction of the essential oils of
Rosemary contains an essential oil to which it owes its interesting properties. It is known for its antioxidant, antimicrobial, anti-inflammatory, anticarcinogenic, antidiabetic [
The essential oil secreted by glandular trichomes is mainly located in leaves and the flowers; the highest quality essential oil is obtained from the leaves [
However, in order to reduce the extraction time and improve the quality of essential oils, new extraction techniques have been developed such as microwave assisted extraction, solvent extraction under pressure, supercritical fluid extraction, and ultrasound-assisted extraction [
This work aims to make a comparative study of two methods of extraction of essential oils of Moroccan
The samples of rosemary were harvested at the flowering stage during the month of May 2018 in the region of Fez (406 m, 34°01′59′′ Latitude North and 5°00′01′′ Longitude West). Only the aerial part of plant was used; the leaves and the apical parts were dried in the shade for eight days at a temperature room fixed at 25°C.
The microwave-assisted hydrodistillation was carried out using an assembly consisting of a domestic microwave oven (MWD 119 WH, whirlpool, China, 20L, 1100 W), directly connected to a Clevenger-type extractor and a cooling system to condense the distillate continuously. The excess of Condensed water was refluxed to the extraction flask in order to restore the water to the plant material (Figure
Schematic representation of the microwave-Clevenger.
Microwave assisted hydrodistillation was carried out under the optimum conditions of the extracting time, microwave power, and ratio water/plant material [
100 g of rosemary samples was placed in a 2-liter flask containing distilled water (200 ml), heated inside the microwave oven cavity, and the mixture was heated at a fixed power of 600 W until extraction of the all essential oils.
The essential oils taken from different extractions are dried under anhydrous sodium sulphate and stored in the dark until they are used for analysis. The extractions were done at least three times and mean values of the yield and standard deviation were determined.
For the extraction of essential oils from rosemary by hydrodistillation under optimal operating conditions, a quantity of 100 g of rosemary was added to 800 ml of distilled water in a 2-liter flask [
The yields of essential oil of rosemary were expressed in g relative to 100 g of dry vegetable matter; it was calculated according to Equation (
The energy consumption required to carry out the CH and MAH extractions was determined by a watt-meter connected to the input of the microwave generator and that of the heater.
The carbon dioxide released into the atmosphere is calculated according to the literature: to obtain 1 kWh of coal or other fossil fuels, 800 g of CO2 will be released into the atmosphere during combustion [
The chemical composition of the rosemary essential oils extracted by both methods is performed by gas chromatography coupled with mass spectrometry (GC/MS).
The GC analysis was performed using a chromatography equipped with a flame ionization detector (FID) and two capillary columns of different polarities OV type: 101 (25 m x 0.22 mm x 0.25 mm) and Carbowax 20 M (25 m x 0.22 mm x 0.25
The descriptive statistics of the yield including mean, standard deviation, standard error, maximum, and minimum from the three repetitions were presented in Table
Mean value, maximum, minimum, range, Standard error, and Standard deviation of essential oil yield of rosemary.
Minimum (%) | Maximum (%) | Range (%) | Mean (%) | Standard deviation (%) | Standard error (%) | |
---|---|---|---|---|---|---|
MAH | 0,32 | 0,39 | 0,07 | 0,353 | 0,035 | 0,020 |
CH | 0,31 | 0,37 | 0,06 | 0,347 | 0,032 | 0,019 |
The cumulative yield of the essential oils from rosemary obtained during a single extraction from the three repetitions for each extraction method as a function of time is shown in Figure
Yield profiles as a function of time for CH and MAH isolations of essential oil from rosemary.
Several studies have reported that the heat generated by the microwave heating involves a partial pressure gradient of volatile compounds and internal overheating leading to embrittlement or rupture of the cell walls more rapidly and more efficiently [
The results relating to the chemical composition of the essential oils of
Chemical composition of rosemary essential oils obtained by CH and MAH.
No. | Compounds | Kovat’s index | MAH (%) | CH (%) |
---|---|---|---|---|
| | | ||
1 | 939 | 15,4 | 15,82 | |
2 | Camphene | 954 | 9,16 | 9,77 |
3 | 979 | 3,72 | 3,56 | |
4 | 1017 | 2,49 | 2,44 | |
5 | para-Cymene | 1025 | 4,15 | 4,79 |
6 | Limonene | 1028 | 0,92 | 0,81 |
| | | ||
7 | Cineole | 1030 | 32,18 | 31,2 |
8 | 1048 | 4 | 3,75 | |
9 | Linalool | 1097 | 1,37 | 1,49 |
10 | Camphor | 1146 | 16,2 | 16,54 |
11 | Borneol | 1169 | 1,64 | 1,47 |
12 | 1199 | 7,36 | 7,16 | |
13 | Verbenone | 1205 | 0,28 | 0,15 |
| | | ||
14 | 1419 | 0,12 | 0,08 | |
15 | 1423 | 0,15 | 0,03 | |
| | | ||
16 | Bornyl acetate | 1289 | 0,61 | 0,74 |
| | | ||
| | | ||
| | |
Chromatogram of essential oils of rosemary extracted by CH.
Chromatogram of essential oils of rosemary extracted by MAH.
The analysis of the results shows that the chemical composition of the essential oils obtained by the two methods is identical between the two MAH and CH methods with slight quantitative differences in certain constituents. Indeed, the cineole has the major constituent with a slightly higher rate for MAH compared to CH which is, respectively, 32.18% and 31.20%.
However, the percentages of camphor (16.54% in CH and 16.20% in MAH) and
A critical observation of the composition of the oils has revealed that the amounts of oxygenated compounds are substantially higher and the amounts of monoterpene hydrocarbons are lower in MAH extracted rosemary oil in comparison with CH.
These results are consistent with those of Bousbia et al. [
Oxygen compounds are more valuable than hydrocarbons in terms of their contribution to the fragrance and therapeutic properties of the essential oil and can be used as essential oil quality measures.
The reduced cost of extraction is clearly advantageous for MAH method in terms of time and energy. The time required for extraction of the essential oils contained in 100 g of rosemary was found at 180 min for the CH and 20 minutes for the MAH, while the energy required to perform this extraction is 2.25 kWh for the CH and 0.23 kWh for the MAH (Table
Energy consumption and CO2 rejected of CH and MAH methods.
MAH | CH | |
---|---|---|
Extraction time (min) | 20 | 180 |
Electric consumption (kWh) | 0,23 | 2,25 |
CO2 rejected (g) | 184 | 1800 |
Regarding environmental impact, the amount of carbon dioxide released into the atmosphere during CH (1800 g CO2) extraction is higher than that released during MAH extraction (184 g CO2). Therefore, the MAH represents a "green technology" for the extraction of essential oils.
The essential oils extracted by MAH are quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by conventional hydrodistillation, although the treatment time has been significantly reduced in the case of MAH (20 min) by relative to CH (180 min). Microwave-assisted hydrodistillation provides an essential oil with higher amounts of oxygenates substantial energy savings, reduced cost, and reduced environmental burden with less CO2 released into the atmosphere. It can be concluded that the MAH method is a good alternative for extracting essential oils of rosemary.
No data were used to support this study.
The authors declare that they have no conflicts of interest.