New Small Scale Equipment for Obtaining Dill and Cumin Essential Oils

DENISA E. DUTA, DAVID L. COMANICIU, ALINA CULETU, MIOARA NEGOITA, VALENTIN IONESCU, HARALD BARZAN, VALENTIN L. ORDODI*, GABRIELA BARZAN National Institute of Research and Development for Food Bioresources, IBA Bucharest, 6 Dinu Vintila, 021102, Bucharest, Romania 2 SC Natural Ingredients R&D SRL, 10/1 Tabacari Str., 505200, Fagaras, Romania 3 Politehnica University of Timisoara, 2 Victoriei Sq., 300006, Timisoara, Romania


The experimental equipment
The equipment is fitted with an industry-standard stainless steel cauldron (2) sporting a total volume of Vtotal = 9 L and a fill volume Vfill = 7 L. The plant material is placed inside a wire netting on a metal holder 3 cm above the bottom of the cauldron, thus avoiding direct contact of the plant material with the hot surface of the bottom, which could lead to the alteration of the obtained essential oils. The cauldron is thermally insulated (6) with mineral wool. A tap allows the interior of the cauldron to communicate with the outside, but the tap is shut once the cauldron has been filled. The cauldron is heated up using a 1 kW electric heater (1). The resulting steam is led through a double pipe (or 'pipe-inpipe') heat exchanger (7) through a mineral wool insulated copper duct with an internal diameter of 15 mm. Steam condensation occurs at the heat exchanger, whose cooling is provided by the laboratory's water supply. The entrained oil then accumulated inside the 300 mL copper-made collector vessel (11) and separates from the aqueous phase (condensate) due to their immiscibility. The condensate is then led back to the cauldron via two routes, the choice of which depends on the density of the oil: one route (12) for oils with a density lower than water, and another route (13) for oils with higher density. Both routes are fitted with taps. After the steam distillation procedure is finished, the collector vessel (11) containing the essential oils and excess condensate is drained inside a recipient (16) through a drain tap (15).

Obtaining cumin and dill seed essential oil
Two kilograms of dill (Anethum graveolens L.) and cumin (Cuminum cyminum), acquired from a local producer (both seeds and grass of each species) were used to obtain the essential oils. They were split into batches according to Table 1 and fed into the extraction equipment. The steam distillation period for each batch was 12 h. After the separation and weighing of the crude essential oil resulted from each batch, the batch-wise and global yields were computed for each essential oil type. https://doi.org/10.37358/RC.20.2.7932

GC-MS and 1 H-NMR analysis of the extracted essential oils
For the GC-MS analysis a gas chromatograph (Focus GC) coupled with an ion-trap mass spectrometer (POLARIS Q) (Thermo Fisher Scientific, US) was used. The gas chromatograph was fitted with a TriPlus autosampler (Thermo Fisher Scientific, US) and a SSL injector. Separation of the compounds from the essential oils was made using a TG-5SILMS (60 mx, 0.25 mm, film thickness 0.25 pm; 5% phenyl methylpolysiloxane) (Thermo Fisher Scientific, US) capillary column with helium as carrier gas, at a constant flow of 1 mL/min. Sample analysis was conducted at 70 eV with positive electron impact ionization (EI + ) in full-scan mode, with a mass range m/z = 40-350. Injector and transfer line temperatures were set at 250 and 300 °C, respectively. GC oven temperature was set at 40 °C for the first 2 min, then linearly heated up to 280 °C with a rate of 5 °C/min, and maintained for 10 min. 1 µL of each oil sample (diluted 1/10, 1/100, 1/200, 1/600, 1/5000, 1/5500 in hexane, v/v) was injected (split injection, 1:100 ratio). The data was acquired and processed using the Xcalibur software package.
For 1 H-NMR analysis, a Bruker Ascend 400MHz spectrometer was used with the following parameter: 45° pulse angle, no power attenuation, acquisition time 2.05 sec, 6.4 KHz spectral window, 16 scans, 26K sampled points with delay d1 = 1 s. Free induction delay (FID) was not processed before the Fourier transform. The average acquisition duration of a 1 H-NMR spectrum was ~2 min. The spectra were acquired after diluting the samples with deuterated chloroform (CDCl3) at a 2:8 v/v ratio. Table 2 shows the entrainment yields for each batch and processed plant, as well as the average yield for each resulting product. The extracted dill seed oil is a pale yellow liquid. Its smell is cumin-like, fresh, neat and spicy. Its taste is warm, lightly spicy, with an intense sweet-aromatic flavor. Its relative density was 0.9274 and its refractive index nD 20 was 1.5178.

Results and discussions
The extracted cumin seed oil is a pale yellow liquid with a penetrating smell and a warm, spicy taste. Its relative density was 0.9201 and its refractive index nD 20 was 1.4933.
The peaks from the chromatogram of each extract were identified by comparing their retention times to reference standards. Identification of the constituting chemical compounds was done by analyzing GC retention times, and the confirmation and interpretation of mass spectra was done using the NIST Mass Spectral Library provided by the GC-MS software and data from other studies. Quantitative data was expressed as non-corrected percentage of area. Each probe (and its dilutions) was injected thrice. The relative standard deviations for the major components did not exceed 2%. Tables 3 and 4 show the composition of the oils extracted from dill and cumin, respectively. Figure 2 shows the chromatograms for the dill seed and grass essential oils compared to a reference dill seed oil from Sigma. https  From the 1 H-NMR analysis, the content of alpha-phellandrene, carvone and limonene from the extracted essential oils and from a reference dill grass essential oil (SIGMA) were determined. Table 5 presents the experimental results. The experimental data showed that the highest carvone content was in the essential oil obtained by processing of cumin seeds. Cumin seed oil extraction also has the highest steam distillation yield, making them the best source of natural carvone in advantageous conditions.

Conclusions
The presented steam distillation equipment is very well suited for the extraction of essential oils from various raw plant materials. Due to the design of the equipment, contact of the plant material with the overheated bottom side of the cauldron is avoided, thus the essential oil yield will be of superior quality, as far as both physicochemical and