Yield, Quality and Composition of Cumin Essential Oil as Affected by Storage Period

Essential oils from newly produced (2017) and previous season crop (2016) of cumin (Cuminum cyminum L.) seeds collected from local farmers in Dongla area, north Sudan were extracted and analyzed to determine the effect of storage period on volatile oil yield and quality. The essential oil was extracted using hydro distillation method. Identification of the volatile compounds was performed using gas chromatography-mass spectrometry (GC/MS). Results revealed that oil obtained from cumin (Cuminum cyminum L.) was pale yellow. With respect to oil characteristics, the specific gravity, refractive index, acid value, ester value and other quality characters were not significantly different between the stored and newly harvested seeds. Thirty-eight compounds were separated and identified in cumin seeds essential oil in both seasons with some minor differences in some components between 2016 and 2017 samples. Major effective components of cumin seeds volatile oil were cumin alcohol (4-isopropylbenzyl alcohol), cumin aldehydes as 4-Isopropylbenzaldehyd and 7,7-dimethylbicyclo (4.1.0) hept-3-ene-4-carbaldehyde known as carenal, terpinenes as γ-terpinene and α-terpinene (1,4-Cyclohexadiene, 1-methyl-4(1-methylethyl) and 1,3-cyclohexadine-1-methanol, 4(1-methethyle)-), β-pinene, o-cymene and p-menthadienol in both stored and newly harvested samples. Differences between the samples season wise were very minor with respect to type of volatile components but percentage oil yield was largely decreased by storage period.


Introduction
Cumin (Cuminum cyminum L.), belonging to the family Umbelliferae, is be-lieved to be a native from the East Mediterranean to East India.It is a herbaceous and medicinal crop and one of the oldest and popular seed spices worldwide after black pepper.It is known under various names in different countries [1] [2].Cumin seed is generally used as a spice for foods in the form of powder for flavoring different food preparations [3].It also has a variety of medicinal properties [4].
In Sudan, cumin spread along the Nile valley and some other parts where it continues to be sown by smallholders in the winter season to provide flavoring material.The cultivation of the crop is widely spreading especially in the Northern parts of Sudan, but very few or no attention was given by researchers to the plant [5].
Essential oils are the volatile fragrant components from various plants with significant trade value, nationally and internationally, for several uses [6].All true essential oils are volatile aromatic secondary metabolites of plant origin.
Their occurrences differ from one plant to other according to type of plant part containing oil [7].Cumin seeds contain 2.5% -4.0% volatile oil and aldehydes or cuminol, which attributes to the aroma, and are considered as the major oil constituents [1].
Very few works were devoted by Sudanese researchers to improve crop productivity and processing, therefore, the general and the main objective of this study is extraction and characterization of essential oil from cumin (Cuminum cyminum L.) seeds with specific objectives of: − Extraction of the volatile oil of cumin (Cuminum cyminum L.) by hydro distillation.
− Identification of volatile components of oils using gas chromatography-mass spectrometry (GC/MS).− Investigation of the effect of one season storage of cumin (Cuminum cyminum L.) schizocarp fruits (traditionally called seeds) on their volatile oil qualities.

Oil Analysis Procedure
The composition of the essential oil was analyzed using gas chromatography-mass spectroscopy technique.GC-MS instrument used was model QP2010-Ultra, Shimadzu Company, Japans, with serial number 020525101565SA equipped with capillary column (Rtx-5 ms-30 m × 0.25 mm × 0.25 µm) and flame ionization detector (FID).The sample was injected using split mode (Split ratio: 1:100), helium as carrier gas passed with flow rate 1.69 ml per minute, the temperature program was started from 50˚C with rate 7˚C per minute to 180˚C then the rate was changed to 10˚C per minute reaching 300˚C as final temperature degree, with 3 min hold time.The injection port temperature was 300˚C, the ion source temperature was 200˚C and the interface temperature was 250˚C.
The sample was analyzed using scan mode in the range of m/z 40 -550 charges to ratio and the total run time was 28 min.Identification of components for the

Results and Discussion
Oil obtained from cumin (Cuminum cyminum L.) was pale yellow.Hydro distillation of cumin seeds produced a percentage yield of cumin essential oil of  1).
Identification of cumin seeds volatile oil components extracted by hydro distillation and analyzed using GC/MS are shown in Table 2 and Table 3. From the results, 38 compounds were separated and identified in cumin seeds in both newly harvested and stored sample (Figure 1 and Figure 2) compared with 49      (1.56%).Results obtained were comparable to that obtained by [11].Major compounds and their molecular weight, formula and chemical structure were presented in Table 4.Most cited literature refer to the fact that cuminaldehyde considered the major compound followed by alpha or gamma terpinene [12] [13] [14].Many researchers stated that the composition and characteristics of herb essential oil differ according to many factors among them cultivar, growing condition, harvesting method and time, storage condition and finally oil extraction technique [15] [16] [17] [18].Differences between the sample season wise were very minor with respect to percentage and type of volatile components.

Conclusion
Storage period reduced oil yield but oil characteristics including chemical, physical and constituent properties remain with negligible change.
sample was achieved comparing their retention times and mass fragmentation results automatically by instrument software with those available in the libraries of the National Institute of Standards and Technology (NIST), US National Library of Medicine (PUBCHEM), The National Center for Biotechnology Information (NCIB) and Royal Society of Chemistry (Chem Spider).

Table 1 .
Physical and chemical characteristics of essential oil of Cuminum cyminum L.

Table 2 .
The results of the analysis of the GC/MS spectrum of the different constituents of the essential oil extracted from cumin (2017) by hydrodistillation.

Table 3 .
The results of the analysis of the GC_MS spectrum of the different constituents of the essential oil extracted from cumin (2016) by hydrodistillation.