Eur Food Res Technol (2002) 214:105–107 DOI 10.1007/s00217-001-0429-2
O R I G I N A L PA P E R
Amr E. Edris · Hoda M. Fadel
Investigation of the volatile aroma components of garlic leaves essential oil. Possibility of utilization to enrich garlic bulb oil Received: 21 June 2001 / Revised version: 28 August 2001 / Published online: 1 December 2001 © Springer-Verlag 2001
Abstract The volatile aroma components of Egyptian green garlic leaves essential oil was investigated for the first time. After the utilization of garlic bulbs to prepare garlic oil or after drying the bulbs to produce garlic powder, garlic leaves are considered to be waste material, which is disposed of without any benefit. In this investigation, green garlic leaves were distilled and the essential oil was subjected to GC and GC-MS identification. The yield of the oil was 0.06% (based on wet weight of the leaves). The most prominent compounds of the essential oil were diallyl trisulfide (32.32%), followed by diallyl disulfide (31.35%) and methyl allyl trisulfide (11.40%); these compounds are the same as those found in garlic bulb oil. This means that garlic leaf oil is a rich, renewable and priceless source of garlic aroma compounds which could be utilized in fortification and enriching of garlic bulb essential oil to increase its quantity without changing the quality. Utilization of green garlic leaves for production of essential oil will also save, to some extent, the costs of disposing of large amounts of leaves in garlic possessing factories, transforming them into profits. Keywords Volatile aroma components · Garlic leaves · Garlic bulb oil · Gas chromatography
Introduction Garlic (Allium sativum L. Liliaceae) is an important crop for culinary purposes, its pungent flavor adding a special taste to food. In some traditional Chinese and Egyptian dishes, garlic is fried in vegetable oil before adding food, which imparts a special taste and smell to the dish [1]. Garlic oil is also important in the food and pharmaceutical industries. Garlic oil is used in food preservation, A.E. Edris (✉) · H.M. Fadel Aroma and Flavor Chemistry Department, National Research Centre, Dokki, Giza, Egypt e-mail:
[email protected]
especially cured meat and pickles. In the pharmaceutical industry, garlic oil is much used due to its adaptogenic, anticarcinogenic [2] and antithrombotic, antiplateletaggregating properties [3]. Many publications have discussed the chemical composition of garlic oil using different techniques of extraction and identification [4, 5, 6, 7]. We noticed a scarcity of publications and information about the composition of garlic leaf oil. Screening the literature using two databases, the Commonwealth Agricultural Bureau Abstracts and the Food Science and Technology Abstracts, we found no literature investigating the volatile aroma compounds of garlic leaf oil. We justified that scarcity of information about garlic leaf oil on the basis of the importance of the green garlic leaves (bearing the oil) to extend the shelf life and storability of garlic pulp. It prevents them from drying or being infected by fungi during storage. For this reason, green garlic leaves are not allowed to be detached from the bulb if garlic is cultivated for market consumption, in order to tolerate long periods of storage when commercialized. So, only when the leaves reach a moisture content of 30–40% and the green color has turned to white, can harvesting of garlic bulbs be started. At this stage garlic leaves have not attracted investigators to study its oil composition, due to the lack of the characteristic garlic aroma components which could be detected from the green leaves. But in this investigation we look at garlic which is cultivated for another reason than marketing and long term storage, such as garlic utilized at processing factories which produce garlic oil or garlic powder for food and pharmaceutical applications; in this case, the shelf life of garlic is not important due to the immediate utilization of the pulps. Here green garlic leaves could be of importance as a by-product due to their abundance and possible utilization as a renewable, priceless source of volatile oil. At this stage we found no investigator had reported the chemical composition of garlic green leaf oil. The few reports we found were about the utilization of garlic leaf oil as an organic pesticide. Purnima et al. [8] studied
106 Table 1 Chemical composition of the sulfur-containing aroma volatile compounds of essential oil isolated from green garlic leaves
a Based on using 3-nonanone as internal standard; area correction for FID (response factor) was not calculated b Authentic samples were injected for retention time matching with unknowns
Identified peak number
Component
Retention index
1 2 3 4 5 6 7 8 9 10 11 12 13
Diallyl sulfideb 3-methyl-2-cyclopentene-1-thion 1-Propenyl methyl disulfide Methyl allyl disulfideb Dimethyl trisulfideb Propyl allyl disulfideb Diallyl disulfideb 1,2-Dimercaptocyclopentane Methyl allyl trisulfideb Isobutyl isothiocyanate 3 Vinyl-4H-1,2-dithiin Diallyl trisulfideb 2-vinyl-4H-1,3-dithiin
1147 1260 1270 1281 1380 1430 1490 1520 1591 1752 1760 1805 1871
the inhibition of fruit rot fungus (Aspergillus niger) and fruit fly by extracts of garlic and onion leaf oil. He found that garlic leaf oil was more effective in inhibiting spore germination and growth of A. niger. Costa et al. [9] studied the pharmaceutical effects of garlic leaf extract in addition to the stem and pulp, he found that the extracts from the three parts showed analgesic and hyperalgesic properties in addition to long-lasting anti-hypertensive effects. Given this situation regarding the paucity of research in this area, we have devoted this study to investigate the important aroma components of garlic green leaf oil, aiming at its possible utilization in fortifying or enriching garlic oil, and at the same time decreasing the cost of disposing of this waste material.
Materials and methods Green garlic leaves were collected from a conventional garlic farm a few kilometers from Cairo. The garlic pulp were 115 days old when the leaves were detached, 5 cm away from the pulp. The last irrigation of garlic occurred 7 days before harvesting of the green leaves. The leaves were hydrodistilled using a Klevinger type apparatus for 1.5 h. The yield of the oil was 0.06% (w/w, based on fresh leaf weight). The oil obtained was immediately analyzed using GC and GC-MS. Components were identified using the MS library NBS or comparing their mass spectral data with that of published data [10]. Retention index was also used to help confirm the identification of compounds [11]; some available standard samples were injected for further confirmation. GC analysis. Garlic leaf volatile oil was analyzed on a HewlettPackard model 5985 B equipped with a flame ionization detector (FID). A 60 m×0.32 mm i.d. fused silica capillary column coated with carbowax was used. The oven temperature was programmed from to rise from 50 to 200 °C at a rate of 2 °C/min. The injector and detector temperatures were 250 °C. Helium was used as a carrier gas at a flow rat of 0.8 ml/min. Values reported were an average of two analyses. The linear retention indices of the volatile components were calculated with hydrocarbons (C8-C30 Aldrich Chemical Company) as references. GC-MS analysis. This was conducted on a Hewlett-Packard 5985B coupled with an HP MS instrument system. The ionization voltage was 70 eV and the ion source temperature was 200 °C. Other parameters were as in the GC conditions.
Concentration (%)a 0.40 0.29 0.13 1.81 0.41 2.33 31.35 2.06 11.40 2.28 0.13 32.32 3.50
Results and discussion Table 1 shows the chemical composition of sulfur-containing compounds found in the essential oil isolated from green garlic leaves. It is evident that diallyl disulfide (31.35%), methyl allyl trisulfide (11.40%) and diallyl trisulfide (32.32%) constitute the major components of the oil. Although there is no data available in the literature about garlic leaf oil with which to compare our data, we found that our data agree with that reported on garlic bulb essential oil [6, 7] concerning the abundance of these three allyl compounds as major components. These compounds are essential for giving the characteristic pungent garlic flavor. From the pharmaceutical point of view the presence of allyl group-containing compounds at high concentrations is very important for the anticarcinogenic effect of these compounds, especially diallyl disulfide (31.35%) which was found to be the most potent allyl-containing compound, that has reduced forestomach tumors by more than 90% [12]. Table 1 also showed the presence of other sulfur-containing compounds also present in garlic bulb oil e.g. methyl allyl trisulfide (1.81%), propyl allyl trisulfide (2.33%) and isobutyl isothiocyanate (2.28%). There are also some small amounts of components present in garlic leaf oil which are considered to be potent garlic flavoring compounds e.g. dimethyl trisulfide (0.41%) and diallyl sulfide (0.40%). The latter compound is interesting for its inhibition of nuclear damage to murine colon mucosal cells which occurred as a result of exposure to radiation treatment [13]. From these results it is evident that garlic green leaf oil is a good renewable by-product source for the production of essential oil, and resembles in composition to a great extent the oil obtained from garlic bulbs. The yield of garlic leaf oil obtained by distillation is 0.06% (based on fresh leaf weight) which is about 60% of the yield of Egyptian garlic pulp oil (0.1%) and about 30% of the yield of Chinese garlic bulb oil (0.2%) (unpublished data). Fortification of garlic pulp oil with green garlic leaf oil means an increase of bulb oil quantity of 30–60% as well as an enrichment of the bulb oil with po-
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tent flavoring and pharmaceutical components. Another advantage of using garlic green leaf oil is reducing the cost of disposing of a waste material and turning it into profits, with the possibility of using the exhaust leaves after distillation as a cattle food.
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