Clove: A review of a precious species with multiple uses

Abstract

Clove (Syzygium aromaticum) is one of the most valuable spices that have been used traditionally as food preservative and for many therapeutic purposes. Clove is native of Indonesia but it has also been cultured in several parts of the world including Pakistan. This plant represents one of the richest sources of phenolic constituents as eugenol, and eugenol acetate and posseses great potential for pharmaceutical, cosmetic, food and agricultural applications. This article includes main studies reporting the phytochemical profile and pharmacological activities of clove and eugenol. The antioxidant and antimicrobial activities of clove are higher than many fruits, vegetables and other spices. Toxicological studies are also mentioned. The different studies reviewed in current work authenticate the traditional use of clove as food preservative and medicinal plant.

Full text

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Hussain et al., 2017 129
Clove: A review of a precious species with multiple uses
Shahid Hussain1, Rafia Rahman1 and Ayesha Mushtaq1*, Asma El Zerey-Belaskri2
1Department of Chemistry, University of Agriculture, Faisalabad, Pakistan and 2Faculté des Sciences de la nature et de la Vie,
Université de Sidi Bel Abbes, Algérie
Abstract
Clove (Syzygium aromaticum) is one of the most valuable spices that have been used traditionally as food preservative and for
many therapeutic purposes. Clove is native of Indonesia but it has also been cultured in several parts of the world including
Pakistan. This plant represents one of the richest sources of phenolic constituents as eugenol, and eugenol acetate and posseses
great potential for pharmaceutical, cosmetic, food and agricultural applications. This article includes main studies reporting the
phytochemical profile and pharmacological activities of clove and eugenol. The antioxidant and antimicrobial activities of clove
are higher than many fruits, vegetables and other spices. Toxicological studies are also mentioned. The different studies reviewed
in current work authenticate the traditional use of clove as food preservative and medicinal plant.
Key words: Syzygium aromaticum, eugenol, antioxidant
Full length article *Corresponding Author, e-mail: ayesha_mushtaq123@yahoo.com
1. Botany
1.1. Introduction
Clove (Syzygium aromaticum) a precious spice, is a
member of Mirtaceae family which has been employed for
centuries as food preservative and medicine because of its
antimicrobial and antioxidant properties. Syzygium is the
largest genus of Mirtaceae family, comprising of about 1200
to 1800 species of flowering plants, which are widely
distributed in tropical and subtropical areas of Asia, Africa,
Madagascar, and throughout Pacific and Oceanic regions [1].
Cloves contain appreciable amounts of volatile oil (used for
flavouring foods and pharmaceuticals), which is mainly
confined in aerial parts of plant. The yield and composition
of volatile oil are variable and are thought to be linked to
growing conditions, genetic factors, different chemotypes,
geographic origins, and differences in the nutritional status of
plant [2-4]. Clove is known by different vernacular names in
different languages. It is known as qaranful (Arabic),
Karamfil (Bulgarian), Ding xiang (Chinese), Kruidnagel
(Danish), Garifalo (Greek), Mikhaki (Georgian), Nelke
(German), Szegfu (Hungarian), Cengkeh (Indonesian), Choji
(Japanese), Jeonghyang (Korean), Krustnaglinas (Latvian),
Lwaang (Nepalese), Carvo de India (Portuguese), Mikhak
(Persian), Kala (Pashto), Gvosdika (Russian), Clavo
(Spanish), Carenfil (Turkish), Garn ploo (Thai), Dhing huong
(Vietnamese), and Laung (Urdu/Punjabi/Hindi) [5].
1.2. History
Clove is an ancient spice, which is believed to be
originated in the first century, before Christ. The first clue
about clove’s fragrance was given by the ancient Chinese
(207 B.C. to 220 A.D.). At that time, a Chinese Physician
wrote that court visitors were required to hold clove in their
mouth to prevent the Emperor from visitor’s bad breath.
Cloves were traded to Europe by the Arabs in 4th century
A.D. The origin and source of clove was a mystery, until the
discovery of Indonesia or Moluccas Island, by Portuguese,
in 16th century. In 17th century A.D., cloves were introduced
to Sri Lanka. In 18th century A.D., cloves were established
in India by East India Company. In European countries,
there is a tradition to make “Pomanders” by studding
oranges with clove buds, and to hang them around the
homes, during Christmas, for decorative purpose and to
spread fragrance.
1.3. Demography/Location
Clove requires damp tropical and sub-tropical
environments for growth. It has been cultivated in the
following countries: Indonesia, Sri-Lanka, India, Tanzania,
Malaysia, Madagascar, and Pakistan.
1.4. Botany, Morphology, Ecology
Clove is a scented dried bud of Syzgium
aromaticum tree, used as seasoning in food cuisines. S.
aromaticum is an evergreen tree which grows upto a height
of 8 to 12m; having large quadrangle leaves and cheerful
flowers arranged in form of clusters. Young flower buds are
of pale color and slowly changes to green, which changes to
bright red when buds are ready for harvesting. Harvesting
should be done when buds have 1.5–2 cm length, long calyx
terminating in four closed petals (forming a tiny ball in the
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core) and spreading sepals. Clove growth requires well-
drained, loamy, and organic matter rich soils. Constant
temperature above 10ºC is crucial, while, optimum
temperature is around 20 to 30 ºC. This species cannot
tolerate water logged conditions. Areas having annual
rainfall of 150 to 300 cm are best for its growth [5].
2. Chemistry
Clove is a vital source of phenolic compounds such
as flavonoids, hydroxycinamic acids, hydroxybenzoic acids,
and hydroxyphenyl propenes. Eugenol is the chief bioactive
constituent of clove, which is present in concentrations
ranging from 9 381.70 to 14 650.00 mg/100 g of fresh plant
weight. With regard to the phenolic acids, gallic acid is
found in higher concentration (783.50 mg/100 g fresh
weight) [6]. Other phenolic acids found in clove are caffeic,
ferulic, elagic and salicylic acids. Flavonoids including
kaempferol, quercetin and its derivates (glycosilated) are
also found in trace amounts. Appreciable amounts of
essential oil are present in aerial parts of clove. Chemical
profile of this oil is generally found by GCMS analysis [7-
11]. Good quality clove bud contains volatile oil (15 to
20%), which mainly comprises of eugenol (70 to 85%),
eugenyl acetate (10 to 15%), and beta-caryophyllene (5 to
12%). Other minor constituents including methyl amyl
ketone, kaempferol, gallotannic acid, α-humulene, β-
humulene, methyl salicylate, crategolic acid, and
benzaldehyde are responsible for the characteristic pleasant
fragrance of clove [12]. Figure 1 shows structures of some
important compounds of clove.
Quercetin
Kaempferol
Eugenol
Eugenol acetate
Fig.1. Structures of some important phytochemicals
found in Syzygium aromaticum L.
3. Post-harvest technology
Clove trees begin to flower in four years and the
full bearing stage is achieved only in 15 years. Flowering
period varies from September-October to December-January
depending on tree locality. Clove buds are formed on young
branches and take 4-6 months to become ready for harvest.
Buds should be harvested when color of petals changes to
yellow pink from green. Harvesting can be done by hand or
by using stepladder. Harvesting should be done carefully to
prevent breakage of branches. An average 15 to 20 year old
tree yields 3 to 4 kg of dried clove buds. Optimum time for
harvesting clove seeds is 75-90 days after fruit set. After
harvesting, clove buds are separated from their stalks by
hand and spread on mats for drying. Drying may take 4 to 5
days. Well dried buds are hard, crisp and dark brown,
having moisture content (<12%), which can be stored for 1
to 2 years in gunny bags. Approximately, 15-20% volatile
oil can be produced from dried buds [13].
4. General uses
Cloves have many uses ranging from culinary to
medicine. Clove is a valuable kitchen spice which can be
used for studding onions, tomatoes, salads, herbal teas, and
soups. It is also used to flavor meat products, cookies,
chewing gums, spiced fruits, pickles, chocolates, soft drinks,
puddings, sandwiches, pastries, and candies. Volatile oil is
used to impart essence to perfumes soaps, toothpastes, and
pharmaceuticals. In Indonesia, mixture of clove and tobacco
in a ratio of 1:2 is used to make a special cigarette “Kretek”.
Clove possesses antibacterial potential and is used in a
variety of mouth washes, dental creams, throat sprays, and
tooth pastes to kill pathogens. It is also used to relive sore
gums. Mixture of eugenol (major bioactive constituent of
clove) and zinc oxide is used for short-term filling of dental
cavities [14]. Clove oil has anti-inflammatory properties due
to the presence of flavonoids. Pure clove oil is used in
aromatherapy of arthritis and rheumatism. Paste of clove
powder and honey is used to cure skin conditions. Paste of
water and clove powder boosts healing process of bites and
cuts. Clove is used to treat various digestive disorders
including loose motion, flatulence, nausea, and dyspepsia.
Clove oil improves body defense system and help to fight
against invading microbes. It is also used to cure
Onychomycosis and Athlete’s foot disease. Inhalation of
clove essential oil soothes various respiratory conditions
such as asthma, cold, cough, sinusitis, and bronchitis.
Cloves have anticancer potential and are used to cure skin
and lung carcinoma. Clove is good for diabetic patients as it
controls the blood level of glucose. Eugenol prevents the
formation of blood clots. Topical application of clove oil
relieves muscular cramps. Cloves also prevent the
breakdown in eye’s retina, which slows down muscles
degeneration and assists vision in the old age. Sniffing of
clove aroma reduces lethargy, restlessness, and headaches.
Application of one drop of clove oil can soothe headaches.

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Clove improves memory by relieving mental fog,
drowsiness, and depression. Clove oil is mosquito repellent
[15]. Antioxidant potential of clove is higher than many
other medicinal plants. One drop of clove oil is 400 times
more potent than blueberries. Cloves are used as part of
herbal formulations to cure animals. The clove oil has
potential of curing ear infection in dogs and cats.
Peppermint tea with a sprinkle of cloves and ginger has been
used to treat vomiting in dogs; 1 tbsp or more, according to
the size of the animal, being given 3 times daily.
5. Pharmacological uses
5.1. Antimicrobial activity
Antimicrobial properties of Syzygium aromaticum
and Rosmarinus officinalis essential oils were tested against
multidrug resistant isolates including Pseudomonas
aeruginosa, Enterococcus feacalis, Acinetobacter
baumannii, and Staphylococcus aureus, and two controlled
strains Pseudomonas aeruginosa-ATCC27853 and
Staphylococcus aureus-ATCC29213, using agar well
diffusion model. Both oils exhibited significant inhibition
against tested strains, with minimum inhibitory
concentrations ranging from 0.312-1.25% (v/v) for clove oil,
and 0.312- 5% (v/v) for rosemary oil [16]. A comparative
analysis was carried out to evaluate the antiseptic potential
of clove extract (ethanolic) and clove oil against some food
borne pathogens. Ten bacterial and seven fungal strains
were tested using agar well diffusion method. Sodium
propionate was used as a standard food preservative. Results
revealed the greater antimicrobial effect of clove oil, when
compared to extract and sodium propionate. In another
study, clove oil was tested against five dermophytes
including Trichophyton rubrum, Epidermophyton
floccosum, Microsporum canis, Microsporum gypseum, and
Trichophyton mentagrophytes. Maximum inhibitory effect
(≈60%) against all fungal strains was shown at dose of
0.2mg/ml [17]. Antibacterial activity of six spices (clove,
mint, cinnamon, ginger, mustard, and garlic) was evaluated
against Escherichia coli, Bacillus cereus, and
Staphylococcus aureus, using dilution, cup, and paper disc
diffusion assays. Results revealed the maximum inhibitory
action of clove, mustard, and cinnamon at 1% concentration.
Garlic showed good inhibitory action at 3% concentration.
However, mint and ginger had negligible inhibition at same
concentration [18]. Essential oils of Piper nigrum, Syzygium
aromaticum, Pelargonium graveolens, Myristica fragrans,
Origanum vulgare, and Thymus vulgaris were evaluated for
antimicrobial activity against twenty five bacterial strains,
including food borne, animal, and plant
pathogens.considerable inhibitory action was observed by
the volatile oils in a dose dependent behavior [19].
5.2. Cytotoxic activity
Anti-oxidant, genotoxic and cytotoxic potentials of
borneol and eugenol (clove oil derivative) were evaluated as
the capability of modulating resistance against DNA
damaging effects of H2O2, on different strains of human
cells: malignan hepatome cells (HepG2), malignan colon
cells (caco-2) and non malignan human fibroblast (VH10).
Results revealed the remarkable anti-oxidative potential of
eugenol at all the tested doses. It was also verified that the
citotoxic potential of eugenol was more powerful than
borneol. With regard to toxicity, eugenol exhibited strong
DNA damaging effects on human fibroblast (VH10),
medium damaging effects on colon cells (caco-2) and non
genotoxic effects on hepatome cells (HepG2) [20].
5.3. Antioxidant activity
A study was performed to assess the antioxidant potential of
aqueous and alcohol extracts of some selected spices
including onion, garlic, pepper, cinnamon, mint, ginger, and
clove. Generally phenolic and flavonoids are responsible for
antioxidant activities of the oil [21]. All spices inhibited
lipid oxidation in a dose dependent manner. Among all,
clove showed maximum, whereas, onion showed minimum
inhibitory potential [22]. Antioxidant activities of clove,
sage, and oregano essential oils were evaluated using DPPH
(2,2-diphenyl-1-picrylhydrazyl) free radical quenching,
BCB (β-carotene bleaching), and FRP (Fe(lll) reducing
power) methods. Butylated hydroxytoluene was used as
standard antioxidant. Essential oils were added to soybean
oil at doses of 0.006 and 0.01g/ml, for thirty days, at
accelerated oxidation level. Among all examined oils, the
clove oil showed more potent (p<0.05) antioxidant activity
followed by oregano and sage oils [23].
5.4. Antiviral activity
Eugenin isolated from clove bud essential oil
exhibited a potent inhibitory effect against herpes simplex
virus at a dose of 10µg/ml [24].
5.5. Hepatoprotective activity
Hepatoprotective potential of clove aqueous extract
was evaluated at doses of 0.1 and 0.2g/kg, using
paracetamol intoxicated hepatic damage assay, in Wistar
albino rats. The degree of hepatic damage was evaluated by
increased levels of cytopalsmic enzymes (aspartate
aminotransferase and alanine aminotransferase). Clove
extract restored the normal concentrations of enzymes in
serum [25].
5.6. Analgesic activity
Eugenol was administrated intravenously and
intragastrically to rabbits to examine its analgesic effect.
Paracetamol was a standard drug. Eugenol showed greater
fever reducing potential than paracetamol [26].
5.7. Anesthetic activity
Anesthetic effect of eugenol was studied in
Oncorhynchus mykiss (juvenile rainbow trout). Anesthesia
induction and recovery times were compared with standard
drug, tricaine methanesulfonate (MS-222). Eugenol induced
anaesthesia at relatively lower concentration than standard
drug. Moreover, the recovery time was 6-10 times longer for
fishes exposed to eugenol than those exposed to same doses

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of tricaine methanesulfonate. Above study suggested the
anesthetic use of clove oil derivative “Eugenol” [27].
6. Toxicity
The clove oil is considered safe when consumed in
doses (<1.5g/kg). However, the WHO (World Health
Organization) established the acceptable dose of clove 2.5
mg/kg/day in humans. The toxicity of clove oil was
evaluated in aquarium fish species, Poecilia reticulata and
Danio rerio. The LD50 values were (18.2±5.52) mg/ml and
(21.7±0.8) mg/ml in Danio rerio and Poecilia reticulate,
respectively, at 96 h [28].
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