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Essential oils in foods: extraction, stabilization, and toxicity
Accepted Manuscript Title: Essential oils in foods: extraction, stabilisation and toxicity Author: Cristian Dima Stefan Dima PII: DOI: Reference:
S2214-7993(15)00095-8 http://dx.doi.org/doi:10.1016/j.cofs.2015.07.003 COFS 76
To appear in: Received date: Revised date: Accepted date:
19-5-2015 13-7-2015 14-7-2015
Please cite this article as: Dima, C., Dima, S.,Essential oils in foods: extraction, stabilisation and toxicity, COFS (2015), http://dx.doi.org/10.1016/j.cofs.2015.07.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Highlights Extraction and processing of essential oils
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Stabilisation of essential oils
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Essential oils in foods and safety issues
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Essential oils in foods: extraction, stabilisation and toxicity
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Cristian Dima1 and Stefan Dima2
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Str. 111, RO-800201, Galati, Romania (Corresponding author: [email protected])
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”Dunărea de Jos” University of Galati, Faculty of Food Science and Engineering, ”Domneasca”
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111, RO-800201, Galati, Romania
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”Dunărea de Jos” University of Galati, Faculty of Science and Environment, ”Domneasca” Str.
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Abstract
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Due to its biological properties, essential oils are used as ingredient for different products in
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order to increase their functionality such as foodstuff, drinks, perfumaries, pharmaceuticals,
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cosmetics or green pesticides. Current researches are manly focussed on developing innovative
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and friendly techniques for essential oils extraction and their afterword stabilization through
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incapsulation in order to obtain GRAS (general recognized as safe) natural products. The
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blooming grouth of essential oils market, require analytical methods diversification and
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improved regulations for their marketing and utilization.
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Introduction
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It can be said that through plants essential oils accompanied humanity during its entire history.
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There are numerous written testimonials attesting extraction and utilization of essential oils in
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different regions, such as India (5000 b.c.) and Mesopotamia or Greese (3000 b.c.) [1, 2••].
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From the very beginig of their discovery essential oils were used as food flavors and additives, as
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cures for different disseases, aphrodisiacs, cosmetics or during coult ritulas. Nowadays, the
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interest for essential oils increased both in terms of academical research and diversification of
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application domains. The use of essential oils in a large variety of areas like foode industry,
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medicine, farmaceutic industry, cosmetics and perfumery, aromatherapy and agriculture the
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increase of essential oils market demand[1-8]. Thus it was quantified that annually there are
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obatined around 40,000-60,000 tones of essential oils with an estimated market value of 700
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million US dolars [4]. Products` prices depends on plants` quality, extraction methods and area of
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application (http://www.edenbotanicals.com; http:/www. newdirectionsaromatics.ca 19.03.2015).
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The present paper aimed to emphasise the main research directions regarding essential oils`
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extraction, stabilization and their utilization as natural compnents in food industry.
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Extraction and processing of essential oils
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Essential oils (EOs) are complex mixtures of volatile compounds extracted from plants. They are
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insoluble in water and have a low molecular mass. However the exact definition of essential oils
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remain a matter of debate in scientific community. The majority accept the definition given by
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the International Standards Organization (ISO), which limits the extraction methods used for
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essential oils obtainig. According to ISO 9235.2 speciffications essential oils` definition is ”A
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product obtained from vegetable raw material—either by distillation with water or steam or—
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from the epicarp of Citrus fruits by a mechanical process, or—by dry distillation” [2, 9••]. The
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regulation also states that steam distillation can be conducted with of without the precence of
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water in the distillery, while for dry distillation it is forbidden the presence of water or water
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vapours in the still. Also the possibility of raw essential oil processing by different methods like
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redistillation, rectification, aeration etc. is pointed out.
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Aromatic plants used for essential oils extractions are found on all continents. Some aromatic
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plants are collected from wild flora (wild collection) that benefit from the advantages of natural
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developing conditions. However most of the aromatic herbs are harvested from systematic crops,
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which are cultivated in ecological conditions.
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There are known more than 3000 essential oils types from which only about 300 are of
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commertial interest[1, 5•].
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Essential oils are biosinthetised in diffent parts of herbs and are then released in the form of
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perfume through petals` epidermal cells, or can accumulate and store in different anatomical
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parts of the plant, such as cells with intracellular secretion, glandular trichomes, secretory canals
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and pockets [9,10] .
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Whole aromatic herbs or parts like leaves, flowers, buds, seeds, fruits, roots, wood or bark are
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harvested during certain maturity stages characteristic for each plant, stored in controlled
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conditions of light, temperature and humidity and then subjected to different extraction methods
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[10].
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Systemized extraction techniques as a function of required quantities, process complexity and
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essential oils` utilization field are presented in figure 1. Thus it can be seen that obtaining of high
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quantities of essential oils for commertial interest is performed by classical methods such as
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distillation, organic solvent extraction and cold pressing.
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Figure 1.
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Distillation is known to be the oldest and the simplest method of essential oils extraction. It can
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be applied in various technological options. The presence or absence of water in contact with
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vegetal material are the main technological differences which gives us hidrodistillation, vapor-
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hidrodistilation and steam distillation. However, the previously mentioned methods have some
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disadvantages like high energy consumption, long extraction time (4-6 h), simultaneous
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extraction of other polar components (coumarins, plant pigments), degradation of temperature
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sensitive compounds and environment pollution [9, 11].
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Citrus essential oils are obtained through cold pressing methods where the oil glands localized in
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the external part of the mesocarpe break down and release essential oils which are further
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separated by centrifugation.
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During last years new extraction technologies have been developed which eliminate some of the
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classical methods disadvanages. In some methods alternative sources of energy like ultrasound
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assisted extraction [12], or microwave assisted extraction [13-15]. are used, while other methods
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improved solvent characteristics: supercritical fluid extraction [16-19] or subcritical water
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extraction [9, 20].
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When speaking of supercritical fluid extraction, CO2 is mostly used due to its special properties:
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decreased values of critical parameters (Tcr = 31.1oC and Pcr = 7.4 MPa), low chemical reactivity,
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low toxicity and reasonable price. In the supercritical phase (31-55 oC and 0.5-7.4 MPa), CO2
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behaves as a nonpolar liquid with high diffusivity which allow the extraction of nonpolar
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components from targeted material.
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Subcritical water extraction (SWE) also known as pressurized hot water extraction (PHWE) or
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pressurized low polarity water extraction (PLPWE) is a new technique used for essential oils
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extraction where superheated water is used, at temperatures ranging between 100 and 375 oC
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(critical temperature) at high pressures (>20 bar). In these conditions water polarity decreases
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due to its dielectric constant decline until 14.86 (350 oC and 250 bar) thus ensuring nonpolar
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components solubilisation and their extraction from plant materials [9, 11]. Generally SWE are
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mainly used at lab and pilot plants scale for obtaining reduced quantities of essential oils. The
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most important advantages of these new techniques with regard to traditional ones are reduced
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power consumption and extraction time, extraction of a much higher number of components in a
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larger quantity, avoiding the degradation of temperature sensitive components and decreased
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environment pollution.
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Unconventional methods` description together with their application for bioactive components
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extraction are reported by research articles and review papers [12-18]. Of high interest is
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especially parameters` optimization such as to increase extraction yield and product`s quality
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[11, 18]. Microextraction methods are also gaining attention aiming mainly the rapid analyses of
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extract components. Low quantities of row material are used and all analyses are performed
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immediately after extraction (head space techniques, solid-phase microextraction). Most of the
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times row essential oils are further processed through redistillation, molecular distillation or
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rectification in order to remove any traces of lipids or natural waxes such as to obtain bioactive
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reach fractions of high purity [23••].
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A important problem regarding essential oils is their authenticity. The most used falsification
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methods are utilization of other herbs instead of authentic ones, addition of natural volatile
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compounds of poor quality or even mixing with other simple vegetable oils [23]. Falsification
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modifies essential oils` quality and affects products` safety where these are subsequntly used (
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foodstuff, cosmetics, drugs). This is why as a way of falsification prevention and detection
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international control organisations initiated rules and standards for essential oils usage. Also new
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authentification techniques were developed as CG, Chiral GC, Isotope-ratio mass spectrometry,
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HPLC and (HP)TLC analysis, Vibrational spectroscopy (IR, FTIR, NIR), Coupled and
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multidimensional chromatography (GC-GC, GC-MS) [24, 25].
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Chemical composition and biological activity of essential oils
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Essential oils chemical components are produced through three different pathways of
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biosynthesis processes: methyl-eritrytol pathway for mono and diterpenes, the mevalonate
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pathway for sesquiterpenes and the shichimic acid for phenylpropanoides [9,10]. Over 100
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different comoponents in various ratios (1-70%) can be found in a single type of essential oil.
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However a systematic chemical nomenclature for chemical compounds found in essential oils
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does not exist. Their scientifical names are given after their properties or provenince sources
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(e.g. terpenes, limonene, pinene, thymol, etc.). Generally EO`s chemical compounds are
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classified in terpenes, phenylpropanoids, sulfur or nitrogen compounds [2-4, 26]. In these groups
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cyclic and acyclic compounds from different classes can be found, like alcohols, esters, phenols,
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ketones, lactones, aldehydes and oxides (Figure 2).
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Figure 2
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Also essential oils` composition depends on plant`s specie and subspecie from which was
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extracted, plant`s part used for extraction geographic location, harvest time, extraction
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techniques and processing methods. Thus, terpens rich essential oils are extracted from
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Apiaceae, Asteraceae and Lamiaceae families; phenylpropanoids rich essential oils are extracted
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from Apiaceae (Umbelliferae), Lamiaceae, Myrtaceae, Piperaceae and Rutaceae families; while
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essential oils rich in sulfur and nitrogen compounds are found in plant families such as Alliaceae,
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Rutaceae and Brassicaceae [26].
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Chemical components found in essential oils account for their different biological properties like
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antibacterial, antifungal, anticancer, antiviral, antimutagenic, antiprotozoal, anti-inflamatory,
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antidiabetic or antioxidant ones [27-30]. These very qualities represent hopes for developing
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innovative farmaceutics or functional food products which would contribute to consummers
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health.
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Stabilisation of essential oils
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There are few physicochemical factors to which essential oils are sensitive like oxygen, light,
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temperature or pH. Thus, oxygen in the presence of light leads to oxidation of the unsaturated
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compounds resulting free radicals. By storing at high temperatures EO`s loose small quantities of
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volatile compounds. Also, there are some components which are highly instable at pH variations,
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like citral which is easily decomposed in acidic environment [31]. Encapsulation of essential oils
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is a way to protect them during storage, transport and processing. Encapsulation can ensure not
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only EO`s protection against various physicochemical factors but also flavor protection,
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preservation of its biological activity, masking the odor/smell and taste and oils transformation in
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water soluble pouders[32]. By slowly releasing EO`s components, microcapsules ensure flavor
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preservation and extends shelf life of food products in which they are added. The design of EO`s
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loaded micro- and nano- particles is an integrated process with interrelated stages. The process
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should ensure that obtained micro- and nano- particles could truly contribute to developing
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required attributes for a functional foodstuff, such as safety and security, increased nutrition
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value, health benefits, good sensorial properties and affordable price [33-36]. Choosing the food
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grade encapsulant material together with encapsulating techniques should be in agreement with
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the food nature matrix in which essential oils are to be introduced. For exemple, in order to
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introduce essential oils in drinks, these must be converted into liquid colloidal dispersions, nano-
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and micro- emulsions [37••, 38], or can be included in water soluble molecular systems such as
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cyclodextrines [39]. Polymer micro- and nano- capsules loaded with essential oils are used in
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dairy products [40, 41],
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Different delivery systems applied for food industry are presented in figure 3.
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Figure 3
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meat products [42-44], or backery and confectionery products[1].
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Essential oils in foods and safety issues
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Plants have been a part of humans life throughout its history. Life experience lead to
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plant choosing as a function of their benefits. Most of the times plants are used for foodstuff
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preservation or as a cure for different health issues. However, the quantity of used plants and
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plants extracts is limited by the sensitivity of the olfactory and taste sensors. Thus there was not
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identified safety problems for these type of “natural products”, the area being mostly neglected.
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Concepts like “long history of safe use” and the “principle of self-limitation” were considered 9
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satisfactory as for the natural flavor complexes to be considered ”safe under intended condition
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of use”. Generally based on the two consideration previously mentioned, US Food and Drug
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Administration (FDA), decided that 160 essential oils are ”generally recognized as safe” (GRAS)
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for utilizing in food preparation, drugs and beauty products [45••]. Among these in food industry
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are mainly used cinnamom, citrus, clove, lemon grass, coriander, oregano, sage, pimento, thyme
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and rosemary essential oils [46].
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With increasing consummers demands for “natural products” increased the necessity of
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testing such products composition. As a result, lately increased attention is given to chemical and
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toxicological characterization of essential oils used in food industry. International organisms like
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FDA, Codex Alimentarium, Food Chemical Codex (FCC), Flavor and Extract Manufactures
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Association (FEMA), International Organisation of Flavor Industries (IOFI) and Concil of
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Europe (CoE) established the chemical and toxicological analyses protocols, provided good
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practice guides for aromatic plants` and essential oils` processing, established limits for minimal
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and maximal volatile components quantities that should be found in essential oils. According to
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FCC for EO`s commercialization as food flavors must be stated the mean concentrations of the
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congener components group, with confidence limits for sufficient number of EO`s lots; its key
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constituents, with a zinc daily intake higher than 1.5 mg/day, which may be used for monitoring
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EO`s quality; and the trace constituents that could affect EO`s safety. Also three classes of toxic
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contituents were established: The first class include low toxicity compounds, which does not
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demand special investigations having the “fifth percentile no-observed-effect-level” (NOEL) of
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3.0 mg/Kg/d; the second class include less harmless components than the first class` ones and
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does not raise majour toxicity suspitions with the fifth percentile NOEL of 0.91 mg/Kg/d; and
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finally the third class which contains components with significant toxicity, which decreases the
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EO`s safety degree, with the fifth percentile NOEL of 0.15 mg/Kg/d. Also to the third class are
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associated unidentified components [47]. The coriander essential oil, one of the most used essential oils in food industry, belongs
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to the first class and can be safely consumed when used appropriately. The calculated individual
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consumption of coriander essential oil is 0.3624 mg/day or 0.00604 mg/Kg/day (total lower-
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intake value; FEMA) and 2.9476 mg/day or 0.0478 mg/kg/day (high-intake value; National
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Academy of Science). Based on FEMA, the maximum quantities of coriander essential oil that
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can be used in various domains of food industry are as follows: meat products (68.47 ppm),
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alcoholic beverages (121.20 ppm), nonalcoholic beverages (8.94 ppm), baked goods (62.06ppm),
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frozen dairy (47.35 ppm), chewing gum (6.62 ppm) [1]. In the EU countries are registered and
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generally recognized as safe following chemical components of EOS , used as flavoring agents:
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carvacrol, carvone, cinnamaldehyde, citral, p-cymene, eugenol, limonene, menthol and thymol.
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Estragole and methyl eugenol were removed from the safe list [48].
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Conclusions
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The specific taste and flavor of traditional kitchen together with its antibacterial and antioxidant
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characteristics, determined the use of essential oils as alternatives to synthetical aditives in order
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to cook tasty foodstuff with a high safety degree. Recent researches are focused on essential oils
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embedding in micro- and nano- particles which could be used for food processing or for
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developing new packaging technologies. However, there are needed more toxicologic studies on
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essential oils together with their effect on consumers security.
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pimento [Pimenta dioica (L) Merr.] by chitosan/k-carrageenan complex
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An excellent review of the design, formulation, and production of beverage emulsions. The
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authors performed a theoretical and experimental study on emulsion stability , physicochemical
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properties and fabrication methodology. These strategies can be adopted for utilization of the
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essential oils in beverage industry.
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40. Boroski M, Giroux HJ, Sabik H, Hélène V. Petit HV, Visentainer JV, Matumoto-Pintro
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PT, Britten M: Use of oregano extract and oregano essential oil as antioxidants in
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42. Jayasena DD, Cheorun J: Essential oils as potential antimicrobial agents in meat and meatproducts: A review. Trends Food Sci Tech 2013, 34: 96-108.
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43. Pesavento G, Calonico C, Bilia AR, Barnabei M, Calesini F, Addona R, Mencarelli L,
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Carmagnini L, Di Martino MC, Lo Nostro A: Antibacterial activity of Oregano,
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Rosmarinus and Thymus essential oils against Staphylococcus aureus and Listeria
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monocytogenes in beef meatballs. Food Control 2015, 54: 188-199.
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44. Dussault D, Dang Vu K, Lacroix M: In vitro evaluation of antimicrobial activities of
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various commercial essential oils, oleoresin and pure compounds against food
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pathogens and application in ham. Meat Sci, 2014, 96: 514–520.
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45. Tisserand R, Young R: Essential Oil Safety. A Guide for Health Care Professionals,
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Figure Caption:
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Figure 1. Essential oils extraction methods
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Figure 2. The main chemical compounds in essential oils
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Figure 3. Micro and nano systems used to encapsulation of essential oils
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S2214-7993(15)00095-8 http://dx.doi.org/doi:10.1016/j.cofs.2015.07.003 COFS 76
To appear in: Received date: Revised date: Accepted date:
19-5-2015 13-7-2015 14-7-2015
Please cite this article as: Dima, C., Dima, S.,Essential oils in foods: extraction, stabilisation and toxicity, COFS (2015), http://dx.doi.org/10.1016/j.cofs.2015.07.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Highlights Extraction and processing of essential oils
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Stabilisation of essential oils
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Essential oils in foods and safety issues
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Essential oils in foods: extraction, stabilisation and toxicity
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Cristian Dima1 and Stefan Dima2
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1
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Str. 111, RO-800201, Galati, Romania (Corresponding author: [email protected])
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”Dunărea de Jos” University of Galati, Faculty of Food Science and Engineering, ”Domneasca”
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2
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111, RO-800201, Galati, Romania
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”Dunărea de Jos” University of Galati, Faculty of Science and Environment, ”Domneasca” Str.
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Abstract
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Due to its biological properties, essential oils are used as ingredient for different products in
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order to increase their functionality such as foodstuff, drinks, perfumaries, pharmaceuticals,
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cosmetics or green pesticides. Current researches are manly focussed on developing innovative
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and friendly techniques for essential oils extraction and their afterword stabilization through
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incapsulation in order to obtain GRAS (general recognized as safe) natural products. The
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blooming grouth of essential oils market, require analytical methods diversification and
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improved regulations for their marketing and utilization.
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Introduction
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It can be said that through plants essential oils accompanied humanity during its entire history.
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There are numerous written testimonials attesting extraction and utilization of essential oils in
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different regions, such as India (5000 b.c.) and Mesopotamia or Greese (3000 b.c.) [1, 2••].
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From the very beginig of their discovery essential oils were used as food flavors and additives, as
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cures for different disseases, aphrodisiacs, cosmetics or during coult ritulas. Nowadays, the
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interest for essential oils increased both in terms of academical research and diversification of
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application domains. The use of essential oils in a large variety of areas like foode industry,
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medicine, farmaceutic industry, cosmetics and perfumery, aromatherapy and agriculture the
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increase of essential oils market demand[1-8]. Thus it was quantified that annually there are
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obatined around 40,000-60,000 tones of essential oils with an estimated market value of 700
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million US dolars [4]. Products` prices depends on plants` quality, extraction methods and area of
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application (http://www.edenbotanicals.com; http:/www. newdirectionsaromatics.ca 19.03.2015).
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The present paper aimed to emphasise the main research directions regarding essential oils`
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extraction, stabilization and their utilization as natural compnents in food industry.
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37
Extraction and processing of essential oils
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Essential oils (EOs) are complex mixtures of volatile compounds extracted from plants. They are
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insoluble in water and have a low molecular mass. However the exact definition of essential oils
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remain a matter of debate in scientific community. The majority accept the definition given by
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the International Standards Organization (ISO), which limits the extraction methods used for
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essential oils obtainig. According to ISO 9235.2 speciffications essential oils` definition is ”A
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product obtained from vegetable raw material—either by distillation with water or steam or—
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from the epicarp of Citrus fruits by a mechanical process, or—by dry distillation” [2, 9••]. The
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regulation also states that steam distillation can be conducted with of without the precence of
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water in the distillery, while for dry distillation it is forbidden the presence of water or water
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vapours in the still. Also the possibility of raw essential oil processing by different methods like
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redistillation, rectification, aeration etc. is pointed out.
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Aromatic plants used for essential oils extractions are found on all continents. Some aromatic
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plants are collected from wild flora (wild collection) that benefit from the advantages of natural
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developing conditions. However most of the aromatic herbs are harvested from systematic crops,
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which are cultivated in ecological conditions.
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There are known more than 3000 essential oils types from which only about 300 are of
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commertial interest[1, 5•].
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Essential oils are biosinthetised in diffent parts of herbs and are then released in the form of
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perfume through petals` epidermal cells, or can accumulate and store in different anatomical
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parts of the plant, such as cells with intracellular secretion, glandular trichomes, secretory canals
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and pockets [9,10] .
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Whole aromatic herbs or parts like leaves, flowers, buds, seeds, fruits, roots, wood or bark are
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harvested during certain maturity stages characteristic for each plant, stored in controlled
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conditions of light, temperature and humidity and then subjected to different extraction methods
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[10].
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Systemized extraction techniques as a function of required quantities, process complexity and
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essential oils` utilization field are presented in figure 1. Thus it can be seen that obtaining of high
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quantities of essential oils for commertial interest is performed by classical methods such as
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distillation, organic solvent extraction and cold pressing.
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Figure 1.
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Distillation is known to be the oldest and the simplest method of essential oils extraction. It can
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be applied in various technological options. The presence or absence of water in contact with
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vegetal material are the main technological differences which gives us hidrodistillation, vapor-
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hidrodistilation and steam distillation. However, the previously mentioned methods have some
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disadvantages like high energy consumption, long extraction time (4-6 h), simultaneous
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extraction of other polar components (coumarins, plant pigments), degradation of temperature
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sensitive compounds and environment pollution [9, 11].
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Citrus essential oils are obtained through cold pressing methods where the oil glands localized in
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the external part of the mesocarpe break down and release essential oils which are further
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separated by centrifugation.
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During last years new extraction technologies have been developed which eliminate some of the
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classical methods disadvanages. In some methods alternative sources of energy like ultrasound
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assisted extraction [12], or microwave assisted extraction [13-15]. are used, while other methods
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improved solvent characteristics: supercritical fluid extraction [16-19] or subcritical water
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extraction [9, 20].
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When speaking of supercritical fluid extraction, CO2 is mostly used due to its special properties:
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decreased values of critical parameters (Tcr = 31.1oC and Pcr = 7.4 MPa), low chemical reactivity,
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low toxicity and reasonable price. In the supercritical phase (31-55 oC and 0.5-7.4 MPa), CO2
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behaves as a nonpolar liquid with high diffusivity which allow the extraction of nonpolar
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components from targeted material.
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Subcritical water extraction (SWE) also known as pressurized hot water extraction (PHWE) or
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pressurized low polarity water extraction (PLPWE) is a new technique used for essential oils
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extraction where superheated water is used, at temperatures ranging between 100 and 375 oC
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(critical temperature) at high pressures (>20 bar). In these conditions water polarity decreases
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due to its dielectric constant decline until 14.86 (350 oC and 250 bar) thus ensuring nonpolar
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components solubilisation and their extraction from plant materials [9, 11]. Generally SWE are
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mainly used at lab and pilot plants scale for obtaining reduced quantities of essential oils. The
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most important advantages of these new techniques with regard to traditional ones are reduced
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power consumption and extraction time, extraction of a much higher number of components in a
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larger quantity, avoiding the degradation of temperature sensitive components and decreased
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environment pollution.
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Unconventional methods` description together with their application for bioactive components
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extraction are reported by research articles and review papers [12-18]. Of high interest is
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especially parameters` optimization such as to increase extraction yield and product`s quality
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[11, 18]. Microextraction methods are also gaining attention aiming mainly the rapid analyses of
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extract components. Low quantities of row material are used and all analyses are performed
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immediately after extraction (head space techniques, solid-phase microextraction). Most of the
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times row essential oils are further processed through redistillation, molecular distillation or
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rectification in order to remove any traces of lipids or natural waxes such as to obtain bioactive
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reach fractions of high purity [23••].
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A important problem regarding essential oils is their authenticity. The most used falsification
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methods are utilization of other herbs instead of authentic ones, addition of natural volatile
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compounds of poor quality or even mixing with other simple vegetable oils [23]. Falsification
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modifies essential oils` quality and affects products` safety where these are subsequntly used (
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foodstuff, cosmetics, drugs). This is why as a way of falsification prevention and detection
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international control organisations initiated rules and standards for essential oils usage. Also new
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authentification techniques were developed as CG, Chiral GC, Isotope-ratio mass spectrometry,
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HPLC and (HP)TLC analysis, Vibrational spectroscopy (IR, FTIR, NIR), Coupled and
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multidimensional chromatography (GC-GC, GC-MS) [24, 25].
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Chemical composition and biological activity of essential oils
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Essential oils chemical components are produced through three different pathways of
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biosynthesis processes: methyl-eritrytol pathway for mono and diterpenes, the mevalonate
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pathway for sesquiterpenes and the shichimic acid for phenylpropanoides [9,10]. Over 100
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different comoponents in various ratios (1-70%) can be found in a single type of essential oil.
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However a systematic chemical nomenclature for chemical compounds found in essential oils
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does not exist. Their scientifical names are given after their properties or provenince sources
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(e.g. terpenes, limonene, pinene, thymol, etc.). Generally EO`s chemical compounds are
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classified in terpenes, phenylpropanoids, sulfur or nitrogen compounds [2-4, 26]. In these groups
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cyclic and acyclic compounds from different classes can be found, like alcohols, esters, phenols,
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ketones, lactones, aldehydes and oxides (Figure 2).
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Figure 2
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Also essential oils` composition depends on plant`s specie and subspecie from which was
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extracted, plant`s part used for extraction geographic location, harvest time, extraction
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techniques and processing methods. Thus, terpens rich essential oils are extracted from
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Apiaceae, Asteraceae and Lamiaceae families; phenylpropanoids rich essential oils are extracted
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from Apiaceae (Umbelliferae), Lamiaceae, Myrtaceae, Piperaceae and Rutaceae families; while
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essential oils rich in sulfur and nitrogen compounds are found in plant families such as Alliaceae,
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Rutaceae and Brassicaceae [26].
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Chemical components found in essential oils account for their different biological properties like
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antibacterial, antifungal, anticancer, antiviral, antimutagenic, antiprotozoal, anti-inflamatory,
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antidiabetic or antioxidant ones [27-30]. These very qualities represent hopes for developing
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innovative farmaceutics or functional food products which would contribute to consummers
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health.
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Stabilisation of essential oils
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There are few physicochemical factors to which essential oils are sensitive like oxygen, light,
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temperature or pH. Thus, oxygen in the presence of light leads to oxidation of the unsaturated
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compounds resulting free radicals. By storing at high temperatures EO`s loose small quantities of
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volatile compounds. Also, there are some components which are highly instable at pH variations,
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like citral which is easily decomposed in acidic environment [31]. Encapsulation of essential oils
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is a way to protect them during storage, transport and processing. Encapsulation can ensure not
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only EO`s protection against various physicochemical factors but also flavor protection,
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preservation of its biological activity, masking the odor/smell and taste and oils transformation in
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water soluble pouders[32]. By slowly releasing EO`s components, microcapsules ensure flavor
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preservation and extends shelf life of food products in which they are added. The design of EO`s
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loaded micro- and nano- particles is an integrated process with interrelated stages. The process
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should ensure that obtained micro- and nano- particles could truly contribute to developing
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required attributes for a functional foodstuff, such as safety and security, increased nutrition
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value, health benefits, good sensorial properties and affordable price [33-36]. Choosing the food
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grade encapsulant material together with encapsulating techniques should be in agreement with
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the food nature matrix in which essential oils are to be introduced. For exemple, in order to
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introduce essential oils in drinks, these must be converted into liquid colloidal dispersions, nano-
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and micro- emulsions [37••, 38], or can be included in water soluble molecular systems such as
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cyclodextrines [39]. Polymer micro- and nano- capsules loaded with essential oils are used in
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dairy products [40, 41],
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Different delivery systems applied for food industry are presented in figure 3.
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meat products [42-44], or backery and confectionery products[1].
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Essential oils in foods and safety issues
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Plants have been a part of humans life throughout its history. Life experience lead to
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plant choosing as a function of their benefits. Most of the times plants are used for foodstuff
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preservation or as a cure for different health issues. However, the quantity of used plants and
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plants extracts is limited by the sensitivity of the olfactory and taste sensors. Thus there was not
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identified safety problems for these type of “natural products”, the area being mostly neglected.
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Concepts like “long history of safe use” and the “principle of self-limitation” were considered 9
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satisfactory as for the natural flavor complexes to be considered ”safe under intended condition
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of use”. Generally based on the two consideration previously mentioned, US Food and Drug
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Administration (FDA), decided that 160 essential oils are ”generally recognized as safe” (GRAS)
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for utilizing in food preparation, drugs and beauty products [45••]. Among these in food industry
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are mainly used cinnamom, citrus, clove, lemon grass, coriander, oregano, sage, pimento, thyme
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and rosemary essential oils [46].
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With increasing consummers demands for “natural products” increased the necessity of
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testing such products composition. As a result, lately increased attention is given to chemical and
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toxicological characterization of essential oils used in food industry. International organisms like
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FDA, Codex Alimentarium, Food Chemical Codex (FCC), Flavor and Extract Manufactures
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Association (FEMA), International Organisation of Flavor Industries (IOFI) and Concil of
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Europe (CoE) established the chemical and toxicological analyses protocols, provided good
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practice guides for aromatic plants` and essential oils` processing, established limits for minimal
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and maximal volatile components quantities that should be found in essential oils. According to
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FCC for EO`s commercialization as food flavors must be stated the mean concentrations of the
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congener components group, with confidence limits for sufficient number of EO`s lots; its key
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constituents, with a zinc daily intake higher than 1.5 mg/day, which may be used for monitoring
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EO`s quality; and the trace constituents that could affect EO`s safety. Also three classes of toxic
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contituents were established: The first class include low toxicity compounds, which does not
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demand special investigations having the “fifth percentile no-observed-effect-level” (NOEL) of
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3.0 mg/Kg/d; the second class include less harmless components than the first class` ones and
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does not raise majour toxicity suspitions with the fifth percentile NOEL of 0.91 mg/Kg/d; and
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finally the third class which contains components with significant toxicity, which decreases the
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EO`s safety degree, with the fifth percentile NOEL of 0.15 mg/Kg/d. Also to the third class are
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associated unidentified components [47]. The coriander essential oil, one of the most used essential oils in food industry, belongs
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to the first class and can be safely consumed when used appropriately. The calculated individual
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consumption of coriander essential oil is 0.3624 mg/day or 0.00604 mg/Kg/day (total lower-
209
intake value; FEMA) and 2.9476 mg/day or 0.0478 mg/kg/day (high-intake value; National
210
Academy of Science). Based on FEMA, the maximum quantities of coriander essential oil that
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can be used in various domains of food industry are as follows: meat products (68.47 ppm),
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alcoholic beverages (121.20 ppm), nonalcoholic beverages (8.94 ppm), baked goods (62.06ppm),
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frozen dairy (47.35 ppm), chewing gum (6.62 ppm) [1]. In the EU countries are registered and
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generally recognized as safe following chemical components of EOS , used as flavoring agents:
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carvacrol, carvone, cinnamaldehyde, citral, p-cymene, eugenol, limonene, menthol and thymol.
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Estragole and methyl eugenol were removed from the safe list [48].
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Conclusions
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The specific taste and flavor of traditional kitchen together with its antibacterial and antioxidant
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characteristics, determined the use of essential oils as alternatives to synthetical aditives in order
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to cook tasty foodstuff with a high safety degree. Recent researches are focused on essential oils
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embedding in micro- and nano- particles which could be used for food processing or for
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developing new packaging technologies. However, there are needed more toxicologic studies on
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essential oils together with their effect on consumers security.
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Figure 1. Essential oils extraction methods
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Figure 2. The main chemical compounds in essential oils
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