ISSN: 2384-6364
Analysis and
Comparative Study of
Essential Oil
Extracted from
Nigerian Orange,
Lemon and Lime
Peels
By
V.I. Njoku
B.O. Evbuomwan
Greener Journal of Chemical Science and Technology
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
Research Article
Analysis and Comparative Study of Essential Oil
Extracted from Nigerian Orange, Lemon and Lime
Peels
*V.I. Njoku, B.O. Evbuomwan
Department of Chemical Engineering, college of Graduate Studies, University of Port Harcourt, Choba, Nigeria.
*Corresponding Author’s Email: letsbeconnected@yahoo.com, Phone: +2348037733196
ABSTRACT
Essential oils are a product obtained from vegetable raw materials and are complex mixtures whose composition
may include volatile terpenic compounds. In this study, the relationship between time and amount of essential oil
extracted from the citrus peels using steam distillation was shown. Orange peel was shown to contain more amount
of essential oil (20ml at 180minutes) than lemon (7ml at 180minutes) and lime (5ml at 180minutes).Using GC-MS
analysis, 11, 12 and 24 chemical constituents were identified in orange, lemon and lime essential oil respectively.
The 3 main components and their percentage compositions are D-Limonene (54.151%), Pulegone (11.652%) and LCarvone (2-cyclohexen-1-one) (5.457%) for orange peel essential oil, D-limonene (64%), 2-cyclohexen-1-ol (6.21%)
and β-Pinene (3.822%) for lemon peel essential oil, and β-Pinene (23.124%), D-limonene (17.07%) and α-Pinene
(10.399%) for lime essential oil. D-limonene was the most prevalent chemical constituent in orange and lemon
essential oil, but β-Pinene was the most prevalent in lime peel essential oil. Although lemon contained more Dlimonene per unit volume of essential oil, application of these percentages on the volume of essential oil obtained
from 370g of the peels at 180minutes showed that orange peel can deliver more D-limonene per unit mass of
available peel. Hence, orange peel essential oil is a more economical source of D-limonene in Nigeria.
Keywords: Quantitative, Analysis, Qualitative, Comparative, Extracted, Essential oil, Orange, Lemon, Lime.
1. INTRODUCTION
Essential oil from citrus is a large type of natural flavours and fragrances, which is popularly used in food
industries, daily chemical product and health care field (Sheng-min et al., 2012). The citrus species are a
potential source of variable oil which might be utilized for edible and other industrial application (Maria et al.,
2012). Essential oils are broadly used as pharmaceutical components, in nutritious supplements and for cosmetic
industry and aromatherapy (Maria et al., 2012). Guenther (1955) also stated that the oil is also employed in
perfumes, toilet waters, eaux de cologne, and in cosmetics to which it impacts a refreshing top note.
Essential oils are a product obtained from vegetable raw materials (Berger, 2007), and are complex
mixtures whose composition may include volatile terpenic compounds, which have the formula (C5H8)n, where the
compounds are monoterpenes if n=2, sesquiterpenes when n=3, diterpenes when n=4 etc (Smith et al., 2001).
These are secondary metabolites in plants (Mazen, 2002) and responsible for the characteristic aroma on the fruit.
Lemon essential oil are complex mixtures of chemical compounds like limonene, Y-terpinene, citral,
linalool and β-caryophyllene among others, which can be represented by three main classes, namely terpenes,
oxygenates, and sesquiterpenes (Benvenuti et al., 2001). The most significant flavour compound is citral, while
linalool possesses highly distinctive organoleptic characteristics. In addition, limonene, myrcene, octanol, and Yterpene among others contribute with high aroma flavour of lemon oil (Benvenuti et al., 2001).
The composition of orange oil varies for several reasons. Region and seasonal changes as well as the
method used for extraction lead to these variation. Gamarra et al. (2006) also stated that the quality of essential
oil depends on different factors; among them are the chemotype and biotype of the plant, the climatic conditions
as well as the extractive process. Several compounds have been identified in orange oil with gas chromatographmass spectrometry. Most of the substances are part of the terpene group (limonene, α-pinene, sabinene, βpinene, myrcene and δ-3-carene) with limonene being the dominant one. Long chain aliphatic hydrocarbon
alcohols and aldehydes like octanol, decanal, and octanal are second important group of substances (Verzera et
al., 2004).
Citrus fruits have a rough, robust and bright (green to yellow) coloured skin. They are usually 4 to 30cm
long and 4 to 20cm in diameter, with a leathery surrounding rind or skin known as epicarp (or flavedo) that cover
the fruits and protect it from damages. Citrus fruits are notable for their fragrance, partly due to flavanoids and
limonoids contained in the rind (Manthey, 2004). The endocarp is rich in soluble sugar and contains significant
www.gjournals.org
6
Greener Journal of Chemical Science and Technology
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
amounts of vitamin C, pectin, fibres, different organic acids and potassium salt which give the fruits its
characteristic citrus flavour (Ezejiofor et al., 2011). Citrus juice also contains a high quality of organic acids (citric,
malic, acetic and formic acids).
In Nigeria and other parts of the world, citrus sinensis (sweet orange) are cheaply available, thus serves
as a major source of vitamins in diets. Orange fruit and its juice have several beneficial, nutritive and health
properties (Okwu and Emenike, 2006). They are rich in vitamins especially ascorbic and folic acids. Over the last
decades, many other virtues and medicinal benefits of orange fruits have been discovered besides their antiscurvy property (Rapisararda, 1999). There is convincing epidemiological evidence that the consumption of
orange fruit is beneficial to health and contributes to the prevention of degenerative process, particularly lowering
incidence of degenerative process, particularly cardio and cerebro- vascular diseases (Rapisararda, 1999). The
protection that orange fruit provides against these diseases has been attributed to the various antioxidant
phytonutrients contained in citrus species (Okwu and Emenike, 2006; Rapisararda, 1999).
The current annual world production of citrus fruits is approximately 110 million tons, of which oranges
constitute about 80 million tons (USDA, 2013). In Nigeria, about 930,000 tons of citrus fruits are produced
annually from an estimate of 3 million hectares (FAO, 2008).
The objective of the research was to:
a.
b.
c.
d.
e.
Determine the relationship between time and quantity of essential oils obtained from citrus peels,
Compare quantitatively the composition of essential oils obtained from orange, lemon and lime peels,
Determine the percentage of components present in the essential oils,
Identify the major components present in the composition, and
Determine the physicochemical properties of the essential oils.
2. MATERIALS AND METHODS
a. Steam Distillation
Oranges used in this work were bought from Rumuokoro market in Portharcourt, Rivers state, Nigeria. They were
washed with de-ionized water, peeled and cut into small pieces. The orange peel was then weighed using
RADWAG WAGI electronic top loading balance (AS 220/C/2) to obtain exactly 370grams. The orange peels were
then pureed using MARLEX ELECTROLINE (Excella) blender.
The pureed orange peel was then carefully transferred into a 1000ml flat bottom flask. 650ml of deionized water was measured using a 1000ml measuring cylinder and then added to the 1000ml flat bottom flask
(distilling flask). Boiling chips was then added to the distilling flask to ensure that boiling occurs calmly without
bumping. The experiment was then set-up as shown in Figure 1 below;
Figure 1: laboratory set-up for the steam distillation of citrus peel.
Heating of the distilling flask was then slowly commenced using STUART HOT PLATE/ MAGNETIC STIRER.
The heat source was adjusted so that the distilling rate is approximately 20 drops per minutes. As the mixture
boils and distils, de-ionized water was added via the separation funnel in the set-up just to keep the water level at
Greener Journal of Chemical Science and Technology
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
the operation level preventing the water level from going too low which can cause the sugar in the puree to
caramelize and burn and also keeping the heat at a low steady level. The experiment was conducted for the
following times; 60, 100, 140 and 180 minutes, in each case, the distillate was collected and transferred into a
250ml separating funnel. 20ml of diethyl ether was added to the distillate in the separating funnel to extract the
oil. It was ensured that there was no flame source or hot plate ‘’on’’ during the use of diethyl ether because
diethyl ether is very, very flammable. The water layer in the separating funnel was then drained off. The diethyl
ether layer was collected and small quantity of anhydrous magnesium sulphate was added to dry off the water
content. The oil was then kept in a fume cupboard for 12 hours to allow all the diethyl ether vapourize. The oil
extracted was then measured and recorded.
b. Quantitative and qualitative analysis of citrus peel essential oils
The quantitative and qualitative analysis of the citrus peel essential oil was done using (5975 Series MSD with an
Agilent 7890A). 0.5 mL of each of the oil samples was diluted to 5 mL by the addition of 4.5 mL of methylene
chloride (diluents). Helium was used as the carrier gas because of its inert nature.
3.0. EXPERIMENTS
3.1. Determination of the solubility of citrus peel essential oil in water
Approximately 6 drops of water was added to the test tube containing 3 drops of orange peel essential oil. The
test tube was stirred thoroughly with a glass stirring rod. Two separate phases was observed.
The pH of the water was measured to determine if the essential oil is partially soluble in water and
whether it has changed the pH of the water. It was observed that the pH paper did not change colour. Thus, the
orange peel essential oil is a water insoluble compound. The above experiment was carried out on lemon and
lime essential oil, and same result was obtained.
3.2.
Determination of the boiling point of citrus peel essential oil
5ml of the essential oil was placed in a small test tube. A capillary, sealed at one end is placed open-end down
into the essential oil. The test tube is firmly attached to a thermometer with a rubber band such that the
thermometer bulb should be even with the test tube’s bottom, and this entire assembly immersed in an oil bath
(half filled 100ml beaker). As the temperature is slowly increased, a rapid evolution of bubbles from the end of the
tube begins. Heating was continued for about 5-10 seconds to be sure that all of the air has been expelled from
the capillary, and the vapours of the essential oil become equal to the atmospheric pressure. As the temperature
decreases, the bubbles slowed down and the essential oil starts rising into the capillary. At the point when the
bubble stops, the thermometer was read and recorded. The above process was repeated 2 more times, and the
temperature reading in each case was recorded. The above experiment was carried out on orange, lemon and
lime essential oil at atmospheric pressure.
3.3.
Determination of specific gravity of orange peel essential oil
Density bottle was used for determining the density of the oil. A clean and dry bottle of 25ml capacity was
weighed (W0) and then filled with the oil, stopper inserted and reweighed to give (W1). The oil was substituted
with water after washing and drying the bottle and weighed to give (W2).The above experiment was done using
orange, lemon, and lime essential oil.
3.4.
Determination of refractive index of citrus peel essential oil
The Abb's refractometer was used for the determination of refractive index. It gives values up to the 4th decimal
place. The refractive index is denoted by nD25” where n is the refractive index at 25°C taken with sodium light (D line). First, the refractometer was standardized with distilled water which has refractive index of nD29.5=
1.3315. Then it was cleaned with acetone and dried with cotton. After this, a drop of orange peel essential oil
was placed between the prisms of refractometer. The telescope was rotated to bring the border line of total
refraction to the junction of cross-wire in the telescope. The refractive index was recorded at room
temperature.
The above experiment was repeated for lemon and lime peel essential oil.
www.gjournals.org
8
Greener Journal of Chemical Science and Technology
3.5.
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
Determination of peroxide value of orange, lime and lemon essential oil
30ml of acetic acid chloroform solution was measured into a flask containing 2g of the oil sample. A 0.5ml
saturated solution of potassium iodide was then added, followed closely by the addition of 30ml of distilled water.
The flask content was then titrated against 0.1M sodium thiosulphate (Na2S2O3) until the yellow colour almost
disappeared. 0.5ml starch indicator was added and the titration continued until the end-point (where the blueblack colour just disappeared). A blank titration was also performed.
Where S and B represent sample and blank titrations respectively.
The peroxide value is thus calculated;
PEROXIDE VALUE =
.
Where S= Sample titration.
B= Blank titration.
3.6.
Determination of saponification value of citrus peel essential oil
5.3716g of orange peel essential oil were weighed into a conical flask separately. 25ml of 0.1N ethanolic
potassium hydroxide was added to the conical flask, and content constantly stirred for 1 hour followed by reflux.
Phenolpthalein indicator was then added to the conical flask and titrated with 0.5M HCl till the solution changes to
colourless. The same procedure was repeated for the blank.
The above experiment was repeated using 5.3014g of lemon and 5.3006g of lime essential oil.
3.7.
Determination of acid value of citrus peel essential oil
25ml of diethyl ether and 25ml of ethanol was mixed in a 250ml beaker. The resulting mixture was added to
5.0858g orange peel essential oil in a 250ml conical flask, and few drops of phenolphthalein were added to the
mixture. The mixture was then titrated with 0.1M KOH to the end point with consistent shaking for which a dark
pink colour was observed and the volume of 0.1M KOH (Vo) was noted.
The above experiment was repeated using 5.0808g lemon and 5.0826g lime essential oil.
4. RESULTS AND DISCUSSION
a. Steam distillation
The time and quantity of essential oil extracted from the citrus peels are presented in Tables 1, 2 and 3, and
Figure 2, 3, 4, and 5 for orange, lemon and lime respectively.
From Table 1, 2 and 3 for orange, lemon and lime respectively, it was observed that the volume of
essential oil extracted from the peels increases with time. It was also noticed that more essential oil (20ml) at 180
minutes of heating was extracted from 370g of the orange peels than from equal mass of lemon and lime peel at
the same time of heating, while lime had the least quantity of essential oil extracted (5 ml). These observations
are in agreement with the findings of Kamal et al.(2011) who reported that among the citrus species tested, C.
Sinensis exhibited the maximum oil yield (0.24-1.07%) followed by C. reticulata (0.30-0.50%) and C. paradisii
(0.20-0.40%). Gamarra et al. (2006) stated that the quality of essential oil depends on different factors; among
them are the chemotype and biotype of the plant, the climatic conditions as well as the extractive process.
Soumaya et al.(2012) also reports that essential oil yield varied during ripening to reach maximum values during
the middle stage of maturity (stage 2) for mandarin and orange, while the highest lemon yield was found at the
beginning of fruit maturation and decreased after that. Also Des Gachons et al. (2005) stated that water supply
during ripening was reported to influence considerably the essential oil content with an enhancement of yield
under moderate water shortage conditions. All these will possibly be responsible for the high yield of orange
essential oil over that of lemon and lime.
www.gjournals.org
9
Greener Journal of Chemical Science and Technology
S/N
1
2
3
4
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
Table 1: Variation of volumes of essential oil extracted from orange peel.
0
Plant
Weight Volume of Time
of Temp.( c) Volume of
essential
material
(gm.)
distilled
heating(min)
water(ml)
oil (ml)
ORANGE 370
650
60
100
14
PEEL
370
650
100
100
16
370
650
140
100
18
370
650
180
100
20
20
15
Volume of orange Oil (ml)
10
Volume of Lemon oil (ml)
Volume of Lime oil (ml)
5
0
60 mins 100 mins 140 mins 180 mins
Figure 2: Volume of essential oils extracted from citrus following different extraction periods.
a.
Physicochemical properties of citrus peels
Table 2: Physicochemical properties of citrus peel essential oils.
Properties
Specific gravity
Boiling point ( OC)
Refractive index
Solubility in water
Saponification value ( mg KOH/g oil)
Acid value ( mg KOH/g oil)
Peroxide value
b.
Orange
0.84
174.6
1.47
Insoluble
16.19
1.99
68.75
Lemon
0.85
176.3
1.48
Insoluble
13.76
1.77
13.57
Lime
0.86
182.3
1.48
Insoluble
13.23
2.20
9.57
Quantitative and qualitative analysis of citrus peel essential oils
The orange, lemon and lime peel essential oils contained a total of 11, 12 and 24 components, respectively.
Table 3 shows the total components and their percentage composition for orange, lemon and lime, essential oils.
The GC-MS chromatogram for orange, lemon and lime are shown in Figures 3, 4 and 5, respectively.
Greener Journal of Chemical Science and Technology
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
Figure 3: Gas chromatographic plot for orange peel essential oil.
Figure 4: Gas chromatographic plot for lemon peel essential oil.
Greener Journal of Chemical Science and Technology
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
Figure 5: Gas chromatographic plot for orange peel essential oil.
Table 3: Components and percentage composition in orange, lemon and lime peel essential oil.
COMPONENT
COMPOSITION (%)
ORANGE LEMON
LIME
1R-α-Pinene
4.45
3.20
10.40
Cyclohexene
1.91
6.92
D-Limonene
54.15
64.00
17.07
(Z)-3-Carene
3.71
1,3,8-p-Menthatriene
2.81
2.91
0.83
Pulegone
11.65
1-Methylcyclohexa-1,3-diene
4.35
1,3-Cycloheptadiene
3.98
2-Cyclohexen-1-ol
5.23
6.21
1,4-Cyclohexadiene
2.30
2.54
5.52
2-Cyclohexen-1-one (L5.46
3.27
Carvone)
β-Phellandrene
3.52
β-Pinene
3.82
23.12
1,4-Cyclohexadiene
1.96
Cis-p-Mentha-2,8-dien-1-ol
3.15
2-methyl-5-(1-methylethenyl)2.97
3-Cyclohexen-1-ol
2.46
4.96
α-Phellandrene
1.33
Ocimene
0.73
Bicyclo[4.1.0]hept-2-ene
1.10
3-Carene
2.03
Bicyclo[3.1.0]heptan-3-ol
1.32
3-Cyclohexene-1-methanol
3.61
E,Z-4-Ethylidenecyclohexene
1.15
2-Cyclohexen-1-ol
1.12
2-Cyclohexen-1-one
0.81
2,6-Octadienal
1.32
1,3-Cyclohexadiene
1.01
Greener Journal of Chemical Science and Technology
1S-α-Pinene
1H-Cycloprop[e]azulene
Caryophyllene
Trans-α-Bergamotene
Bicyclo[3.1.1]hept-2-ene
Caryophyllene oxide
ISSN: 2384-6364
-
Vol. 1 (1), pp. 006-014, May 2014.
-
0.79
1.24
4.80
4.67
2.48
1.67
The three highest occurring components in orange peel essential oil are D-limonene (54.15%), pulegone
(11.65%) and L-carvone (2-cyclohexen-1-one) (5.46%).
The three highest occurring components in lemon peel essential oil are D-limonene (64%), 2-cyclohexen1-ol (6.21%) and β-pinene (3.82%), and the three highest occurring components in lime peel essential oil are βpinene (23.12%), D-limonene (17.07%) and α-Pinene (10.40%). The amount of lemon peel essential oil for Dlimonene and β-pinene is in agreement with Soumaya, et al. (2012) findings that D-limonene (37.63-69.71%) , βpinene (0.63-31.49%), γ-terpene (0.04-9.96%), and p-cymene (0.23-9.84%) were the highest ones in lemon.
However percentage composition of sweet orange did not agree with that of Soumaya et al. (2012), which had a
percentage of (81.52-86.43%). Figueiredo et al. (2008) and Schmidt (2010) also stated that it needs to be kept in
mind that the chemical composition may already vary in the raw material, being influenced by plant health, growth
stage, habitat including climatic, edaphic factors, as well as harvest time.
Widmark and Blohm (1957) also stated that oxygen consumption upon storage of different
monoterpenes has been recorded. El. Nikeety et al. (1998); Turek and Florian (2013) went further to state that
changes in composition as well as physicochemical properties of essential oils were generally more pronounced
in half-filled containers than when only little or no headspace was present.
Asnaashari et al. (2010) stated that the GC-MS analysis of the essential oils of lime (C. aurantifolia) was
also performed and approximately 22 main components, with Limonene (28.27%) being the principal one, were
identified and quantified, as against 24 components identified in this work with β-pinene (23.12%) being the
principal one, and Limonene (17.07%) being the next most abundant.
However, from Table 3, it can be deduced that lemon peel essential oil has the highest percentage of Dlimonene (64%) when compared to the same quantity of the three oil samples. But, from Table 1, it can also be
seen that orange peel produced the highest volume of essential oil when compared with same mass of the three
citrus peels and same time of distillation.
Therefore, taking the longest time of heating (180 minutes) in Table 1 and the percentage composition of
D-limonene in the citrus peels in Table 3, orange peel produced 20 mL of essential oils, whereas lemon produced
7 mL and lime 5 mL. Working out the quantity of D-limonene in the volume of essential oil obtained from the
citrus peels after 180 minutes, using the percentage of D-limonene in the citrus peels as shown in Table 3, lime
peel essential oil contained 0.85 mL D-limonene, lemon 4.48 mL D-limonene, while orange peel essential oil
contained 10.83 mL D-limonene.
5. CONCLUSION
The results obtained showed that lemon peel contains more amount of D-limonene per unit volume of essential
oil, while orange peel contains more amount of essential oil than lime and lemon per unit mass of peel. However,
by obtaining percentage of D-limonene in volume of essential oil obtainable from unit mass of peel, it was
concluded that orange peel is a more viable and economical source of essential oil which is very rich in Dlimonene.
6. RECOMMENDATION
The shelf life of citrus peel essential oil have been established from literature to be greatly affected by its storage
conditions such as wrong storage containers, storage temperature and head space in storage containers. Thus,
citrus essential oil should be stored in amber bottles, and below room temperature, with the avoidance of
headspace in storage containers.
Further research to evaluate the effect of fertilizer application on;
a)
b)
c)
d)
The physicochemical properties of orange peel essential oil.
The chemical constituents in orange peel essential oil.
Volume of essential oil in orange peel.
Pectin content in orange peel.
www.gjournals.org
13
Greener Journal of Chemical Science and Technology
ISSN: 2384-6364
Vol. 1 (1), pp. 006-014, May 2014.
7. REFERENCE
Asnaashari, S; Delazar, A; Habibi, B; Nahar, L; Hamedeyazdan, S; Sarker, S.D., 2010, Essential oil from citrus
aursntifolia prevents ketotifen-induced weight-gain in mice. 24(12): 1893-7. Doi: 1002/ptr.3227.
Benvenuti, F; Gironi, F; Lamberti, L. ,2001, Supercritical deterpenation of lemon essential oil, experimental data
and simulation of their semi continuous extraction process. Journal of supercritical fluids. 20, 29-44.
Berger, R.G., 2007, Flavours and Fragrances, Chemistry, bioprocessing and sustainability P. 118-133, 329.
Springer-Verlag, Berlin, Heidelberg, Germany.
Des, G.C.P.; Van, L.C.; Tominaga, T. S.; Gaudillère J.P.; Dobourdieu, D., 2005, Influence of water and nitrogen
deficit on fruit ripening and aroma potential of Vitis Vinifera L CV Sauvignon blanc infield conditions. Journal
of the science of food and Agriculture. 2005; 85(1): 73-85.
El-Nikeety, M.M.A.; El-Akel, A.T.M.; Abd El-Hady, M.M.I.; Badei A.Z.M., 1998, Changes in physical properties
and chemical constituents of parsley herb volatile oil during storage.Egypt J Food Sci 26–28:35–49.
Ezejiofor, T.I.N.; Eke, N.V.; Okechukwu, R.I., Nwoguikpe, R.N.; Duru, C.M., 2011, Waste to wealth: Industrial raw
materials potential of peels of Nigerian sweet orange (Citrus Sinensis). African Journal of Biotechnology Vol.
10(33), pp 6257-6264.
FAO, 2008
Figueiredo, A.C.; Barroso, J.G.; Pedro, L.G.; Scheffer, J.J.C., 2008, Factors affecting secondary metabolite
production in plants: volatile components and essential oils. Flavour Fragr J 23:213–26.
Gamarra, F.M.C.; Sakanaka, L.S.; Tambourgl, E.B.; Cabral, F.A., 2006, ‘Influence on the quality of essential
lemon (citrus aurantifolia) oil by distillation process’. Brazilian Journal of Chemical Engineering.
Guenther, E., 1955,‘The Essential oils’, Vol.111, Ed. Fritzsche Brothers INC, New York, USA, 777p.
Kamal, G.M.; Anwar, F.; Hussain, A.I.; Sarri, N.; Ashraf, M.Y., 2011, Yield and Chemical composition of Citrus
essential oils as affected by drying pretreatment of peels. International Food research Journal 18(4): 12751282(2011).
Manthey, J.A., 2004, Fractionation of orange peel phenols in ultra filtered molasses and balance studies of their
antioxidant levels. J. Agric. Food Chem. 52:7586-7592
Maria, C. C.; Rubria, E. R.; Jose E.B.; Gloria M. M.; Jose L.N.;Hugo, J., 2012, ‘Characterization of volatile
compounds in the Essential oil of sweet lime’ Chilean journal of Agricultural research 72(2), Pg 275.
Mazen, K.T., 2002, Molecular regulation of plant monoterpene biosynthesis in relation to fragrance 159p. Thesis
Wageningen Universiteit, Wageningen, the Netherlands.
Okwu, D.E. and Emenike, I.N., 2006, Evaluation of the phyto-nutrients and vitamins content of citrus fruits. Int. J.
Mol. Med. Adv. Sci. 2:1-6.
Rapisararda, G.H., 1999, Antioxidant effectiveness as influenced by phenolic content of fresh orange juice. J.
Food Chem. 47: 4718-4723.
Sheng-min1, L.U.;Ying-Chun, S. 1,2; Yang, Y.1., 2012,1. Institute of food science, Zhejiang Academy of
agricultural sciences, Hangzhon 310021, china; 2. Nanjing Agricultural University, Nanjing 210095, china,
Research progress on Extraction and Refining of citrus Essential oil.
Smith, D.C.; Forland, S.; Bachanos, E.; Matejka, M.; Barrett, V., 2001, Qualitative analysis of citrus fruit extracts
by GC/MS: an undergraduate experiment. Chemical educator 6: 28-31.
Soumaya, B.; Fatma, Z.R.; Iness, O.; Moufida, S.T., 2012, Changes of peel Essential oil composition of four
Tunisian citrus during fruit maturation.
Turek, C. and Florian, C.S., 2013, Stability of essential oils: A Review. DOI:10.1111/1541-4337.12006
USDA, 2013
Verzera, A; Trozzi, A; Dugo, G; Di Bella, G; Cotroneo, A., 2004, "Biological lemon and sweet orange essential
oil composition". Flavour and Fragrance Journal 19 (6): 544–548. doi:10.1002/ffj.1348.
∆3
Widmark, G. and Blohm, S.G., 1957, A comparative study of the autoxidation of -carene, α-pinene, β-pinene
and (+)limonene. Acta Chem Scand 11:392–4.
www.gjournals.org
14