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IOP Conference Series: Materials Science and Engineering
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Physicochemical Properties and Antibacterial Activity of Castor Oil and
Its Derivatives
To cite this article: M I Fitranda et al 2020 IOP Conf. Ser.: Mater. Sci. Eng. 833 012009
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The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
IOP Publishing
doi:10.1088/1757-899X/833/1/012009
1
Physicochemical Properties and Antibacterial Activity of
Castor Oil and Its Derivatives
M I Fitranda1, Sutrisno1*, S Marfu’ah1
1Chemistry Department, Faculty of Mathematics and Natural Sciences, State
University of Malang, Jl. Semarang No. 5 Malang
*Corresponding author: sutrisno.kimia@um.ac.id
Abstract. Castor oil is vegetable oil sourced from castor seeds (Ricinus communis Linn). The
main content of fatty acids in castor oil are ricinoleic acid (92%), oleic acid (3.53%), linoleic
acid (2.90%), stearic acid (1.02%), and myristic acid (0.55%). Research on the antibacterial
activity of castor oil and ricinoleic fatty acid has been carried out but for the K-soap and fatty
acids methyl esters of castor oil have not been conducted. This research aims to produce castor
oil derivatives, namely K-soap, free fatty acids (FFAs) and fatty acids methyl esters of
(FAMEs) and evaluate their antibacterial activity. The results of the study included (1) K-soap
(solid, white, melting point 168–175oC), (2) free fatty acids (liquid, yellow, boiling point
210oC , density 0.98 g.mL-1, refractive index 1.46, viscosity 693.22 cSt, and the value of acids,
saponification, and esters are 145.88, 294.52, 148.64), (3) fatty acids methyl esters (liquid,
yellow, boiling point 170oC, density 0.98 g.mL-1, refractive index 1.46, viscosity 27.31 cSt, and
the value of acids, saponification and esters are 0.33, 392.7, 392.37). K-soap, free fatty acids,
and methyl esters from castor oil have antibacterial activity against Escherichia coli and
Staphylococcus aureus bacteria.
1. Introduction
According to renewal, natural resources can be classified into two, namely renewable resources and
unrenewable resources. Unrenewable resources, namely oil, natural gas, and coal are very broad but
still limited. The source of these chemicals will become drained with sustainable exploitation [1].
Conversely, renewable natural resources are reliable resources for fuels and chemicals in the long run
[2]. This natural resource has many forms, namely carbohydrates (starch, cellulose), lignin, and
triglycerides [3].
Triglycerides or oils have high potential to be developed, one of which is castor oil. Castor oil
(Ricinus communis) is one of the vegetable oils with a specific fatty acid content, which contains
hydroxyl groups and unsaturated chains [4]. The presence of hydroxyl groups (-OH) attached to the
hydrocarbon chain in ricinoleic acid makes castor oil chemically different from other oils, especially
its high viscosity and polarity. These properties make it very important for industrial production of
lubrication [5], coatings, plastics, and cosmetics [6].
Castor oil has the potential as an antibacterial or antimicrobial agent [7][8]. The antibacterial
activity of castor oil can be related to the content of fatty acids in it, ricinoleic fatty acid. Ricinoleic
acid inhibits the growth of many viruses, bacteria, yeast, and mold, such as undecylenic acid
derivatives [9][10]. The broad spectrum and strong biological activity of free fatty acids (FFAs), is its
ability to kill or inhibit bacterial growth. The main target of FFAs action is cell membrane, which
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
IOP Publishing
doi:10.1088/1757-899X/833/1/012009
2
interferes with the electron transport chain and oxidative phosphorylation thereby disrupting cellular
energy production [11].
FFAs is a compound produced from chemical or enzymatic hydrolysis of oil or fat. The study of
the antibacterial activity of a variety of pure fatty acids is carried out by taking into account the
variable length of the chain and the presence or absence of a double bond C=C in the fatty acid acyl
groups against Gram-positive and Gram-negative bacteria. In the context of its antibacterial activity,
there are several different results between oil and free fatty acids. Tamarin oil (Tamarindus indica) is
not antibacterial active [12], while free fatty acids are antibacterial against Escherichia coli and
Staphylococcus aureus [13].
FFAs are already known as antibacterial and antifungal substances. In general, free fatty acids
function as anionic surface agents, and the anionic surfactants are less potent at physiological logical
values. The antibacterial activity of free fatty acids has a relationship with its structure. Changing the
COOH group to CONMe2 a increased the activity [14]. Besides FFA as an oil derivative, K-soap also
has antibacterial activity against Staphylococcus aureus bacteria [15].
In the current research, there have been no reported of how antibacterial activity is based on
polarity or ability to produce cell membrane liabilities. So, it is necessary to assess the Gram-positive
and Gram-negative antibacterial activity of the oil, its free fatty acids, its k-soap, and its fatty acid
methyl ester from vegetable oil. The broad spectrum of antibacterial activity, modes of action, and
non-specific safety make it attractive as an antibacterial agent for various applications in medicine,
agriculture and food preservation, especially where the use of conventional antibiotics is undesirable
or prohibited [11]. This research aims to produce castor oil derivatives (K-soap, FFAs, and FAMEs),
evaluate their antibacterial activity against Gram-negative bacteria (Escherichia coli) and Gram-
positive (Staphylococcus aureus), and examine the relationship of polarity with their antibacterial
activity.
2. Experimental Procedure
2.1. Materials, Equipments and Intrumentations
2.1.1. Material. Castor oil is obtained from an online store in Kedungkandang, Malang. The reagents
and solvents used are potassium hydroxide, hydrochloric acid solution, oxalic acid solution, crystalline
sodium chloride, methanol, ethanol, hexane, glycerol, acetone and chloroform, each of which has a p.a
quality.
2.1.2. Equipment and Instrumentation. A set of glassware, magnetic stirrer, stative, dropper pipette,
stirring rod, filter paper, burette, analytical balance, thermometer, hot plate, set of melting point
apparatus, autoclave, microtube, ose needle, Laminar Air Flow (LAF), bunsen, calipers, vortex,
magnetic stirer, incubator, refractometer Abbe, Capillary-viscosimeter, a set of titration tools, a set of
Shimadzu 8400S FT-IR spectrophotometers, and a set of GC-MS Shimadzu QP2010S .
2.2. Synthesis K-soap from Castor Oil
Castor oil (20.00 g) and 130 mL of 3 M potassium hydroxide solution were refluxed at 80 oC for 3 h
and stirred with a magnetic stirrer to form two layers and there was no change anymore. This mixture
is then allowed to stand and separate. Soft potassium soap is added 50 mL saturated sodium chloride
solution and stirred with a magnetic stirrer until all soap is precipitated. Potassium soap deposits are
washed with 20 mL distilled water and filtered with filter paper. Washed potassium soap is heated in
an oven (60 oC, 2 h). Then, mashed with mortar and pastle. Potassium soap powder is characterized
and identified.
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
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doi:10.1088/1757-899X/833/1/012009
3
2.3. Synthesis Free Fatty Acids (FFAs) from K-soap
Potassium soap (10.00 g) and 10 mL of distilled water are put into a 100 mL beaker glass then stirred
with a magnetic stirrer until the K-soap is emulsified. After that, it is added dropwise 1 M
hydrochloric acid solution accompanied by stirring with a magnetic stirrer until it is completely
lumpy. This lump is filtered with filter paper and washed with water until the washing water is neutral.
The residue obtained is left at room temperature until it melts. The liquid obtained was centrifuged at a
speed of 3000 rpm for 20 minutes to separate the liquid from the remaining water and obtained
residues (free fatty acids) and centrates. Free fatty acids are characterized and identified.
2.4. Synthesis Fatty Acids Methyl Esters (FAMEs) from Castor Oil
Castor oil (20.00 g), 15 mL methanol and 0.2 g of potassium hydroxide are refluxed at 60 oC for 4 h
while stirring with a magnetic stirrer. The process is stopped if the mixture does not change and two
layers are formed. The top layer is washed with warm water until the used washing water is neutral.
The obtained mixture is then added to anhydrous magnesium sulfate to bind water. Then the mixture is
filtered with filter paper to obtain water-free methyl ester filtrate. The methyl ester filtrate was
characterized and identified.
2.5. Physicochemical Properties of Castor Oil and Its Derivatives
Physicochemical properties of the components are obtained by analyzing the state and color, boiling
and melting points, density, refractive index, viscosity, solubility, acid value, saponification value and
ester value.
2.5.1. State and Color. State and color are observed visually.
2.5.2. Boiling Point. The sample is put into a test tube that contains boiling stones and perculators.
The test tube is heated to boiling and the boiling point value is constant.
2.5.3. Melting Point. The sample is placed on the glass preparation and inserted into the object into
the melting point apparatus. The device is turned on and the product is observed when it begins to fuse
until the product is completely fused.
2.5.4. Density. The remaining samples attached to the side of the pycnometer are cleaned. Next, the
mass of the pycnometer is weighed with the sample. The mass is recorded and the density of the
sample is calculated.
2.5.5. Refractive Index. Samples were dropped on the surface of the glass preparation, closed, and
read the refractive index on the refractometer Abbe.
2.5.6. Viscosity. The sample is placed in the Capillary-viscosimeter and pumped with filler until it
exceeds the boundary mark. The sample flow time is calculated from the upper boundary mark to the
lower boundary mark that approaches the capillary tube.
2.5.7. Solubility. 3 mL of solvent is put into a test tube. The sample is added dropwise up to 0.2 mL
into the test tube and shake it strongly. Observe the solubility and record the solubility of the sample in
the solvent used.
2.5.8. Acid Value. 1.00 g of sample, 2.5 mL of hexane, and 4 drops of the phenolphtalein indicator
were put into a 100 mL Erlenmeyer. The mixture is shaken to form a solution (homogeneous mixture).
Then the mixture is titrated with 0.1 M KOH solution in water to a constant pink color solution for 20-
30 seconds.
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
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doi:10.1088/1757-899X/833/1/012009
4
2.5.9. Saponification Value. 1.00 g of sample and 25 mL of 0.5 M KOH solution were put into a 250
mL three neck flask. The mixture is heated in a series of reflux apparatus at 60 oC for 1 h while
stirring. Then it is cooled to room temperature and put in a 100 mL Erlenmeyer and 5 drops of
phenolphtalein indicator are added. Then it is titrated with 0.5 M HCl solution until the pink turns
yellow. Titration is also done on blanks.
2.6. Identification of Castor Oil and Its Derivatives
2.6.1. Analysis of Infra-Red Spectrum. Samples are mixed with KBr with a sample-KBr ratio (1: 1),
pressed in a vacuum pump to form chips or pellets. Then the pellets were put into FT-IR
spectrophotometry and analyzed with a frequency of 4000-400 cm-1. The resulting IR spectrum is then
analyzed based on a typical band at a frequency of 4000-400 cm-1 which can be used to identify the
functional groups contained in the sample.
2.6.2. Analysis of Gas Chromatography-Mass Spectrometer. The sample was injected on a GC-MS
Shimadzu QP2010S device. Operational parameters are adjusted to the conditions in GC-MS. Then
the chromatogram produced by the recorder and the mass spectra of each compound was observed.
2.7. Antibacterial Activity
2.7.1. Media preparation. 5 grams of instant Nutrient Agar (NA) is dissolved in 250 mL of distilled
water. Then this mixture is heated while stirring until the mixture is homogeneous. 10 mL of
homogeneous mixture was poured into a petri dish. Subsequently the mixture was sterilized by
autoclaving at 121oC for 15 minutes. Then the temperature and pressure of the autoclave are lowered,
then allowed to reach ambient conditions. NA media are removed from the autoclave and left until the
media solidifies.
2.7.2. Suspension of Escherichia coli and Staphylococcus aureus Bacteria. 10 mL Nutrient Broth
(NB) was put into two test tubes. A total of 1 E. coli bacterial ose needles were inserted aseptically in
the first tube and S. aureus bacteria was inserted in the second tube. Next, each mixture in the tube is
rotated with vortex until a homogeneous mixture is obtained.
2.7.3. Inhibition Test. 6 mm diameter of the wellbore made on the media. Gram-negative (Escherichia
coli) and Gram-positive (Staphylococcus aureus) bacteria are inoculated into the media. Then, 20 µL
of the sample is put into the wellbore. Media that have been planted with bacteria and samples
incubated at 37 ° C for 24 h. The diameter of the clear zone produced is measured by the calipers.
3. Result and Discussion
3.1. Physicochemical Properties of Castor Oil and Its Derivatives
Castor oil is liquid and yellow. Soap that is synthesized from oil is solid and has a white color.
Changes in state during the derivatization reaction from oil (liquid, yellow) to solid and white in the
saponification reaction indicate the formation of potassium soap (K-soap). Likewise, the change in
state and color from the result of the acidification reaction of K-soap (solid, white) to liquid and
yellow, indicates the formation of free fatty acids (FFAs). While indications of the formation of fatty
acid methyl esters (FAMEs) are characterized by viscosity observed visually thinner than castor oil.
The performance states and colors of castor oil and their derivatives are shown in Figure 1.
Physical properties can be influenced by intermolecular forces and molecular weights of
compounds. Based on the results of physicochemical properties can be seen that castor oil has a
different boiling point with fatty acids and methyl esters. Fatty acids have the highest boiling point
than both because they are able to form hydrogen bonds between molecules so that the density of fatty
acids is higher and requires high energy to break bonds between molecules. The difference in boiling
points shows that fatty acids and methyl esters have been successfully synthesized from oil.
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
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doi:10.1088/1757-899X/833/1/012009
5
(a)
(b)
(c)
(d)
Figure 1. Castor oil and its derivative (a) castor oil, (b) K-soap, (c) FFAs, (d) FAMEs
Table 1. Physicochemical Properties Results of Castor Oil and Its Derivatives
Properties
Castor oil
K-soap
FFAs
FAMEs
State
Liquid
Solid
Liquid
Liquid
Color
Yellowish
White
Yellow
Yellowish
Boiling point (oC)
191
-
210
170
Melting point (oC)
-
168-175
-
-
Density (g/cm3)
0.96
-
0.98
0.92
Refractive Index (25 oC)
1.477
-
1.462
1.461
Viscosity (cSt)
520.52
-
693.22
27.31
Solubility in
- water
- methanol
- ethanol
- chloroform
- n-hexane
insoluble
insoluble
insoluble
soluble
insoluble
emulsified
slightly
slightly
insoluble
insoluble
insoluble
soluble
soluble
soluble
insoluble
insoluble
soluble
soluble
soluble
soluble
Acid value, AV
(mg KOH/g sample)
1.23
-
145.88
0.33
Saponification value, SV
(mg KOH/g sample)
406.72
-
294.52
392.70
Ester value (SV – AV)
(mg KOH/g sample)
405.49
-
148.64
392.37
Based on the results of physicochemical properties can be seen that castor oil has a different
viscosity with fatty acids and methyl esters. Fatty acids have the highest viscosity than both because
fatty acids have the highest molecular weight than oils and methyl esters so that the viscosity is
greater. The difference in viscosity shows that fatty acids and methyl esters have been successfully
synthesized from oil.
Based on the results of physicochemical properties can be seen that castor oil has a different
density with fatty acids and methyl esters. Fatty acids have the highest density than both because they
are able to form hydrogen bonds between molecules so that the density of fatty acids is higher. The
difference in density shows that fatty acids and methyl esters have been successfully synthesized from
oil.
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
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The solubility of a compound is influenced by the rules of like dissolves like [16]. Based on the
results of the solubility test, showed that the sequence of the nature of polarity from low to high,
namely castor oil, methyl esters, fatty acids and potassium soap. The difference in solubility shows
that potassium soap, fatty acids, and methyl esters have been successfully synthesized from oil.
Based on the definition of acid numbers, the higher the acid numbers, the higher the amount of free
fatty acids in oil or fat. Based on the results of the characterization, the fatty acids synthesized had
higher acidity than oil and methyl esters. This shows that fatty acids were successfully synthesized
from oil. Based on the results of synthesis, it can be seen that castor oil has the highest saponification
rate. This shows that the triglyceride content in castor oil is the highest compared to fatty acids and
their methyl esters because in the oil structure they have a structure with moles greater than the fatty
acids and methyl esters.
Esters also show the amount of esters in oil or fat. Based on the results of physicochemical
properties, it can be seen that castor oil has the highest ester number. This shows that castor oil
contains quite high esters. Differences in acid numbers, saponification rates and esters indicate that
fatty acids and methyl esters have been successfully synthesized from oil.
3.2. Identification of Castor Oil and Its Derivatives
3.2.1 Infra Red Spectrophotometer Analysis
Other supporting data on the success of synthesis of castor oil derivatives is the result of IR
spectrophotometer identification, with IR spectra as shown in Figure 2- Figure 5.
Figure 2. IR spectrum of castor oil
3360 cm
-1
(-OH)
3007,02 cm
-1
(C-H alkena)
1745,58 cm
-1
(C=O)
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
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Figure 3. IR spectrum of K-soap from castor oil
Figure 4. IR spectrum of FFAs from castor oil
3008,95 cm
-1
(C-H alkena)
1417.68
cm-1
(C=O)
3010,88 cm
-1
(C-H alkene)
3408,22 cm
-1
3388,93 cm-1
(-OH)
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Figure 5. IR spectrum of FAMEs from castor oil
Based on the interpretation of IR spectra in Figure 2-Figure 5, typical bands that distinguish the four
substances summarized in Table 2.
Table 2. IR Spectrum Interpretation of Castor Oil and Its Derivatives.
Vibration
Castor oil
K-soap
Fatty acids
Methyl esters
O-H stretching
3360.00
-
3408.22
3388.93
3419.79
C=O stretching
1745.58
1417.68
-
1741.72
Stretch C-H alkene
3007.02
3008.95
3010.88
3007.02
IR analysis was performed to determine the functional groups contained in castor oil and its
derivatives. Based on the results of the interpretation of the IR spectra (Table 2), there are several
typical absorption bands. Castor oil has a wave number 3360.00 cm-1 with a weak intensity indicating
the existence of O-H bond stretch vibrations and wave number 1745.58 cm-1 with strong and sharp
intensities indicating the existence of stretching vibrations of the C=O bond as esters.
The synthesized potassium soap has a wave number of 1417.68 cm-1 with a strong and sharp
intensity indicating the stretching vibration of the C=O bond as a carboxylic salt [17]. The existence of
stretching vibration C=O bonds as carboxylic salts indicates potassium soap successfully synthesized
from castor oil.
Synthesized fatty acids have wave numbers 3408.22 cm-1 and 3388.93 cm-1 appear with weak
intensity and width indicate the existence of O-H bonding stretch vibrations. The synthesized methyl
ester has a wave number of 1741.72 cm-1 with a strong and sharp intensity indicating the existence of a
stretching vibration C=O as an ester and a wave number 3419.79 cm-1 with a weak intensity indicating
the existence of a stretching vibration O-H bond as an acyl group. Based on the results of the
interpretation of the IR spectrum, the difference in the intensity of the O-H bond stretching vibrations
3419,79 cm
-1
(-OH)
3007,02 cm
-1
(C-H alkena)
1741,72 cm
-1
(C=O)
The 2nd International Conference on Chemistry and Material Science (IC2MS)
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between oil, fatty acids and methyl esters shows that fatty acids and methyl esters have been
successfully synthesized from castor oil.
3.2.2 Gas Chromatography-Mass Spectrometer Analysis
GC-MS analysis was performed to determine the content of fatty acid methyl esters synthesized.
Based on GC- MS results (Table 3), the synthesized methyl esters are composed of 5 fatty acids which
are indicated by the appearance of 5 peaks on the chromatogram. The abundance percentage of fatty
acid content based on its fatty acid methyl ester was obtained from % Area chromatogram data. The
chromatogram of FAMEs are shown in Figure 6.
Figure 6. Chromatogram of FAMEs from castor oil
Type of fatty acids based on its fatty acid methyl ester was obtained from mass-spectrometry data
for each peak on a chromatogram. Analysis of mass spectrometry by EI-MS (electron impact mass
spectrometry) for each peak of the five peaks of GC results obtained by mass spectra as shown in
Figure 7 to Figure 11. The appropriate content of fatty acids from their fatty acid methyl esters as
listed in Table 3, obtained from interpretation of each mass spectrum from nine peaks, and
subsequently refered to WILEY229.LIB.
Table 3. Fatty Acid Content as Methyl Esters from GC-MS Analysis
Peak
Retention time
Relative percentage(%Area)
Fatty acid as its
FAMEs
Fatty acid symbol
1
34.997
0.55
Myristic acid
C 14:0
2
38.516
2.90
Linoleic acid
C 18:2 9c12c
3
38.622
3.53
Oleic acid
C 18:1 9c
4
39.006
1.02
Stearic acid
C 18:0
5
42.521
92.00
Ricinoleic acid
C 18:1 9c 12-OH
92.00
1.02
3.53
2.90
0.55
The 2nd International Conference on Chemistry and Material Science (IC2MS)
IOP Conf. Series: Materials Science and Engineering 833 (2020) 012009
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Figure 7 Mass spectra (EI-MS) of peak 1 (methyl myristate)
Figure 8 Mass spectra (EI-MS) of peak 2 (methyl linoleate)
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Figure 9 Mass spectra (EI-MS) of peak 2 (methyl oleate)
Figure 10 Mass spectra (EI-MS) of peak 2 (methyl stearate)
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Based on the results of EI-MS, it can be seen that the synthesized fatty acids methyl esters are
composed of 0.55% myristic acid, 2.90% linoleic acid, 3.53% oleic acid, 1.02% stearic acid, and
92.00% ricinoleic acid. The retention time, type of fatty acids, %area and fatty acid symbol
summarized in Table 3.
3.3. Antibacterial Activity of Castor Oil Derivatives
Potassium soap, free fatty acids, and methyl esters which were synthesized were tested for their
antibacterial activity against Eschericia coli as gram negative bacteria and Staphylococcus aureus as
gram positive bacteria. The sample was dissolved in ethanol 60% and this ethanol solvent was used as
a negative control. Stunted bacterial development is indicated by the formation of an inhibited zone
around the wellbore. If the inhibited zone formed around the wellbore increases, the antibacterial
activity produced by the sample will be even greater.
Table 4. Diameter of Inhibition Zones
Type of Bacteria
Inhibition Zone Diameter (mm)
Negative
Control
K-soap
Fatty Acids
Methyl
Esters
1 %
2 %
1 %
2 %
1 %
2 %
Escherichia coli
-
18.80
18.90
15.75
17.45
-
8.15
Staphylococcus
aureus
-
14.65
16.90
13.25
16.35
-
8.75
Based on the results of the inhibited zone diameter (Table 4), it can be seen that antibacterial
activity of castor oil derivatives against Escherichia coli bacteria is higher than that of Staphylococcus
aureus. In addition it can be seen that potassium soap has the highest antibacterial activity compared
to its fatty acids and methyl esters. This is due to differences in polarity of the three castor oil
derivatives. The higher the polarity of a substance, the higher its antibacterial properties. Potassium
Figure 11 Mass spectra (EI-MS) of peak 2 (methyl ricioleate)
The 2nd International Conference on Chemistry and Material Science (IC2MS)
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soap which has the highest polarity has the highest antibacterial activity followed by fatty acids and
the weakest methyl esters.
4. Conclusion
Castor oil can be transformed to derivatives, i.e K-soap (solid, melting point 168–175oC), FFAs
(liquid, boiling point 210oC), and FAMEs (liquid, boiling point 170oC). The antibacterial activity of
castor oil derivatives against Escherichia coli bacteria is higher than that of Staphylococcus aureus.
The antibacterial activity of K-soap has a higher activity than free fatty acids and higher free fatty
acids than fatty acid methyl esters.
The result of this research implies that potassium salt from castor oil can be used is the control of
wound, skin infection, throat infection in the skin caused by Staphylococcus aureus, while the fatty
acids from castor oil have the potential as an antibacterial agent.
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