Antibacterial Activity of an Effective Essential Oil Formulated in Liquid Soap Against Skin Bacteria

13 Pages·2014·0.67 MB·English

Chiang Mai J. Sci. 2014; 41(1) 71
Chiang Mai J. Sci. 2014; 41(1) : 71-83
http://epg.science.cmu.ac.th/ejournal/
Contributed Paper
Antibacterial Activity of an Effective Essential Oil
Formulated in Liquid Soap Against Skin Bacteria
Pilanthana Lertsatitthanakorn*[a], Kreepon Manwiwattanakun [a],
Nichthima Paengnakorn [a] and Watcharee Khunkitti [b]
[a] Faculty of Pharmacy, Mahasarakham University, Maha Sarakham 44150, Thailand.
[b] Faculty of Pharmaceutical Sciences, Khon Kaen University, Khon Kaen, 42000, Thailand.
*Author for correspondence; e-mail: [email protected]
Received: 28 November 2012
Accepted: 2 May 2013
ABSTRACT
Skin bacterial flora consisting of Staphylococcus aureus, Staphylococcus
epidermidis, Escherichia coli and Pseudomonas aeruginosa can frequently cause either skin
or systemic infection including the bacterial transmission in healthcare units and
household. The aims of this study were to determine susceptibility of these skin bacteria
to the essential oils distilled from Citrus hystrix DC. (kaffir lime) peel, Cymbopogon
citratus Stapf. (lemongrass) grass, Cinnamomum zeylamicum Nees (cinnamon) bark,
Ocimum basilicum L. (sweet basil) leaves, Alpinia galanga (L.) Willd. (galanga) and Zingiber
officinale Rosc (ginger) rhizome and to develop liquid soap from a selected essential oil.
The results revealed that cinnamon oil possessed the highest activity against all bacterial
strains. Cinnamon oil liquid soap was more effective against Gram positive bacteria than
Gram negative bacteria by day 90. In conclusion, the developed cinnamon oil liquid
soap was a good candidate to eracidate the skin bacterial flora especially, Gram positive
bacteria. However, this preparation should be stored at room temperature with
protection from natural light to extend product shelf-life and skin irritation test of this
liquid soap should be further studied.
Keywords: essential oils, cinnamon oil, liquid soap, antibacterial activity, skin bacteria
1. INTRODUCTION
Bacterial flora mostly found on skin and household. Almost liquid soap claimed
surface including Staphylococcus aureus, to decrease skin normal bacteria contains
Staphylococcus epidermidis, Escherichia coli and triclosan as antibacterial agent. However,
Pseudomonas aeruginosa can frequently cause triclosan is a synthetic biocide which tends
human bacterial infection in some conditions. to cause bacterial tolerance [2]. Attempt to
For example, these microorganisms can find natural antibacterial agents has been
invade into human body and lead to skin explored. Many research works reported the
and soft tissue infections [1]. Antibacterial antibacterial activity of essential oils from
liquid soap is able to reduce the transmission Citrus hystrix DC. (kaffir lime) fruit peel,
of pathogenic bacteria in healthcare units Cymbopogon citratus Stapf. (lemongrass) grass,
72 Chiang Mai J. Sci. 2014; 41(1)
Cinnamomum zeylamicum Nees (cinnamon) bark, Chromatograph Mass Spectrometer (GCMS-
Ocimum basilicum L. (sweet basil) leaves, QP 2010, Shimadzu®, Japan) equipped with
Alpinia galanga (L.) Willd. (galanga) and autoinjector (AOC-5000, Shimadzu®, Japan).
Zingiber officinale Rosc (ginger) rhizome [3-7]. Capillary column used was Rtx®-5 MS (30 m
Thus, the aims of this study were to screen × 0.25 mm id. × 0.25 μm film thickness).
antibacterial activity of these essential Carrier gas used was helium at a flow
oils against skin bacteria. Liquid soap rate 1.55 ml/min. Oven temperature was
containing the most active oil was formulated. started with 80°C and hold for 2 minute,
The developed liquid soap which possesses increased to 280°C at 10°C/min and hold
physical and biological stability was studied for 1 minute. Injection system composed
its ability to decrease bacterial population at of-; injection temperature 250°C, injection
accelerated conditions for 90 days. volume 1μL, split mode 1:100. MS conditions
consisted of-; positive ion detection,
2. MATERIALS AND METHODS interface temperature: 230°C, ion source:
2.1 Materials 0 kV, scan mode: positive ion, full scan m/z
Essential oils from Citrus hystrix DC. over 35-550 amu at 1,111 amu/sec. The
(kaffir lime) fruit peel, Cymbopogon citratus Stapf. compounds were identified by comparing
(lemongrass) grass, Cinnamomum zeylamicum their mass spectra with the NIST mass spectral
Nees (cinnamon) bark, Ocimum basilicum L. libraries. Some constituents were also
(sweet basil) leaves, Alpinia galanga (L.) Willd. compared with the synthetic reference
(galanga) and Zingiber officinale Rosc (ginger) compounds (Fluka, Switzerland).
rhizome were purchased from Thai China
Flavours & Fragrances Industry Co. (Thailand). 2.4 Determination the MIC and MBC
Muller Hilton agar and Muller Hilton broth Values of Six Essential Oils Against the
were provided by Himedia (India). Hexane Tested Bacteria
was obtained from Lab Scan (Ireland). A broth microdilution method was used
Dimethyl sulfoxide was purchased from to determine the minimum inhibitory
Analar (UK). concentrations (MICs) and minimum
bactericidal concentrations (MBCs) of the
2.2 Cultures and Growth Conditions essential oils. Muller Hilton broth was
S. aureus DMST 8013, S. epidermidis supplemented with 10% dimethylsulphoxide
DMST 15505, P. aeruginosa DMST 4739, to dissolve the essential oils. Fifty microliter
E. coli DMST 15537 were obtained from of two folded dilutions of each oil sample
Department of Medical Science, Ministry of were prepared in a 96-well plate. Fifty
Public Health, Thailand. Cultures were microliter of bacterial culture was added to
maintained and grown in Muller Hilton each well to make a final concentration of
broth at 37°C. approximately 107 CFU/ml. In each test,
bacterial strain in Muller Hilton broth and
2.3 Determination an Effective Essential Muller Hilton broth alone were used as a
Oil Constituents by Gas Chromatography positive and negative growth control,
/ Mass Spectrometry (GC / MS) respectively. The plates were then incubated
Chemical constituents of the most at 37°C for 24 hours before the MICs
effective essential oil against the tested were determined. The MIC value was defined
bacteria (10 μl/ml) were identified by Gas as the lowest concentration of essential oil
Chiang Mai J. Sci. 2014; 41(1) 73
inhibiting visible growth of bacteria. mortar using glycerin as levigator. After that,
To determine the MBC value, 10 microliter citric acid dissolved in about 5 ml of water
of broth was removed from each well and the selected oil were added and mixed
and spotted onto Muller Hilton agar. well. Approximately 65 ml of water, patent
After incubation at 37°C for 24 hours, the blue stock solution, sodium chloride and
number of surviving organism was counted. paraben concentrated were then added and
The lowest concentration where less than incorporated throughly. Finally, the perfume
0.1% of the initial inoculum survived was oil was added and the final volume was
defined as a MBC value. Each experiment adjusted to 100 ml with water. Liquid soap
was performed in triplicate. which possessed the best odor was chosen.
The physical stability of the selected liquid
2.5 Time Killing Assay soap was carried out by heating cooling
0.1 ml suspension of each bacteria, cycling method. One cycle consisted of
approximatelty 108 cfu ml-1 was added to keeping the selected soap at 4°C for
0.9 ml solution of the selected essential oil. 24 hours and 45°C for 24 hours. Color,
The solution consisted of 10 % dimethyl odor, pH, viscosity and physical stability
sulfoxide in Muller Hilton broth mixed were recorded after freshly prepared and
with the selected oil to give the required after the 5th cycle. The selected preparation
final concentration. 0.9 ml solution of 10 % (Table 5) was determined its activity.
dimethyl sulfoxide in Muller Hilton broth
mixed with 0.1 ml suspension of each 2.7 Determination a Synergistic Effect
bacteria was used as control. Samples or Between the Selected Essential Oil, Citric
control (0.1 ml) were mixed and transferred Acid and Fragrance Added in Liquid Soap
to 0.9 ml of normal saline solution at 0, 10, To avoid the effect of preservative, three
20, 30 and 60 minutes of contact time. preparations of the liquid soap were prepared
The samples were serially diluted in normal again without paraben concentrated. These
saline solution and 100 microliter of each preparations consisted of the liquid soap
sample was spreaded on Muller Hilton agar containing the selected essential oil with
for viable counting. The experiment was fragrance, the liquid soap containing the
performed in triplicate. Results are presented selected essential oil without fragrance and
graphically as time-log survivors curves the liquid soap base with fragrance.
with bars representing the standard deviation. Approximately 108 CFU/ ml of selected
bacterial strain was seeded into 20 ml- Mueller
2.6 Formulation of Liquid Soap Hinton agar. After that, the 40 μl of each
Containing the Selected Essential Oil liquid soap preparation was aseptically
Various formulations of liquid soap impregnated onto 6-mm paper discs and
containing a suitable concentration of the were dried under ambient temperature for
selected oil were prepared using sodium 30 minutes. 95% ethanol prepared in the
lauryl sulfate as a surfactant. To overcome a same manner was used as a negative control.
spicy odor of the selected essential oil, The sample discs were then placed on the
various perfume oils such as rose, lavender surface of the seeded Mueller Hinton agar.
and jasmine were added in the preparation The Petri dishes were then incubated at
as fragrance. To prepare the liquid soap, 37°C for 24 hours. Antibacterial activity of
sodium lauryl sulfate was levigated in liquid soap was defined by measuring
74 Chiang Mai J. Sci. 2014; 41(1)
the diameter of the growth inhibition zone. 3. RESULTS AND DISCISSION
3.1 Determination of an Effective
2.8 Stability of the Liquid Soap Essential Oil (Cinnamon Oil)
The developed liquid soap was kept at Constituents by Gas Chromatography /
room temperature with natural light and Mass Spectrometry (GC / MS)
45°C without light for 90 days. On day 0, 15, As shown in Table 1, the main
30, 60 and 90, 0.1 ml of bacterial suspension components of cinnamon oil, the most
(approximately 108 CFU ml-1) was added to effective oil to all tested bacteria, were
0.9 ml of liquid soap and mixed well by eugenol (36.49 % v/v), cinnamaldehyde
vortex mixer. 0.1 ml of the sample was (32.66 % v/v), linalool (12.50 % v/v) and
collected at 0 and 10 minutes of contact caryophyllene (11.34 % v/v). The other
time for perform total viable count. The compounds were found in a less amount in
results were presented graphically between comparison with the amount of the main
log reduction of each bacteria and the time components.
intervals.
Table 1. Chemical constituents of cinnamon oil determined by GC / MS.
Peak Retention time Identification
Identified constituents Area percent
number (minute) mode*
1 5.28 Linalool 12.50 a
2 6.31 Benzaldehyde 0.15 a
3 6.71 α-Terpineol 0.21 a
5 7.49 2-Anisaldehyde 0.17 a
6 7.90 Cinnamaldehyde 32.66 a, b
7 9.07 Eugenol 36.49 a, b
8 9.32 Geranyl acetate 0.70 a
9 9.96 Caryophyllene 11.34 a
10 10.21 Cinnamyl acetate 2.17 a
11 10.40 α-Humulene 1.56 a
12 11.22 δ-Cadinene 0.14 a
13 12.04 Caryophyllene oxide 0.28 a
Unknown 1.64
*a = comparing the mass spectra with the NIST mass spectral libraries, b = comparing the
mass spectra with that of synthetic reference compounds
The major components found in cinnamon oil [9]. The different type and
our cinnamon oil were eugenol and amount of chemicals found in essential oils
cinnamaldehyde. This finding was comparable might be attributed to many factors such as
to the work of Singh et al. (2007) who found the origin of the plants, cultivation conditions,
that cinnamaldehyde was the main variety of plants including extraction and
component of cinnamon bark oil [8]. isolation techniques [10-11]. For the major
By contrast, Prabuseenivasan et al., components found in our cinnamon oil,
(2006) reported that cinnamaldehyde and cinnamaldehyde was classified as weak to
benzaldehyde were chief constituents in moderate contact allergen whilst eugenol was
Chiang Mai J. Sci. 2014; 41(1) 75
the weak allergen when using various skin 0.391-1.562 μl/ml for S. epidermidis. MIC
sensitization potency assay methods [12]. and MBC values of the other essential oils
Therefore, the low concentration of 9.375 μl/ against Gram positive skin bacteria were
ml of cinnamon oil added to the developed found at greater than 1.562 μl/ml. As
liquid soap might provide a non-irritate shown in Table 3, the susceptibility of Gram
concentration of cinnamaldehyde and eugenol negative skin bacteria to the essential oils
for most liquid soap users. revealed a similar pattern with that of
Gram positive bacteria. Among six essential
3.2 Determination the MIC and MBC oils, cinnamon oil demonstrated the
Values of Six Essential Oils Against the lowest MIC and MBC at 0.195 - 0.391 and
Tested Bacteria 0.391 - 0.781 μl/ml for P. aeruginosa,
MIC and MBC values of six essential oils respectively. Both MIC and MBC values of
against Gram positive skin bacteria is shown cinnamon oil against E. coli were
in Table 2. Cinnamon oil exhibited the lowest 0.049 - 0.195 μl/ml. MIC and MBC values
minimum inhibitory concentration (MIC) of the other oils against Gram negative skin
and minimum bactericidal concentration bacteria were found at greater than 1.562 μl/
(MBC) at 0.781-1.562 and 3.125 μl/ml for ml. Therefore, cinnamon bark oil was the most
S. aureus, respectively. Both MIC and MBC active oil and selected for development as the
values of cinnamon oil were ranged between liquid soap.
Table 2. MIC and MBC values (μl /ml) of six essential oils against Gram positive skin bacteria.
S. aureus S. epidermidis
Essential oils
MIC MBC MIC MBC
Ginger 50-100 >100 100 > 100
Galanga 12.500 > 100 50-100 >100
Lemongrass 12.500-25 50-100 25-100 50-100
Sweet basil 100 > 100 100 > 100
Kaffir lime 1.562- 6.250 > 50 25-50 > 50
Cinnamon 0.781-1.562 3.125 0.391-1.562 0.391-1.562
Table 3. MIC and MBC values (μl/ml) of six essential oils against Gram negative skin bacteria.
E.coli P. aeruginosa
Essential oils
MIC MBC MIC MBC
Ginger 100 > 100 ≥100 > 100
Galanga 100 > 100 ≥100 > 100
Lemongrass 1.562-3.125 12.500-25 100 100
Sweet basil 100 100 100 > 100
Kaffir lime 50 50 50 50-100
Cinnamon 0.049 - 0.195 0.049-0.195 0.195-0.391 0.391 - 0.781
76 Chiang Mai J. Sci. 2014; 41(1)
Cinnamon oil exhibited the highest 3.3 Time Killing Assay
antibacterial activity against both Gram Time killing assay of cinnamon oil
positive and Gram negative skin bacteria against all tested bacteria was performed to
used in this study. The MIC and MBC determine a suitable concentration of the oil
values of cinnamon oil to all tested bacteria for liquid soap preparation. According to
were rather low which comparable to the Table 2-3, MBC of cinnamon oil against
previous works [3, 9]. The prominent S. aureus (3.125 μl/ml) is higher than those of
antibacterial activity of cinnamon oil might other bacteria. Therefore, 3.125 μl/ml
cause by cinnamaldehyde and eugenol. (1 MBC against S. aureus) and 9.375 μl/ml
Because, cinnamaldehyde and eugenol (3 MBC against S. aureus) were the
revealed a potent antibacterial activity to appropriate concentrations for time killing
Helicobacter pylori and E. coli [13-14]. assay against all tested bacteria. As shown
Moreover, Wei et al. (2011) found that in Figure 1a-d, it was found that 9.375 μl/ml
cinnamaldehyde possessed antibacterial of cinnamon oil was able to decrease at least
activity against B. subtilis and E. coli [15]. 99 % (3 log) of initial population of S. aureus,
In addition, Matan (2007) revealed that E. coli and P. aeruginosa within 10 minutes.
cinnamaldehyde and eugenol possessed By contrast, 9.375 μl/ml of cinnamon oil
antifungal activity against Aspergillus niger was able to decrease 99 % of initial
[16] while the comparable result of S. epidermidis population within 1 hour.
Seesuriyachan (2011) demonstrated that From the time-killing curves (Figure 1a-d),
cinnamon powder was able to inhibit the the log reduction of all tested bacteria after
growth of yeast namely Pichia burtonii 10 minutes exposure with cinnamon oil
DA69 [17]. is summarized in Table 4. In this study,
Although cinnamon oil showed a good 9.375 μl/ml of cinnamon oil was chosen
susceptible to both Gram positive and Gram to incorporate in a suitable liquid soap base.
negative bacteria, our results revealed that Time killing curves of pure cinnamon
MIC values of cinnamon oil to Gram oil showed a comparable trend with the
negative bacteria was less than those of MIC and MBC values against the tested
Gram positive bacteria which similar to the bacteria. Because, Gram negative bacteria
works of Prabuseenivasan et al. (2006) [9] and was higher susceptible to cinnamon oil than
Rodriguez et al. (2007) [18]. The prominent Gram positive bacteria. On the one hand,
antibacterial activity to Gram negative cinnamon oil was able to decrease the
bacteria of cinnamon oil might caused by population of Gram negative bacteria faster
eugenol, one of the main constituent found than that of Gram positive bacteria.
in our cinnamon oil. Because, the previous In addition, time killing curves of cinnamon
research revealed that eugenol was able oil to all tested bacteria showed a dose-
to kill Gram negative bacteria (E. coli) by dependent manner.
disruption the cell membrane of
this bacteria and led to non-specific
permeability [19].
Chiang Mai J. Sci. 2014; 41(1) 77
a - S. aureus b - S. epidermidis
c - E. coli d - P. aeruginosa
Figure 1. Time-killing curves of cinnamon oil on skin bacteria. ♦, control; , 3.125 μl /ml of
cinnamon oil; , 9.375 μl /ml of cinnamon oil (Mean ± SD., n= 3).
Table 4. Log reduction of tested bacteria after 10 minutes exposure with cinnamon oil.
Log reduction*
Tested bacteria
3.125 μl /ml of cinnamon oila 9.375 μl /ml of cinnamon oilb
S. aureus 1 3
S. epidermidis 0.8 1.8
E. coli ≥ 5.5 ≥ 5.5
P. aeruginosa 2 4.8
*Log reduction means log survival bacteria at 0 minute contact time - log survival bacteria at
10 minutes contact time
a, b 1 MBC and 3 MBC of cinnamon oil against S. aureus (S. aureus possessed the highest MBC
among all tested bacteria)
78 Chiang Mai J. Sci. 2014; 41(1)
3.4 Formulation of Liquid Soap with MIC at 2-4 % v/v [20]. In addition,
Containing Cinnamon Oil disc diffusion test revealed that lavender oil
9.375 μl/ml of cinnamon oil was at concentration between 2-10 μl/disc was
incorporated in a liquid soap base using inactive to Listeria innocua, Serratia marcescens
sodium lauryl sulfate as a surfactant. and Pseudomonas fluorescens [21]. The preparation
Lavender oil appeared to blend well with of this formula (Table 5) was chosen for
the cinnamon oil giving a present perfume. physical stability study by heating cooling
0.44 g of lavender oil was used in 100 ml cycling method. According to Table 6, the
of liquid soap. Therefore, the concentration selected cinnamon oil liquid soap showed a
of lavender oil used in this study (0.44 g/100 physical stability. Because, the soap still
ml or 0.44 % w/v) might not have possessed the same color, odor, pH with
antibacterial activity. Because, lavender oil slightly decrease of viscosity after the 5th
possessed antibacterial activity against E. coli heating cooling cycle.
Table 5. Ingredients of the selected cinnamon oil liquid soap.
Ingredients Quantity
Sodium lauryl sulfate 22 g
Sodium chloride 2.2 g
Citric acid 0.68 g
Glycerin 7.2 g
Paraben concentrated* 1 g
Cinnamon oil 937.5 μl
Patent blue stock solution 0.4 g
Lavender oil 0.44 g
Deionized water to 100 ml
*Paraben concentrated consisted of 10 g methyl paraben and 2 g propyl paraben dissolved in
100 ml propylene glycol
Table 6. Physical properties of the selected cinnamon oil liquid soap after freshly prepared
and after the 5th cycle of heating cooling cycling storage.
Physical properties Freshly prepared After heating cooling storage
Color Clear, pale blue Clear, pale blue
Odor Mild lavender Mild lavender
pHa 5.33 ± 0.04 5.30 ± 0.03
Viscositya 15,637 ± 28 cp 12,762 ± 32 cp
Physical stability Stable Stable
aThe experiment was performed in triplicate (Mean ± SD., n= 3)
Chiang Mai J. Sci. 2014; 41(1) 79
3.5 Determination a Synergistic Effect exposure with cinnamon oil than P.
between Cinnamon Oil, Citric Acid and aeruginosa. As shown in Table 7, the
Fragrance Added in Liquid Soap inhibition zones of cinnamon oil liquid soap
Three preparations of the liquid soap with and without lavender oil against Gram
without paraben concentrated were prepared positive bacteria were not different. On the
and determined their antibacterial activity one hand, the clear zones of cinnamon oil
against the selected bacteria by disc liquid soap with and without lavender oil
diffusion method. S. aureus was chosen as against Gram negative bacteria were also
Gram positive bacteria due to the greater comparable. Therefore, low concentration
log reduction after exposure with cinnamon of lavender oil added in cinnamon oil
oil than S. epidermidis. On the one hand, E. coli liquid soap has not affected antibacterial
was a representative Gram negative bacteria activity of the soap as previously described
due to the higher log reduction after in 3.4.
Table 7. Inhibition zone of three preparations of the liquid soap without paraben
concentrated on S. aureus and E. coli.
Inhibition zone (mm)*
Liquid soap
S. aureus E. coli
Liquid soap base with lavender oil 15.0 ± 0.0 15.0 ± 0.0
Cinnamon oil liquid soap with lavender oil 20.0 ± 0.0 14.3 ± 1.5
Cinnamon oil liquid soap without lavender oil 20.7 ± 3.0 15.3 ± 2.1
Negative control (95 % ethanol) 6.0 ± 0.0 6.0 ± 0.0
* Diameter of paper disc is 6 mm
Bhattacharya et al. (2012) found that skin bacteria [23] and our results indicated
sodium lauryl sulfate possessed antibacterial this pronounced synergistic effect on
activity to E. coli DH5α, Bacillus subtilis, Gram positive bacteria.
Micrococcus luteus, S. aureus and multi-drug According to many researches involved
resistant clinical isolates of Shigella flexneri, in irritant patch tests, it was found that
Shigella boydii and Shigella sohnea including high concentration of sodium lauryl sulfate
Vibrio cholerae [22]. Thus, it might be assumed was used as a skin irritant. For example,
that antibacterial activity of 22 % sodium Loden (1997) has used 14% sodium lauryl
lauryl sulfate (detergent) should be higher sulfate as irritant stimuli in skin treated with
than that of 9.375 μl/ml cinnamon oil a moisturizing cream [24]. By contrast,
(active ingredient) used in the liquid soap. Patterson (1999) has used 10% sodium lauryl
Undoubtly, inhibition zones of cinnamon sulfate as irritant that led to contact
oil liquid soap to Gram negative bacteria dermatitis [25]. Therefore, the normal
were comparable to that of liquid soap base. concentration of sodium lauryl sulfate to use
Conversely, inhibition zones of cinnamon as irritant might be increased to 10-14%.
oil liquid soap against Gram positive In addition, Charbonnier (2001) has used
bacteria were clearly higher than that of 5% sodium lauryl sulfate to induce subclinical,
liquid soap base. These phenomena might non-erythematous irritation in open assay
cause by a synergistic antibacterial activity model (washing) and the result showed that
between cinnamon oil and citric acid against no erythema was occurred at any skin sites
80 Chiang Mai J. Sci. 2014; 41(1)
[26]. To avoid skin irritation, our cinnamon its biological stability for 90 days.
oil liquid soap should be diluted three As shown in Figure 2a-b, the log reduction
folds with water before using. After dilution, of Gram positive bacteria when exposed
the concentration of cinnamon oil in the to cinnamon oil liquid soap was ranged
soap would be reduced to 3.125 μl/ml between 3.0 - 6.5 log during day 0 to day
which still be effective for bacterial 60. At day 90, the log reduction of
eradication (see Table 4). On the one hand, Gram positive bacteria was dramatically
the concentration of sodium lauryl sulfate decreased. Figure 2c-d revealed that
would be decreased to 7.33 % which less the log reduction of Gram negative
than its favorite concentrations used as bacteria when exposed to cinnamon oil
irritant (10-14 %) for clinical controlled liquid soap was ranged between 0.5 - 4.0
experiments. log for all sampling days. However,
the difference of bacterial reduction
3.6 Stability of the Liquid Soap ability between the soap kept at room
The cinnamon oil liquid soap formulated temperature with natural light and the
according to Table 5 was kept at two soap kept at 45°C without light was not
accelerated conditions and determined observed.
a - S. aureus b - S. epidermidis
c. E. coli d. P. aeruginosa
Figure 2. Log reduction of the tested bacteria after 10 minutes exposure with cinnamon
oil liquid soap (log survival bacteria at 0 minute contact time - log survival bacteria at 10
minutes contact time). ♦, Room temperature with natural light; , 45°C without light
(Mean ± SD., n= 3).