Solid Lipid Microparticles (SLM) Containing Juniper Oil as Anti-Acne Topical

Carriers: Preliminary Studies

Elisabetta Gavini and Vanna Sanna

Dipartimento di Scienze del Farmaco, University of Sassari, Sassari, Italy

Reeta Sharma

Institute of Pharmacy—Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway

Claudia Juliano and Marianna Usai

Dipartimento di Scienze del Farmaco, University of Sassari, Sassari, Italy

Mauro Marchetti

Sezione di Sassari, Istituto di Chimica Biomolecolare-CNR, Sassari, Italy

Jan Karlsen

Institute of Pharmacy—Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway

Paolo Giunchedi

Dipartimento di Scienze del Farmaco, University of Sassari, Sassari, Italy

Solid lipid microparticles (SLM) were used as carriers of

juniper oil and proposed for the topical treatment of acne vulgare.

The formulations were obtained by the o/w emulsification

method. Compritol and Precirol were employed as lipidic

materials. Emulsions containing 1.5% (w/w) of lipophilic phase

(lipid and oil) and two different lipid to oil ratios (1:1 and 2:1)

were prepared. Blank particles were also prepared, as a com-

parison. The SLM were characterized in terms of encapsulation

efficiency, size, and morphology. The particle size stability in

aqueous dispersions was monitored over one month. Evaporation

of volatile compounds of oil from microparticles by weight loss

was investigated. The qualitative composition of Juniper oil

before and after the encapsulation process was determined by gas

chromatography (GC) and gas chromatography/mass spectrum

(GC/MS) analyses. The antimicrobial activity of the oil

encapsulated into the lipid microparticles against P. acnes was

studied as contact time assay and compared to the activity of the

oil not encapsulated. The emulsification method here described

was a good technique for the encapsulation of essential oils.

Percentage yields of production and encapsulation efficiencies

were higher for Compritol preparations than for these prepared

using Precirol. All preparations were characterized by similar

particle size distributions (dvs about 3–4 mm) regardless of lipid

type and lipid to oil ratios. Microscopy observations showed that

the microparticles in aqueous dispersions had almost spherical

shape, independently from their composition. The scanning

electron microscopy (SEM) analyses showed that when the

particles were dried, they had an irregular shape and a rough

surface. The SLM dispersions based on Compritol revealed

particle size stability over the investigated period of 30 days. In

contrast, an increase of the mean dimensions in the preparations

containing Precirol was observed. A low loss of volatile oil

compounds owing to evaporation from dry particles was found in

all preparations. This indicated that the microparticles were able

to substantially maintain the oil loaded inside their lipidic

structure, reducing its volatility. Some modifications of compo-

sition were found in the oil encapsulated in SLM with respect to

the juniper oil raw material, but these modifications did not

decrease the antibacterial activity of the oil. The SLM here

described are promising carriers for the development of anti-acne

topical formulations containing Juniper oil.

Keywords solid lipid microparticles, juniper oil, particle size

stability, antibacterial activity, GC-analysis

Received 27 January 2005, Accepted 20 April 2005.

Address correspondence to Paolo Giunchedi, Dipartimento di

Scienze del Farmaco, University of Sassari, via Muroni 23/a,

Sassari 07100, Italy; Fax: +39-079-228733; E-mail: pgiunc@

uniss.it

479

Pharmaceutical Development and Technology, 10:479–487, 2005

Copyright D 2005 Taylor & Francis Inc.

ISSN: 1083-7450 print / 1097-9867 online

DOI: 10.1080/10837450500299727

Order reprints of this article at www.copyright.rightslink.com

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INTRODUCTION

Acne vulgaris is an inflammation of sebaceous glands

characterized by pustules and skin lesions. Various

bacteria, including chiefly P. acnes and S. epidermidis,

have been identified as the etiological agents of acne.[1,2]

Current clinical practice for mild to moderate

inflammatory acne frequently involves the topical use of

drugs that affect the main pathogenetic factors responsible

for the development of acne, i.e., hyperseborrhea, hyper-

keratosis, microbial colonization, and inflammation.[3–5]

The juniper berry oil is stated to exhibit a variety of

pharmacological effects such as diuretic, carminative, and

antioxidative;[6,7] it is also effective for acne and

congested skin for its antimicrobial and antiseptic

activities.[8] In recent studies the antifungal and antibac-

terial activities of juniper berry oil have been put into

evidence.[9,10]

Microencapsulation of essential oils is an important

technique that offers protection against oxidation of the

active components[11] and reduces volatility.[12] Further-

more, conversion of the oil to a powder allows easier

handling and preparing of formulations.

Recently, lipid particles have been employed in the

encapsulation of retinol, tocopherol,[13] vitamin-A,[14]

glucocorticoids,[15] and the sunscreen oxybenzone.[16]

Lipid nanoparticles have been also proposed as cosmetic

and dermatological carriers for topical application of

synthetic fragrances and volatile substances.[17] They are

capable of protecting unstable active compounds from

degradation and releasing the actives in a controlled

way.[15,18,19] Essential oil encapsulation into lipid par-

ticles appears attractive also because of the high affinity

of the oil for the lipid materials.

In this study, solid lipid microparticles (SLM) were

proposed as carriers for the topical application of juniper

oil in the treatment of acne.

The SLM-containing Juniper oil were obtained by an

oil in water (o/w) emulsification method. Compritol and

Precirol were employed as lipidic carrier materials. Blank

lipidic microparticles were also prepared as a comparison.

The SLM have been characterized in terms of encapsu-

lation efficiency, yield of production, size, and morphol-

ogy. The particle size stability of SLM was monitored for

one month. Evaporation of volatile compounds of oil from

microparticles was studied.

The commercial oil used as raw material and the

encapsulated oil in SLM were analyzed and compared in

terms of quality composition by GC and GC/MS analyses.

The antimicrobial activity of SLM was tested as contact

time assay and compared to the antimicrobial activity of

the free oil.

MATERIALS

Glycerol behenate (Compritol1 888 ATO) and

glycerol palmitostearate (Precirol1 ATO 5) were obtained

from Gattefosse (Saint-Priest, Cedex, France). The essen-

tial oil of Juniperus communis L (juniper oil) was provided

by Aboca (San Sepolcro, Firenze, Italy). Hexane was

purchased from Carlo Erba Reagenti (Roma, Italy) and

polyoxyethylene-sorbitan monooleat (Tween1 80) from

Sigma-Aldrich Chemie GmbH (Steinheim, Germany).

Propionibacterium acnes ATCC 6919 was obtained

from LGC Promochem (Sesto San Giovanni, Italy). Brain

heart infusion agar (BHA), defibrinated horse blood,

phosphate buffered saline (PBS, Dulbecco A; pH 7.3),

and Gas Generating Kit were purchased from Oxoid

(Basingstoke, United Kingdom).

METHODS

Solid Lipid Microparticles (SLM) Preparation

Solid lipid microparticles were prepared by oil in

water (o/w) emulsification using a method previously

described.[20]

Table 1

Compositions, mean particle sizes, yields of production and encapsulation efficiencies of SLM prepared

SLM Lipid

Lipid-to-oil

ratio

Particle size±SD

(dvs, mm)

Yield of

production±SD (%)

Encapsulation

efficiency±SD (%)

SL C Compritol 1:0 3.3±1.2 60.1±2.5 —

SL P Precirol 1:0 3.1±0.2 51.9±2.3 —

SL 1 Compritol 1:1 4.3±1.3 56.1±4.3 35.0±4.6

SL 2 Compritol 2:1 4.1±1.4 60.0±1.9 34.7±1.8

SL 3 Precirol 1:1 4.6±1.9 53.1±1.6 23.3±4.4

SL 4 Precirol 2:1 4.1±1.3 51.7±6.7 21.8±4.1

E. Gavini et al.480

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Compritol and Precirol were chosen as lipidic

components. Table 1 reports the composition of SLM

microparticles. Emulsions consisting always of 1.5% w/

w of lipophilic phase (lipidic excipient and juniper oil)

in purified water were produced; the lipid-to-oil

weight ratios of 1:1 and 2:1 were used. Two batches of

blank SLM, constituted only by the lipidic excipients

(1.5% w/w) were prepared as a comparison.

Briefly, the lipidic excipients were melted (at a

temperature of 90°C for Compritol and 70°C for Precirol)

and the juniper oil was then slowly added. Distilled water

up to 100 g was heated to the same temperature and then

poured into the hot oily phase.

The emulsions obtained were homogenized by high

shear homogenization (Silverson SL2, Crami, Italy), at

6000 rev/min, for 5 min. The emulsions were then

cooled under magnetic stirring, at room temperature,

until solidification of the microparticles occurred. The

SLM obtained were collected by filtration and dried

at room temperature. Each preparation was carried out

in triplicate.

Yield of Production, Encapsulation Efficiency

and Particle Size

Percentage yield of production, Y%, of dry solid lipid

microparticles was calculated using the following formula:

Y% ¼ ðWa=WtÞ � 100% ½1�

where Wa was the actual amount of dry microparticles

obtained, and Wt was the theoretical amount of lipidic

materials (lipid and oil) introduced for each preparation.

Mean values of three preparations were used to state the

yield of production for every batch.

For the determination of the amount of essential oil

encapsulated it was not possible to distill the oil directly

from the particles, due to the high affinity of the oil to the

lipids. An extraction method of the oil from the lipidic

carrier material was performed using hexane. The extract

phase was then evaporated under vacuum at about 30°C;

the residue obtained was suspended in a suitable volume

of solution containing 0.15% w/v of Tween 80. The

surfactant was used to obtain the optimal dispersion of

the residue.

The suspension was distilled for 3 hr at a distillation

rate of 2–3 mL/min. The lighter than water, slightly

yellow, and limpid oil was then dried over anhydrous

sodium sulfate and stored in sealed containers under

refrigeration. Steam distillation was carried out using the

European Pharmacopoeia hydrodistillation apparatus

(Clevenger type).

Percentage oil encapsulation efficiency, E%, was

defined as follows:

E% ¼ ðW1=W2Þ � 100% ½2�

where W1 was the actual amount of oil encapsulated

in a known amount of microparticles and W2 was

the theoretical amount of oil introduced in the same

amount of particles. Each determination was carried out

in triplicate.

The mean particle size of SLM was determined by

Coulter Laser Diffractometry (Coulter LS 100Q laser

sizer, Beckman Coulter, Miami, FLA). The test was

carried out in triplicate on SLM before the drying process

and, after the filtration, on the dry microparticles

suspended in aqueous medium. The average particle size

was expressed as mean volume-surface diameter (dvs,

mm).[21]

Microscopy Observations

The morphology of SLM in aqueous dispersion was

examined by photomicrography with a stereomicroscope

(magnitude 6.4�10) (Zeiss MC 63, Zeiss, Germany)

connected to a digital camera (Zeiss M 35 Winder). The

morphology of the dry microparticles was examined using

a scanning electron microscope (SEM, Zeiss DSM 962,

Zeiss, Germany). Samples of particles were placed on

double-sided tapes, which had previously been secured on

aluminium stubs, and then analyzed after gold sputtering

at 20 kV acceleration voltage, under argon atmosphere.

Particle Size Stability of SLM

This test was performed on microparticles using the

Coulter Laser Diffraction method previously described to

investigate the possible aggregation of particles during a

defined time period and in relation to the possible

formulation of SLM into an aqueous medium. The

particle size stability was carried out both on the primary

dispersion (i.e., the aqueous medium, purified water, in

which the particles were formed) and on a redispersion

(i.e., the suspension of the dry particles, obtained by

filtration of the primary dispersion, into a solution

containing 0.15% w/v of Tween1 80. This concentration

of surfactant was used to obtain the optimal dispersion

of SLM).

The stability was monitored at day 1 and after 30

days, after storage of the samples in sealed glass vials at

room temperature. All experiments of particle size

stability were performed in triplicate (SD within 1.14).

481SLM-Containing Juniper Oil

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In Vitro Evaporation of Volatile Oil Compounds

from Dry Particles

Evaporation of volatile oil components from the

particles was investigated in terms of percent weight loss.

The tests were carried out on oil loaded microparticles

(SL 1, SL 2, SL 3 and SL 4). A quantity of microparticles

containing 15.0 mg of oil was filled in glass vials and

stored in an oven at 32°C up to 48 hr. At selected time

intervals (from 1 to 6 times every hour and after 10, 24,

and 48 hr) the weight loss of the particles was measured.

Percentage weight loss, W%, was estimated accord-

ing to the equation:

W% ¼ ½ðWiÿWfÞ=Wi� � 100% ½3�

where Wi and Wf were the initial and final weight of

samples, respectively. Each experiment was performed in

triplicate and the mean percentage was calculated.

GC Analyses

For the evaluation of the composition of oil en-

capsulated in SLM, a distillation process of the oil from

the lipidic particles was carried out and then the oil was

analyzed by GC. In fact it was not possible to perform

direct GC analyses on SLM particles due to the

interference of the lipidic material with the oil.

Oil Distillation

The juniper oil encapsulated in SL 1 (chosen on the

basis of the results obtained previously) was extracted

from lipid material using n-hexane after breaking the

particles in a mortar. This extract was treated following

the procedure described earlier for the determination of

the encapsulation efficiency.

Oil Analyses

The commercial oil and the oil distilled from SL 1

microparticles were analyzed to compare their composi-

tion. Analyses were performed by GC and GC/MS.

The GC- four replicates of each sample were

analyzed by using a Hewlett-Packard Model 5890A GC

equipped with a flame ionization detector and fitted with

a 60 m�0.25 mm, thickness 0.25 mm AT-5 fused silica

capillary column (Alltech). Injection port and detector

temperature were 280°C. The column temperature was

programmed from 50°C to 135°C at 5°C/min (1 min),

5°C/min up 225°C (5 min), 5°C/min up 260°C, and held

for 10 min.

The samples (0.2 ml each), analyzed without dilution

with 2,6-dimethylphenol as internal standard, were

injected using a split/splitless automatic injector HP

7673 and using helium as the carrier gas. Measurements

of peak areas were performed with an HP workstation; the

threshold was set at 0, peak width at 0.02. The data

reported in Table 2 are the average of four GC injections.

The quantization of each compound was expressed as

absolute weight percentage using internal standard and

response factors. The detector response factors (RFs) were

determined for key components relative to 2,6-dimethyl-

phenol and assigned to other components on the basis of

functional group and/or structural similarity.[22]

The GC/MS analyses were carried out with a Hewlett

Packard G1800B-GCD System using the same conditions

and column described earlier. The column was connected

with the ion source of the mass spectrometer. Mass units

were monitored from 10 to 450 at 70 eV. The samples

(0.1 mL each), analyzed diluted in hexane, were injected

manually. The identification of compounds was based on

comparison with their Kovat’s Indexes (KI) and by

comparison with their mass spectra with those of

published data and HP libraries.[23,24]

Contact Time Assay

This assay was performed on pure oil (commercial

juniper oil), on oil distilled from SL 1 formulation, and on

SL 1 loaded microparticles. For this test, essential oils

were dissolved in PEG 200 at 100 mg/mL concentration.

Empty Compritol (SL C) microparticles were used as a

comparison. P. acnes was selected as bacterium to test the

potential anti-acne activity of SL 1.

Contact time was determined as the exposure time

required by fixed amount of oil to kill a standardized

microbial inoculum of P. acnes. Microorganisms in the

logarithmic phase of growth were suspended at a density

of 5�105–1�106 colony forming units (c.f.u.)/mL in 10

mL of PBS containing 2 mg/mL of the commercial oil or

distilled oil from SL 1 formulation, or a quantity of

microparticles corresponding to the same oil concentra-

tion. Two control tubes (bacteria suspended in PBS alone

at the same density and bacteria suspended in PBS+PEG

200) were included in each experiment. At time zero and

at regular intervals, 0.5 mL of suspension were removed,

subjected to serial 10-fold dilutions in PBS and seeded on

blood agar plates (BHA+10% horse blood) for P. acnes.

The number of viable microorganisms at each time was

evaluated counting colonies after anaerobic incubation for

24 hr at 35°C.

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Table 2

Some of the main components (%) of the pure juniper oil compared with those of the distilled oil from SL 1

Compoundsa KIb Commercial juniper oil (%) SL 1 (%)

a-thujene 931 1.91

a-pinene 939 22.75 0.16

Camphene 953 0.47

Sabinene 976 0.35

b-pinene 980 2.89

b-myrcene 991 11.88 0.36

a-phellandrene 1005 0.62

d-3-carene 1011 3.95

Para-cymene 1026 2.12 0.70

Limonene 1031 6.56

g-terpinene 1062 6.11

Terpinolene 1088 2.98 0.71

Terpinen-4-ol 1177 8.14 3.34

a-terpineol 1189 0.75 0.47

Merthyl citronellate 1261 0.53

Bornyl acetate 1285 1.22

2-undecanone 1291 0.32

a-cubebene 1351 0.87 3.91

a-copaene 1376 0.40 2.68

Geranyl acetate 1383 0.51

b-elemene 1391 0.85 6.30

Trans-a-ambrinol 1412 1.08

b-cedrene 1418 0.41

b-caryophyllene 1418 3.01 7.32

g-elemene 1433 3.21 4.33

a-caryophyllene 1454 3.22 6.27

9-epi-caryophyllene 1467 1.72

Germacrene D 1480 0.65 4.40

Epi-cubebol 1493 2.34

a-selinene 1494 2.65

Eudesma-4(14),11-diene 1494 0.45 2.43

a-muurolene 1499 2.78

g-cadinene 1513 0.65 3.62

d-cadinene 1524 0.61 5.11

a-cadinene 1538 0.72 1.18

Selina-3,7(11)-diene 1542 2.16 0.58

a-calacorene 1542 1.19

Sesquisabinene hydrate 1545 0.58

Germacrene B 1556 1.43

b-calacorene 1563 0.48

Caryophyllene alcohol 1568 3.15

Caryophyllene oxide 1581 2.06

Trans-b-elemenone 1600 1.94

Humulene epoxide II 1606 2.20

2-caren-4-ol 4.09

5-cedranone 1618 0.51

Cedr-8-(15)-en-alpha-ol 1644 1.97

a-muurolol 0.63

a-cadinol 1653 3.18 3.10

5-neo-cedranol 1677 0.59

Crysolide 1721 1.04

aCompounds are listed in elution order.bKovat Index.

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RESULTS AND DISCUSSION

SLM Preparation and Characterization

The high shear homogenization used in the experi-

mental conditions previously described was a good

technique for the preparation of SLM: it was a one-step

process that involved simply the preparation of an

emulsion containing a lipophilic phase (lipid and oil)

and water.

Table 1 reported mean particle size, as dvs (mm),

percentage yields of production, and encapsulation

efficiencies of the SLM prepared. Particle size analyses

revealed no significant differences comparing the

different batches: oil empty microparticles were charac-

terized by dvs of about 3 mm, while for oil-loaded

particles the mean diameter was about 4 mm, independent

of their compositions.

As shown in Table 1, the yields of production of SLM

varied from 52% to about 60%; microparticles constituted

by Compritol showed the highest values compared to

those made of Precirol. The relatively lower yields of

production found in the case of Precirol preparations were

probably due to the consistency of the microparticles

observed during the filtering process, which was ‘‘wax

like,’’ with consequent sticking of the particles to the

filter and difficulty in their collection. Compritol micro-

particles did not have this consistency and consequently

the difficulty in the collection was not found. These two

behaviors could be due to the different chemical

composition of the two lipids used as carriers.

Relatively low values of encapsulation efficiency

were found for all SLM: as reported in Table 1 the

percentage of the oil encapsulated into microparticles

varied from 22% to about 35%. These values appeared to

depend on the lipid employed and on the lipid-to-oil ratio.

SLM containing Compritol always showed higher values

of encapsulation efficiency compared to Precirol prepara-

tions. As reported in literature, the chemical composition

of the lipid can influence determining drug incorpora-

tion.[25] In all cases, an increase in the encapsulation of oil

was obtained for batches having a lipid to oil ratio of 1:1 in

comparison with formulations with a 2:1 ratio.

Microscopy Observations

Shape and surface of microparticles were analyzed by

stereomicroscopy and SEM analyses (photos not

reported). Photomicrographies of SLM in aqueous

dispersions revealed that the particles for all the batches

prepared had an almost spherical shape, were well

separated, and did not form aggregates.

Particles after filtration and drying had an irregular

shape and a rough surface, characterized by numerous

lipidic slivers regardless of lipidic composition and lipid-

to-oil ratio.

Particle Size Stability of SLM

In Figure 1A–B the diagrams of mean particle sizes

(expressed as dvs, mm) of the primary SLM aqueous

dispersions containing the Compritol (SL 1, SL 2, and SL

C) and Precirol microparticles (SL 3, SL 4, and SL P)

were reported. The analyses were performed at two

different time periods (day 1 and day 30).

Right after production (day 1), the particle size for all

batches is of about 3–4 mm. The lipidic microparticles

based on Compritol were characterized by a good long-

term stability as the particle size of SLM dispersions

remained unchanged during 1 month (Figure 1A). A

different behavior was found for batches containing

Figure 1. Particle size stability of SLM primary dispersions

containing Compritol (a) and Precirol (b).

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Precirol: in this case a significant particle size increase

occurred (Figure 1B).

As reported by Jenning and Gohla,[26] large amounts

of glycerides like monoglycerides are possibly responsi-

ble for physical destabilization. The amount of mono-

glycerides for Precirol is higher than that for Compritol;

thus, this could result in unstable forms and particle

dimension growth taking place.

In both cases (Compritol and Precirol particles) the

presence of the oil did not influence particle stability, as

their behavior was similar both on oil-loaded and oil-

empty microparticles.

Figure 2A–B reported mean particle sizes (dvs, mm)

of redispersed dry microparticles in Tween 80 solution at

day 1 and day 30. Immediately after the redispersion

(day 1), the mean particle size of oil-loaded SL 1 and SL 2

resulted in about 7 mm while the dvs of particles in the

primary dispersion was 3–4 mm. On the contrary, the oil-

empty microparticles (SL C) maintained their original size.

After 30 days, the dvs values of SL 1 and SL 2

microparticles remained unchanged while SL C particle

size slightly increased from 3 mm to about 5 mm

(Figure 2A).

The redispersion of particles based on Precirol was

characterized at the day 1 by an increased dvs to 8–9 mm

in the case of the oil-loaded SLM (SL 3 and SL 4), and to

about 6 mm for the oil-empty microparticles SL P.

After 1 month SL 3 and SL 4 showed similar particle

size while SL P particles reveal an increased value of dvs

to approximately 9 mm (Figure 2B).

When the dry microparticles are redispersed, the

increase of particle size observed was probably due to

formation of small aggregates (hence leading to increased

mean values compared to the primary dispersion). This

was more evident for the oil-loaded SLM compared to the

oil-empty SLM, indicating that, in this case, the presence

of the oil promoted particle aggregation.

However the particle size values were stable during

the investigated period (1 month); it can be due to the

influence of surfactant in the aqueous medium used for

the redispersion.

In Vitro Evaporation of Volatile Oil Compounds

The evaporation tests were performed in order to

evaluate the loss of the volatile compounds of the oil. The

obtained profiles were illustrated in Figure 3.

A relatively low percentage evaporation of volatile

compounds was achieved for all formulations: from 12%

to about 3%.

Compritol seemed to preserve the evaporation of

volatile compounds more efficiently as both preparations

SL 1 and SL 2 showed low amounts of oil evaporated

(about 5% and 1.5%), dependent on the lipid-to-oil ratios.

Precirol preparation SL 3 (characterized by the lipid-

to-oil ratio 1:1) showed the highest loss (12%), while only

SL 4 microparticles had an oil loss of about 3% in 10 hr.

Figure 3. Evaporation profiles of volatile compounds from dry

microparticles upon storage at 32°C.

Figure 2. Particle size stability of redispersed dry micro-

particles containing Compritol (a) and Precirol (b).

485SLM-Containing Juniper Oil

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GC Analyses

Thirty-one compounds were identified in the com-

mercial juniper oil used as raw material, representing

97.4% of the total oil. As shown in Table 2 a change in

the chemical composition was observed when juniper oil

was encapsulated into SL 1 microparticles. The analyses

showed that juniper oil raw material was dominated by

the monoterpenes a-pinene (22.75%), b-myrcene

(11.88%), limonene (6.56%), g-terpinene (6.11%), and

the alcohol terpinen-4-ol (8.14%). The juniper oil

recovered from SL 1 showed a decrease of the named

monoterpenes, in particular, the monoterpenes hydrocar-

bon disappeared completely and constituents such as b-

elemene, b-caryophyllene, a-caryophyllene, and d-cadi-

nene were present in higher values compared to the

commercial juniper oil. Moreover series of new com-

pounds were detected in the distilled essential oil from SL

1. Among the new compounds, the more representative

were oxygenated terpenes, such as 2-caren-4-ol and

caryophyllene alcohol.

The modification of oil composition (distilled from

SL 1) compared to the commercial juniper oil, could be

due to the different loading of the oil components into

the microparticles (the observed order of loading was:

b-pinene= limonene=gamma;-terpinene<a-pinene<bÿmircene<terpinen-4-ol) and/or to chemical reactions

(such as oxidation and isomerization) of the oil

encapsulated.[27]

Contact Time Assay

The results of the contact time tests were shown in

Figure 4. At a concentration of 2 mg/mL, the essential oils

were able to decrease microbial viability in a time-

dependent way. In particular, the commercial oil was able

to completely inactivate P. acnes in 1 hr while oil loaded

into microparticles killed 60% of P. acnes after 1.5 hr.

The oil obtained by distilling SL 1 microparticles

resulted as more effective on bacterial inocula: it killed

100% of P. acnes in only 30 min.

The killing effect of the microparticles can be

explained by the prolonged delivery rate of the oil from

microparticles. The more potent activity against P. acnes

of the distilled oil compared with the commercial oil

could be ascribed to the different composition of the oils.

CONCLUSIONS

The incorporation of juniper oil into SLM provided a

microparticulate system that can offer possible topical

applications. Both lipids used (Compritol and Precirol)

were able to entrap the oil, but higher values for yield of

production and encapsulation efficiency were achieved

for particles based on Compritol.

Long-term particle size stability of dispersions based

on Compritol was better compare to Precirol. Dry

particles redispersed in Tween 80 solution showed

stability in particle size over the investigated period for

both Compritol and Precirol formulations.

According to the results, Compritol can be proposed

as a lipidic carrier suitable for the preparation of topical

suspensions based on microparticles. The SL 1 particles

maintained the antibacterial activity against P. acnes. The

higher killing activity of the distilled oil for the micro-

particles could be related to the relatively higher fraction

of new oxygenate compounds of the distilled oil com-

pared to the commercial juniper oil shown by GC.

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487SLM-Containing Juniper Oil

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