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Научни трудове на Съюза на учените в България-Пловдив Серия Г. Медицина, фармация и дентална медицина т.ХХ1. ISSN 1311-9427 (Print), ISSN 2534-9392 (On-line). 2017. Scientific works of the Union of Scientists in Bulgaria-Plovdiv, series G. Medicine, Pharmacy and Dental medicine, VoLXXI. ISSN 1311-9427 (Print), ISSN 2534-9392 (On-line). 2017.
ОПРЕДЕЛЯНЕ НА ОПТИМАЛНА ХЛР СТОЙНОСТ НА ЛАВАНДУЛОВОМАСЛО- ВАЖЕНПАРАМЕТЪР ПРИ РАЗРАБОТВАНЕТО ИА ФАРТЕЖЦДОСИЧИО ВМУЛСИИ Мартвнъ Атвотд ВеровикзХ-истова, Диличева*
Ка-едра „Фармацевтирнт науни", Фармнцсврдчен факуитет, Медицински Универеит"т-Щ10вддв, Бнавтрид *Технологи-енценрът зл рнишннмедсцииа,цв. Плодрнв, България
DETERMINATION OF THE OPTHMUMHLB VALUE OF LAVENDER OIL - AN ESSENTIAL PARAMETER FOR THE DEVELOPMENT OF EMULSION FOIUIULATIONS Martina Savova, Veronika Hristova, Bissera Pilicheva* Department of pharmaceutical sciences, Faculty of pharmacy, MedicalUniversity-Plovdiv,Bulgaria *Technological center for emeraenca medidne, Plovdiv, Bulgaria
Abstract
Lavender oil is an essential oil that has been widely used in food industry and aromatherapy. It has a variety of cosmetic applications as well as therapeutic purposes in herbal medicine. Emulsification and further microencapsulation of lavender oil is a reliable approach for the enhancement of its stability in terms of oxidation, chemical interactions, or volatilization. To limit the composition degradation and loss during processing and storage, the formulation of a stable emulsion of lavender oil is essential. Since determination of the hydrophilic-lipophilic balance (HLB) value of oils appears as a crucial step for the development of emulsions, evaluation of optimum HLB value for lavender oil was the aim of the present study. A series of emulsions with varied HLB values were developed and the stability of the formulated coarse disperse systems was evaluated in terms of droplet size distribution, degree of creaming, effect of centrifugation and turbidimetry. Keywords: lavender oil, HLB value, emulsion
Introduction
Essential oils have been widely used as natural preservatives, fragrances or flavourants (Hammer, 1999). Recently, significant data concerning various therapeutic applications has been piled, which entails the evaluation of their capacity for incorporation in various delivery systems. Lavender oil has a variety of cosmetic applications as well as therapeutic purposes in herbal medicine. It is generally obtained from species of the family Lamiaceae (Lavandula angustifolia, L. latifolia, L. stoechas and L. x intermedia). Lavender oil, like most essential oils consists of volatile components, which is often a cause of instability during formulation and storage. Microencapsulation is a feasible approach to incorporate liquid substances into carriers, thus
preventing the essential oils from decomposition or evaporation and improving their stability. The development of a stable coarse formulation of essential oils into the wall material solution is of crucial importance. A critical step in this process is the estimation of optimum hydrophilic-lipophilic balance value (HLB) which is required of the oil phase. Currently, there is no data in the published literature concerning the optimum HLB value for lavender oil. Therefore, the present study aimed at the estimation of required HLB value for that essential oil which would serve as a prerequisite for the development of a stable emulsion and effective microencapsulation.
Materials and methods
Lavender oil (Ph.Eur.), sorbitan monooleate (Span® 80, Sigma Aldrich, USA) and polysorbate (Tween® 80, Sigma Aldrich, USA) were used. Preparation of the emulsions
Essential oil emulsions were prepared at a final volume of 100 mL, containing 10% essential oil, 5 % emulsifying blend and 85 % purified water (table 1). Both emulsifiers were dissolved in the oil phase and the mixture was heated up to 40oC. The aqueous phase was heated up to 70oC and both phases were mixed by the inversion method under constant stirring at 600rpm for 20 minutes. A series of eight emulsions at varied HLB values in the range from 8 to 12 were developed. All the emulsions were stored in capped test tubes at room temperature 25±1oC throughout the experiment. Optical microscopy
The emulsions were observed at magnification x400 using an optical microspcope Leica DM2000 LED (Leica Microsystems, Germany), equipped with a camera and software for image processing.
Droplet size analysis
The droplet size was determined by dynamic light scattering after proper dilution using a Nanotrac Wave II instrument (Microtrac, USA). Degree of creaming
A 25 mL emulsion sample was poured into a graduated cylinder. The volume ratio of the separated aqueous phase to the total volume of the emulsion was calculated after 7 and 20 days storage at room temperature. Another 10 mL sample was subjected to centrifugation for 15 min at 3000 rpm and the same calculations were made. Turbidimetric method
1 mL sample was withdrawn from the bottom of the emulsion and was further diluted with 25 mL purified water. The percentage transmission was measured spectrophotometrically at 600 nm using UV/Vis spectrometer Evolution 300 (Thermo Fisher Scientific, USA) after 7, 20 and 30 days.
Results and discussion
A series of eight emulsions was developed varying the ratio of the surfactant blend (Table 1). Table 1. Composition, mean droplet size and zeta potential of the sample emulsions
HLB value EO % Emulsifying blend 5 % Purified water % Mean droplet size ^m
Span 80 % Tween 80 %
8 10 65,4 34,6 85 0,546
9 10 56 44 85 0,587
9,8 10 48,6 51,4 85 0,615
10 10 46,7 56,3 85 0,450
10,2 10 44,9 55,1 85 0,659
10,6 10 41,1 58,9 85 0,601
11 10 37,4 62,6 85 0,571
12 10 28 72 85 0,593
i® %
HLB 9,8
S>
HLB 10
HLB 10,2
HLB 10,6
HLB II
HLB 12
>o
¿a.
Figure 1. Photomicrographs of the emulsions at magnification x400.
E
D
0.8 0.6
.!S 0.4 Q
0.2
10 HLB
11 12 13
Figure 2. Mean droplet size, analyzed by dynamic light scattering
The obtained disperse systems were analyzed in terms of the droplet size as an indicator for the emulsion stability (figure 1). Higher dispersity is generally related to enhanced formulation stability (Orafidiya, 2002). According to our results, the samples having HLB values in the range 10 - 10.6 showed smaller droplet size compared to the rest of the models and therefore are more stable than the others. That was confirmed when droplet size was analyzed by advanced equipment based on dynamic light scattering (figure 2).
Moreover, a tendency towards coalescence and increased droplet size after storage was observed
in emulsions of low HLB values, whereas at HLB>10 the initial droplet size was retained to a certain degree (figure 3). This fact is a clear indicator for the higher stability of these emulsions. Table 2 features the effect of HLB varying on the degree of creaming. It is evident that the models with HLB>10 have greatest stability after centrifugation. Similar results were obtained for the same samples after storage for 7, respectively for 20 days.
—1.4
E
31.2
fC 1
Q
0.8
0.6
0.4
0.2
0
HLB
□ day 1
□ day 7
8 9 9.8 10 10.210.6 11 12
Figure 3. Mean droplet size immediately after emulsification, compared to that after 7 days storage
Table 2. Effect of HLB value on the degree of creaming
HLB value % (v/v) separated aqueous phase
After centrifugation After 7 days storage After 20 days storage
8 90.5 10 12
9 90 8 10
9.8 86 6 8
10 84 0 0
10.2 84.5 0 0
10.6 84.5 0 0
11 85.5 0 0
12 84.5 10 12
It is common for unstable emulsions to coalescent during storage, which results into lifting of the oil droplets to the surface depriving the lower segments of dispersed phase. Measuring the transmission of that aqueous phase could serve as another approach for stability assessment (Fernandes, 2012). Higher transmission corresponds to lower concentration of emulsified phase, respectively to lower stability. Our results clearly show significantly higher transmission percentage at low HLB values 7 days after preparation compared to those at HLB>10 (figure 4). In addition, a further clarification of these emulsions occurred after storage for 20 and 30 days. Unlike them, the HLB=10 model exhibited low transmission not only at the early stage, but also during storage, which clearly indicated the enhanced stability of the emulsion.
50
40
30
• A------
-I.....f...................
---8
.............9,8
---10
-10,2
-------10,6
----12
20
10
Conclusion The present work focuses on the application of
various methods for the evaluation of emulsion stability so that an optimum HLB value for lavender essential oil could be estimated. Although there was no definitive method applicable for that purpose and all the methods should therefore be used to support one
another, HLB=10 might be considered optimum for the enhanced stability of lavender oil
emulsions.
Acknowledgements
This work was supported financially by Medical University-Plovdiv (University project № HO-12/2015).
E............
E-----
i=T===
0
7
12
17
22
27
days
Figure 4. Transmission of emulsions of varied HLB values after 7, 20 and 30
days storage
References
Fernandes CP, Mascarenhas MP, Zibetti FM, Lima BG, Oliveira RP, Rocha L, Falcao DQ. HLB value, an important parameter for the development of essential oil phytopharmaceuticals. Braz J Pharmacogn. 2012,23(1): 108-114.
Hammer KA, Carson CF, Riley TV. Antimicrobial activity of essential oils and other plant extracts. J Appl
Microbiol. 1999,86:985-990. Orafidiya LO, Oladimeji FA. Determination of the required HLB values of some essential oils. Int J Pharm. 2002, 237:241-249.
