International Journal of Cosmetic Science, 2015, 37, 408–416
doi: 10.1111/ics.12211
Stability of cosmetic emulsion containing different amount of hemp oil † _ M. Kowalska*, M. Ziomek* and A. Zbikowska
*Department of Chemistry, Faculty of Material Science, Technology and Design, Kazimierz Pulaski University of Technology and Humanities, Chrobrego st. 27, 26-600 Radom, and †Department of Food Technology, Faculty of Food Sciences, Warsaw University of Life Sciences (WULSSGGW), Nowoursynowska st. 159C, 02-787 Warsaw, Poland
Received 26 November 2014, Accepted 1 February 2015
Keywords: droplet size, emulsion, hemp oil, stability, Turbiscan test
Synopsis OBJECTIVE: The aim of the study was to determine the optimal conditions, that is the content of hemp oil and time of homogenization to obtain stable dispersion systems. METHODS: For this purpose, six emulsions were prepared, their stability was examined empirically and the most correctly formulated emulsion composition was determined using a computer simulation. Variable parameters (oil content and homogenization time) were indicated by the optimization software based on Kleeman’s method. Physical properties of the synthesized emulsions were studied by numerous techniques involving particle size analysis, optical microscopy, Turbiscan test and viscosity of emulsions. RESULTS: The emulsion containing 50 g of oil and being homogenized for 6 min had the highest stability. Empirically determined parameters proved to be consistent with the results obtained using the computer software. The computer simulation showed that the most stable emulsion should contain from 30 to 50 g of oil and should be homogenized for 2.5–6 min. CONCLUSIONS: The computer software based on Kleeman’s method proved to be useful for quick optimization of the composition and production parameters of stable emulsion systems. Moreover, obtaining an emulsion system with proper stability justifies further research extended with sensory analysis, which will allow the application of such systems (containing hemp oil, beneficial for skin) in the cosmetic industry. sume Re OBJECTIF: L’objectif de l’etude etait de determiner les conditions savoir le contenu en huile de chanvre et la duree de optimales a l’homogeneisation pour obtenir des systemes de dispersion stables. METHODES: A cet effet, six emulsions ont ete preparees, leur stabilite a ete examinee de maniere empirique et la composition de l’emulsion la plus correctement formulee a ete determinee en utilisant une simulation par ordinateur. Les parametres variables (teneur en huile et le temps d’homogeneisation) ont ete indiques par le logiciel d’optimisation base sur la methode de Kleeman. Les proprietes physiques des emulsions synthetisees ont ete etudiees par de Correspondence: Malgorzata Kowalska, Department of Chemistry, Faculty of Material Science, Technology and Design, Kazimierz Pulaski University of Technology and Humanities, Chrobrego st. 27, 26-600 Radom, Poland. Tel.: +48 48 3617547; fax: +48 48 3617500; e-mail: [email protected]
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nombreuses techniques impliquant l’analyse granulometrique, la microscopie optique, l’essai au Turbiscan et la viscosite des emulsions. RESULTATS: L’emulsion contenant 50 g d’huile et homogeneisee pendant 6 min avait la plus haute stabilite. Les parametres determines empiriquement se ont reveles ^etre compatibles avec les resultats obtenus en utilisant le logiciel de l’ordinateur. La simulation par ordinateur a montre que l’emulsion la plus stable doit contenir de 30 a 50 g de l’huile et doit ^etre homogeneise pendant 2.5 a 6 min. CONCLUSIONS: Le logiciel base sur la methode de Kleeman s’est avere utile pour l’optimisation rapide de la composition et de la production des parametres de systemes d’emulsion stables. En outre, l’obtention d’un systeme d’emulsion avec une bonne stabilite justifie la poursuite de la recherche etendue a l’analyse sensorielle, ce qui permettra l’application de ces systemes (contenant de l’huile de chanvre, benefiques pour la peau) dans l’industrie cosmetique.
Introduction Emulsion systems consist of two or more liquid immiscible phases, where one of the liquids is dispersed in the other as small (0.1– 100 lm) spherical droplets [1]. The basic condition to form a homogeneous emulsion from two immiscible liquids is to disperse one phase in the other. This process counteracts the surface tension forces present at the interface. Overcoming these forces occurs in two stages. Addition of an emulsifier at the first stage of emulsification contributes to reduction of the surface tension. At the second stage, the rest of the surface tension is overcome by energetic stirring [2, 3]. One of the most important elements necessary to obtain an emulsion with proper stabilization is the fragmentation of large droplets of oil to small particles with a narrow size distribution. The well-homogenized emulsion contains oil molecules that are appropriately small and reveal little tendency to increase in size and consequently to separate [4]. It is assumed that emulsions are generally thermodynamically unstable and can undergo a number of different instabilities such as gravitational separation, creaming, flocculation, coalescence, phase inversion and Ostwald ripening. The main factors affecting these processes can be identified as average particle size and distribution; furthermore, they also include the state of aggregation of the droplets, pH, energy input during emulsification, osmotic pressure, viscosity of the bulk phase and the presence of various additives [3, 5–7].
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie
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Sability of the emulsion based on hampseed oil Table I Changing components/parameter of emulsions
Furthermore, blocking conversion of LA to GLA in the skin can also lead to undesirable changes in the appearance of the body [8]. EFA application to the skin surface is very important to maintain its proper appearance and function [9]. For this reason, hemp oil can be used in cosmetics (as an additive to lotions, moisturizes, lip balms), but also in food and aromatherapy [10, 11]. The aim of the study was to determine the optimal conditions, that is the content of hemp oil and time of homogenization to obtain stable dispersion systems by evaluating their physical properties such as particle size, microscopy, dispersion index, viscosity and the photon backscattering profiles. The last parameter was obtained using the Turbiscan Lab Expert, an innovative optical analyser, which allows one to scan the turbidity profile of an emulsion along the height of a glass tube filled with the emulsion, following the turbidity profile changes over time [12]. The optimization of the software based on Kleeman’s method [13] was used to help indicate the most stable emulsion. It was expected that the software would indicate the emulsion with proper stability after one measurement. Proposing a tool allowing for fast evaluation and possible design of the emulsion is a very important issue for technologists, especially to reduce the time of an experiment.
Emulsion Component (%w/w)/parameter
I
II
III
IV
V
VI
Water Hemp oil Mixing time (min)
83.75 10 1.5
43.75 50 1.5
63.75 30 3.0
63.75 30 4.5
43.75 50 6.0
83.75 10 6.0
Vegetable oils are the most frequently used fatty base for cosmetic emulsions. Currently, on the market, there is a growing variety of oils that contain unsaturated fatty acids having a great importance in cosmetics. Hemp oil is one of such oils. Hempseed is rich in minerals, vitamins (A, C and E), b-carotene, a-linolenic acid (ALA) and linoleic acid (LA). Additionally, because of the presence of c-linolenic acid (GLA), hemp oil is perfect as an ingredient in the light body oils and lipid-enriched creams, known for their ability to penetrate the skin. The first symptom of essential fatty acids (EFA) deficiency is body changes (atopic dermatitis, psoriasis, acne).
Table II Average particle size, dispersion index, number and percentage of emulsion fractions 24 h, and 2, 4, 6 and 10 weeks after preparation, and the increase of average particle size during the storage period
Emulsion
Content of oil/time of homogenization Average particle size (lm) X SD 24 h 2 weeks 4 weeks 6 weeks 10 weeks Dispersion index X SD 24 h 2 weeks 4 weeks 6 weeks 10 weeks Increase of average particle size after 10 weeks Number and percentage of emulsion fraction 24 h
I
II
III
IV
V
VI
10 g/1.5 min
50 g/1.5 min
30 g/3.0 min
30 g/4.5 min
50 g/6.0 min
10 g/6.0 min
3.35aA 3.39a 3.45a 3.62b 4.61c
0.02 0.01 0.01 0.01 0.01
10.65aC 11.38b 12.04c 12.28d 12.20cd
0.01 0.03 0.03 0.01 0.02
3.69aA 3.70a 3.80a 3.97b 4.18c
0.01 0.02 0.01 0.00 0.02
3.50aA 3.52a 3.74a 3.83a 3.92a
0.02 0.02 0.01 0.01 0.00
5.75aB 5.77a 5.76a 5.77a 5.80a
0.01 0.01 0.01 0.02 0.02
3.80bA 3.52a 3.70b 4.11c 4.44d
0.01 0.02 0.01 0.01 0.01
1.87cC 1.80b 1.63a 1.70a 1.69a 1.26
0.01 0.01 0.02 0.02 0.01
1.12aA 1.13a 3.08b 5.07c 6.26d 1.55
0.00 0.01 0.01 0.02 0.01
1.64aB 1.76c 1.69b 1.96d 2.20e 0.50
0.01 0.01 0.02 0.01 0.01
1.62abB 1.55a 1.65b 2.07c 2.10c 0.42
0.01 0.01 0.01 0.01 0.02
1.18bA 1.13a 1.13a 3.30c 3.39d 0.05
0.01 0.01 0.01 0.02 0.01
2.49eD 2.20d 1.93b 1.78a 2.02c 0.65
0.01 0.01 0.01 0.01 0.02
I – 100%
2 weeks
I – 100%
4 weeks
I – 100%
6 weeks
I – 100%
10 weeks
I – 100%
I – 80% II – 20% I – 87% II – 13% I – 100% I – 46% II – 54% I – 41% II – 59%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 76% II – 24% I – 79% II – 21% I – 79% II – 21% I – 46% II – 54% I – 45% II – 55%
I – 100% I – 100% I – 100% I – 100% I – 100%
a, b, c – Different letters in columns indicate mean values that differ statistically significantly (P < 0.05). A, B, C – Different letters in rows indicate mean values that differ statistically significantly (P < 0.05).
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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(a)
(b)
Figure 1 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion II (b).
Figure 2 Appearance of the emulsions after 14 days of manufacturing.
Spain) sodium benzoate (Orff Food Eastern Europe, Marki/Warsaw, Poland), aloe vera (FLP), Scottsdale, Arizona, United States, citric acid (Jungbunzlauer Basel, Switzerland).
Materials and methods Materials Emulsions were prepared using the following ingredients: distilled water, carboxymethylcellulose (Barentz Hoofddorp, Netherlands), cold pressed, unrefined (Gracefruit Ltd Stirlingshire, United Kingdom) (INCI: Cannabis Sativa Seed Oil) hemp oil containing the following fatty acids (FA): palmitic acid C16:0 – 5.7%, palmitoleic acid C16:1 – 0.15%, stearic acid C18:0 – 2.5%, oleic acid C18:1 9c – 11.4%, linoleic acid C18:2 9c12c – 55.4%, alpha linolenic acid C18:3 9c12c15c – 17.2%, gamma linolenic acid C18:3 6c9c12c – 3.6%, eicosenoic acid C20:0 – 0.6%, eicosenoic acid C20:1 – 0.4%, docosanoic acid C22:0 – 0.3%, tetracosanoic acid C24:0 – 0.2%, sunflower lecithin (Lasenor, Emul, S.L. Barcelona,
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Preparation of emulsions The composition of changing parameters in the experimental emulsions was optimized with the software based on Kleeman’s method, its constant parameters were chosen according to our previous research [14, 15]. Lecithin (5.2%) was added to the oil phase (hemp oil). Carboxymethylcellulose (0.6%) was dispersed in distilled water, and then, aloe vera (0.2%) was added. Both solutions (oil and aqueous phases) were heated at 50–55°C in a water bath. Homogenization of the aqueous phase with the oil phase was achieved with a high shear mixer at an equal speed of 36288 RCF
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
M. Kowalska et al.
Sability of the emulsion based on hampseed oil
(a)
(b)
Figure 3 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion I (b).
(a)
(b)
Figure 4 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion III (b).
for an appropriate time (given in Table I). Finally, the emulsions were cooled to room temperature, and a preservative sodium benzoate (0.25%) was added. Then pH was adjusted to 5.5 by addition of citric acid using a Mettler Toledo pH-meter equipped with a calomel combined pH electrode. The content of changing components was presented in Table I.
nation of each sample was 30 s. Each measurement was repeated three times and given as the average value. Dispersion index It was calculated on the basis of particle size measurements using laser diffraction according to the formula:
Methods Determination of mean particle size and particle size distribution The average particle size and distribution were determined after 24 h, 2, 4, 6 and 10 weeks of cold storage at +/7°C in a fridge. For measurements, the emulsions were diluted 1 : 200 with distilled water. The particle size was measured in the range 0.12– 704 lm by laser scattering using a Microtrac Particle Size Analyzer (Leeds & Northrup, Philadelphia, PA, U.S.A.); total time of determi-
k¼
AB ; C
where A, B and C are the biggest sizes of oil droplets for 90%, 10% and 50% of all particles, respectively. Turbiscan test The samples stored at 40°C in thermostat for 10 weeks were used to evaluate destabilization of emulsions by the Turbiscan
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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(a)
(b)
Figure 5 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion IV (b).
(a)
(b)
Figure 6 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion VI (b).
test (Turbiscan Lab. Formulation L’Union - France). Emulsions placed in the glass cells were scanned, each 40 mm, by a pulsed near infrared light source (k = 880 nm) and two synchronous detectors. The transmission detector receives the light through the sample at 0° from the incident beam, whereas the backscattering detector receives the light scattered by the sample at 135° from the incident beam. The results were presented as the dependency of backscattered light intensity as a function of sample height. Analysis of curves with the percentage of backscattered light for the studied emulsions in time allowed for evaluation of the intensity of the destabilization processes occurring in the samples. Determination of emulsion stability using the centrifugal test The determination of emulsion stability was measured in the centrifugal machine (Nahita Centrifuges Model 2652; Auxilab, S.L.,
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Beriain, Navarra, Spain) at 1008 RCF. Test tubes were filled with 15–20 mL of the emulsion and then centrifuged for 30 min, with the state of emulsion checked every 10 min. If the emulsion remained homogeneous after 30 min, it was considered to have proper stability. Structure of emulsions Structure of emulsions was investigated with an optical microscope (Nikon Alphaphot combined with a CCD camera and picture analysis software (Nikon - producer PZO, Warsaw Poland, lens Nikon 4 4/0.10 (160/-WD 25), ocular Nikon China CF WE 15/12, camera Panasonic type GP-KR 222, software MICROSCAN for Windows). The prepared emulsion was placed on the microscopic slide. A cover slip was placed on the sample. No air or bubbles were trapped between the sample and cover slip, and the samples were tested with a 40 9 objective.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil
(a)
(b)
Figure 7 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion V (b).
Figure 8 Optical microphotographs of the emulsions at a magnification G 940. Scale bar (white line) in photos corresponds to 10 lm.
Viscosity examination The viscosities of the samples were determined at 25°C at the speed of 10 rpm, spindle RV3, using a Brookfield Rheometer DV-I ( Middleboro, Massachusetts, USA) + after 24 h, and 2, 4, 6 and 10 weeks of cold storage. Optimization of parameters of emulsion stability Optimization of oil content and mixing time was performed using software developed for the Department of Technology the KATESKOR Footwear and Tanning at the Faculty of Materials Science, Technology and Design at the University of Technology and Humanities in Radom. This program is based on Kleeman’s method [13]. The software allows the number of experiments (six different samples) to be minimized by selection of the compromise optimum according to the experimenters’ expectations. The method selects and determines the limits of the measured parameters and suggests a range of pre-
ferred parameters for which an emulsion should have high stability. In this study, the initial parameters (measured 24 h after the preparation of emulsions) were used as input data for the software and then optimized according to Kleeman’s procedure. As an output, we obtained the set of calculated parameters, which were further employed to perform the optimization of parameters for which the stable emulsions should be formed. Further, the limits of the measured parameters were chosen and then a range of selected parameters, for which the emulsion should have the best stability, was calculated. According to the program, we have adopted a model of emulsion characterized by the following input parameters for optimization purposes: dispersion index – 1.6, viscosity – 500 mPa s, number of fractions – 1, average particle size – 6 lm, maximum particle size – 16 lm, minimum particle size – 0.7 lm. Using optimization software, the range of changing parameters, for which the emulsion system should have the best stability, was defined.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Figure 9 Viscosity of the investigated emulsions (T = 20°C).
Figure 10 Compromise optimum of parameters of investigated emulsions.
Statistical analysis The results were subjected to one-way ANOVA. The Duncan test was used to assess the differences between means. The level of P < 0.05 was considered significant. STATGRAPHICS PLUS 4.1 package (Statistical Graphics Corp., Warrenton, VA, U.S.A.) was used. Results and discussion Analysing the results of the average particle size of all tested emulsions, the highest value of this parameter was observed for emulsion II (Table II). This system was definitely different from the others – the value of particle size was at least three times higher (throughout the whole storage period). Other parameters such as number of fractions (2) and the dispersion index (6.26 after 10 weeks) confirmed destabilization of this system (Fig. 1, Table II). An additional symptom of destabilization was a negative result of the centrifugal test: after 10 min of centrifugation, emulsion II was delaminated. However, the curves of backscattered light showed that, relative to the emulsions (I, III, IV or VI), destabilization started later. There were changes in the course of the curves in subsequent measurements. The first change in the profile of the emulsion was smaller values of DBS (delta backscattering) at the bottom of the cell, more noticeable after 14 days. The observations indicated the occurrence of migration of the particles – the creaming process.
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According to Kowalska et al. [16], physicochemically, emulsion instabilities can be divided into two types: reversible and irreversible. Reversible instabilities include creaming and sedimentation, in which the dispersed phase particles do not change their size, but tend only to the surface of the emulsion. This type is more frequent in O/W than W/O systems. Confirmation of initiation of changes in emulsion II was provided by the delicate crack shown in Fig. 2. A relatively low value of the particle size within the range of 3.35– 4.44 lm for emulsions (I, III, IV, VI) was observed during the entire time of the experiment. The number of fractions of each emulsion was one (Figs 3–6). Dispersion index values were in the range 1.12–2.49 (Table II). Based on the above data, it can be concluded that all of these systems had comparable stability. However, observing the curves of DBS showed that the delamination process for emulsions I and VI started on the second day of the experiment (Figs 2, 3 and 6). Subsequent measurements of the intensity of backscattered light for emulsion I were almost unchanged (overlapping of curves) (Fig. 6). This means that this emulsion showed a highly unstable character. In the case of emulsion VI, significant decreasing values of DBS at the bottom of the cell during storage were observed. This meant that the creaming process was extended over time (Fig. 3). Analysing the appearance of the emulsions after 14 days of storage in a dryer at 40°C, it was observed that the lower layer of emulsion I was clear, whereas that of emulsion VI was turbid; therefore, for those systems, various values of DBS at the bottom of the measuring cell were recorded (Fig. 2). It is well known that the percentage curves of transmitted and backscattered light as a function of cell height reflect the status of the emulsion. When curves for subsequent measurements overlap, this indicates high stability of the sample, whereas when curves are variable it indicates instability [17, 18]. It was noticed that the homogenization time for these two systems (emulsions I and VI) was chosen incorrectly. In emulsion I, 1.5 min turned out to be insufficient time to properly homogenize this system. In contrast to emulsions I, for emulsion VI, 6 min was too long, which resulted in destabilization. Longer homogenization caused better dispersion of oil droplets, but did not result in a proper emulsion system. Both above-mentioned emulsions were also delaminated after the centrifugal test. The effect of mixing time on destabilization of emulsion systems was also confirmed by the results of DBS intensity for emulsions III and IV.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil Table III Influence of oil content and time of homogenization on the input parameters according to optimization software
Input parameters
Oil content ↑
Homogenization time ↑
Viscosity
↑
Dispersion index Average particle size
↓ ↑
Minimum particle size
↑
Maximum particle size
↓
There is some optimum (area) within (160–300 s) in which the homogenization time is irrelevant to the viscosity value. Below and above this range, the viscosity decreases ↑ There is some optimum (area) within (100–280 s) in which the homogenization time is irrelevant to the average particle size. Below and above this range, the average particle size increases There is some optimum (area) within (120–250 s) in which the homogenization time is irrelevant to the minimum particle size. Below and above this range, the average particle size increases ↑
Creaming began after 6 days in emulsion III and 9 days in emulsion IV (Figs 4 and 5). The curves on the left side of the graph did not overlap, which was proved to reduction of DBS intensity at the bottom of the measuring cell. It was caused by decreased concentration of the dispersed phase particles in that part of the measuring cell. Longer time of homogenization allowed for an increase of stability of the systems and slightly reduced the particle size of emulsion IV (Table II). Emulsions III and IV did not pass the centrifugal test. The final examined system was emulsion homogenized for 6 min and with 50 g of oil. Addition of oil to this system resulted in an increase of average particle size (Table II). The value was slightly higher than for emulsions I, III, IV, VI, but about half the size of emulsion II. It can be concluded that the high amount of oil in the case of emulsions V and II resulted in the appearance of an additional fraction and increase of the average particle size (Fig. 7, Table II). However, in the case of emulsion V, an additional 4.5 min. of homogenization allowed us to obtain a stable and homogeneous system. Its DBS remained almost unchanged during storage, showing great stability (Fig. 7). Emulsion V was unique because it passed the centrifugal test – it did not delaminate after 30 min. For this emulsion, there was the smallest increase of the average particle size, which was 0.22 during the whole flow of time. Microscopic structure of all tested emulsions was comparable (Fig. 8). All emulsions, except emulsion II, exhibited similar size and distribution of particles. Emulsion II showed heterogeneous microstructure with grouped, bigger droplets compared to the others, which confirmed the previously discussed average particle size. Rheologically, the viscosity of the emulsion determines the physical properties of the liquid. The resistance of the emulsion during its movement is one of the most important properties. Viscosity measurements with hydrodynamic theory enable one to obtain information on the structure and stability of the emulsion [16]. Maximum viscosity values were observed for systems containing the highest amount of oil. Much lower viscosity values characterized emulsions containing 30 g of oil (emulsions III and IV). Homogenization time did not influence the value of this parameter for these two emulsions. Similar results were obtained by Kulawik et al. [19], who observed that the viscosity of the emulsions was affected by the technique of preparation of the emulsion, and the concentration of the oil phase and lecithin. The lowest value of viscosity was observed for emulsion VI, containing the least oil and homogenized for 6 min. This confirms that the homogenization time for this emulsion had a negative impact on its stability. Generally, in all emulsions, a decrease of viscosity during storage was observed (Fig. 9). These viscosity changes in time were noted as statistically significant. Similar results were obtained by the author [20]
who stated that the viscosity over time may decrease, until stabilized and changes of the rheological properties during ‘ageing’ are irreversible. Similarly, other authors also confirmed the validity of the use of emulsions containing hemp oil as a fatty base. They claimed that these emulsions were stable and showed a pseudoplastic–Newtonian flux. Beside they showed that emulsions with hempseed oil were easily sprayable on the skin and had a pleasant skin feel and texture [21]. In this study, we carried out optimization of emulsion parameters, based on Kleeman’s method. The analysis using the software KATESKOR of optimization of emulsions’ stability (Fig. 10) showed that in the case of manufactured emulsions, with parameters which were specified at the beginning of the experiment, the optimum amount of hemp oil is in the range from 29.77 to 50.0 g, whereas the optimum homogenization time is in the range of 149.38 s to 360 s. Therefore, it can be concluded that emulsions within the range indicated as optimal by the software were emulsions IV (30 g of oil, homogenized for 4.5 min) and V (50 g of oil, homogenized for 6 min). A detailed analysis on the influence of the oil content and the time of homogenization on the input parameters of the emulsion was presented in Table III. Considering the above results of the study, it can be concluded that emulsion V showed extremely high stability and had a good quality composition (50 g oil). The high content of hemp oil in the discussed emulsion made it more attractive due to the relatively high content of valuable unsaturated fatty acids and natural antioxidants presented in the oil [22, 23]. Conclusions It was found that the most stable system was the emulsion containing 50 g of hemp oil and homogenized for 6 min. The average particle size of the emulsion did not undergo significant changes during the time of the experiment. Also, the Turbiscan test showed no destabilization. Empirically obtained results and those obtained by the optimization software proved to be consistent. Using this type of program reduces the time of the experiment and helps properly design a stable dispersion. In this study, we obtained an emulsion system with proper stability, justifying further research extended with sensory analysis, which will allow the application of such systems (containing hemp oil, beneficial for skin) in the cosmetic industry. Acknowledgements The financial support from the Faculty of Material Science, Technology and Design of Kazimierz Pułaski UTH – Radom, Poland is acknowledged.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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9. Nicolaou, A. Eicosanoids in skin inflammation. Prostag. Leukotr. Ess. 88, 131–138 (2013). 10. Anwar, F., Latif, S. and Ashraf, M. Analytical characterization of hemp (Cannabis sativa) seed oil from different agro-ecological zones of Pakistan. J. Am. Oil Chem. Soc. 83, 323–329 (2006). 11. Abuzaytoun, R. and Shahidi, F. Oxidative stability of flax and hemp oils. J. Am. Oil Chem. Soc. 83, 855–861 (2006). 12. Huck-Iriart, C., Candal, R.J. and Herrera, M.L. Effect of processing conditions and composition on sodium caseinate emulsions stability. Procedia Food Sci. 1, 116–122 (2011). 13. Kleeman, W. Plast und Kautschuk. Das Leder. 11, 723 (1964). 14. Kowalska, M., Zbikowska, A., Smiechowski, K. and Marciniak-Lukasiak, K. Wpływ ilosci lecytyny słonecznikowej i czasu homogenizacji na stabilnosc emulsji spo_zywczej zawierajaz cej olej z orzech ow włoskich. Zywn-Nauk. Technol. Ja. 92, 78–91 (2014). 15. Kowalska, M., Pazdzior, M. and Smiechowski, K. Wykorzystanie programu komputerowego opartego na metodzie Klemmana jako narzez dzia pozwalajaz cego uzyskac stabilnaz emulsjez spo_zywczaz . Postezpy Techniki Przetworstwa Spo_zywczego 24/44, 41–47 (2014). _ 16. Kowalska, M., Zbikowska, A. and Gorecka, A. Wpływ wybranych zagez stnik ow na rozkład kropel oleju w emulsjach niskotłuszczo-
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© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
doi: 10.1111/ics.12211
Stability of cosmetic emulsion containing different amount of hemp oil † _ M. Kowalska*, M. Ziomek* and A. Zbikowska
*Department of Chemistry, Faculty of Material Science, Technology and Design, Kazimierz Pulaski University of Technology and Humanities, Chrobrego st. 27, 26-600 Radom, and †Department of Food Technology, Faculty of Food Sciences, Warsaw University of Life Sciences (WULSSGGW), Nowoursynowska st. 159C, 02-787 Warsaw, Poland
Received 26 November 2014, Accepted 1 February 2015
Keywords: droplet size, emulsion, hemp oil, stability, Turbiscan test
Synopsis OBJECTIVE: The aim of the study was to determine the optimal conditions, that is the content of hemp oil and time of homogenization to obtain stable dispersion systems. METHODS: For this purpose, six emulsions were prepared, their stability was examined empirically and the most correctly formulated emulsion composition was determined using a computer simulation. Variable parameters (oil content and homogenization time) were indicated by the optimization software based on Kleeman’s method. Physical properties of the synthesized emulsions were studied by numerous techniques involving particle size analysis, optical microscopy, Turbiscan test and viscosity of emulsions. RESULTS: The emulsion containing 50 g of oil and being homogenized for 6 min had the highest stability. Empirically determined parameters proved to be consistent with the results obtained using the computer software. The computer simulation showed that the most stable emulsion should contain from 30 to 50 g of oil and should be homogenized for 2.5–6 min. CONCLUSIONS: The computer software based on Kleeman’s method proved to be useful for quick optimization of the composition and production parameters of stable emulsion systems. Moreover, obtaining an emulsion system with proper stability justifies further research extended with sensory analysis, which will allow the application of such systems (containing hemp oil, beneficial for skin) in the cosmetic industry. sume Re OBJECTIF: L’objectif de l’etude etait de determiner les conditions savoir le contenu en huile de chanvre et la duree de optimales a l’homogeneisation pour obtenir des systemes de dispersion stables. METHODES: A cet effet, six emulsions ont ete preparees, leur stabilite a ete examinee de maniere empirique et la composition de l’emulsion la plus correctement formulee a ete determinee en utilisant une simulation par ordinateur. Les parametres variables (teneur en huile et le temps d’homogeneisation) ont ete indiques par le logiciel d’optimisation base sur la methode de Kleeman. Les proprietes physiques des emulsions synthetisees ont ete etudiees par de Correspondence: Malgorzata Kowalska, Department of Chemistry, Faculty of Material Science, Technology and Design, Kazimierz Pulaski University of Technology and Humanities, Chrobrego st. 27, 26-600 Radom, Poland. Tel.: +48 48 3617547; fax: +48 48 3617500; e-mail: [email protected]
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nombreuses techniques impliquant l’analyse granulometrique, la microscopie optique, l’essai au Turbiscan et la viscosite des emulsions. RESULTATS: L’emulsion contenant 50 g d’huile et homogeneisee pendant 6 min avait la plus haute stabilite. Les parametres determines empiriquement se ont reveles ^etre compatibles avec les resultats obtenus en utilisant le logiciel de l’ordinateur. La simulation par ordinateur a montre que l’emulsion la plus stable doit contenir de 30 a 50 g de l’huile et doit ^etre homogeneise pendant 2.5 a 6 min. CONCLUSIONS: Le logiciel base sur la methode de Kleeman s’est avere utile pour l’optimisation rapide de la composition et de la production des parametres de systemes d’emulsion stables. En outre, l’obtention d’un systeme d’emulsion avec une bonne stabilite justifie la poursuite de la recherche etendue a l’analyse sensorielle, ce qui permettra l’application de ces systemes (contenant de l’huile de chanvre, benefiques pour la peau) dans l’industrie cosmetique.
Introduction Emulsion systems consist of two or more liquid immiscible phases, where one of the liquids is dispersed in the other as small (0.1– 100 lm) spherical droplets [1]. The basic condition to form a homogeneous emulsion from two immiscible liquids is to disperse one phase in the other. This process counteracts the surface tension forces present at the interface. Overcoming these forces occurs in two stages. Addition of an emulsifier at the first stage of emulsification contributes to reduction of the surface tension. At the second stage, the rest of the surface tension is overcome by energetic stirring [2, 3]. One of the most important elements necessary to obtain an emulsion with proper stabilization is the fragmentation of large droplets of oil to small particles with a narrow size distribution. The well-homogenized emulsion contains oil molecules that are appropriately small and reveal little tendency to increase in size and consequently to separate [4]. It is assumed that emulsions are generally thermodynamically unstable and can undergo a number of different instabilities such as gravitational separation, creaming, flocculation, coalescence, phase inversion and Ostwald ripening. The main factors affecting these processes can be identified as average particle size and distribution; furthermore, they also include the state of aggregation of the droplets, pH, energy input during emulsification, osmotic pressure, viscosity of the bulk phase and the presence of various additives [3, 5–7].
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie
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Sability of the emulsion based on hampseed oil Table I Changing components/parameter of emulsions
Furthermore, blocking conversion of LA to GLA in the skin can also lead to undesirable changes in the appearance of the body [8]. EFA application to the skin surface is very important to maintain its proper appearance and function [9]. For this reason, hemp oil can be used in cosmetics (as an additive to lotions, moisturizes, lip balms), but also in food and aromatherapy [10, 11]. The aim of the study was to determine the optimal conditions, that is the content of hemp oil and time of homogenization to obtain stable dispersion systems by evaluating their physical properties such as particle size, microscopy, dispersion index, viscosity and the photon backscattering profiles. The last parameter was obtained using the Turbiscan Lab Expert, an innovative optical analyser, which allows one to scan the turbidity profile of an emulsion along the height of a glass tube filled with the emulsion, following the turbidity profile changes over time [12]. The optimization of the software based on Kleeman’s method [13] was used to help indicate the most stable emulsion. It was expected that the software would indicate the emulsion with proper stability after one measurement. Proposing a tool allowing for fast evaluation and possible design of the emulsion is a very important issue for technologists, especially to reduce the time of an experiment.
Emulsion Component (%w/w)/parameter
I
II
III
IV
V
VI
Water Hemp oil Mixing time (min)
83.75 10 1.5
43.75 50 1.5
63.75 30 3.0
63.75 30 4.5
43.75 50 6.0
83.75 10 6.0
Vegetable oils are the most frequently used fatty base for cosmetic emulsions. Currently, on the market, there is a growing variety of oils that contain unsaturated fatty acids having a great importance in cosmetics. Hemp oil is one of such oils. Hempseed is rich in minerals, vitamins (A, C and E), b-carotene, a-linolenic acid (ALA) and linoleic acid (LA). Additionally, because of the presence of c-linolenic acid (GLA), hemp oil is perfect as an ingredient in the light body oils and lipid-enriched creams, known for their ability to penetrate the skin. The first symptom of essential fatty acids (EFA) deficiency is body changes (atopic dermatitis, psoriasis, acne).
Table II Average particle size, dispersion index, number and percentage of emulsion fractions 24 h, and 2, 4, 6 and 10 weeks after preparation, and the increase of average particle size during the storage period
Emulsion
Content of oil/time of homogenization Average particle size (lm) X SD 24 h 2 weeks 4 weeks 6 weeks 10 weeks Dispersion index X SD 24 h 2 weeks 4 weeks 6 weeks 10 weeks Increase of average particle size after 10 weeks Number and percentage of emulsion fraction 24 h
I
II
III
IV
V
VI
10 g/1.5 min
50 g/1.5 min
30 g/3.0 min
30 g/4.5 min
50 g/6.0 min
10 g/6.0 min
3.35aA 3.39a 3.45a 3.62b 4.61c
0.02 0.01 0.01 0.01 0.01
10.65aC 11.38b 12.04c 12.28d 12.20cd
0.01 0.03 0.03 0.01 0.02
3.69aA 3.70a 3.80a 3.97b 4.18c
0.01 0.02 0.01 0.00 0.02
3.50aA 3.52a 3.74a 3.83a 3.92a
0.02 0.02 0.01 0.01 0.00
5.75aB 5.77a 5.76a 5.77a 5.80a
0.01 0.01 0.01 0.02 0.02
3.80bA 3.52a 3.70b 4.11c 4.44d
0.01 0.02 0.01 0.01 0.01
1.87cC 1.80b 1.63a 1.70a 1.69a 1.26
0.01 0.01 0.02 0.02 0.01
1.12aA 1.13a 3.08b 5.07c 6.26d 1.55
0.00 0.01 0.01 0.02 0.01
1.64aB 1.76c 1.69b 1.96d 2.20e 0.50
0.01 0.01 0.02 0.01 0.01
1.62abB 1.55a 1.65b 2.07c 2.10c 0.42
0.01 0.01 0.01 0.01 0.02
1.18bA 1.13a 1.13a 3.30c 3.39d 0.05
0.01 0.01 0.01 0.02 0.01
2.49eD 2.20d 1.93b 1.78a 2.02c 0.65
0.01 0.01 0.01 0.01 0.02
I – 100%
2 weeks
I – 100%
4 weeks
I – 100%
6 weeks
I – 100%
10 weeks
I – 100%
I – 80% II – 20% I – 87% II – 13% I – 100% I – 46% II – 54% I – 41% II – 59%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 100%
I – 76% II – 24% I – 79% II – 21% I – 79% II – 21% I – 46% II – 54% I – 45% II – 55%
I – 100% I – 100% I – 100% I – 100% I – 100%
a, b, c – Different letters in columns indicate mean values that differ statistically significantly (P < 0.05). A, B, C – Different letters in rows indicate mean values that differ statistically significantly (P < 0.05).
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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(a)
(b)
Figure 1 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion II (b).
Figure 2 Appearance of the emulsions after 14 days of manufacturing.
Spain) sodium benzoate (Orff Food Eastern Europe, Marki/Warsaw, Poland), aloe vera (FLP), Scottsdale, Arizona, United States, citric acid (Jungbunzlauer Basel, Switzerland).
Materials and methods Materials Emulsions were prepared using the following ingredients: distilled water, carboxymethylcellulose (Barentz Hoofddorp, Netherlands), cold pressed, unrefined (Gracefruit Ltd Stirlingshire, United Kingdom) (INCI: Cannabis Sativa Seed Oil) hemp oil containing the following fatty acids (FA): palmitic acid C16:0 – 5.7%, palmitoleic acid C16:1 – 0.15%, stearic acid C18:0 – 2.5%, oleic acid C18:1 9c – 11.4%, linoleic acid C18:2 9c12c – 55.4%, alpha linolenic acid C18:3 9c12c15c – 17.2%, gamma linolenic acid C18:3 6c9c12c – 3.6%, eicosenoic acid C20:0 – 0.6%, eicosenoic acid C20:1 – 0.4%, docosanoic acid C22:0 – 0.3%, tetracosanoic acid C24:0 – 0.2%, sunflower lecithin (Lasenor, Emul, S.L. Barcelona,
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Preparation of emulsions The composition of changing parameters in the experimental emulsions was optimized with the software based on Kleeman’s method, its constant parameters were chosen according to our previous research [14, 15]. Lecithin (5.2%) was added to the oil phase (hemp oil). Carboxymethylcellulose (0.6%) was dispersed in distilled water, and then, aloe vera (0.2%) was added. Both solutions (oil and aqueous phases) were heated at 50–55°C in a water bath. Homogenization of the aqueous phase with the oil phase was achieved with a high shear mixer at an equal speed of 36288 RCF
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil
(a)
(b)
Figure 3 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion I (b).
(a)
(b)
Figure 4 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion III (b).
for an appropriate time (given in Table I). Finally, the emulsions were cooled to room temperature, and a preservative sodium benzoate (0.25%) was added. Then pH was adjusted to 5.5 by addition of citric acid using a Mettler Toledo pH-meter equipped with a calomel combined pH electrode. The content of changing components was presented in Table I.
nation of each sample was 30 s. Each measurement was repeated three times and given as the average value. Dispersion index It was calculated on the basis of particle size measurements using laser diffraction according to the formula:
Methods Determination of mean particle size and particle size distribution The average particle size and distribution were determined after 24 h, 2, 4, 6 and 10 weeks of cold storage at +/7°C in a fridge. For measurements, the emulsions were diluted 1 : 200 with distilled water. The particle size was measured in the range 0.12– 704 lm by laser scattering using a Microtrac Particle Size Analyzer (Leeds & Northrup, Philadelphia, PA, U.S.A.); total time of determi-
k¼
AB ; C
where A, B and C are the biggest sizes of oil droplets for 90%, 10% and 50% of all particles, respectively. Turbiscan test The samples stored at 40°C in thermostat for 10 weeks were used to evaluate destabilization of emulsions by the Turbiscan
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil
(a)
(b)
Figure 5 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion IV (b).
(a)
(b)
Figure 6 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion VI (b).
test (Turbiscan Lab. Formulation L’Union - France). Emulsions placed in the glass cells were scanned, each 40 mm, by a pulsed near infrared light source (k = 880 nm) and two synchronous detectors. The transmission detector receives the light through the sample at 0° from the incident beam, whereas the backscattering detector receives the light scattered by the sample at 135° from the incident beam. The results were presented as the dependency of backscattered light intensity as a function of sample height. Analysis of curves with the percentage of backscattered light for the studied emulsions in time allowed for evaluation of the intensity of the destabilization processes occurring in the samples. Determination of emulsion stability using the centrifugal test The determination of emulsion stability was measured in the centrifugal machine (Nahita Centrifuges Model 2652; Auxilab, S.L.,
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Beriain, Navarra, Spain) at 1008 RCF. Test tubes were filled with 15–20 mL of the emulsion and then centrifuged for 30 min, with the state of emulsion checked every 10 min. If the emulsion remained homogeneous after 30 min, it was considered to have proper stability. Structure of emulsions Structure of emulsions was investigated with an optical microscope (Nikon Alphaphot combined with a CCD camera and picture analysis software (Nikon - producer PZO, Warsaw Poland, lens Nikon 4 4/0.10 (160/-WD 25), ocular Nikon China CF WE 15/12, camera Panasonic type GP-KR 222, software MICROSCAN for Windows). The prepared emulsion was placed on the microscopic slide. A cover slip was placed on the sample. No air or bubbles were trapped between the sample and cover slip, and the samples were tested with a 40 9 objective.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil
(a)
(b)
Figure 7 Delta back scattering (DBS) profile as a function of cell height with storage time (samples were stored for 10 weeks) (a) and distribution of particle size in emulsion V (b).
Figure 8 Optical microphotographs of the emulsions at a magnification G 940. Scale bar (white line) in photos corresponds to 10 lm.
Viscosity examination The viscosities of the samples were determined at 25°C at the speed of 10 rpm, spindle RV3, using a Brookfield Rheometer DV-I ( Middleboro, Massachusetts, USA) + after 24 h, and 2, 4, 6 and 10 weeks of cold storage. Optimization of parameters of emulsion stability Optimization of oil content and mixing time was performed using software developed for the Department of Technology the KATESKOR Footwear and Tanning at the Faculty of Materials Science, Technology and Design at the University of Technology and Humanities in Radom. This program is based on Kleeman’s method [13]. The software allows the number of experiments (six different samples) to be minimized by selection of the compromise optimum according to the experimenters’ expectations. The method selects and determines the limits of the measured parameters and suggests a range of pre-
ferred parameters for which an emulsion should have high stability. In this study, the initial parameters (measured 24 h after the preparation of emulsions) were used as input data for the software and then optimized according to Kleeman’s procedure. As an output, we obtained the set of calculated parameters, which were further employed to perform the optimization of parameters for which the stable emulsions should be formed. Further, the limits of the measured parameters were chosen and then a range of selected parameters, for which the emulsion should have the best stability, was calculated. According to the program, we have adopted a model of emulsion characterized by the following input parameters for optimization purposes: dispersion index – 1.6, viscosity – 500 mPa s, number of fractions – 1, average particle size – 6 lm, maximum particle size – 16 lm, minimum particle size – 0.7 lm. Using optimization software, the range of changing parameters, for which the emulsion system should have the best stability, was defined.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil
Figure 9 Viscosity of the investigated emulsions (T = 20°C).
Figure 10 Compromise optimum of parameters of investigated emulsions.
Statistical analysis The results were subjected to one-way ANOVA. The Duncan test was used to assess the differences between means. The level of P < 0.05 was considered significant. STATGRAPHICS PLUS 4.1 package (Statistical Graphics Corp., Warrenton, VA, U.S.A.) was used. Results and discussion Analysing the results of the average particle size of all tested emulsions, the highest value of this parameter was observed for emulsion II (Table II). This system was definitely different from the others – the value of particle size was at least three times higher (throughout the whole storage period). Other parameters such as number of fractions (2) and the dispersion index (6.26 after 10 weeks) confirmed destabilization of this system (Fig. 1, Table II). An additional symptom of destabilization was a negative result of the centrifugal test: after 10 min of centrifugation, emulsion II was delaminated. However, the curves of backscattered light showed that, relative to the emulsions (I, III, IV or VI), destabilization started later. There were changes in the course of the curves in subsequent measurements. The first change in the profile of the emulsion was smaller values of DBS (delta backscattering) at the bottom of the cell, more noticeable after 14 days. The observations indicated the occurrence of migration of the particles – the creaming process.
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According to Kowalska et al. [16], physicochemically, emulsion instabilities can be divided into two types: reversible and irreversible. Reversible instabilities include creaming and sedimentation, in which the dispersed phase particles do not change their size, but tend only to the surface of the emulsion. This type is more frequent in O/W than W/O systems. Confirmation of initiation of changes in emulsion II was provided by the delicate crack shown in Fig. 2. A relatively low value of the particle size within the range of 3.35– 4.44 lm for emulsions (I, III, IV, VI) was observed during the entire time of the experiment. The number of fractions of each emulsion was one (Figs 3–6). Dispersion index values were in the range 1.12–2.49 (Table II). Based on the above data, it can be concluded that all of these systems had comparable stability. However, observing the curves of DBS showed that the delamination process for emulsions I and VI started on the second day of the experiment (Figs 2, 3 and 6). Subsequent measurements of the intensity of backscattered light for emulsion I were almost unchanged (overlapping of curves) (Fig. 6). This means that this emulsion showed a highly unstable character. In the case of emulsion VI, significant decreasing values of DBS at the bottom of the cell during storage were observed. This meant that the creaming process was extended over time (Fig. 3). Analysing the appearance of the emulsions after 14 days of storage in a dryer at 40°C, it was observed that the lower layer of emulsion I was clear, whereas that of emulsion VI was turbid; therefore, for those systems, various values of DBS at the bottom of the measuring cell were recorded (Fig. 2). It is well known that the percentage curves of transmitted and backscattered light as a function of cell height reflect the status of the emulsion. When curves for subsequent measurements overlap, this indicates high stability of the sample, whereas when curves are variable it indicates instability [17, 18]. It was noticed that the homogenization time for these two systems (emulsions I and VI) was chosen incorrectly. In emulsion I, 1.5 min turned out to be insufficient time to properly homogenize this system. In contrast to emulsions I, for emulsion VI, 6 min was too long, which resulted in destabilization. Longer homogenization caused better dispersion of oil droplets, but did not result in a proper emulsion system. Both above-mentioned emulsions were also delaminated after the centrifugal test. The effect of mixing time on destabilization of emulsion systems was also confirmed by the results of DBS intensity for emulsions III and IV.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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Sability of the emulsion based on hampseed oil Table III Influence of oil content and time of homogenization on the input parameters according to optimization software
Input parameters
Oil content ↑
Homogenization time ↑
Viscosity
↑
Dispersion index Average particle size
↓ ↑
Minimum particle size
↑
Maximum particle size
↓
There is some optimum (area) within (160–300 s) in which the homogenization time is irrelevant to the viscosity value. Below and above this range, the viscosity decreases ↑ There is some optimum (area) within (100–280 s) in which the homogenization time is irrelevant to the average particle size. Below and above this range, the average particle size increases There is some optimum (area) within (120–250 s) in which the homogenization time is irrelevant to the minimum particle size. Below and above this range, the average particle size increases ↑
Creaming began after 6 days in emulsion III and 9 days in emulsion IV (Figs 4 and 5). The curves on the left side of the graph did not overlap, which was proved to reduction of DBS intensity at the bottom of the measuring cell. It was caused by decreased concentration of the dispersed phase particles in that part of the measuring cell. Longer time of homogenization allowed for an increase of stability of the systems and slightly reduced the particle size of emulsion IV (Table II). Emulsions III and IV did not pass the centrifugal test. The final examined system was emulsion homogenized for 6 min and with 50 g of oil. Addition of oil to this system resulted in an increase of average particle size (Table II). The value was slightly higher than for emulsions I, III, IV, VI, but about half the size of emulsion II. It can be concluded that the high amount of oil in the case of emulsions V and II resulted in the appearance of an additional fraction and increase of the average particle size (Fig. 7, Table II). However, in the case of emulsion V, an additional 4.5 min. of homogenization allowed us to obtain a stable and homogeneous system. Its DBS remained almost unchanged during storage, showing great stability (Fig. 7). Emulsion V was unique because it passed the centrifugal test – it did not delaminate after 30 min. For this emulsion, there was the smallest increase of the average particle size, which was 0.22 during the whole flow of time. Microscopic structure of all tested emulsions was comparable (Fig. 8). All emulsions, except emulsion II, exhibited similar size and distribution of particles. Emulsion II showed heterogeneous microstructure with grouped, bigger droplets compared to the others, which confirmed the previously discussed average particle size. Rheologically, the viscosity of the emulsion determines the physical properties of the liquid. The resistance of the emulsion during its movement is one of the most important properties. Viscosity measurements with hydrodynamic theory enable one to obtain information on the structure and stability of the emulsion [16]. Maximum viscosity values were observed for systems containing the highest amount of oil. Much lower viscosity values characterized emulsions containing 30 g of oil (emulsions III and IV). Homogenization time did not influence the value of this parameter for these two emulsions. Similar results were obtained by Kulawik et al. [19], who observed that the viscosity of the emulsions was affected by the technique of preparation of the emulsion, and the concentration of the oil phase and lecithin. The lowest value of viscosity was observed for emulsion VI, containing the least oil and homogenized for 6 min. This confirms that the homogenization time for this emulsion had a negative impact on its stability. Generally, in all emulsions, a decrease of viscosity during storage was observed (Fig. 9). These viscosity changes in time were noted as statistically significant. Similar results were obtained by the author [20]
who stated that the viscosity over time may decrease, until stabilized and changes of the rheological properties during ‘ageing’ are irreversible. Similarly, other authors also confirmed the validity of the use of emulsions containing hemp oil as a fatty base. They claimed that these emulsions were stable and showed a pseudoplastic–Newtonian flux. Beside they showed that emulsions with hempseed oil were easily sprayable on the skin and had a pleasant skin feel and texture [21]. In this study, we carried out optimization of emulsion parameters, based on Kleeman’s method. The analysis using the software KATESKOR of optimization of emulsions’ stability (Fig. 10) showed that in the case of manufactured emulsions, with parameters which were specified at the beginning of the experiment, the optimum amount of hemp oil is in the range from 29.77 to 50.0 g, whereas the optimum homogenization time is in the range of 149.38 s to 360 s. Therefore, it can be concluded that emulsions within the range indicated as optimal by the software were emulsions IV (30 g of oil, homogenized for 4.5 min) and V (50 g of oil, homogenized for 6 min). A detailed analysis on the influence of the oil content and the time of homogenization on the input parameters of the emulsion was presented in Table III. Considering the above results of the study, it can be concluded that emulsion V showed extremely high stability and had a good quality composition (50 g oil). The high content of hemp oil in the discussed emulsion made it more attractive due to the relatively high content of valuable unsaturated fatty acids and natural antioxidants presented in the oil [22, 23]. Conclusions It was found that the most stable system was the emulsion containing 50 g of hemp oil and homogenized for 6 min. The average particle size of the emulsion did not undergo significant changes during the time of the experiment. Also, the Turbiscan test showed no destabilization. Empirically obtained results and those obtained by the optimization software proved to be consistent. Using this type of program reduces the time of the experiment and helps properly design a stable dispersion. In this study, we obtained an emulsion system with proper stability, justifying further research extended with sensory analysis, which will allow the application of such systems (containing hemp oil, beneficial for skin) in the cosmetic industry. Acknowledgements The financial support from the Faculty of Material Science, Technology and Design of Kazimierz Pułaski UTH – Radom, Poland is acknowledged.
© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
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© 2015 Society of Cosmetic Scientists and the Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 37, 408–416
