Formulation and characteristics of skin cream with the addition of essential oil blend

The use of natural ingredients in cosmetics, such as essential oils, is gaining increasing attention today due to their perceived safety for health, attributed to their antioxidant properties. This research aims to determine the formulation of cream by adding an essential oil blend and analyzing physicochemical, microbiological and hedonic characteristics of the skin cream. The study comprises two phases: selecting the preferred essential oil blend by a panel of evaluators and preparing the skin cream with the addition of the chosen essential oil blend. The essential oils used in this study included clove, ginger, cinnamon, galangal, nutmeg, and citronella, with concentrations of 0.5%, 1%, and 1.5%. The research results reveal that the skin cream with the highest antioxidant activity is the one with the addition of a blend of clove and citronella essential oils. However, based on hedonic testing results, the most preferred skin cream formulation is the one with a mix of clove, citronella, and ginger essential oils. Physical characteristics and microbial contamination testing of the cream formulation with a blend of clove, citronella, and ginger essential oils show that the skin cream meets the viscosity and microbial contamination requirements set by SNI 16-4399-1996, with a spreading capacity of 5.07 cm.


Introduction
The skin is one of the most vital organs in the human body, serving as a barrier against various physical and mechanical threats, temperature fluctuations, as well as microbial and bacterial attacks.Therefore, skin protection and care are of paramount importance [1].The awareness of the significance of appearing beautiful with well-maintained skin significantly influences the cosmetics industry, particularly skin care products such as creams.However, with the growth of the industry, some cosmetic products available in the market contain hazardous substances such as mercury, synthetic dyes, hydroquinone, and retinoic acid [2].
The utilization of natural ingredients in cosmetics, such as essential oils, is garnering increasing attention nowadays due to their perceived safety for health.Essential oils are derived from aromatic plants and contain terpenoid compounds, such as monoterpenes, sesquiterpenes, phenols, and alcohols.Aromatic compounds in essential oils find widespread use in various fields, including beauty, health, and food [3].Essential oils also possess diverse biological activities, such as anti-inflammatory, antibacterial, antiviral, antifungal, and antioxidant properties [4].
Antioxidants in essential oils become exceedingly important in cosmetic products as they can shield the skin from damage caused by free radicals.Exposure to sunlight and pollution increases free radicals that can harm skin cells and cause premature aging [5].Antioxidants are substances designed to 1297 (2024) 012080 IOP Publishing doi:10.1088/1755-1315/1297/1/012080 2 neutralize these free radicals, making their incorporation into cosmetic products such as skin creams vital [6].
This research was conducted to examine the formulation of cream with the addition of clove (Syzygium aromaticum), ginger (Zingiber officinale), cinnamon (Cinnamomum burmanii), galangal (Alpinia galanga), nutmeg (Myristica fragrans) and citronella (Cymbopogon nardus) essential oils.The selection od essential oil types is representative of the spice and non-spice groups of essential oils.The use of essential oils in a mixture of several essential oils is expected to reduce the sensory effect of the aroma of the use of essential oils in products and is also expected to produce a synergistic effect of higher antioxidant activity.
This research investigates the use of essential oils as natural antioxidants in skin creams.The addition of a blend of several essential oils to the cream is expected to enhance antioxidant activity, surpassing that of single essential oils.Moreover, this study will also explore the appropriate skin cream formulation to meet the established cream quality standards [7].
This study aims to determine the formulation of cream by adding an essential oil blend and analyzing physicochemical, microbiological and hedonic characteristics of the skin cream.The research results are expected to provide benefits as an alternative for the safe utilization of natural ingredients in cream production and enhance the value-added from essential oils.

Research design
This research consists of two stages.The first stage is determining the panelists' preferred blend of essential oil aromas.The essential oils used are clove oil (MC = M1), ginger oil (MJ = M2), cinnamon oil (MK = M3), galangal oil (ML = M4), nutmeg oil (MP = M5), and citronella oil (MS = M6).The second stage is the formulation of skin cream with the addition of essential oils, utilizing two factors: the first factor is the panelists' preferred blend of essential oils (M) with three levels, namely: C1 = Blend of essential oils ranking 1, C2 = Blend of essential oils ranking 2, and C3 = Blend of essential oils ranking 3. The second factor is the concentration of the essential oil blend (K) with three levels, namely K1 = 0.5%, K2 = 1.0%, and K3 = 1.5%.The experiments were repeated three times, resulting in 27 experimental units.

Determining the combination of essential oils
The first stage of the research aims to combine aromas from six types of essential oils to obtain an aroma preferred by the panelists.The essential oils used include clove oil (M1), ginger oil (M2), cinnamon oil (M3), galangal oil (M4), nutmeg oil (M5), and citronella oil (M6).Each essential oil was used in the amount of 0.01 ml.Organoleptic (hedonic) testing of the blended essential oil aromas was conducted using 25 semi-trained panelists, with a scale of 1-4 (very like, like, dislike, and very dislike).The top three samples from the aroma testing, as determined by ranking, were then used as the first factor for the second phase of the research.

Skin cream formulation
The second stage of the research aims to obtain the best formulation to produce a cream that meets the quality standards specified in the SNI cream standard number 16-4399-1996.The cream formulation is based on the research by [8] with some modifications.The oil phase ingredients (propylparaben, stearyl alcohol, stearic acid, cetyl alcohol) and the aqueous phase ingredients (potassium hydroxide, methylparaben, glycerin, tween 80, distilled water) were each heated to 70°C separately using a water bath.Subsequently, both phases were mixed using stirring at 22000 rpm for 5 minutes to form the cream base.The blend of essential oils was gradually added while stirring at 22000 rpm for 1 minute.The cream was stored for 3 weeks, and the analysis included antioxidant activity testing [9], pH measurement [10], spreadability testing [8], homogeneity assessment [8], specific gravity measurement [11], and organoleptic evaluation [12].

Data analysis
The data obtained was analyzed statistically using ANOVA (analysis of variance).If the treatment test shows a significant effect between treatments, then continue with the Duncan's Multiple Range Test (DMRT).

Determining the combination of essential ols
Based on the ranking test results, three combinations of essential oil blends with highly favored aromas were obtained, namely M1 + M6 (clove oil + citronella oil), M1 + M4 + M6 (clove oil + galangal oil + citronella oil), and M1 + M2 + M6 (clove oil + ginger oil + citronella oil).These three combinations of essential oil blends were then used in the second phase of the research for cream formulation (Table 1).

Skin cream formulation 3.2.1 pH value
The pH test was conducted to determine whether the produced skin cream was acidic or alkaline.This test is crucial because it affects the cream's impact when applied to the skin [13].If the cream's pH is too acidic or alkaline, it can cause skin irritation.According to SNI 16-4399-1996, the safe pH range for use is 4.5-8.The analysis of variance shows that the interaction between the blend of essential oils and the concentration of essential oils (MK) significantly affects the pH value of the skin cream (Figure 1).

Figure 1.
The interaction effect of essential oil blend and concentration of essential oils on pH value of the skin cream (values followed by different letters showed a significant difference in the DMRT0.05 and coefficient of variation = 0.0334%) The cream has a pH range of 7.59 -7.63, which meets the requirements of SNI 16-4399-1996, i.e., 4.5 -8.0.According to Forestryana and Rahman [13], pH changes can be attributed to unstable environmental storage conditions and the ingredients contained in the cream.

Specific gravity
Specific gravity testing on the cream aims to assess the quality and purity of a compound.Specific gravity values also provide information about the cream's ability to be cleansed with water [14].The analysis of variance indicates that only the blend of essential oils (M) significantly affects the cream's specific gravity.
The specific gravity value of the cream ranges from 0.95 to 0.99, with an average of 0.97 (Figure 2).This value aligns with the requirements of SNI 16-4399-1996, which stipulates a range of 0.95-1.05.Generally, oxygenated terpene components have a higher specific gravity than non-oxygenated terpenes [15].Effect of essential oil blend on specific gravity of the skin cream (values followed by different letters showed a significant difference in the DMRT0.05 and coefficient of variation = 0.0075%)

Antioxidant Activity
Antioxidant activity was measured as the IC50 value, representing the concentration of a substance that can inhibit 50% of free radicals [16].The IC50 values of the skin cream range from 8.03 to 12.09 ppm, with an average IC50 value of 10.82.The analysis of variance indicates that the interaction between the blend of essential oils and the concentration of essential oils (MK) significantly affects the IC50 value of the cream (Figure 3).The cream, with the addition of a blend of clove and citronella essential oils at a concentration of a higher antioxidant activity of a substance.An IC50 value of less than 50 ppm classifies a substance as having very strong antioxidant activity.According to [17], a lotion with very strong antioxidant activity has an IC50 value of less than 50 ppm.The research by [18] demonstrated that clove has a free radical scavenging capacity with an IC50 value of 2.75 μg/ml.Furthermore, [19] stated that the n-hexane fraction of citronella exhibits antioxidant activity at 8.23 ppm, categorizing it as strong in protecting body cells from oxidative damage.This suggests that the active compounds in clove and citronella have the potential as natural antioxidants.Clove essential oil contains eugenol (58.56%), which is the major component belonging to the phenylpropanoid group [20], while citronella oil contains citronellal (43.02%), classified as a monoterpenoid aldehyde [21].

Organoleptic evaluation
Hedonic testing was conducted to determine the panelists' preferences for the cream.The hedonic evaluation included assessments of aroma, color, and texture.The analysis of variance reveals that the concentration of the essential oil blend (K) significantly affects the cream's scent (Figure 4) and color (Figure 5).In contrast, the combination of essential oils (M) significantly affects the cream's texture.The panelists preferred the cream with a 1% concentration of the essential oil blend in terms of aroma (Figure 4).This preference may be because the aroma is not strong enough at lower concentrations (0.5%), while at higher concentrations, the aroma becomes overpowering.Regarding color, the panelists favored the cream with 1% and 1.5% concentrations of the essential oil blend (Figure 5).This preference may be attributed to the fact that the cream's color is less white at higher concentrations.
In terms of texture, the panelists preferred the cream with a combination of clove, citronella, and ginger essential oils (Figure 6).Based on the hedonic testing results for aroma, color, and texture, the cream with a 1% concentration of a blend of clove, citronella, and ginger essential oils is the best formulation.Subsequently, physical characteristics and microbial contamination tests were conducted.

Physical characteristics and microbial contamination of the best cream
Viscosity testing was conducted to determine the thickness of the cream.Cream thickness is the resistance of the formulation to flow and higher resistance results in higher viscosity.Viscosity also affects the cream's spreadability.The results of the viscosity test show that the cream meets the requirements of SNI 16-4399-1996.Spreadability testing aimed to assess the cream's ability to spread evenly on the skin's surface.This is important because the cream's spreading ability can impact the absorption process and the release rate of active ingredients within the formulation [22].The research results indicate that the cream has a spreadability of 5.07 cm.The standard for optimal cream spreadability is 5-7 cm.
Microbial contamination testing aims to identify microbiological contamination in cosmetic products.Microorganisms can cause infections and skin irritation.Microbial contamination tests conducted include total plate count, fungi, coliforms, Staphylococcus aureus, and Pseudomonas aeruginosa, following the procedure outlined in SNI 16-4399-1996.All microbial contamination parameters meet the requirements specified in SNI 16-4399-1996, which are as follows: total plate count maximum of 10 2 colonies/g, absence of fungi, coliform less than 3, absence of S. aureus, and absence of P. aeruginosa.According to the Regulation of the Head of the Indonesian National Agency of Drug and Food Control (BPOM) Number HK.03.1.23.07.11.6663 of 2014 regarding requirements for microbial and Keavy metal contamination in cosmetics, the total plate count is not more than 10 3 colonies/g or colonies/mL.

Conclusions
All creams have pH values and specific gravities that meet the requirements of SNI 16-4399-1996.The cream with the highest antioxidant activity is the one with a combination of clove and citronella essential oils.However, based on the hedonic test results, the cream preferred the most is the one with a combination of clove, citronella, and ginger essential oils.The results of the physical characteristics and microbial contamination tests for the cream with the addition of a blend of clove, citronella, and ginger essential oils indicate that the cream meets the requirements of SNI 16-4399-1996.Additionally, the skin cream has a spreadability of 5.07 cm.

Figure 2 .
Figure 2.Effect of essential oil blend on specific gravity of the skin cream (values followed by different letters showed a significant difference in the DMRT0.05 and coefficient of variation = 0.0075%)

Figure 3 .
Figure 3.The interaction effect of essential oil blend and concentration of essential oils on IC50 of the skin cream (values followed by different letters showed a significant difference in the DMRT0.05 and coefficient of variation = 0.0725%)

Figure 4 .
Figure 4. Effect of essential oil concentration on aroma of the skin cream ((values followed by different letters showed a significant difference in the DMRT0.05 and coefficient of variation = 0.0542%)

7 Figure 5 .
Figure 5.Effect of essential oil concentration on color of the skin cream ((values followed by different letters showed a significant difference in the DMRT0.050,054176 and coefficient of variation = 0.0798%)

Figure 6 .
Figure 6.Effect of essential oil concentration on texture of the skin cream ((values followed by different letters showed a significant difference in the DMRT0.05 and coefficient of variation = 0.0878%)

Table 1 .
Aroma ranking test results of combinations of essential oil mixtures No Combination of essential oil mixtures 1.5% (M1K3), has the lowest IC50 value, which is 8.11 ppm.It significantly differs from other treatments, indicating that this cream has the strongest antioxidant activity.A lower IC50 value indicates

Table 2 .
Physical characteristics and micriobial contamination of skin cream with the addition of mixture of clove + citronella + ginger essential oil