J. Cosmet. Sci., 71, 411–424 (November/December 2020) 411 Determination of Required HLB Values for Citrus unshiu Fruit Oil, Citrus unshiu Peel Oil, Horse Fat and Camellia japonica Seed Oil YU-YEON LEE and KYUNG-SUP YOON , Department of Chemistry and Cosmetics, Jeju National University, Jeju-do 63243 , Korea (Y.-Y.L., K.-S.Y.) Accepted for publication August 5, 2020 . Synopsis In the present study, the required hydrophilic lipophilic balance (HLB) values of Citrus unshiu fruit oil (CUFO), Citrus unshiu peel oil (CUPO), horse fat (HF), and Camellia japonica seed oil were determined empirically by preparing oil-in-water (O/W) emulsions. Lipophilic and hydrophilic surfactants were prepared in various ratios in O /W emulsion. The droplet size of the emulsion was measured using a particle size analyzer, and the turbidity was measured using a turbidity meter and a ultraviolet (UV)-vis spectrophotometer. According to the Orafi diya– Oladimeji method, the HLB value of the emulsion having the minimum dispersion ratio, the minimum droplet size, and the maximum turbidity degree was determined as the required HLB value for each essential oil. Based on these methods, the required HLB values of CUFO, CUPO, HF, and Camellia japonica seed oil were determined as 14.75–14.90, 15.35–15.40, 6.30–7.06, and 5.94–6.30, respectively. INTRODUCTION Essential oils are commonly used as preservatives and fragrances in cosmetics. However, in recent years, the medical values of essential oils such as antimicrobial properties, and their other various applications, for example, as food additives, organic pesticides, and natural insecticides are being actively explored. The oil-in-water (O/W) emulsion is one of the preferred techniques to minimize evaporation of the volatile essential oils, and thereby increase their shelf life (1–4). However, the O /W emulsion is thermodynamically unstable and can lead to various types of phase separations. These phase separation phe- nomenon can pose a problem to the functionality and stability of the active ingredient in the product, so the emulsifi cation technology in cosmetics is very important (5–7). To produce a stable emulsion, emulsifi ers or combinations of emulsifi ers are used with the required hydrophilic lipophilic balance (HLB) values depending on the oil phase. Optimal stability is achieved when the HLB value of the surfactant mixture is close to that of the required oil (8–13). Required HLB means that when two or more emulsifi ers Address all correspondence to Kyung-Sup Yoon at ksyoonjh@jejunu.ac.kr.

JOURNAL OF COSMETIC SCIENCE 412 are mixed with a given oil, the HLB value is presented as the optimum ratio that provides optimum emulsifi cation (14–18). UHTXLUHG +/% +/%UHTXLUHG L L I q œ , where fi is the mass (or weight) fraction of the oil i. The required HLB values are used not only to calculate the required HLB values of the oil phase but also to estimate the values of each component of the oil phase. HLB values are known to be affected by signifi cant errors. Therefore, the required HLB values should be determined experimentally (19,20). Experiments were conducted using three types of essential oils from Jeju Island and Jeju horse fat (HF). Citrus unshiu fruit oil (CUFO) has antibacterial activity against the main causes of acne (21). Citrus unshiu peel oil (CUPO) has physiological activities, such as antioxidant and antibacterial activities (22). Camellia japonica seed oil (CJSO) has a wrinkle improvement effect by inhibiting matrix metalloproteinase activity and by inducing human type I procollagen synthesis (23). In addition, Camellia japonica seed oil is known to have a dietary effect by reducing low-density lipoprotein choles- terol level and increasing high-density lipoprotein cholesterol level (24). HF could be used as cosmetic and pharmaceutical materials with anti-infl ammatory effects by re- ducing of erythema and Immunoglobulin E level and recovering of histopathological features of skin (25). In the present study, to determine the required HLB value of essential oils, the method of Orafi diya and Oladimeji was used in which stable emulsions were based on minimum droplet size and maximum turbidity (1). To verify our results, we also carried out related experiments using liquid paraffi n as a reference standard. MATERIALS AND METHODS MATERIALS Liquid paraffi n (paraffi n oil, Sigma-Aldrich, St. Louis, MO), sorbitan sesquioleate (Rheodol AO-15V, Kao, Tokyo, Japan HLB = 3.70), polysorbate 60 (Rheodol TW-S120V, Kao, Tokyo, Japan HLB = 14.90), and polysorbate 20 (Rheodol TW-L120V, Kao HLB = 16.70) were used. Citrus unshiu fruit oil (Human Island, Jeju, Korea), Citrus unshiu peel oil (Human Island), horse fat (Ecotech, Bucheon, Korea), Camellia japonica seed oil (CJSO, Daebongs, Incheon, Korea), and pure water (k 3 μS/cm, Pure RO 130, Human Corporation) were used. See Tables 1 and 2. Table I Description of Raw Materials Used INCI name Science name Manufacturing method Specifi c gravity (d20/20) Refraction indexa Citrus unshiu fruit oil Citrus unshiu Markovich Steam distillation 0.856 1.471 Citrus unshiu peel oil Citrus unshiu Markovich Cold press 0.862 1.470 Horse fat Horse fat Fermentation 0.860 1.469 Camellia japonica seed oil Camellia japonica L. Cold press 0.911 1.467 a Refractometer (NAR-1T, Atago, Japan). INCI, International Nomenclature Cosmetic Ingredient.