70 Address all correspondence to Panagiota Eleni, peleni@central.ntua.gr Preparation, Quality Characterization, and Shelf-Life Evaluation of Facial Cosmetic Cream Enriched with Encapsulated Tea Tree Oil PANAGIOTA ELENI, KLEOPATRA KALOUTA, NIKOLAOS PANAGIOTOU, KATERINA VASSILATOU AND MAGADALINI KROKIDA School of Chemical Engineering, Laboratory of Process Analysis and Design, National Technical University of Athens, Athens, Greece (P.E., K.K., N.P., M.K.) Cosmetics Innovation Consultant, The NuCLab, Athens, Greece (K.V.) Accepted for publication January 14, 2022. Synopsis Because of their effectiveness against microorganisms, a recent trend in the cosmetics industry is the replacement of specific chemical compounds with safe natural substances. However, many of the natural extracts that could replace these chemical components present nondesirable sensory properties to final products that prevent their usage. This study aims to present and characterize cosmetic facial cream with acceptable sensory characteristics and shelf-life that contain encapsulated tea tree oil (TTO). For the encapsulation of TTO in β-cyclodextrin’s polymeric matrix, microfibers were applied during the electrohydrodynamic process and scanning electron microscopy images were analyzed to select the optimum conditions. The microfibers were then incorporated into a facial cosmetic cream. All samples were stored at three different temperatures and microbiological analysis for color and pH measurements were performed for all formulations. Microbial analysis reveal no microbial contamination at all storage temperatures. Moreover, the pH and color of the creams that contained TTO microfibers performed differently than the base cream, which was expected due to the TTO quantities released over time. In general, all of the formulated creams presented similar characteristics that were not affected by different storage conditions. The addition of encapsulated TTO in cosmetic creams could develop formulations suitable for use due to their microbiological aspects and quality characteristics. The electrohydrodynamic process could be the key to the formation of cosmeceutical products containing selected compounds regardless of their undesirable sensory characteristics or the thermosensitivity of the compounds. INTRODUCTION There is a recent trend toward replacing chemical compounds in cosmetic formulations following consumer requirement that natural compounds be incorporated into cosmetic products. Negligent use of synthetic components has been proven to provoke harmful consequences in consumer health and cause several skin issues, like irritations and allergies, with the most reported cases after use of facial cosmetic products (1). Irritant reactions are J. Cosmet. Sci., 73, 70–83 (March/April 2022)

71 ENCAPSULATED TTO IN FACIAL CREAMS more common than allergies and constitute more than 90% of reported adverse reactions to cosmetic products (2,3). Common components in cosmetic products that cause these side effects are preservatives, fragrances, and dyes. Generally, these groups may be natural or synthetic, with the latter being more likely of side effects but having some major advantages over natural components that makes them more attractive in cosmetic industry (e.g., purity, compatibility, cost, quality control, etc.) (3). To avoid these side effects the newest trend in cosmetics has been to formulate innovative products that minimize the use of synthetic compounds by replacing them. Materials like herbal extracts, essential oils, and in general plant origin raw materials are effective against microorganisms and have other desirable effects like antiaging properties (4–7). Essential oils are aromatic plants known to produce a large array of secondary metabolites that produce volatile oils (8). Essential oils exhibit antibacterial and anti-inflammatory traits that have made them very popular in the cosmetic, pharmaceutical, and food industries, among others (9). In terms of composition, purity, and the extraction process, there are significant differences between crude plant extracts and essential oils, which is also responsible for the high price variation (8). Tea tree oil (TTO) is an essential oil, extracted using steam-distillation from the Australian Melaleuca alternifolia plant of the Myrtaceae family of aromatic plants (10–12). In the 1920s, the medical properties of TTO were reported in a large survey on Australian essential oils with economic potential. Following this, TTO was successfully introduced to the cosmetics industry. However, the commercialization of TTO began many years later when the industry could produce a consistent product in large quantities (11). TTO contains more than 100 components, mainly monoterpenes and related alcohols (minimum content of 30% of terpinen-4-ol), that are responsible for its proven medicinal properties (e.g., antimicrobial and antioxidant activity, anti-inflammatory properties, etc.) (12–16). It has been used for many years in the pharmaceutical industry due to its effective action against a variety of bacteria, fungi, viruses, and mites (15,17,18). Several dermatological studies have been conducted that show the excellent effects of TTO in numerous skin infections and diseases (e.g., seborrheic dermatitis, acne chronic gingivitis, vulgaris, head lice, dandruff, wound healing, recurrent herpes labialis, etc.), typically found to be either similar or better than traditional treatment and often with fewer side effects (12,19– 22). TTO is an increasingly popular ingredient in a variety of cosmetic products (e.g., shampoos, facial creams, cosmetic oils, and more). The unique properties of TTO makes it a desirable component for cosmetic products because it can be an antioxidant factor and offer other complementary actions (e.g., acne treatment as a component in a facial cosmetic cream). However, TTO presents a significant disadvantages from its sensory characteristics, namely the sharp camphoraceous odor, the menthol-like cooling sensation, and the pale yellow color (20). Generally, incorporating TTO and natural plant extracts or their derived products has resulted in unwanted deterioration phenomena, including change of color, odor, and emulsion instability (6,23). Thus, the challenge to developing such cosmetic products is to deliver a desirable formulation and concentration. Although there are several technologies that develop cosmeceutical products, nanotechnology can be applied to produce elegant and effective products and overcome the possible side effects of several incorporated compounds (24). Specifically, the micro- and nanoencapsulation of cosmetic ingredients (e.g., antioxidants, unsaturated fatty acids, vitamins, etc.) can improve their stability, ability to target a desired site, and controlled release, as well as smooth their undesirable sensory characteristics and more (7,25,26). The use of the nanoencapsulation