J. Cosmet. Sci., 62, 393–404 ( July/August 2011) 393 A study of four antioxidant activities and major chemical component analyses of twenty-fi ve commonly used essential oils CHIU-CHING HUANG, HSIAO-FEN WANG, CHIA-HUI CHEN, YA-JU CHEN, and KUANG-HWAY YIH, Department of Applied Cosmetology, Hungkuang University, Shalu, No. 34, Chung-Chie Rd., Taichung, Taiwan, 433 R. O. C. Accepted for publication April 19, 2011. Synopsis Twenty-fi ve essential oils and their major chemical components were screened for their possible antioxidant activities by assaying their DPPH free-radical scavenging activity (DFRS), total phenolic contents (TPC), trolox equivalent antioxidant capacity (TEAC), and ferric thiocyanate (FTC). Based on the TPC and TEAC assays, the essential oil ajowan is among the best essential oils studied. Furthermore, the DFRS and FTC as- says reveal that the essential oils cinnamon bark extra and oregano are also among the best oils studied. More specifi cally, at a concentration of 1 mg ml−1, the essential oils cinnamon bark extra and benzoin showed 93.75 ± 0.01% and 90.64 ± 0.01% DFRS, while the essential oils ajowan and oregano showed TEAC values of 4374.72 ± 0.01 and 4023.49 ± 0.01 μM of trolox per mg, respectively. In addition, the essential oils oregano and ajowan showed 29.17 ± 0.02% and 25.26 ± 0.03% FTC based on the assay results. At a concentration of 10 mg ml−1, the essential oils ajowan and oregano showed 1845.20 ± 0.04 and 1665.36 ± 0.04 μg of TPC relative to GAE, respectively. Two major chemical components of the essential oils cinnamon bark extra, ajowan, and oregano were trans- cinnamaldehyde (90.61%), eugenol (2.58%), carvacrol (61.20%), p-cymene (37.44%), thymol (77.09%), and p-cymene (10.01%). It is clear that phenolic compounds in the aforementioned essential oils yield a positive correlation with the DFRS, TPC, TEAC, and FTC assays. INTRODUCTION Essential oils are commonly used in the food and aromatherapies industries and have in- creased the value of products and also enlightened the cosmetics industry. Other applica- tions include, but are not limited to: antioxidant, antimicrobial (1), anti-infl ammatory, anti-cholinesterase (2), anti-thrombotic (3), anxiolytic (4), EEG (5) and blood-pressure infl uential (6) properties. Essential oils are commonly considered to be volatile oils, which give rise to the rich fragrance found in aromatics. Many chemical components in natural Address all correspondence to Kuang-Hway Yih at khyih@sunrise.hk.edu.tw.

JOURNAL OF COSMETIC SCIENCE 394 plants have exhibited antioxidant properties, and they often contain similar, but low, levels of essential oils and therefore antioxidant components. The compositions of the es- sential oils from the same plants may be different due to (i) the age of the plant, (ii) the time of harvesting, and (iii) the extraction methods. Many articles have shown that aging is closely related to the presence of free radicals (7). Free radicals have weak bonds with atoms, molecules, or ions and contain unpaired electrons in the outer shells. Those unpaired electrons try to (and usually do) capture electrons from the nearest stable molecule to gain stability. When the “attacked” mole- cule loses its electron, it becomes a free radical itself, initiating a chain reaction (8,9). Our skin inhibits the pressure of being oxidized from environmental pollution and ultraviolet rays (10) by using antioxidants contained naturally within the body. Many artifi cial anti- oxidants—such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ), and propylene glycol (PG)—are added to food as well as cosmetics to prevent free radical formation. However, due to safety concerns (11), natural antioxidant alternatives have become more reliable. Natural antioxidants/essen- tial oils such as Cleistocalyx operculatus and Artemisia scoparia have strong DFRS (12,13), while Psammogeton canescens, Pistacia lentiscus, and Myrtus communis extracts contain high levels of phenolic compounds (14,15). The extracts Rosmarinus offi cinalis and Nigella sativa have shown good TEAC capacities (16), whereas the essential oils Ocimum basilicumru and Dorystoechas hastate inhibit linoleic acid peroxidation based on results from the FTC assay (17,18). These examples show that essential oils have favorable antioxidation properties. Previously we studied forty-fi ve essential oils from an Australian company (19,20) and compared their antioxidant activities. In order to explore the sources of essential oils for functional foods, and their applications in cosmetic products, and to investigate their antioxidant activities, DFRS, TPC, TEAC, and FTC assays were employed. Herein we have extended our studies by analyzing the antioxidant activities and the major chemical components of an additional twenty-fi ve essential oils from Ayus GmbH (Baden, Ger- many). MATERIALS AND METHODS MATERIALS Butyl hydroxyl toluene (BHT), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and 3,4,5-trihy- droxybenzoic acid (gallic acid) were purchased from TCI (Shanghai, China). Ammonium thiocyanate (NH4SCN), disodium hydrogenphosphate (Na2HPO4), iron(II) chloride tet- rahydrate (FeCl2 . 4H2O), sodium dihydrogenphosphate (NaH2PO4), and sodium car- bonate (Na2CO3) were purchased from Showa (Tokyo, Japan). Folin-Ciocalteu’s phenol reagent, eugenol, potassium persulfate, and linalool were purchased from Merck (Darm- stadt, Germany). Hydrochloric acid was purchased from MP (Eschwege, Germany). Lino- leic acid, p-cymene, and thymol were purchased from Acros Organics (Geel, Belgium). Trans-cinnamaldehyde was purchased from Alfa Aesar (Karlsruhe, Germany). In addi- tion, 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid), diammonium salt (ABTS), 6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic acid (trolox), and carvacrol were purchased from Sigma (St. Louis, MO). The twenty-fi ve essential oils (of 100% purity) were purchased from Ayus GmbH (Baden, Germany). All other chemicals and solvents