J. Cosmet. Sci., 62, 483–503 (September/October 2011) 483 Chemical stability and degradation mechanisms of ferulic acid (F.A) within various cosmetic formulations QIU-JING WANG, XIANG GAO, HUI GONG, XIN-RONG LIN, DIDIER SAINT-LEGER, and JEROME SENEE, Chemistry Department, Fudan University, No. 220, Handan Road, Yangpu District, Shanghai 200433 (Q.-J.W.,X.G.), and L’Oreal (China) Pudong R&D, No. 1028, Yun Qiao Road, Pudong, Shanghai 200040 (Q.-J.W., H.G., X.-R.L., D.S.-L., J.S.), China. Accepted for publication May 12, 2011. Synopsis Ferulic acid (F.A) receives signifi cant interest in the beauty industry with regard to its skin-whitening and anti-oxidant properties. However, its use in cosmetics is limited due to pH- and temperature-related insta- bilities. In this study, we investigated the stability of F.A in eight different prototype formulae. The results confi rmed that in our conditions the stability of F.A is pH- and temperature-related. Additionally, the nature of the solvent dipropylene glycol (DPPG) showed a capacity to stabilize F.A. A series of experiments was further planned for studying the mechanism of degradation of F.A. In a prototype of a cosmetic medium, F.A degrades fi rst through a decarboxylation step, leading to 4-hydroxy-3-methoxystyrene (PVG). Further, F.A and PVG are both involved in an additional reaction, resulting in the trans-conjugation dimer of PVG. The consequences of these results in formulating F.A are discussed. INTRODUCTION Traditional Chinese medicine (TCM) is probably the most ancient (ca. 30 centuries) hu- man medical or paramedical approach for preventing diseases, curing or sustaining body health. It comprises thousands of preparations from either vegetal, animal, or mineral extracts. These are blended by Chinese TCM pharmacists, according to “recipes” accumu- lated for centuries, written in secular texts. In brief, TCM can be regarded as the fi rst human pharmacopeia. In practice, the TCM composition given to a patient by a pharma- cist, for a given affl iction, is rarely one extract but a mixture of different extracts that, according to TCM theories, work in a complementary or synergistic way. Most generally these are absorbed by an oral route. Beyond medical purposes, there is considerable public and scientifi c interest in the topical use of TCM ingredients as beauty magnifi ers in the cosmetic fi eld (1). Address all correspondence to Q.-J. Wang and X. Gao.

JOURNAL OF COSMETIC SCIENCE 484 Ferulic acid (F.A) is a phenolic phytochemical of the cinnamate family, present in a signifi - cant amount in vegetables, fruits, and beverages—e.g., in tomatoes, sweet corn, rice bran, coffee, peanuts, etc. It is also widely abundant in the TCM plant kingdom, such as in danggui (Angelica sinensis), chuanxiong (Ligusticum wallichii), muzei (Equisetum), and shengma (Rhizoma Cimicifugae), which are commonly used in TCM preparations. F.A is known as a major active ingredient of many TCMs and is therefore considered as a pivotal compound against a wide range of skin problems and is of interest to the cosmetics industry (2). F.A is claimed to possess a wide spectrum of benefi cial activities for skin care, i.e., alleviat- ing cutaneous pigmentation (3), sun-induced darkening (4), infl ammatory reactions (5), and the skin-aging process (6). Most of these properties seem linked to its strong anti- oxidative activity with regard to its phenolic nucleus and extended side-chain conjugation (Figure 1). A few works report that F.A can inhibit melanin production (7) and tyrosinase activity (8), making it a potential candidate for whitening products. In cosmetics formula- tions, F.A exhibits stability issues during long storage times, leading to color and/or odor changes in the fi nal product. The work presented in this paper reports the stability criteria of F.A in various cosmetic formulations, together with its mechanism of degradation, in an attempt to defi ne appropriate stabilizing conditions of F.A in cosmetic preparations. MATERIALS AND METHODS MATERIALS Trans-ferulic acid ( 98% purity) was purchased from Ichimaru Pharcos Co., LTD (Lots No. U-808 and Q-728, Gifu, Japan) and used as received. HPLC-grade methanol was purchased from Merck (Darmstadt, Germany). Water was supplied by a MilliQ water purifi er system (Millipore, Bedford, MA). Sigma Chemical Co. (St. Louis, MO) provided 4-hydroxy-3-methoxystyrene (98%), and 1,3-bis (4-hyroxy-3-methoxyphenyl) -1-butene was purifi ed by column chromatography in our laboratory to reach a purity 98%, as confi rmed by HPLC. Sodium hydroxide, triethanolamine (TEA), and dipropylene glycol (DPPG) were obtained from industrial suppliers to the cosmetic industry, all of high purity grade. Silica gel-coated TLC plates (silica gel 60, 0.10–0.20-mm thickness) and 100–200-mesh silica gel for column chromatography was purchased from Wusi Chemi- cal Company. All solvents and solutions for HPLC analysis were fi ltered, prior to use, through a Millipore fi lter (pore size 0.45 μm). METHODS Preparation of F.A in existing and modifi ed formulae. Eight representative formulae were de- fi ned in formulating 1% F.A (w/w) at different pH levels. Cream-based formulae were pH Figure 1. Molecular structure of trans-ferulic acid.