J. Cosmet. Sci., 55, 1-12 Qanuary/February 2004) The stabilization of L-ascorbic acid in aqueous solution and water-in-oil-in-water double emulsion by controlling pH and electrolyte concentration JONG-SUK LEE, JIN-WOONG KIM, SANG-HOON HAN, IH-SEOP CHANG, HAK-HEE KANG, OK-SUB LEE, SEONG-GEUN OH, and KYUNG-DO SUH, Amore Pacific Corporation R&D Center, 314-1, Bora-ri, Giheung-eup, Yongin-si, Gyeonggi-do 449-729 U.-S.L., j.-W.K., S.-H.H., 1.-S.C., H.-H.K., 0.-S.L.), and Division of Chemical Engineering, College of Engineering, Hanyang University, Seoul 133-791 (S.-G.O., K.-D.S.), Korea. Accepted for publication September 11, 200 3. Synopsis This study presents a new approach that can stabilize effectively 1-ascorbic acid in water-in-oil-in-water (w/o/w) double emulsions. Basically, the behavior of 1-ascorbic acid in the aqueous phase was observed, considering its molecular deformation. Then, it was found that the stability determined in the aqueous phase by high-performance liquid chromatography (HPLC) showed that the collapse of ionization of 1-ascorbic acid played a crucial role in protecting the molecular deformation. Then, the stable aqueous system was incorporated into the internal aqueous phase of the double emulsions. From the HPLC analysis, it was observed that the 1-ascorbic acid in an appropriate system showed high molecular stability for a long time. Moreover, in the measurement of in vitro skin permeation, the L-ascorbic acid stabilized in this study showed considerable skin permeation ability, indicating its potential applicability in pharmaceutics and cosmetics. INTRODUCTION 1-ascorbic acid has many biological functions, such as the inducement of collagen synthesis, the strengthening of skin tissues against external attacking factors, reduction in the loss of pigmentation, and anti-free-radical activity (1-6). Unfortunately, however, 1-ascorbic acid is very sensitive to light, to the action of oxidizing agents and metal ions, and even to slight heating. Therefore, 1-ascorbic acid degrades unavoidably in aqueous solution (7). In order to overcome those problems, a number of methods have been proposed, including the chemical modification of 1-ascorbic acid, microencapsulation, and complexation with other moieties (8-12). However, to the best of our knowledge, Address all correspondence to Jin-Woong Kim. 1

2 JOURNAL OF COSMETIC SCIENCE the ultimate stabilization of 1-ascorbic acid in the aqueous phase has not been reported in the literature. The degradation processes of 1-ascorbic acid are very complex and contain a number of oxidation/reduction and intermolecular rearrangement reactions (13). Scheme 1 shows well the degradation pathway of 1-ascorbic acid in the aqueous solution. Dehydro-1- ascorbic acid, an oxidation form of 1-ascorbic acid, is highly unstable in an aqueous solution, which may convert to a variety of species, such as 2,3-diketo-L-gulonic acid, 1-xylosome, etc. (14, 15 ). An important clue in the degradation process is chat the degradation is initiated by the ionization of the hydroxy groups in the 1-ascorbic acid molecule. The control of ionization may provide us a potential route that can protect fundamentally the degradation of 1-ascorbic acid in the aqueous system. In our previous studies, we developed stable w/o/w double emulsions by two-step emulsification method (16). In those studies it was shown chat the stable w/o/w double emulsions produced can be used as a useful tool for the stabilization of water-soluble, unstable 1-ascorbic acid. In the present contribution, 1-ascorbic acid located in the internal aqueous phase of w/o/w double emulsions was stabilized, controlling the pH and ionization property. The effectiveness was then evaluated according co the experimental parameters. EXPERIMENT AL MATERIALS 1-ascorbic acid (99.9% assay, Shinyo Pure Chemicals, Japan), magnesium sulfate (MgSO4 , Aldrich Chemical Co., USA), and sodium hydroxide (NaOH, Aldrich) were all of reagent grade and used without any further purification. In the preparation of w/o/w double emulsions, the lipophilic primary surfactant was Arlacel P135, a polyethylene glycol (30) dipolyhydroxystearate (Uniquema Americas). The hydrophilic secondary surfactant was Synperonic PE/F 127, an echoxylaced propylene oxide copolymer (ICI, France). Puresyn 4, a hydrogenated polydecene (ExxonMobil Chemical) and xanthan gum (Kelco Biopolymers) were used as oil and emulsion stabilizers, respectively, in the preparation of w/o/w double emulsions. PREPARATION OF w/o/w DOUBLE EMULSIONS The double emulsions were produced by two-step process (17-19). In the first step, L-ascorbic acid was dissolved in water together with MgSO 4 . The adjustment of pH was OH OH I I H OH 2CHC ):: 0 '( 0 .:_:_ H OH 2CHC ti 0 ----+ HO OH O 0 COOH I C=O I C=O I ____. HC-OH I HO-yH CH20H CHO I C=O I HC-OH I HO-yH CH20H L-Ascorbic acid Dehydro-L-ascorbic acid 2,3-diketo-L-gulonic acid L-xylosome Scheme 1. Schematic representation of the degradation of L-ascorbic acid in aqueous solution.