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j. Cosmet. sci., 50, 221-229 (July/August 1999) Comparison of antioxidant activity of extract from seeds of white pepper (Piper nigrurn, Linn.) to commercial antioxidants in 2% hydroquinone cream ARANYA MANOSROI, MASAHIKO ABE, and JIRADEJ MANOSROI, Pharmaceutical-Cosmetic Raw Materials and Natural Products Research and Development Center (PCRNC), Natural Products for Thai Traditional Medicines Research Unit, Department of Pharmaceutical Technology, Faculty of Pharmacy, Chiang Mai University, Chiang Mai 50200, Thailand (A.M., J.M.) The Cosmetic Quality Control Subcommittee, FDA, Ministry of Health, Nontaburi, Thailand (A.M.) Faculty of Science and Technology, Science University of Tokyo, Yamazaki 2641, Noda, Chiba 278, Japan (M.A.) and Institute of Colloid and Interface Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku, Tokyo 162, Japan (M.A.). Accepted for publication June 30, 1999. Synopsis Powdered dry fruits of white pepper (Piper nigrum, Linn.) were extracted with dichloromethane and frac- tionareal into various portions. The powder obtained from the aqueous weakly acidic fraction, which gave a yield of 1.09% w/w of crude pepper, was tested for antioxidative activity in comparison with commercial antioxidants (sodium metabisulfite and BHT) at 0.1%, 0.5%, and 1.0% w/w in 2% w/w hydroquinone cream. The systems were incubated in a dark room at 24 ø + 1.0øC for two weeks and at 45 ø + 0.5øC for three months. The physical stability and the percentages of hydroquinone remaining after two weeks and one, two, and three months were determined by UV spectrophotometry at 294 nm according to official standard procedures. The experiment revealed that oxidation degradation of hydroquinone was accelerated by heat even with the existence of antioxidants. The higher percentages of remaining hydroquinone were observed for higher antioxidant concentration but showed lower physical stability of the formulation, especially in the cases of 1% BHT and 1% extract. In two months at 45 ø + 0.5øC, the extract demonstrated the same activity as the other two commercial antioxidants at all concentrations, with about 20-30% more hydroquinone remaining than in the control system. The creams containing 0.1% and 0.5% extract gave good physical formulation stability, with about 66% and 72% of hydroquinone remaining. This suggested the possibility of using an extract from white pepper at 0.1% and 0.5% as a water-soluble antioxidant for substances that are oxidation-susceptible. INTRODUCTION One of the most important characteristics of many cosmetic products is stability. Hy- droquinone, a hypopigmenting agent employed percutaneously to lighten localized 221