224 JOURNAL OF COSMETIC SCIENCE Ex•acts Aqueous layer Discarded Ground peper seeds Soaked in dichloroTethane for 24 hrs. Extracted •d filtered Re•fidue Discar• Washed with water and extracted with 2N-HC1 Organic layer Extracted with saturated NaHCCh solutio AqueOus layer Organi I layer Discarded Extracted wi• 1N-NaOH Aqueo• layer Organi I layer Addified and extrac•d with CH2C12 Discarded Aqueous•layer Organi• layer Discarded (weakly addic fracUon) Evaporate on water bath I Dried powder Figure 1. Extraction and fractionation of aqueous weakly acidic fraction from white pepper seeds. for three months to evaluate formulation stability. Another set was kept in a dark room at 24 ø + 1.0øC for two weeks. Samples at each concentration of the extract and com- mercial antioxidants were done in triplicate. Physical stability behaviors, i.e., changes in color and separation of emulsion, were observed optically every week. For the determination of the average percentages of hydroquinone remaining after two weeks in the dark room and for formulation stability studies at 45 ø + 0.5øC in two weeks and one, two, and three months, one gram of the tested samples was extracted with methanol and the amount of hydroquinone was measured by an UV spectrophotometer (Spectronic 301, Milton Roy Company, USA) at 293 nm according to the official standard hydroquinone assay (11). RESULTS AND DISCUSSION The white powder was obtained when the aqueous weakly acidic fraction was evaporated,

ANTIOXIDANT ACTIVITY OF P. NIGR URI 225 Table II -- Comparison of Average Percentages (X _+ SD) of Hydroquinone Remaining in 2% Hydroquinone Cream Containing White Pepper Extract and Commercial Antioxidants After Incubation in a Dark Room at 24 ø +_ 1.0øC and at 45 ø +_ 0.5øC for 2 Weeks Systems* Dark room at 24 ø +_ 1.0øC Dark room at 45 ø +_ 0.5øC CB + HY 66.76 _+ 1.38 61.33 +_ 4.22 CB + HY + SM 0.1% 85.13 +_ 1.89 73.49 _+ 4.50 CB + HY + SM 0.5% 86.26 _+ 1.65 79.27 _+ 4.92 CB + HY + SM 1.0% 89.63 _+ 1.73 82.11 +_ 4.67 CB + HY + BHT 0.l% 78.00 _+ 2.76 75.35 +_ 4.51 CB + HY + BHT 0.5% 88.65 _+ 1.35 87.52 +_ 5.00 CB + HY + BHT 1.0% 96.60 •: 1.44 85.53 +_ 4.13 CB + HY + EXT 0.1% 90.42 +_ 0.47 86.46 +_ 4.17 CB + HY + EXT 0.5% 91.85 _+ 3.75 84.68 +_ 1.88 CB + HY + EXT 1.0% 93.19 -+ 2.90 88.70 +_ 1.67 * CB, cream base HY, hydroquinone, SM, sodium metabisulfite BHT, butylated hydroxy toluene EXT, white pepper seed extract. 100 - 7o- 50- ao- 80 - 10 - O - + 45•o.5 c I I I I I I I I I I A B C D E F G H I J Figure 2. Comparison of average percentages of hydroquinone remaining incubated at 24 ø _+ 1.0øC and 45 o +_ 0.5øC for two weeks. A, CB + HY B, CB + HY + SM (0.1%) C, CB + HY + SM (0.5%) D, CB + HY + SM (1.0%) E, CB + HY + BHT (0.1%) F, CB + HY + BHT (0.5%) G, CB + HY + BHT (1.0%) H, CB + HY + EXT (0.1%) I, CB + HY + EXT (0.5%) J, CB + HY + EXT (1.0%). and the yield was 1.09% w/w of the dry white pepper seeds. The powder appeared to be water-soluble and a 1% solution gave a pH of 6.75 + 0.25. It has been previously revealed that the structure of the major compounds of this acidic fraction are phenolic amides, which are N-trans-feruloyl tyramine, coumaperine, N-trans-feruloyl piperidine,