Judul: Penapisan senyawa penciri inhibitor tirosinase pada batang xylocarpus granatum
Abstrak: Penelitian ini bertujuan untuk menapis senyawa penciri inhibitor tirosinase pada batang Xylocarpus granatum. Bagian kulit batang dan batang tanaman diekstraksi dengan metanol dan diuji aktivitas penghambatan tirosinase baik monofenolase dan difenolase. Ekstrak batang X granatum (IC50 monofenolase: 45.12 μg/mL dan difenolase: 31.59 μg/mL) memiliki sifat sebagai inhibitor tirosinase yang lebih baik dibandingkan ekstrak kulit batang. Nilai IC50 ekstrak batang X granatum tidak berbeda nyata (p< 0.05) dengan asam kojat sebagai kontrol positif (IC50 monofenolase: 17.43 μg/mL dan difenolase: 20.69 μg/mL). Fraksinasi dilakukan terhadap ekstrak batang X. granatum menggunakan kromatografi kolom silika gel. Hasil fraksinasi diperoleh 13 fraksi (1-13) dan fraksi teraktif adalah fraksi 3 (IC50 monofenolase: 18.02 μg/mL dan difenolase: 21.15 μg/mL). Fraksi 3 dipisahkan lebih lanjut dengan kromatografi lapis tipis (KLT) preparatif dan diperoleh 8 fraksi (A-H). Fraksi D memiliki aktivitas inhibitor tirosinase yang paling baik (IC50 monofenolase: 18.73 μg/mL dan difenolase: 21.92 μg/mL). Penciri yang didapat, yaitu Rf 0.25 dan 0.63 pada plat KLT G60F254. Hasil KLT uji fitokimia, spektroskopi ultraviolet-sinar tampak, dan inframerah pada fraksi D menunjukan senyawa yang aktif sebagai inhibitor tirosinase adalah kelompok flavonol.
Keyword: Monophenolase, Diphenolase, Flavonols, Bogor Agricultural University, Institut Pertanian Bogor, IPB

Judul: Penapisan Senyawa Penciri Inhibitor Tirosinase pada Batang Xylocarpus granatum
Abstrak: The purpose of this study is to screen marker component as tyrosinase inhibitor of Xylocarpus granatum’s stem. The bark and stem were extracted with methanol and tested for tyrosinase inhibitory activity (monophenolase and diphenolase). The stem extract (IC50 monophenolase: 45.12 μg/mL and diphenolase: 31.59 μg/mL) was more potent as tyrosinase inhibitor compared to the bark extract. The IC50 values of stem extract are not significantly different (p< 0.05) with respect to kojic acid as positive control (IC50 monophenolase: 17.43 μg/mL and diphenolase: 20.69 μg/mL). Fractionation was performed on stem extract using silica gel column chromatography and yielded 13 fractions (1 to13). Fraction 3 was the most active fraction (IC50 monophenolase: 18.02 μg/mL and diphenolase: 21.15 μg/mL). This fraction was separated further with preparative thin layer chromatography (TLC) resulted 8 fractions (A to H). Fraction D was the most potent extracts as tyrosinase inhibitor (IC50 monophenolase: 18.73 μg/mL and diphenolase: 21.92 μg/mL). The marker components are compounds with Rf values of 0.25 and 0.63 at TLC plate G60F254. The results of phytochemical test, ultraviolet-visible, and infrared spectroscopy on fraction D showed that the active compounds as tyrosinase inhibitors are flavonols.
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Judul: Approximation of the Median of Poisson Distribution Using the Relation of Poisson-Gamma Distribution
Abstrak: A major drawback of median is that median cannot usually be defined in closed form, even in the cases where their distribution functions are known. This study gives an approximation of the closed form for the median of the Poisson distribution by using the relation of Poisson-Gamma distribution. The approximation uses elementary techniques based on the monotonicity of certain sequences involving tail probabilities of the Poisson distribution and the Central Limit Theorem. Furthermore, a closed form expression for the mean absolute deviation 􀜧|􀜰􀰒 􀵆 􀜯􀝁􀝀􁈺􀜰􀰒􁈻| is also studied. The median is relevant because of the fact that it minimizes the mean absolute deviation of a Poisson random variable (􀜰􀰒􁈻 by considering median as central tendency.
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