Judul: Determination of Total Phenolics and Flavonoids Content of Ethyl Acetate and Water of Red Betel Extract (Piper crocatum Ruiz & Pav.) and Their Inhibition of Tyrosinase Enzyme
Abstrak: Sirih merah (Piper crocatum Ruiz & Pav.) memiliki senyawa potensial seperti flavonoid yang dapat berperan sebagai inhibitor tirosinase. Penelitian ini bertujuan untuk menentukan kadar total fenolik dan flavonoid ekstrak sirih merah berdasarkan perbedaan pelarut serta aktivitas inhibisinya terhadap enzim tirosinase. Ekstrak yang mampu menginhibisi enzim tirosinase mampu bekerja sebagai agen pemutih, yang bisa digunakan dalam suatu krim pemutih. Metode ekstraksi yang digunakan yaitu maserasi untuk pelarut etil asetat dan perebusan untuk pelarut air, dilanjutkan dengan uji kadar total fenolik, flavonoid, dan uji inhibisi tirosinase yang berpotensi sebagai agen pemutih. Hasil yang diperoleh pada penelitian ini menunjukkan ekstrak etil asetat menjadi sampel terbaik dengan nilai total fenolik sebesar 56,255 mg GAE/g DW, kadar total flavonoid sebesar 48,631 mg QE/g DW, dan berpotensi sebagai penghambat tirosinase dengan nilai IC50 1600,38 mg/L. Sementara ekstrak air memiliki nilai kadar total fenolik sebesar 44,2 mg GAE/g DW, kadar total flavonoid sebesar 39,812 mg QE/g DW, dan berpotensi sebagai penghambat tirosinase dengan nilai IC50 1764,39 mg/L., Red betel (Piper crocatum Ruiz & Pav.) is a plant with flavonoid-like potential compound that can act as tyrosinase inhibitor. This research aimed to determine the total phenolic and flavonoid concentration of red betel extract based on different solvents and its inhibition activities against the tyrosinase enzyme. Extract capable of inhibiting the tyrosinase enzyme had potential to act as a whitening agent, which could then be utilized in a whitening cream product. The extraction methods include: maceration for the ethyl acetate solvent; and boiling for the water solvent, continued with measuring the phenolic and flavonoid content, with the tyrosinase inhibition test for solvents with whitening agent potential. Results indicated that the ethyl acetate solvent was the best sample with a total phenolic value of 56,255 mg GAE/g DW, total flavonoid content of 48,631 mg QE/g DW, and the potential to inhibit tyrosinase with an IC50 value of 1600,38 mg/L. Meanwhile, the water extract resulted in a total phenolic value of 44,2 mg GAE/g DW and a total flavonoid content of 39,812 mg QE/g DW, with the potential to inhibit tyrosinase with an IC50 value of 1764,39 mg/L.
Keyword: flavonoid, phenolic, red betel, solvent, tyrosinase

Judul: Kadar Total Fenolik, Flavonoid, dan Aktivitas Inhibisi Tirosinase dari Fraksi Ekstrak Sirih Merah (Piper crocatum Ruiz  & Pav) Asal Semarang
Abstrak: Sirih merah (Piper crocatum Ruiz & Pav) merupakan tanaman obat potensial yang dapat menyembuhkan berbagai jenis penyakit seperti diabetes mellitus, asam urat, hipertensi, dan kanker. Selain itu, daun sirih merah diketahui dapat mencegah dan menyembuhkan jerawat, dan mencerahkan kulit wajah kusam. Senyawa aktif pada sirih merah seperti fenolik dan flavonoid dapat berperan dalam menangani hiperpigmentasi dengan menghambat enzim tirosinase. Penelitian ini bertujuan menganalisis kadar total fenolik, flavonoid, dan aktivitas inhibisi tirosinase dari hasil fraksinasi ekstrak etanol sirih merah asal Semarang. Ekstraksi dilakukan dengan maserasi menggunakan etanol 70%, dan selanjutnya difraksinasi dengan 3 pelarut, yaitu n-heksana, etil asetat, dan air. Kadar total fenolik dan flavonoid tertinggi terdapat pada fraksi etil asetat yaitu sebesar 80.294 mg GAE/g dan 61.537 mg QE/g. Nilai penghambatan terhadap tirosinase terbesar juga terdapat pada fraksi etil asetat (65.86%). Aktivitas penghambatan tirosinase menunjukkan bahwa fraksi etil asetat memiliki nilai IC50 3470.53 ppm. Fraksi etil asetat daun sirih merah asal Semarang memiliki kemampuan sebagai inhibitor tirosinase lebih baik dibandingkan dengan fraksi n-heksana, fraksi air, dan ekstrak etanol 70%., Red betel (Piper crocatum Ruiz & Pav) is a potential medicinal plant that can cure various types of diseases such as diabetes mellitus, gout, hypertension, and cancer. Furthermore, red betel leaves are known to prevent and cure acne, and able to brighten facial skin. Active compounds in red betel such as phenolics and flavonoids are able to treat hyperpigmentation by inhibiting the tyrosinase. This research aimed to analyze total phenolics contents, flavonoids contents, and tyrosinase inhibitory activity from the fractionated ethanol extract of red betel from Semarang. The extraction was performed using maceration with 70% ethanol, and then fractionated with 3 solvents, n-hexane, ethyl acetate, and water. The highest total phenolics and flavonoids contents were found in the ethyl acetate fraction with values of 80.294 mg GAE/g and 61.537 mg QE/g. The highest inhibition value of tyrosinase was also found in the ethyl acetate fraction (65.86%). Tyrosinase inhibition activity showed that the ethyl acetate fraction has IC50 value of 3470.53 ppm. Therefore, the ethyl acetate fraction of red betel leaves from Semarang is proven to be a better tyrosinase inhibitor compared to the n-hexane fraction, water fraction, and 70% ethanol extract.
Keyword: phenolic, flavonoid, tyrosinase enzyme, red betel

Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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