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: Total Phenolics, Flavonoids, and ɑ-Glucosidase Inhibitory Activity of n-Hexane, Ethyl Acetate and Methanol Extracts of Red Betel (Piper crocatum)
Abstrak: Sirih merah (Piper crocatum) mempunyai berbagai senyawa dengan kemampuan penghambatan enzim ɑ-glukosidase. Penelitian ini bertujuan menentukan ekstrak yang memiliki tingkat kandungan fenolik dan flavonoid yang optimal, serta penghambatan tertinggi pada enzim α-glukosidase. Metode maserasi bertingkat digunakan untuk mengekstraksi senyawa bioaktif sirih merah menggunakan pelarut-pelarut dengan peningkatan kepolaran (n-heksana, etil asetat, metanol). Pengujian dilakukan terhadap kadar fenolik total, flavonoid, serta kemampuan inhibisi ɑ-glukosidase. Hasil pengukuran total kadar fenolik, flavonoid, dan aktivitas penghambatan α-glukosidase menunjukkan nilai yang secara signifikan berbeda (p<0,05) pada semua ekstrak dengan total kadar fenolik dan flavonoid tertinggi pada ekstrak n-heksana berturut-turut sebesar 25,68 ± 0,29 mg GAE/g dan 65,84 ± 0,96 mg QE/g. Sementara itu, ekstrak metanol daun sirih merah memiliki daya hambat diantara semua ekstrak dengan nilai persen inhibisi α-glukosidase sebesar 43,87 ± 1,83%., Red betel leaf (Piper crocatum) had various compounds with the ability to inhibit α-glucosidase enzymes. The research aimed to determine the extract with optimal levels of phenolic and flavonoid content, as well as the highest inhibition of α-glucosidase enzyme. A multistage maceration method was used to extract bioactive compounds from red betel leaf using solvents with increasing polarity (n-hexane, ethyl acetate, methanol). Tests were conducted on the total phenolic content, flavonoids, and α-glucosidase inhibition ability. The measurement results of the total phenolic content, flavonoids, and α-glucosidase inhibition activity showed significantly different values (p<0,05) in all extracts with the highest total phenolic and flavonoid content in n-hexane extract, respectively, at 25,68 ± 0,29 mg GAE/g and 65,84 ± 0,96 mg QE/g. Meanwhile, the methanol extract of red betel leaf had inhibitory power among all extracts with a percentage inhibition of α-glucosidase at 43,87 ± 1,83%.
Keyword: ɑ-glukosidase/ɑ-glucosidase, antidiabetes/antidiabetic, fenolik/phenolic, flavonoid/flavonoid, sirih merah/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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