Judul: Fraksionasi Ekstrak Kulit Petai Berpotensi Antioksidan
Abstrak: Many medicinal plants have been used in traditional treatment and are known to be potencial as antioxidant. Petai is one of the medicinal plants having high antioxidant activity. This study aimed to study the cytotoxicity and antioxidant activity of the exterior and interior parts mixture of petai seed coat with brine shrimp lethality test and 1,1-diphenyl-2-picrylhydrazyl methods. Petai seed coat was extracted with methanol and liquid-liquid partitioned by using n-hexane, chloroform, and ethyl acetate. The 50% lethal concentration (LC50) values of ethyl acetate and water fractions were 49.51 and 118.01 mg L-1, respectively. These results showed that both fractions were potencial as active compounds and toxic. Ethyl acetate fraction had the highest antioxidant activity with the 50% inhibition concentration (IC50) value of 2 mg L-1. Water and solid fractions had IC50 values of 5.37 and 4.05 mg L-1, respectively. Gallic acid was used as positive control and gave IC50 value of 0.48 mg L-1. Based on these results, all 3 fractions of petai seed coat extract had very high antioxidant activities.
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Judul: Daun Ki Pahit (Tithonia diversifolia) sebagai Sumber Antibakteri dan Antioksidan
Abstrak: Antibacterial and antioxidant analysis have been assayed on extracts and essential oil of ki pahit leaves (Tithonia diversifolia). The antibacterial activity was tested toward Staphylococcus aureus and S. epidermidis, and the antioxidant activity was assayed toward 1,1-diphenyl-2-picryl hydrazyl (DPPH). The most active extract was the residual methanol extract with minimum inhibitory concentration (MIC) values against S. aureus and S. epidermidis were 1.00 and 2.00 mg/mL, respectively, the minimum bactericidal concentration (MBC) value >2.00 mg/mL, and the inhibition of 50% DPPH, IC50 was 27.88 μg/mL. The residual methanol extract was fractionated using column chromatography to obtain 13 fractions. F1 was the most active fraction with MIC values against S. aureus and S. epidermidis with 0.25 and 1.00 mg/L and MBC values were 0.50 and 2.00 mg/mL, respectively. The IC50 of the antioxidant was 22.88 μg/mL. The F1 fraction was further fractionated by thin layer chromatography to obtain 11 fractions. The F1.2 fraction was the most active fraction as indicated by inhibition the growth of S. aureus and S. epidermidis that of 0.25 and 0.50 mg/mL and indicated by killing the bacteria that of 0.50 and 2.00 mg/ml, respectively, and 50% DPPH that could inhibit was 30.94 μg/mL. Based on identification using ultraviolet-visible and fourier transform infrared spectrophotometers, the active compound was indicated to be in auron group.
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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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