Judul: Aktivitas Antioksidan Ekstrak Pelepah Pohon Aren (Arenga pinnata Merr.)
Abstrak: Stem sugar palm has been reported to contain tannin compound, however, there is no scientific information about its potential as antioxidant. Hence, the objective of this research was to measure the antioxidant activity of stem sugar palm extract (Arenga pinnata Merr.) in vitro. This research used water, ethanol 70% and ethanol 96% as solvents. The stem sugar palm was extracted in water solvent by boiling method and by maceration in ethanol 70% and 96% solvents. Bioactive compounds in the extracts were determined by phytochemical method. Antioxidant activity of stem sugar palm extracts were determined by 1,1-diphenyl-2-picrylhydrazyl radical absorption method (DPPH) and the content of the total phenolic measured in colometric with Folin-Ciocalteu method. The result showed that the stem sugar palm extracts contained saponin, tannin and phenol, and steroids and triterpenoid. Analysis of antioxidant activity showed that both ethanol 70% and 96% stem sugar palm extracts were potential as natural antioxidant. The highest antioxidant activity and the total phenolic value were showed by ethanol 96% extract (IC50 = 2.570 μgL-1; 3.75 GAE mgg-1).
Keyword: phenolic, phytochemical, stem sugar palm, DPPH, Antioxidant

Judul: Aktivitas Antioksidan Fraksi Teraktif Buah dan Daun Asam
Abstrak: Tamarind plant (Tamarindus indica) contain tannins, flavonoids, and saponins which are usually have antioxidant activity. The purpose of this study was to determine antioxidant activity and total phenolic content of the most active fraction of tamarind fruits and leaves. Antioxidant activity was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method and total phenolic content by Folin-Ciocalteu method. The result showed that the most active fraction of tamarind fruits and leaves had IC50 value of 293.22 mg/L and 57.89 mg/L, respectively. These results were higher compared to ascorbic acid as positive control which was 2.12 mg/L. Total phenolic content of the most active fraction of tamarind fruits and leaves was 100.48 mg gallic acid equivalent/100 g dry fruits and 107.44 mg gallic acid equivalent/100 g dry leaves, respectively. The most active fraction of tamarind leaves had higher antioxidant activity compared to its fruit, however both fractions were lower compared to ascorbic acid.
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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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