Judul: Aktivitas Antioksidan dan Inhibisi Enzim α Glukosidase serta Toksisitas Ekstrak Air-Etanol dan Heksan Anggrek Merpati (Dendrobium cruminatum SW)
Abstrak: Dendrobium cruminatum are anggrek that grow in almost all regions of Indonesia. Dendrobium cruminatum leaves contain flavonoid compounds that are useful as an antioxidant and antidiabetic. This study aims to determine the ability of the anggrek merpati extract as an antioxidant and it’s potential to inhibition activity of α-glucosidase enzyme and also as a compound that toxic to the larvae of shrimp Artemia salina Leach with different solvents. The antioxidant activity was measured by using DPPH method and antidiabetic measured by the formation of p-nitrifenol-α-D-glukopiranosida (p-NPG) were measured with a spectrophotometer at a wavelength of 410 nm. The results of antioxidant activity and cytotoxicity testing showed that the best solvent used for the extraction of anggrek merpati leaf is water solvent with IC50 value of 153.565 μg / mL and the level of cytotoxicity was 889.641 mg / mL. whereas the activity of the inhibition of α-glucosidase enzyme is owned by the highest percentage of etanol by 64% at a concentration of 1000 μg / mL or IC50 value of 435 μg / mL.
Keyword: Bogor Agricultural University (IPB), antidiabetic and cytotoxicity., antioxidant, Dendrobium cruminatum

Judul: Aktivitas Antioksidan Ekstrak Etanol Daun Serai (Cymbopogon citratus) dan Potensinya Sebagai Pencegah Oksidasi Lipid
Abstrak: Cymbopogon citrates is usually used as spices by Indonesian people. The utilization of lemongrass is only limited on it stem, but the leaf remain as waste. The aim of this research was to analyze phytochemical components and to determine the phnolic content and antioxidant assay with ethanol solvent each 30%, 70% and 96%. The extraction of lemongrass leaf was performed by maceration. The result of phytochemical analysis indicated that the ethanolic extract of lemongrass leaf contains alkaloid, saponin, tannin, flavonoid, phenol and steroid. The phenol content determination was performed by Folin- Ciocalteau method with the highest phenolic content was obtained on ethanolic extract 30% was 50.017 GAE (Gallic Acid Equivalent) mg/g. The ethanol extract of lemongrass leaves through its inhibitory potency as an antioxidant against free radical DPPH (2,2-diphenyl-1-pikrylhydrazyl) with with the highest IC50 on 70% ethanol was 79.444 mg/L. The antioxidant activity on lipid system with rancimat method was obtained on 70% ethanol as 1.19 and the longest induction time was 6.15 hours.
Keyword: Bogor Agricultural University (IPB), DPPH., rancimat, total phenolic, antioxidant, lemongrass leaf

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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