Judul: Eksplorasi Potensi Bahan Aktif Berkhasiat Antioksidan Pada Daun dan Buah Mangrove Jenis Sonneratia alba (JE Smith, 1816)
Abstrak: Sonneratia alba has been used traditionally by coastal communities for drugs and foodstuffs. Antioxidants are compounds that was result from plant secondary metabolites and that has been helpful for humans to protect from free radical attack when it consumed. The purpose of this research is to obtain a total phenol values, IC50 concentrations and the relationship of both, from methanol extract of young leaves, old leaves and fruits of Sonneratia alba then to identify the phytochemical content. The experiments antioxidant activity using 1,1-diphenyl-2-pikrilhidrazil (DPPH). Total phenol values in the three extracts showed theres no significantly values. DPPH test showed that IC50 concentrations in the sample extracts are classified into three powerful antioxidants, the young leaf extract showed highest antioxidant activity of 37.43 ppm. Regression between total phenols with IC50 showed no significant. So, there are other compounds that affect the value of IC50. Based on phytochemical test, the chemical components of dried simplicia contained flavonoids, saponins, tannins, and steroids on the three samples.
Keyword: Bogor Agricultural University (IPB), Sonneratia alba, DPPH, leaves, fruits, antioxidants

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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