Judul: Total Flavonoid, Total Fenolik dan Aktivitas Antioksidan Ekstrak Metanol Temulawak yang Dibudidayakan dengan Kombinasi Pupuk N,P, dan K
Abstrak: Temulawak (Curcuma xanthorriza roxb.) dilaporkan mengandung senyawa fitokimia dan aktivitas antioksidan tinggi. Tujuan penelitian ini adalah mengukur total flavonoid, total fenolik dan aktivitas antioksidan ekstrak temulawak yang dibudidaya dengan kombinasi pupuk NPK menggunakan metode DPPH dan ABTS. Sampel diekstraksi menggunakan maserasi bertingkat dan dievaporasi dengan vacuum evaporator. Kandungan total flavonoid tertinggi yaitu sampel dengan pupuk NPK sebesar 50±23,81 mg QE/bobot kering dan kandungan total fenolik tertinggi juga terdapat sampel dengan pupuk NPK sebesar 34,67±3,79 mg GAE/bobot kering. Uji antioksidan metode DPPH menunjukkan sampel dengan pupuk NK memiliki aktivitas antioksidan tertinggi sebesar 169,67±8,5 µmol TE/g bobot kering. Hasil berbeda pada metode ABTS pada sampel dengan pupuk NPK sebesar 261,67±29,69 µmol TE/g bobot kering. Pupuk NPK berpotensi sebagai pupuk terbaik untuk meningkatkan kandungan metabolit sekunder dan aktivitas antioksidan temulawak., Temulawak (Curcuma xanthorriza roxb.) is reported to contain phytochemicals and high antioxidant activity. The purpose of this reasearch was to measure the flavonoid content, phenolic content, and the antioxidant activity of methanol extract of temulawak cultivated by using NPK fertizer combination. The samples were extracted with graded maceration and evaporated with vacuum evaporator. The extracts were subjected to total flavonoid, total phenolic, and antioxidant activity assays. The antioxidant activity was measured using the DPPH and ABTS methods. The highest total flavonoid content was sample from NPK fertilizer of 50±23,81 mg QE/dry weight, and the highest phenolic content was from NPK fertilizer of 34,67±3,79 mg GAE/dry weight. The antioxidant test using the DPPH method showed that the extract from NK fertilizer had the highest antioxidant activity of 169,67±8,5 µmol TE/dry weight. Different results were obtained in ABTS method, was found in extract with NPK fertilizer is 261,67±29,69 µmol TE/g dry weight. NPK fertilizer gave the best result for increase secondary metabolites and antioxidant activity of temulawak.
Keyword: antioxidant, NPK, temulawak, flavonoid, phenolics

Judul: Pengaruh Variasi Pelarut dan Waktu Ekstraksi Rimpang Temulawak terhadap Total Fenolik, Flavonoid, dan Aktivitas Antioksidan
Abstrak: Temulawak (Curcuma xanthorrhiza) mengandung senyawa metabolit sekunder seperti fenolik dan flavonoid yang berpotensi sebagai antioksidan. Senyawa metabolit sekunder yang banyak ditemukan dalam temulawak adalah kurkuminoid yang tergolong dalam senyawa polifenol. Maserasi merupakan metode sederhana untuk mengekstrak senyawa metabolit sekunder dari tumbuhan. Selama prosesnya, jenis pelarut dan waktu maserasi menjadi faktor penting yang dapat memengaruhi hasil ekstraksi. Penelitian ini bertujuan untuk menganalisis pengaruh pelarut (akuades, etanol 50%, metanol 50%, dan aseton 50%) dan waktu ekstraksi (12, 24, 36, dan 48 jam) terhadap kadar total fenolik, total flavonoid, dan aktivitas antioksidan. Hasil pengujian menunjukkan bahwa etanol 50% memberikan hasil terbaik dengan kadar fenolik 36,29 mg GAE/g, flavonoid 66,96 mg QE/g, dan aktivitas antioksidan (metode CUPRAC) 117,13, Temulawak (Curcuma xanthorrhiza) contained secondary metabolite compounds such as phenolics and flavonoids with potential antioxidant activity. The most abundant secondary metabolite compound found in temulawak was curcuminoid. Maceration was a simple method for extracting secondary metabolite compounds from plants. During maceration, the type of solvent and the maceration time were crucial factors that affected the test results. This study aimed to analyze the effect of solvent (aquadest, 50% ethanol, 50% methanol, and 50% acetone) and extraction time (12, 24, 36, and 48 hours) on total phenolics, total flavonoids, and antioxidant activity. The results showed that 50% ethanol yielded the highest phenolic content (36,29 mg GAE/g), flavonoid content (66,96 mg QE/g DW), and antioxidant activity (CUPRAC method) of 117.06
Keyword: antioxidant, phenolic, flavonoid, solvent, time

Judul: Bifurkasi Hopf pada siklus bisnis IS-LM tanpa dan dengan waktu tunda
Abstrak: One of business cycle models in dynamical economics is the IS-LM business cycle model with time delay, where the time delay lies in stock capital variables. It is a time delay between the existence of stock capital and the time to get ready to invest. In a model without time delay, changing the parameter of investment rate on income could affect the system stability. On the other hand, in a model with time delay, there exists critical time delay changing the system stability. This shows limit cycle, which can be concluded that Hopf bifurcation occurs
Keyword: Bogor Agricultural University (IPB), time delay, Hopf bifurcation, business cycle model