Judul: Optimasi pH dan Waktu Ekstraksi dengan Teknik Microwave terhadap Total Fenolik, Total Flavonoid, dan Kapasitas Antioksidan Tanaman Krokot
Abstrak: Tanaman krokot (Portulaca grandiflora Hook.) memiliki potensi sebagai antioksidan karena memiliki kandungan metabolit sekunder antara lain fenolik dan flavonoid. Faktor-faktor yang mempengaruhi hasil ekstraksi antara lain waktu ekstraksi dan pH. Penelitan ini bertujuan menentukan pH dan waktu ekstraksi optimum untuk mengekstrak metabolit sekunder krokot berdasarkan kadar total fenolik, flavonoid, dan kapasitas antioksidan menggunakan response surface methodology. Sampel diekstraksi dengan metode microwave assisted extraction. Data hasil optimasi menunjukkan total fenolik tertinggi saat waktu ekstraksi 3,53 menit dan pH 6 sebesar 3,25 mg GAE/g DW. Total flavonoid tertinggi pada waktu ekstraksi 5 menit dan kombinasi pH 4,20 sebesar 13,85 mg GAE/g DW. Kapasitas antioksidan DPPH tertinggi saat waktu ekstraksi 5 menit dan pH 2,50 sebesar 1,18 µmol TE/g DW sedangkan FRAP saat waktu ekstraksi 3,66 menit dengan pH 2 sebesar 25,70 µmol TE/g DW. Solusi optimasi yang didapatkan pada waktu ekstraksi 4,69 menit dan pH 6 dengan desirability sebesar 0,58., The purslane plant (Portulaca grandiflora Hook.) has potential as an antioxidant because it contains secondary metabolites, including phenolics and flavonoids. Factors that influence result of extraction is extraction time and pH. This research aimed to determine the best pH value and extraction time to extract secondary metabolites of purslane based on total phenolic, flavonoid and antioxidant capacity levels using response surface methodology. Samples were extracted using the microwave assisted extraction method. Optimization data shows that the highest value of phenolic content when the extraction time was 3,53 minutes and pH 6, that is 3,25 mg GAE/g DW. The highest value of flavonoid content was at extraction time of 5 minutes and a combination of pH 4,20 that is 13,85 mg GAE/g DW. The highest value of antioxidant capacity of DPPH when the extraction time was 5 minutes and pH 2,50 was 1,18 µmol TE/g DW, while FRAP when the extraction time was 3,66 minutes with pH 2 was 25,70 µmol TE/g DW. The optimization solution obtained was an extraction time of 4,69 minutes and a pH of 6 with a desirability of 0,58.
Keyword: antioxidant, extraction, flavonoid, optimization, phenolic

Judul: Total Phenolic, Flavonoid, and Antioxidant Activity of Purslane Flower Extract (Portulaca grandiflora Hook.) Optimized Using Simplex-Centroid Design
Abstrak: Krokot (Portulaca grandiflora Hook.) memiliki kemampuan sebagai antioksidan karena kandungan metabolit sekunder seperti senyawa fenolik dan flavonoid yang dimiliki, salah satunya pada bagian bunganya. Kandungan fenolik dan flavonoid yang terekstrak serta nilai aktivitas antioksidan dapat dipengaruhi oleh penggunaan pelarut ekstraksi. Penelitian ini bertujuan menentukan pelarut terbaik untuk ekstraksi bunga krokot menggunakan microwave-assisted extraction berdasarkan kadar total fenolik (TPC), flavonoid (TFC), serta aktivitas antioksidan (metode DPPH dan FRAP). Pelarut optimal yang direkomendasikan oleh piranti lunak Design Expert menggunakan metode simplex-centroid design (SCD) adalah campuran aseton 41% dan metanol 59%. Hasil penelitian dinyatakan sesuai dengan nilai prediksi berdasarkan uji verifikasi, dengan respon TPC sebesar 3,599 mg GAE/g bobot basah, TFC sebesar 1,796 mg QE/g bobot basah, dan aktivitas antioksidan sebesar 0,669 μmol TE/g bobot basah (DPPH) serta 9,231 μmol TE/g bobot basah (FRAP) dengan nilai desirability sebesar 0,712. Metode SCD terbukti dapat mengoptimalkan pelarut ekstraksi bunga krokot dengan respon TPC, TFC, dan aktivitas antioksidan., Purslane (Portulaca grandiflora Hook.) has the ability as an antioxidant due to the presence of secondary metabolites such as phenolic compounds and flavonoids, one of which is found in its flowers. The extracted phenolic and flavonoid contents, as well as the antioxidant activity, can be affected by the use of extraction solvent. This study aimed to determine the best solvent for extracting the flowers of purslane using microwave-assisted extraction based on the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities (DPPH and FRAP method). The optimal solvent determined by the Design Expert software using the simplex-centroid design (SCD) method is a mixture of 41 % acetone and 59% methanol. The research results obtained align with the predicted values based on verification tests, yielding TPC of 3,599 mg GAE/g fresh weight, TFC of 1,796 mg QE/g fresh weight, and antioxidant activity of 0,669 μmol TE/g fresh weight (DPPH) and 9,231 μmol TE/g fresh weight (FRAP), with a desirability value of 0,712. SCD method has proven to optimize the extraction solvent for purslane flower in response to TPC, TFC, and antioxidant activity.
Keyword: antioxidant, flavonoid, optimization, phenolic, purslane

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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