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: Optimization Extraction of Total Flavonoid and Antioxidant Capacity of Purslane (Portulaca grandiflora Hook.) using Two-half Factorial Design
Abstrak: Krokot (Portulaca grandiflora Hook.) merupakan tanaman liar yang memiliki potensi sebagai antioksidan. Penelitian bertujuan mengidentifikasi faktor rasio cairan/padatan, suhu, konsentrasi etanol, waktu, dan pH, selama proses ekstraksi krokot yang berkontribusi signifikan terhadap nilai total flavonoid dan kapasitas antioksidan FRAP. Faktor rasio cairan/padatan menunjukan pengaruh paling signifikan (p<0.0001) untuk mengasilkan nilai total flavonoid dan kapasitas antioksidan FRAP. Kadar total flavonoid (TFC) dihitung menggunakan metode AlCl3 dan kapasitas antioksidan menggunakan metode FRAP. Kadar total flavonoid tertinggi terdapat pada perlakuan 14 (22,4262 ± 3,192 mg QE/g BK). Kapasitas antioksidan FRAP tertinggi terdapat pada perlakuan 13 (511,8949 ± 6,030 µmol TE/g BK). Hasil optimasi menunjukan kondisi ekstraksi yang direkomendasikan sebagai solusi kombinasi perlakuan optimum dengan rasio cairan/padatan 100 ml/g, suhu 68°C, konsentrasi etanol 80%, waktu 300 menit dan pH 2 dengan nilai desirability 0,839. Verifikasi solusi optimasi dilakukan secara triplo menghasilkan TFC dengan nilai %RSE 3,349 dan FRAP dengan %RSE sebesar 0,003%. Two-half factorial Design mampu mengoptimalkan proses ekstraksi krokot dengan respon kadar total flavonoid dan kapasitas antioksidan., Purslane (Portulaca grandiflora Hook.) is a wild plant with potential as an antioxidant. This study aimed to identify the factors of liquid/solid ratio, temperature, ethanol concentration, time, and pH during the purslane extraction process, which significantly contributed to total flavonoid value and antioxidant capacity of FRAP. Of all the factors, the liquid/solid ratio showed the most significant effect (p<0.0001) on producing total flavonoid value and antioxidant activity of FRAP. Total flavonoid content (TFC) was calculated using the AlCl3 method, and antioxidant activity using the FRAP method. The highest levels of total flavonoids were found in treatment 14 (22.4262 ± 3.192 mg QE/g DM). The highest antioxidant activity of FRAP was found in Treatment 13 (511.8949 ± 6.030 µmol TE/g DM). The optimization results show the recommended extraction conditions as the optimum treatment combination solution with a liquid/solid ratio of 100 ml/g, temperature of 68°C, 80% ethanol concentration, time of 300 minutes, and pH 2 with a desired value of 0.839. The verification solution was verified in triplicate to produce a TFC with a %RSE value of 3.349% and a FRAP with a %RSE of 0.003%. The two-half factorial design can optimize the purslane extraction process in response to total flavonoid levels and antioxidant activity.
Keyword: antioksidan, ekstraksi, flavonoid, krokot

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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