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: 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: Analysis of Unequal Income Distribution with Cobb-Douglas Production Function
Abstrak: This paper studies the economic growth model by Moav (2002). Moav model shows the existence of unequal income distribution between low-income with high-income community. That kind of unequal income distribution is caused by uneven distribution of income. On this Moav model, there is one area called the threshold. Threshold becomes a benchmark to determining whether a society is categorized into low- or high- income community. The production function used in this paper is the Cobb-Douglas function. The dynamics of this model is described as difference equation of low-income, threshold, and high-income community. Simulation study on the model is carried out using Maple 13 and Mathematica 7.0 software. Overall, from the observed case, high-income community will reach a stable condition earlier, followed by the threshold, and then the low-income community.
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