Judul: Effect of Flour Processing and Steaming on Physicochemical and Sensory Characteristic of Purple Sweet Potato Analog Rice
Abstrak: Beras analog ubi jalar ungu memiliki peluang untuk dikembangkan sebagai alternatif makanan pokok. Ubi jalar ungu sebagai bahan dasar dikenal memiliki karbohidrat dengan indeks glikemik rendah serta kandungan antosianin dan senyawa fenolik yang cukup tinggi. Proses pembuatan beras analog ubi jalar ungu dari tepung menghasilkan beras yang cenderung berwarna gelap akibat degradasi senyawa antosianin selama proses pengolahan. Upaya untuk menghasilkan beras analog ubi jalar ungu dengan karakteristik warna dan total fenolik yang lebih baik dapat dilakukan dengan proses pengukusan. Pengukusan ubi jalar ungu dapat mencegah terjadinya oksidasi antosianin dan memperkuat warna pigmen. Penelitian ini bertujuan membandingkan karakteristik beras analog ubi jalar ungu dengan proses penepungan dan proses pengukusan berdasarkan parameter fisik, kimia, dan sensori. Pembuatan beras analog menggunakan dua formula dengan bahan utama yang berbeda, yaitu tepung dan pasta ubi jalar ungu. Karakteristik beras analog didapatkan dengan melakukan analisis fisik, kimia dan sensori. Hasil analisis menunjukkan formula menghasilkan beras dengan warna yang berbeda. Beras analog dengan proses pengukusan mengandung total fenolik dan aktivitas antioksidan yang lebih tinggi. Uji RATA menunjukkan beras analog dengan penepungan didominasi oleh atribut brown color, sedangkan beras analog dengan proses pengukusan didominasi oleh atribut purple color, sweet, purple sweet potato aroma, dan chewiness. Kedua formula beras memiliki tingkat kesukaan yang sama dan masih dapat diterima oleh panelis.
Keyword: analog rice, flour processing, steaming, sweet purple potato, total  phenolic

Judul: Perubahan Komponen Kimia Fungsional Umbi, Tepung, dan Beras Analog Ubi Jalar Ungu
Abstrak: Ubi jalar ungu dapat dikembangkan menjadi produk pangan fungsional seperti beras analog. Penilitian ini bertujuan untuk mengevaluasi komponen kimia fungsional dan aktivitas antioksidan selama pengolahan umbi menjadi tepung dan beras analog ubi jalar ungu. Hasil penelitian pada umbi diperoleh: kadar air 78,00% basis basah (bb), kadar abu 9,70% basis kering (bk), kadar lemak 5,47% (bk), kadar protein 26,93% (bk), kadar karbohidrat 58,41% (bk), kadar antosianin 31,79 mg/100 g (bk), kadar β-karoten 1,77 mg/100 g (bk), dan aktivitas antioksidan 65,70%. Hasil penelitian pada tepung ubi diperoleh: kadar air 6,71% (bb), kadar abu 2,40% (bk), kadar lemak 1,06% (bk), kadar protein 3,80% (bk), kadar karbohidrat 92,75% (bk), kadar antosianin 3,47 mg/100 g (bk), kadar β-karoten 0,15 mg/100 g (bk), dan aktivitas antioksidan 45,59%. Hasil penelitian pada beras analog ubi diperoleh: kadar air 8,43% (bb), kadar abu 1,78% (bk), kadar lemak 1,62% (bk), kadar protein 4,13% (bk), kadar karbohidrat 92,50% (bk), kadar antosianin 0,71 mg/100 g (bk), kadar β-karoten 0,11 mg/100 g (bk), dan aktivitas antioksidan 8,38%. Analisis statistik menunjukkan bahwa proses pengolahan umbi menjadi tepung serta tepung menjadi beras analog menyebabkan perbedaan yang nyata pada parameter yang diamati., Purple sweet potato can be developed into functional food products like analog rice. This study aims to evaluate the functional chemical components and antioxidant activity during the processing of purple sweet potato into flour and purple sweet potato analog rice. The results of research on sweet potato obtained: water content 78,00% wet basis (wb), ash content 9,70% dry basis (db), fat content 5,47% (db), protein content 26,93% (db), carbohydrate content 58,41% (db), anthocyanin content 31,79 mg/100 g (db), β-carotene content 17,73 mg/100 g (db), and antioxidant activity 65,70%. The results of research on sweet potato flour obtained: water content 6,71% (wb), ash content 2,40% (db), fat content 1,06% (db), protein content 3,80% (db), carbohydrate content 92,75% (db), anthocyanin content 3,47 mg/100 g (db), β-carotene levels 1,51 mg/100 g (db), and antioxidant activity 45,59%. The results of the research on sweet potato analog rice obtained: water content 8,43% (wb), ash content 1,78% (db), fat content 1,62% (db), protein content 4,13% (db), carbohydrate content 92,50% (db), anthocyanin content 0,71 mg/100 g (db), β-carotene content 1,05 mg/100 g (db), and antioxidant activity 8,38%. Statistic analysis shows that the processing of purple sweet potato into flour and flour into analog rice causes a significant difference in the observed parameters.
Keyword: antioxidant, anthocyanin, beta carotene, carbohydrate, food processing

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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