Judul: Antioxidant Capacity of Yogurt with Parijoto Fruit Juice (Medinilla speciosa Blume.)
Abstrak: Stres oksidatif merupakan kondisi tingginya radikal bebas yang dapat dicegah melalui diet kaya antioksidan. Parijoto (Medinilla speciosa Blume.) adalah buah kaya antioksidan yang masih terbatas pemanfaatannya. Penelitian ini bertujuan membuat produk yogurt dengan tambahan sari buah parijoto yang disebut “Yorito” serta mengkaji potensi antioksidan dan nilai gizinya. Formulasi berupa variasi proporsi susu dan sari buah parijoto yaitu F0(100:0), F1(90:10), F2(80:20), F3(70:30). Analisis yang dilakukan adalah uji karakteristik fisik, uji organoleptik, kandungan gizi, kapasitas antioksidan, dan kadar antosianin yogurt. Kapasitas antioksidan ekstrak metanol buah parijoto dikategorikan sebagai antioksidan kuat dengan IC50 sebesar 68,26 μg/ml dan Ascorbic acid Equivalent Antioxidant Capacity (AEAC) 38.135 mg vitamin C/100 g. Kadar antosianin tanpa pemisahan 16,62 mg/L dan dengan pemisahan dietil eter 16,78 mg/L. Penambahan sari buah parijoto menurunkan viskositas yogurt (p<0,05) dan tidak memengaruhi pH yogurt. Kandungan gizi formula terpilih (F2) yaitu, kadar air 81,37%, abu 0,82%, lemak 2,86%, protein 3,34%, dan karbohidrat 11,65%. Kapasitas antioksidan “Yorito” dinyatakan dalam IC50 yang nilainya sebesar 120,52 mg/ml, atau setara 21,60 mg vitamin C/100 g. “Yorito” mengandung antosianin sebanyak 0,42 mg/L dan dapat dikategorikan sebagai pangan kaya antioksidan., Oxidative stress is a condition of high free radicals that can be prevented with an antioxidant-rich diet. Parijoto (Medinilla speciosa Blume.), is a finite antioxidant-rich fruit. This study aimed to make yogurt products with the addition of parijoto fruit juice called “Yorito”, examine its antioxidant potential and nutritional content. The formulations were variations of milk and parijoto fruit juice, namely F0(100:0), F1(90:10), F2(80:20), and F3(70:30). The analysis carried out were the physical characteristics, organoleptic tests, nutritional content, antioxidant capacity, and anthocyanin levels of the yogurt. The antioxidant capacity of parijoto fruit methanol extract were categorized as strong antioxidant with IC50 68.26 μg/ml and Ascorbic acid Equivalent Antioxidant Capacity (AEAC) 38.135 mg of vitamin C/100 g. Anthocyanin levels without separations were 16.62 mg/L, and with-diethyl ether separations were 16.78 mg/L. The addition of parijoto fruit juice lowered viscosity (p<0.05) and did not affect yogurt pH. The nutritional content of the selected formula (F2) was moisture 81.37%, ash 0.82%, fat 2.86%, protein 3.34%, and carbohydrates 11.65%. The “Yorito” antioxidant capacity was expressed in IC50, which is 120.52 mg/ml, equivalent to 21.60 mg of vitamin C/100 g. “Yorito” contains anthocyanins as much as 0.42 mg/L and can be categorized as an antioxidant-rich food.
Keyword: anthocyanin, antioxidant capacity, parijoto, yogurt

Judul: Antioxidant Activity, Characterization,  and Organoleptic Test of Goat's Milk Yogurt with Addition of Purslane Extract
Abstrak: Yogurt susu kambing merupakan salah satu produk pangan fungsional yang memiliki potensi sebagai sumber antioksidan yang diperlukan oleh tubuh. Pada penelitian ini yogurt susu kambing dimaksimalkan potensinya dengan penambahan ekstrak krokot (Portulaca oleracea) yang berasal dari Banyumas, Jawa Tengah. Penelitian ini bertujuan menentukan formula yogurt susu kambing dan ekstrak krokot yang optimum berdasarkan nilai aktivitas antioksidan tertinggi serta karakteristik yang sesuai dengan SNI. Metode penelitian meliputi ekstraksi, formulasi yogurt, karakterisasi fisik dan kimia, uji organoleptik, dan uji proksimat. Perlakuan terdiri atas F1 (susu kambing tanpa ekstrak krokot), F2 (susu kambing + 2.5% ekstrak krokot), F3 (susu kambing + 5% ekstrak krokot), F4 (susu kambing + 7.5% ekstrak krokot), dan F5 (susu kambing + 10% ekstrak krokot). Hasil penelitian menunjukkan bahwa yogurt formula F2 sebagai yogurt yang paling optimum dengan karakteristik fisik, organoleptik, dan proksimat yang sesuai dengan SNI serta aktivitas antioksidan yang tinggi. Simpulan penelitian ini yaitu F2 merupakan yogurt hasil formulasi dengan karakteristik terbaik., Goat milk yogurt is one of the functional food product that have the potential as a source of antioxidants needed by the body. In this study, the potency of goat's milk yogurt was maximized by the addition of purslane extract (Portulaca oleracea) from Banyumas, Central Java. The aim of this study was to determine the optimum formula for goat's milk yogurt and purslane extract based on the highest antioxidant activity value and characteristics according to SNI. The research steps consisted of extraction, yogurt formulation, physical and chemical characterization, organoleptic test, and proximate test. The treatments consisted of F1 (goat's milk without purslane extract), F2 (goat's milk + 2.5% purslane extract), F3 (goat's milk + 5% purslane extract), F4 (goat's milk + 7.5% purslane extract), and F5 (goat's milk + 10% purslane extract). The results showed that the yogurt formula F2 was the most optimum yogurt with physical, organoleptic, and proximate characteristics in accordance to SNI and the high antioxidant activity. It was concluded that F2 was yogurt with the best characteristics.
Keyword: Antioxidant, DPPH, Formulation, Goat's Milk Yogurt, Portulaca  oleracea

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.
Keyword: