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: Physicochemical Characteristics, Antioxidant Activity, and Organoleptical Quality of Greek Yogurt with Addition of Pomegranate Peels Extract
Abstrak: Yoghurt termasuk produk pangan fungsional yang sering dimodifikasi salah satunya dengan penambahan sumber komponen bioaktif alami seperti ekstrak kulit delima (Punica granatum L.). Penelitian bertujuan untuk menganalisis karakteristik fisikokimia, aktivitas antioksidan, dan mutu organoleptik greek yoghurt dengan penambahan ekstrak kulit delima pada taraf berbeda. Greek yoghurt diberi penambahan ekstrak kulit delima sebanyak 0% (kontrol), 0,5%, 1,5%, dan 2,5% dari berat greek yoghurt kontrol. Penelitian dilakukan menggunakan rancangan acak lengkap (RAL) dengan penambahan ekstrak kulit delima sebagai perlakuan. Hasil penelitian menunjukkan bahwa penambahan ekstrak kulit delima pada greek yoghurt berpengaruh nyata (p<0,05) terhadap penurunan pH dan peningkatan aktivitas serta kapasitas antioksidan. Penambahan ekstrak kulit delima meningkatkan kesukaan panelis terhadap atribut rasa namun berlaku sebaliknya pada atribut warna. Makin besar taraf ekstrak kulit delima mengakibatkan kenaikan intensitas warna, aroma, dan rasa ekstrak kulit delima. Sebagai kesimpulan, penambahan 1,5% ekstrak kulit delima dapat memperbaiki karakteristik fisikokimia dan meningkatkan aktivitas antioksidan dengan mutu organoleptik greek yoghurt yang lebih baik., Yogurt is a functional food that is often modified by adding bioactive component such as pomegranate peel extract (Punica granatum L.). This study was aimed to analyze physicochemical characteristics, antioxidant activity, and organoleptical quality of greek yogurt with the addition of pomegranate peels extract at different levels. Greek yogurt was added by pomegranate peels extract at levels of 0% (control), 0,5%, 1,5%, and 2,5% of greek yogurt control's weight. The study was conducted using a completely randomized design (CRD) with the addition of pomegranate peel extract as a treatment. The results showed that pomegranate peels extract added to greek yogurt had significant effects (p<0.05) on decreasing pH and increasing antioxidant activity and capacity. Pomegranate peels extract addiction increased the taste preference but decreased the color preference. Higher level of pomegranate peels extract caused higher intensity of color, aroma, and taste of pomegranate peels extract. In conclusion, the addition of 1,5% pomegranate peels extract improved physicochemical characteristics and increased antioxidant activity with better organoleptic quality of greek yogurt.
Keyword: Antioxidant, Organoleptic, Physicochemical, Pomegranate peels, Yogurt

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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