Judul: Penghambatan dan kebocoran membran sel Staphylococcus aureus oleh getah pepaya
Abstrak: Dangke merupakan produk curd susu tradisional atau biasa dikenal dengan tahu susu yang dibuat melalui proses koagulasi susu menggunakan getah pepaya. Produk ini biasanya disimpan pada suhu ruang hingga akan dikonsumsi dan mampu bertahan selama kurang lebih 24 jam. Getah pepaya pada pembuatan dangke diperkirakan tidak hanya berperan dalam proses kogulasi, melainkan juga memiliki peran sebagai antibakteri. Efek antibakteri getah pepaya terhadap S. aureus ditentukan dengan menggunakan metode kontak pada media cair dan dangke.
Keyword: cell membrane leakage, dangke, dried papaya latex

Judul: Inhibiton and Staphylococcus aureus Cell Membrane Leakage by Papaya Latex.
Abstrak: Dangke is a traditional milk curd product, made by coagulation of milk using fresh papaya latex. This product is usually kept at room temperature until consumption and it can lasting until 24 hours. Dried papaya latex in dangke production was considered not only as coagulant but also act as antibacterial agent. In this study, the antibacterial activity of dried papaya latex toward S. aureus was determined by direct contact in broth media and dangke. Fresh papaya latex was dried using vacuum oven at 50-55 for 22 hours. As much as 0.0277 g/100 mL in concentration of dried papaya latex could reduce approximately 1 log CFU/mL of S. aureus and 0.0011 g/100 mL of papain showed inhibition effect instead of reducing effect against S. aureus in broth after 24 hours. Dried papaya latex and papain also showed ability to inhibit S. aureus growth in dangke within 24 hours storage at room temperature. The antibacterial activity of non-proteolytic compound of papaya latex, i.e ethanolic extract of papaya latex was determined by macrodilution method, resulted in the MIC90 of 8 mg/mL. Antibacterial agent could inhibit bacterial growth by some mechanisms, one of them is cell membrane damage, protein synthesize and DNA synthesize disruption. Papaya latex which contains proteolytic enzyme as bioactive compound was considered can cause the cell membrane leakage. The antibacterial activity toward cell membrane caused the leakage of 260 nm absorbing material from cell. In this study, the cell membrane leakage after exposure was detected by measuring the optical density of bacterial supernatant at 260 nm. The result showed that exposure to increasing antibacterial concentration resulted in increasing of optical density of S. aureus supernatant, indicating that the antibacterial caused the S. aureus membrane leakage. Imaging by fluorescence microscopy showed that S. aureus exposure to antibacterial caused the membrane leakage thus gave Propidium Iodide (PI) chance to penetrate onto the cell, which indicated by the changing of fluorescence color from green fluorescence to red fluorescence.
Keyword: cell membrane leakage, dangke, dried papaya latex

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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