Judul: Kualitas mikrobiologi keju: keberadaan staphylococcus aureus pada tahap pembuatan keju gouda
Abstrak: Milk and its derivative products could potentially transmit pathogenic microorganisms from animals to human. Staphylococcus aureus is one of the microorganisms that commonly presents in milk and dairy products. This bacteria is often associated with foodborne disease outbreaks due to the ability of some strains to produce thermostable enterotoxins. The aim of this study was to analyze the presence of S. aureus during the Gouda cheese manufacturing process. Samples were obtained from every stages of Gouda cheese production. Staphylococcus aureus analysis was performed using pour plate method in Vogel Johnson agar. The number of S. aureus in raw milk was 2.4 x 103 CFU/ml (exceeding the maximum level for contaminant specified by BSN in SNI No. 3141.1-2011). The number of this bacteria increased in the following stages. The highest level was reached in young Gouda cheese (3.6 x 106 CFU/g). This level significantly increased from ripened cheese to become young Gouda cheese and remained stable during the ripening process. The high level of S. aureus in Gouda cheese (exceeding the maximum level for contaminant specified by BSN in SNI No. 7388-2009) indicates it could be potentially cause foodborne disease.
Keyword: foodborne disease, Gouda cheese, milk, Staphylococcus aureus

Judul: Kualitas Mikrobiologik pada Keju Gouda
Abstrak: The aim of this study was to observe the total number of microorganism and coliforms in Gouda cheese. Samples were taken every week for three consecutive weeks. As many as 10 samples of each Gouda cheese (Gouda young, middle, and old) were examinated using plate count method (pour plate method). The data was analyzed with t-student and Duncan test to compare the total number of microorganism and coliforms. The result showed that Gouda old cheese has the highest average number of total microorganism (1.4x108 cfu/gram). There was not any significant difference in the total number of microorganism between Gouda young cheese and Gouda middle cheese. The significant (p<0.05) difference in the total number of microorganism was showed with Gouda young cheese and Gouda old cheese; Gouda middle cheese and Gouda old cheese. The highest average number of coliform was found in Gouda young cheese (4.3x105 cfu/gram). There was not any significant difference in the total number of coliforms among all the three types of Gouda cheese (p>0.05). The presence of coliforms in Gouda cheese indicated any contamination during the process and reduced the quality.
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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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