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: Kajian Listeria monocytogenes pada Keju Gouda
Abstrak: Listeria monocytogenes is a foodborne pathogen, which has been associated with several outbreaks of human listeriosis especially in high risk groups. L. monocytogenes could present in Gouda cheeses because it was influenced by various factors, including unsatisfactory pasteurization treatment, contamination after heat treatment, improper sanitizing procedures and ability of this bacteria to forming biofilms. In addition, this bacteria could survive during the process of cheese making and ripening. The purpose of this study were to examine the presence of L. monocytogenes in Gouda cheeses and to provide an overview of Gouda cheese safety of in regards with L. monocytogenes. The samples of this study consisted of 15 local Gouda cheese and 15 imported Gouda cheese which were sold in supermarkets. The samples were taken with considering production code and expired date. The method to detect presence of L. monocytogenes which referred to the Bacteriological Analytical Manual, US Food and Drug Administration and Bergey's Manual of Determinative Bacteriology. The first step was enrichment of samples in Listeria enrichment broth, then isolated in oxford agar and identification step using catalase test, 3% KOH test, Gram stain, carbohydrate fermentation test (mannitol, rhamnose, xylose), motility test and CAMP test. The results of this study showed that L. monocytogenes was not found in 15 samples of local Gouda cheese (0%) and 15 samples of imported Gouda cheese (0%). The absence of L. monocytogenes in local and imported Gouda cheeses was related to combination of preservative factors in Gouda cheese such as pasteurization of milk as raw material for making of Gouda cheese, decrease in pH was caused by the addition of lactic acid bacteria starter cultures, and decline in water activity during the ripening process of Gouda cheeses. The combination of these preservative factors could inhibit the growth of L. monocytogenes could even inactivate L. monocytogenes. In addition, there was not contamination of L. monocytogenes after the pasteurization and during processing of milk to become cheeses. Another factor that could affect the absence of L. monocytogenes in Gouda cheese samples was the number of L. monocytogenes in the samples below the detection limit of conventional method which used in this study. The study could be concluded that all of samples of Gouda cheese were not found the existence of L. monocytogenes and relatively safe from contamination of L. monocytogenes and fulfilled the standard that determined by national standard of Indonesia 7388:2009 about Maximum Limit of Microbial Contamination in Food.
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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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