Judul: Analysis of Dominant Bacteria  Various Fermented Milk Products Using 16S rRNA Sequencing
Abstrak: Yogurt, Yakult, dan kefir merupakan produk fermentasi berbahan dasar susu, diproduksi melalui proses fermentasi oleh berbagai jenis bakteri asam laktat. Namun, selama proses fermentasi dominasi bakteri dalam produk dapat berubah. Kemungkinan bakteri pembusuk lain dapat mendominasi produk, kemungkinan ini bergantung pada berbagai faktor proses pasca produksi. Penelitian ini bertujuan untuk mengetahui bakteri dominan pada berbagai produk susu fermentasi menggunakan sekuensing 16S rRNA. Total DNA genomik langsung diekstraksi dari produk dan digunakan sebagai template untuk amplifikasi gen 16S rRNA menggunakan primer 9F dan 1541R. Amplikon diurutkan dan dianalisis menggunakan server BLAST. Sebagai data pendukung, nilai pH masing-masing produk juga diukur. Hasil menunjukan bahwa nilai pH produk ditemukan berbeda nyata (P<0,05). Analisis sekuens 16S rRNA yogurt adalah Streptococcus thermophilus strain ATCC 19258 dan pada kefir adalah Lactococcus cremoris strain NCDO 607 dan L. cremoris strain NBRC 100676. Sementara, amplikon 16S rRNA dari produk yogurt B tidak dapat diurutkan karena kualitasnya yang rendah., Yoghurt, Yakult, and kefir are milk-based fermented products, produced through fermentation process by different types of lactic acid bacterial. Nevertheless, during fermentation process, domination of bacteria in product might changed. The possibility of other spoilage bacteria can dominate the products, this possibility depend on various factors of post-production process. This study was aimed to investigate the dominant bacteria in different fermented milk products using 16S rRNA sequencing. The total genomic DNA directly extracted from products and used as a template for 16S rRNA gene amplification using 9F and 1541R primers. The amplicon was sequenced and analyzed using BLAST server. To supporting data, pH value of each product also be measured. The results showed that pH values of products were found significanly different (P<0.05). Sequence analysis 16S rRNA revaled that yoghurt is dominated by Streptococcus thermophilus strain ATCC 19258 and for kefir is Lactococcus cremoris strain NCDO 607 and L. cremoris strain NBRC 100676. Meanwhile, 16S rRNA amplicon from yoghurt B product was unable to be sequence due to low quality.
Keyword: 16S rRNA, Dominant bacteria, Susu fermentasi, Sekuensing

Judul: Validasi dan verifikasi metode analisis bakteri asam laktat pada produk susu
Abstrak: Lactic acid bacteria (LAB) is a group of bacteria that capable converting carbohydrates (glucose) into lactic acid and mostly grow at facultatif anaerobic condition. At present, the most widely method used to enumerate LAB in some laboratory in Indonesia is incubation in aerob condition. In order to ensure that the method has a good performance, there is a need of method validation. Validation is the confirmation by examination and provision of objective evidence that particular requirements for specified intended use are fulfilled. The purpose of this study is to validate the quantitative method for enumeration of lactic acid bacteria. Two methods of enumeration of LAB in yoghurt were studied, i.e. ISO 7889-2003(E) as a reference method and SNI 2981-2009 as an alternative method. The principle of this method is to grow the facultative anaerobic bacteria in aerobic and anaerobic condition incubated for 3 days at 37 oC on MRSA media. The anaerobic condition was made using Anaxomat jar whose enrich with 10% CO2. The result obtained by these two method were compared. Therefore several parameters such as precision (RSD), relative accuracy, linearity, limit of detection, and limit of quantification were evaluated. The results showed that RSD of these methods between 0.44% and 3.03%, percent recovery of these methods between 97% and 101%, and limit of detection are 3 cfu/mL. It can be concluded that these two methods have good performance characteristics.
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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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