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: Analysis of Dominant Bacteria in Cow's Milk During Storage at Refrigerator Temperature Using 16S rRNA Sequencing
Abstrak: Susu sapi selain sebagai sumber nutrisi yang baik untuk dikonsumsi, juga merupakan media yang sesuai untuk pertumbuhan bakteri. Kajian mengenai profil bakteri di dalam susu erat kaitannya dengan kualitas mikrobiologi susu sapi, tetapi terbatas pada profil bakteri yang bisa dikulturkan (cultivable) saja. Pendekatan molekuler identifikasi menggunakan 16S rRNA saat ini memungkinkan untuk mengidentifikasi bakteri pada susu tanpa proses kultivasi. Penelitian ini bertujuan untuk menganalisis dominan bakteri yang ada pada susu sapi selama penyimpanan pada suhu refrigerator dengan menggunakan metode 16S rRNA sekuensing. Hasil penelitian menunjukkan bahwa pH sampel susu sapi berkisar antara 6,47–6,67. Konsentrasi dan kemurnian total DNA bakteri cenderung fluktuatif pada setiap sampel. Total DNA genomik kemudian diekstraksi dan digunakan sebagai template amplifikasi gen 16S rRNA menggunakan primer 9F dan 1541R. Hasil analisis sekuens 16S rRNA menunjukkan bahwa bakteri dominan sampel susu sapi S0 adalah Bifidobacterium sp., bakteri dominan sampel susu sapi S3 adalah Acinetobacter sp., dan bakteri dominan sampel susu sapi S7 adalah Enterococcus sp.., Apart from being a good source of nutrition for consumption, cow's milk is also a suitable medium for bacterial growth. The study of the bacterial profile in milk is closely related to the microbiological quality of cow's milk but is limited to the profile of cultivable bacteria only. Molecular identification approaches using 16S rRNA currently allow the identification of bacteria in milk without a cultivation process. This research aims to analyze the dominant bacteria in cow's milk during storage at refrigerator temperature using the 16S rRNA sequencing method. The research results showed that the pH of cow's milk samples ranged from 6,47–6,67. The concentration and purity of total bacterial DNA tend to fluctuate in each sample. Total genomic DNA was then extracted and used as a template for 16S rRNA gene amplification using primers 9F and 1541R. The results of 16S rRNA sequence analysis showed that the dominant bacteria in cow's milk sample S0 was Bifidobacterium sp., the dominant bacteria in cow's milk sample S3 was Acinetobacter sp., and the dominant bacteria in cow's milk sample S7 was Enterococcus sp..
Keyword: 16S rRNA, bacteria, cow's milk, sequencing

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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