Judul: Pengaruh Waktu Penyimpanan Ekstrak Rennet Abomasum Domba Lokal terhadap Kualitas Keju
Abstrak: The study was aimed to examine the storage effect of rennet extracted from abomasum of local sheep on the texture and organoleptic qualities of cheese including color, flavor, salty taste, and bitter taste. Each five samples of crude rennet extract was stored for 2 weeks and 24 weeks respectively. The rennet extract was then used as milk clotting agent in cheese making process. Streptococcus thermophilus and Lactobacillus bulgaricus were used as starter in those process. The fresh cheese was coated with beeswax and ripened for 20 days in refrigerator. The ripened cheese was analyzed for the quality. The texture was analyzed by using warner blatzer shear (INSTRON®) and the data were evaluated with completely randomized design (CRD). The result showed that both time storage of rennet extract were not significantly influence on cheese texture (P<0.05). The organoleptic tests of color, flavor, salty taste, and bitter taste were rated by 25 panelists and then the data were analyzed with Friedman test. The time storage of rennet extract resulted variation on organoleptic quality of cheese. Descriptive statistical analyses provided information that each panelist has varied preferences on cheese samples. It can be concluded that the storage of rennet extract had no significantly influence on the texture of cheese and provided variation on organoleptic test.
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Judul: Pengaruh netralisasi pH terhadap kualitas Rennet yang diisolasi dari abomasum domba lokal
Abstrak: Penelitian ini bertujuan untuk mengetahui pengaruh netralisasi pH terhadap kualitas rennet dari ekstrak mukosa daerah fundus abomasum domba lokal usia dewasa muda (5-12 bulan). Kualitas rennet diuji dengan uji koagulasi susu dan analisis proteinnya menggunakan SDS-PAGE. Sebanyak empat sampel mukosa fundus abomasum domba lokal diekstraksi dengan metode Qadri et al. (1962) dan diberi perlakuan netralisasi mengunakan NaOH 1N sampai pH 5.4 serta tidak dinetralisasi. Parameter yang diamati adalah bentuk koagulan (curd), waktu koagulasi susu, dan gambaran pita protein. Data kuantitatif diuji dengan uji T Berpasangan (paired t-test), sedangkan data nonkuantitatif dianalisis secara deskriptif. Hasil uji koagulasi susu menunjukkan rennet yang dinetralisasi memberikan koagulan yang lebih padat dan kompak dibandingkan dengan rennet yang tidak dinetralisasi. Waktu koagulasi dari kedua perlakuan tersebut menunjukkan perbedaan yang nyata (p < 0.05). Gambaran pita protein menunjukkan bahwa sampel yang dinetralisasi memiliki pita yang tebal dan intensitas warna yang lebih gelap, sementara sampel yang tidak dinetralisasi menunjukkan pita yang lebih tipis dan intensitas warna lebih terang. Dari hasil penelitian ini dapat disimpulkan bahwa netralisasi pH sangat berpengaruh terhadap kualitas rennet.
Keyword: Neutralization, Rennet, Abomasum, SDS-PAGE

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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