Judul: Pengaruh perendaman umbi singkong dalam larutan asam asetat terhadap karakteristik mutu keripik singkong
Abstrak: Processing modification of cassava tubers is expected to produce the cassava chips with specific quality characteristics. One form of the modification process is by using acetic acid as medium of soaking of cassava tubers. This study was aimed to know the effects of soaking of cassava tubers in acetic acid solution on quality characteristics of cassava chips. The treatments of this research were soaking cassava tubers in acetic acid solution with concentrations of 0.5; 1.0; 2.0 and 3.0 for 2 hours; 4 hours; and 6 hours. Soaking of cassava tubers in acetic acid solution for 2 hours and 4 hours resulted cassava chips with the lowest brittleness and hardness. Then, soaking treatments of cassava tubers in acetic acid solution with concentrations of 0.5 and 1.0 for 0.5 hour; 1 hour; 1.5 hours; and 2 hours showed that cassava chips with soaking treatment in acetic acid solution for 0.5 hour and 1.5 hours resultedthe lowest brittleness. Organoleptic test showed that cassava chips with soaking treatment in acetic acid solution with concentration of 1.0 for 1.5 hours had the greatest sensory value and be the best cassava chips. The soaking treatment in acetic acid solution acid has produced cassava chips with specific quality characteristics, such as brighter on colors, reduced bitter taste, flavor was preferred, and the texture wasn’t harder. The best cassava chipswas stored for 4 weeks in polypropylene plastic packaging at room temperature. The brightness ofboth of cassava chips with soaking treatment inacetic acid solution with concentration of 1.0 for 1.5 hours (the sample) and cassava chips without acetic acid soaking treatment (control) increased during storage. The increased of brightness was also followed by a decreased in the value of a and b. The rate of increase in the value of brittleness and hardness in the sample were greater than that of control. The sensory value for sample and control decreased, and it showed the decreased of quality characteristics of cassava chips during storage. Up to second week of storage, the peroxide value of sample was greater than that of control. The peroxide value of sample increased at greater rate than that of control during storage.
Keyword: Bogor Agricultural University (IPB), peroxide value., chips, cassava, acetic acid

Judul: Pengaruh Metode Pengeringan terhadap Mutu dan Sifat Fisiko-kimia Tepung Kasava Terfermentasi
Abstrak: Cassava is one important food crops in Indonesia. Carbohydrate is major components in cassava tubers, and made it suitable used for food and energy sources. Nowadays cassava is mainly utilized as direct food, cassava flour and cassava starch (tapioca). But high moisture and prussic acid (HCN) contents in cassava tuber made limitation for human consumption. Fermentation and drying of cassava plays important roles in cassava flour production, since they can influence to the flour characteristics. This research investigated the effect of drying methods of fermented cassava slurry to the flour’s chemical composition and its physico-chemical properties. Fermentation of cassava tuber was conducted using standard operation procedure for MOCAF (modified cassava flour) prepared by Dr. Achmad Subagio (Jember University). There were three drying methods used in research; direct sundrying (16 hours), green house effect drying (hours), and oven drying (12 hours). It is also investigated the duration of drying process; especially for sundrying and green house effect drying, as 3, 5, and 7 hours and then furthered with oven drying for 9, 7 and 5 hours. Solar energy, especially ultra violet irradiation has been proven improved the flour quality. Drying on the green house effect chamber (40,1oC) provided higher average drying temperature compared to direct sundrying (33,5oC), but lower than oven drying (52,6oC). Differences in drying methods gave significant effects on moisture, ash, crude fiber, fat, protein, starch and HCN contents; whiteness degree of flours, total of microbes, microscopic appearance of starch granules, water and oil absorptions, solubility and swelling power at 90oC, and visco-amylography characteristics. All drying methods significantly reduced the HCN contents of flours, but direct sundrying and green house effect drying accelerate the liberation of starch, and caused high final viscosity of flours. Full green house effect drying (16 hours) was recommended for fermented cassava flour since it produced the flour with higher maximum and final viscosity compared to others.
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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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