Judul: Pengaruh Penambahan Jenis Susu terhadap Karakteristik Yogurt Kacang Kedelai (Soygurt)
Abstrak: Soygurt is fermented soy milk products are made by using lactic acid bacteria, that are Streptococcus thermophilus and Lactobacillus bulgaricus. The aim of this research were to determine the effect of adding kind of milk on characteristics, physichochemical, and organoleptic of soygurt. This research were divided into three stages, which are 1) Soy milk production, 2) Soygurt production, and 3) physicochemical analysis and sensory evaluation. The obtained data were treated by analysis of variance followed by Duncan’s test. The results of this research indicate that addition of kind of milks as much as 2%, 4%, 6%, and 8% give significant effect on pH value, total lactic acid, viscosity, texture, aroma, taste, and acceptability (overall). However, the addition of kind of milk did not give significant effect on appearance of soygurt. Best formula of this research is soygurt with the addition of skim and full cream milk as much as 6%.
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Judul: Formulasi Sari Kedelai Fermentasi (Soygurt) dengan Penambahan Susu Skim dan Pengamatan Sifat Fisikokima Selama Penyimpanan
Abstrak: Soygurt is a fermented soybean product which be processed using Lactobacillus bulgaricus and Streptococcus thermophilus, which also be used in yoghurt processing. The objectives of this research are to determine the effect of skim milk addition to the consumer acceptance (using hedonic test), and physicochemical properties of the product (viscosity, pH value, total titrable acid), and the changing of physicochemical properties during storage. This research consisted of two stages. The first stage was determining the concentration of skim milk to the consumer acceptance and physicochemical properties analysis. The next stage was the production of soygurt using the chosen formula and analyze its physicochemical properties during 14 days of storage at 4-8 0C. The optimum concentration determined from this research with significance level 5% was 5% of skim milk (w/v) with the value of the viscosity 376.25 cP, pH 3.62, and total titrable acid 0.73% of lactic acid. During the storage there were changing of in viscosity value, pH, and total titrable acid, the viscosity increased from 235.00 to 485.00 cP, pH decreased from 3.64 to 3.43, and total titrable acid increased from 0.76 to 0.94% of lactic acid.
Keyword: storage, physicochemical, formula, fermentation, soygurt

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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