Judul: Physical Characteristic and Organoleptik Test of Yogurt with Stevia rebaudiana (Bertoni) as a Natural Sweetener.
Abstrak: Yogurt merupakan produk olahan susu yang diperoleh dari fermentasi asam laktat melalui aktivitas Lactobacillus bulgaricus dan Streptococcus thermophilus. Pembuatan yogurt ini memanfaatkan penambahan Stevia rebaudiana sebagai subtitusi pemanis alami rendah kalori pada pembuatan produk pangan. Stevia dapat menurunkan kadar gula darah dan tidak menyebabkan metabolisme insulin sehingga baik untuk penderita diabetes, dan obesitas. Penelitian ini bertujuan menganalisis karakteristik fisik (nilai pH, nilai aw, viskositas dan total asam tertritasi) dan organoleptik (warna, flavor, kekentalan, dan aroma) yogurt yang diberi penambahan Stevia rebaudiana. Yogurt ini menggunakan penambahan pemanis 10% dengan kombinasi penambahan sukrosa dan stevia. Penelitian ini menggunakan rancangan acak lengkap (RAL) dengan dilakukan tiga kali pengulangan. Hasil penelitian menunjukkan bahwa penambahan stevia tidak berpengaruh (P>0,05) terhadap karakteristik fisik yogurt. Data Sifat Organoleptik menunjukkan hasil penambahan stevia berpengaruh nyata (P<0,05) terhadap parameter rasa dan aroma pada uji hedonik, namun pada uji mutu hedonik menunjukkan adanya pengaruh nyata (P<0,05) penambahan stevia terhadap parameter rasa., Yogurt is a dairy product obtained from lactic acid fermentation through the activity of Lactobacillus bulgaricus and Streptococcus thermophilus. Making this yogurt utilizes the addition of Stevia rebaudiana as a low calorie natural sweetener substitute in the manufacture of food products. Stevia can lower blood sugar levels and does not cause insulin metabolism so it is good for people with diabetes, and obesity. This study aims to analyze the physical characteristics (pH, activity water, viscosity and total acid concentration) and organoleptic (color, flavor, viscosity, and aroma) yogurt with the addition of Stevia rebaudiana. This yogurt uses the addition of 10% sweetener with a combination of the addition of sucrose and stevia. This study used a completely randomized design (RAL) with three repetitions. The results showed that the addition of stevia had no effect (P>0.05) on the physical characteristics of yogurt. The organoleptic test data showed that the addition of stevia had a significant effect (P<0.05) on the taste and aroma parameters in the hedonic test, but the hedonic quality test showed a significant effect (P<0.05) on the addition of stevia to the taste parameters.
Keyword: pemanis alami, stevia rebaudiana, susu, yogurt

Judul: Physical Characteristic and Organoleptic Test of Yogurt with Monk Fruit Sugar (Siraitia grosvenorii) as a Natural Sweetener
Abstrak: Yogurt merupakan produk olahan susu yang diperoleh dari fermentasi asamlaktat melalui aktivitas bakteri Lactobacillus bulgaricus dan Streptococcus thermophilus. Pembuatan yogurt ini memanfaatkan penambahan gula buah monk (Siraitia grosvenorii) sebagai pemanis alami rendah kalori pada pembuatan produk pangan. Gula buah monk dapat menjaga kadar gula darah dan tidak menyebabkan metabolisme insulin sehingga baik untuk penderita diabetes dan obesitas. Penelitian ini bertujuan menganalisis karakteristik fisik (nilai pH, nilai aw, viskositas dan total asam tertitrasi) dan organoleptik (warna, aroma, rasa, kekentalan, dan after taste) yogurt yang diberi penambahan gula buah monk (Siraitia grosvenorii). Yogurt ini menggunakan kombinasi penambahan sukrosa dan gula buah monk. Penelitian ini menggunakan rancangan acak lengkap (RAL) dengan tiga kali ulangan. Hasil penelitian menunjukan bahwa penambahan gula buah monk tidak berpengaruh nyata (P>0,05) terhadap karakteristik fisik yogurt dan uji hedonik pada sifat organoleptik yogurt. Data sifat organoleptik uji mutu hedonik menunjukan hasil penambahan gula buah monk berpengaruh nyata (P<0,05) terhadap parameter aroma yogurt yang dihasilkan. Yogurt dengan penambahan 10 gram sukrosa : 40 gram gula buah monk terbaik, lebih disukai panelis dan layak untuk dikonsumsi., Yogurt is a dairy product obtained from lactic acid fermentation through the activity of Lactobacillus bulgaricus and Streptococcus thermophilus. Making this yogurt utilizes the addition of monk fruit as a low-calorie natural sweetener substitute in the manufacture of food products. Monk fruit able to reduce blood sugar levels and doesnot cause insulin metabolism so it is good for people with diabetes and obesity. This study aims to analyze the physical characteristics (pH, water activity, viscosity, and total acid concentration) and organoleptic (color, aroma, flavor, viscosity, and after taste) yogurt with the addition of monk fruit (Siraitia grosvenorii) sugar. This yogurt uses a combination of the addition sucrose and monk fruit. This study used a completely randomized design (RAL) with three repetitions. The results showed that the additional monk fruit sugar had no effect (P>0,05) on the physical characteristics and on the hedonic test of organoleptic. The hedonic quality test of organoleptic data showed that adding monk fruit sugar had a significant effect (P<0,05) on the aroma parameters of the yogurt produced. Yogurt with addition of 10 gram sucrose : 40 gram monk fruit sugar gave the best result, preferred by panelists and accepted for consumptions.
Keyword: milk, monk fruit, natural sweetener, Siraitia grosvenorii, yogurt

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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