Judul: Physical, Chemical Characteristics and Organoleptic Test of Gelato Yogurt with Addition of Plum Juice (Prunus salicina) as a Natural Flavour
Abstrak: Yogurt merupakan salah satu bentuk produk susu yang memanfaatkan mikroba dalam proses fermentasi susu segar menjadi produk dengan rasa asam. Pembuatan gelato bisa bervariasi dengan menambahkan berbagai jenis buah, salah satunya plum. Rasa buah plum yang manis dan asam dapat dijadikan sumber bahan penambah rasa alami yang rendah kalori dan aman dikonsumsi, Tujuan penelitian ini adalah untuk menganalisis pengaruh karakteristik fisik, kimia dan sifat organoleptik panelis terhadap yogurt gelato dengan penambahan sari buah plum (Prunus salicina) sebagai perisa alami. Penelitian ini menggunakan rancangan acak lengkap (RAL) dengan penambahan sari buah plum (Prunus salicina) yang berbeda yaitu 0%, 5%, dan 10%. Hasil penelitian menunjukkan bahwa penambahan sari buah plum pada gelato yogurt berpengaruh nyata (P<0,05) terhadap nilai viskositas, daya leleh, dan overrun tetapi tidak berpengaruh nyata (P>0,05) terhadap nilai pH, kadar lemak, dan kadar protein. Data sifat organoleptik uji hedonik menunjukan hasil penambahan sari buah plum berpengaruh nyata (P<0,05) terhadap parameter rasa gelato yogurt yang dihasilkan. Data sifat organoleptik uji mutu hedonik menunjukan hasil penambahan sari buah plum tidak berpengaruh nyata (P>0,05) terhadap parameter tekstur gelato yogurt yang dihasilkan., Yogurt is a form of dairy product that utilizes microbes in the fermentation process of fresh milk into a product with a sour taste. Making gelato can be varied by adding various types of fruit, one of which is plum. The sweet and sour taste of plums can be used as a source of natural flavor enhancers that are low in calories and safe for consumption. The purpose of this study was to analyze the effect of the physical, chemical and organoleptic characteristics of the panelists on yogurt gelato with the addition of plum juice (Prunus salicina) as a natural flavoring. This study used a completely randomized design (RAL) with different percentages of plum juice (Prunus salicina) addition namely 0%, 5%, and 10%. The results showed that the addition of plum juice to yogurt gelato had a significant (P<0,05) effect on the viscosity, melting time, and overrun but had no significant effect (P>0,05) on the pH, fat and protein contents. Data on the organoleptic properties of the hedonic test showed the results of plum juice addition had a significant effect (P<0,05) on the taste parameters of the resulting yogurt gelato. Data on the organoleptic properties of the hedonic quality test showed that the results of the plum juice addition had no significant effect (P>0,05) on the texture parameters of the yogurt gelato.
Keyword: plums, gelato, natural flavors, 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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