Judul: Potensi Antimikroba Kayu Siwak (Salvadora persica Wall.) terhadap Staphylococcus aureus dan Pseudomonas aeruginosa serta Aplikasi pada Bakso Daging
Abstrak: Preservation of processed meat products have been carried out with the aim of extending the shelf life. Preserving is one important factor considering the risks that may be posed and one of them is the use of hazardous chemicals as preservatives. One of food product which is vulnerable given the addition of formalin was the meatball. Siwak has been known to have antimicrobial activity but its application for foods has not been widely explored. The study consist of four phases, extraction of siwak well diffusion test, dillution broth to determine MIC, and applications in meatballs. Well diffusion test showed that siwak’s extract has antimicrobial activities against Staphylococcus aureus bacteria and Pseudomonas aeruginosa bacteria which have inhibition zones of 21.10 mm and 20.11 mm respectively. Dillution broth test showed that the minimum concentration which is can inhibit bacterial growth was 50% (v/v) of siwak’s aqueous extract. Application in meatballs showed that siwak extract can hold down bacterial growth up to 98,17% in Staphylococcus aureus bactery.
Keyword: natural preservative., antimicrobial activity, siwak, preservation

Judul: Aplikasi Substrat Antimikroba dari Bakteri Asam Laktat sebagai Biopreservatif pada Bakso Daging dengan Penyimpanan Dingin
Abstrak: Meetball (bakso) is a popular meat product in Indonesia. As other meat products, beef bakso has short shelf life at ambient temperature. The objective of this research were observed the effect of antimicrobial substrat as natural preservative on beef bakso at low temperature., which was isolated from Lactobacillus fermentum 2B4. The complete randomize design two factors was used to analyzed the effect of antimicrobial substrat to physical quality of beef bakso. Beef bakso with antimicrobial substrat 50% at 2 and 4 days preservation showed strong activity in inhibit growth of E. coli populations (P<0.05) Key word: beef, meat ball, substrat antimicrobials, microbiologic quality
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Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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