Judul: Screening of Significant Medium Components for Biosurfactant Production by Potential Bacteria of DSW17 using Plackett- Burman Experimental Design and Its Application as Food Preservative Agent
Abstrak: Biosurfactant or microbial surfactants produced by variety of microbes are capable of reducing surface and interfacial tension and have a wide range of industrial and environmental applications. Potential biosurfactant-producing microbe was successfully isolated from the Laboratory of Bioenergy and Bioprocess, Research Center for Biotechnology, LIPI. Based on the analysis of 16S rRNA sequence and phylogenetic tree, microorganisms DSW17 was 97% identical to Bacillus altitudinis TAZ1-5 HQ236061. In the present research, statistical screening of media components for biosurfactant production by microorganism DSW17 was carried out using Plackett-Burman experimental design. Nine out of eleven factors of the production medium were found to be significantly affecting the production process of biosurfactant. FeSO4.7H2O, NaNO3, waste vegetable oil, CaCl2.2H2O, K2HPO4 and sucrose were directly proportional to the biosurfactant production while ZnSO4.7H2O, KH2PO4 and MgSO4.7H2 showed inversely proportional correlation with the biosurfactant production in the selected experimental range. Several modified mediums were formulated based on the statistical Plackett-Burman screening result in order to validate the optimum media composition in producing biosurfactant. Modified medium combination 1 (MM1) as an optimized medium (2.13 g/L) showed 124% increase in biosurfactant production over the unoptimized medium or MM6 (0.95 g/L). From the validation result obtained, it was known that the optimized medium was proven to show better performance in the biosurfactant production, while it was also economically applicable compared to the other modification media. The biosurfactant produced by Bacillus sp. DSW17 in optimized medium showed antimicrobial activity against spoilage microorganisms. Based on the antimicrobial properties of the biosurfactant, it was then applied as a preservative agent in foods (tofu, beef and chicken meat) and also beverages (strawberry and tomato juice). Biosurfactant from Bacillus sp. DSW17showed the ability to extend the shelf life of tofu, strawberry juice and tomato juice for 4 hours, 2 hours and 1 hour, respectively. While in beef and chicken meat, biosurfactant were not able to extend its shelf-life.
Keyword: biosurfactant, biosurfactant production, statistical optimization, Plackett-Burman, preservative agent

Judul: Biosurfactant Production of Bacillus subtilis from Tofu Liquid Waste
Abstrak: Biosurfaktan merupakan substansi permukaan aktif yang diproduksi oleh mikroorganisme dan telah diterapkan dalam metode microbial enhanced oil recovery. Biosurfaktan kurang ekonomis jika diproduksi dalam skala besar karena biaya produksi yang tinggi. Alternatif yang digunakan untuk menekan biaya produksi dalam penelitian ini digunakan limbah organik sebagai media tumbuh, yaitu tahu cair. Tujuan penelitian ini adalah memperoleh biosurfaktan yang diproduksi Bacillus subtilis ATCC 19659 menggunakan media limbah tahu cair serta mendapatkan kondisi optimum produksi meliputi tingkat salinitas dan pH media. Adanya biosurfaktan dibuktikan dengan uji emulsifikasi. Hasil penelitian menunjukkan bahwa densitas sel bakteri di limbah tahu cair (0.1622‒1.0594) lebih rendah dibandingkan di nutrient broth (0.0401‒3.0600). Produksi biosurfaktan optimum di media limbah tahu cair didapatkan pada jam ke-96. Waktu optimum tersebut lebih lama dibandingkan produksi di media nutrient broth, yaitu 72 jam. Indeks emulsifikasi di media limbah tahu cair juga lebih rendah (40.0 %) dibandingkan pada media kaldu nutrien (48.3 %). Indeks emulsifikasi produksi biosurfaktan tertinggi diperoleh pada tingkat salinitas media 1 % (w/v) dan rentang pH 6 ‒ 8.
Keyword: Bogor Agricultural University, Institut Pertanian Bogor, IPB, biosurfactant, Bacillus subtilis, tofu liquid waste, emulsification index, Indeks emulsifikasi, Pertumbuhan bacillus subtilis, Bakteri penghasil biosurfaktan

Judul: Cycle Hamilton pada Graf Lengkap, Graf Regular, dan Graf 2-Connected 4-Regular Berorder Kurang dari Sepuluh.
Abstrak: Suatu graf disebut graf Hamilton apabila graf tersebut memuat cycle Hamilton, yaitu cycle yang melewati setiap vertex tepat satu kali. Menentukan keberadaan cycle Hamilton pada suatu graf dapat menggunakan syarat cukup yang berupa teorema-teorema yang telah diperkenalkan sejak tahun 1950-an. Beberapa syarat cukup yang dibahas dalam karya ilmiah ini adalah syarat cukup yang berhubungan dengan graf lengkap dan graf regular. ,,,
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular.