Judul: Karakteristik Mikrokapsul Lactobacillus plantarum dan : Stabilitas dalam Selai Salak Selama Penyimpanan
Abstrak: Modern consumers expect their food to be healthy and to prevent illness. Therefore the demand of functional food including probiotic products growing significantly. Functional foods containing probiotic bacteria generally are dominated by milk-based foods. Recently, the incorporation of probiotic bacteria in various food products especially fruit-based products have been studied. Probiotic strains in this research had been isolated from saurkraut (Lb. plantarum BSL) and beef (Lb.plantarum 2C12). Many reports indicated that there were poor survival of probiotic bacteria in food products containing free probiotic cells. Providing probiotic living cells with a physical barrier such as microencapsulation to resist adversed effect of environmental conditions is therefore an approach currently receiving considerable interest. The objectives of the study were 1) to evaluate the effect of Lb. plantarum microencapsulation by emulsion technique toward the resistancy to heat, injured cell, low pH (2.0) and bile salt (0.5%) and its antimicrobial activity. 2) to determine the most suitable temperature for incorporation probiotic into snake fruit jam. 3) to study the viability of free and encapsulated Lb. plantarum in snake fruit jam, total yeast mold, pH changes and water activity during room storage. The first stage of this study was microencapsulation of probiotics by emulsion method with sodium alginate as encapsulanting material. Characterization of the encapsulated probiotic were conducted including resistance to heat, injured cell, low pH and bile salt resistance, antimicrobial activity againts E. coli ATCC 25922, Salmonella typhii ATCC 14038, S. aureus ATCC 25923, S. cereviseae ATCC 9763 and Aspergillus niger. The second stage was incorporating the encapsulated probiotic into snake fruit jam. The most suitable temperature for incorporate based on the result of heat resistance.The last stage was evaluation of the probiotic viability in snake fruit jam during storage in room temperature for 4 weeks. The results showed that high survival number (11 log cfu g-1) of both Lb. plantarum strains were achieved after encapsulation. Heat resistance of the encapsulated strains at 50oC was better than their free cells, but the higher the temperature applied the lower the number of survivors would be. Heating at 70oC was more detrimental to all encapsulated probiotics with a decrease of more than 5 log cell numbers. Heating at 50o-70oC caused injury to all probiotics cells. Encapsulation probiotics also showed significantly higher survival (P<0.05) in bile salt (0.5%) and low pH (pH 2) treatments compared to their free cells. All encapsulated Lactobacillus strains could inhibit the growth of E. coli, Salmonella typhii and S. aureus as well as their free cells, but none of them could inhibit S. cereviseae and Aspergillus niger. Encapsulated probiotic bacteria in snake fruit jam showed good viability throughout the four weeks of storage, whereas the free probiotic lost their viability within two weeks. No changes of pH and water activity of the products were observed between free and encapsulated probiotic. The overall results suggested that microencapsulated probiotic prepared by emulsion method is suitable to be incorporated in snake fruit jam and provided good stability during 4 weeks of storage at room temperature.
Keyword: probiotics, Lb. plantarum, snake fruit jam, microencapsulation

Judul: Campuran Enkapsulan dan Pemanasan Sub-Letal Meningkatkan Kualitas Mikrokapsul Lactobacillus plantarum dalam Serbuk Jambu Biji Kering Semprot.
Abstrak: The demand for nondairy probiotic foods in the global market has increased recently. Innovation today is to develop probiotic foods such as fruit based probiotics. One problem pose is that the number of probiotics generally decreased during food processing and storage conditions and when consumed through the digestive tract. Microencapsulation technique by spray drying method has been reported can increase the survival of probiotic when exposed to these environment. Factors that influence the effectivity of this method are the type of microencapsulating material and sub-lethal temperature performed on the probiotic culture before spray drying. The objectives of this study were to select the suitable encapsulating material for microencapsulation of two probiotic strains L. plantarum (2C12 and BSL) in guava juice by spray drying and to obtain the optimum sublethal pre-heating temperature exposed to probiotic culture before spray drying. The temperatures of the spray dryer were set at 1200C (inlet) and 700C (outlet). Encapsulating materials used in this study were maltodextrin (MD) and mixture of MD-Arabic gum, MD-Inulin, and MD-GOS (galactoorigosaccaride). In separate experiment, optimization of the sublethal pre-heating temperature (500C, 52.50C, and 550C) were studied. The quality of microcapsules of both L. plantarum obtained was evaluated including probiotic survival after spray drying and resistance to heat (500C, 600C, and 700C), low pH (2.0), and bile salt (0.5%). The results showed that all encapsulating materials produced good quality microcapsules of both L. plantarum strains based on the probiotic survival after spray drying and improved the resistance of probiotic after heat, low pH, and bile salts. Mixture of maltodextrin and arabic gum was considered as the best encapsulating materials in producing spray dried microcapsules with the highest cell number of both L. plantarum strains. The resistance of encapsulated probiotics to heat, low pH and bile salt was varied by the type of encapsulating materials and L. plantarum strain. Microencapsulating using maltodextrin could be able to protect the probiotic strain toward heating at 500C by 2-3 log cfu g-1 guava powder compared to free cells. While mixture of maltodextrin and GOS showed the highest protection toward low pH and bile salt, except for L. plantarum BSL, maltodextrin alone demonstrated the best protection toward bile salt. Antimicrobial activity of the probiotics after microncapsulation againts Eschericia coli did not change significantly. The optimum sublethal temperature before spray drying was at 550C which was effective in increasing the survival of probiotic about 1.0 log cfu g-1 in guava powder. The spray dried guava powder probiotic had water activity (0.4), good water solubility (90-95%), and the color measured by chromameter (L, a, b) were 84.11, 2.35, 7.85, respectively.
Keyword: guava powder, Lactobacillus plantarum, microencapsulation, spray drying

Judul: Ongkos irregularitas sebuah graf
Abstrak: Tulisan ini mengkaji bagaimana cara mcngubah sualu graf menjadi graf yang irregular, yaitu dengan menambahkan beberapa edge pacta graf asal. Untuk sebuah graf G, didefinisikan ongkos irregularitas ic(G) yaitu jumlah minimum tambahan edge sedemikian sehingga menjadi Multigraf H yang merupakan multigraf G irregular. Akan ditentukan ongkos irregularitas dari graf regular, graf mendekati regular, dan graf mendekati irregular.
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