Judul: Stability and Antimicrobial Activity of Plantaricin Produced by Lactobacillus plantarum at Alkaline pH
Abstrak: Plantaricin produced by L. plantarum is known to display an adaptive response to alkali stress that enhances its capacity to more effectively stable at alkali condition. The aim of the research was to examine the stability of plantaricin produced by L. plantarum 1A5, 1B1, 2B2 and 2C12 and its antimicrobial activity at alkaline pH. The experiment was done based on completely randomized design (CRD) with factorial arrangement 2 x 4, two levels of pH value and four levels of L. plantarum strains in three replications. Variables analyzed were protein concentration, inhibition zone of the antagonistic test was assayed by agar well diffusion and antimicrobial activity of plantaricin against indicator bacteria at alkaline pH. Plantaricin was found to be sensitive to alkaline treatment. No interaction between pH and strains of L. plantarum to antimicrobial activity of plantaricin (P>0.05). Plantaricin showed antimicrobial activity against Gram positif and Gram negatif bacteria including S. typhimurium ATCC 14028, S. aureus ATCC 25923, E. coli ATCC 25922, P. aeruginosa ATCC 27853 and B. cereus. Plantaricin produced by L. plantarum 1A5, 1B1, 2B2 and 2C12 was stable at alkaline pH but the stability of plantaricin decreased because of alkaline treatment to S. typhimurium ATCC 14028 (P<0.01). Stability of plantaricin after alkaline treatment showed plantaricin potentially could be used as biopreservative on alkali products.
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Judul: Produksi Bakteriosin Asal Lactobacillus plantarum sebagai Antimikrob dan Pengujian Ketahanannya terhadap Panas
Abstrak: Bacteriocin is commonly used to biopreservative agent in food. Bacteriocin is an antimicrobial substance that is capable to inhibit toward pathogenic and food borne bacteria. It was reported that indigenous isolate of Lactobacillus plantarum isolated from Indonesian local beef producing an antimicrobial substance (Arief et al., 2008). The objective of this research was to characterize the heat stability of plantaricin at pasteurization and sterilization temperature. The treatments were heat temperature (80 °C for 30 minutes and 121 °C for 15 minutes) and strains of Lactobacillus plantarum (2C12, 1A5, 1B1 and 2B2) usage. The variable was diameter of inhibition zone of antagonistic activity. Antimicrobial activity of plantaricin of Lactobacillus plantarum 2C12, 1B1, 2B2, and 1A5 did not lost after treated at 80 °C for 30 minutes or at 121 °C for 15 minutes. That result showed that plantaricin was stable at pasteurization and sterilization temperature. Plantaricin produced by strains of L. plantarum against indicator bacteria such as Pseudomonas ATCC 27853, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Salmonella enteriditis ser. Typhimurium ATCC 14028 had different activity each other. However, inhibition activity of plantaricin did not lead against Bacillus cereus. Stability of antimicrobial activity of plantaricin to inhibit indicator bacteria after heat treatment proved that plantaricin has a potential as food biopreservative.
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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. Suatu graf lengkap berorder 𝑛������ ≥ 3 dan graf r-regular berorder 𝑛������ ≤ 2𝑟������ + 1 merupakan graf Hamilton, Karena kedua graf tersebut memuat cycle Hamilton. Selanjutnya, syarat cukup tersebut digunakan untuk menentukan keberadaan cycle Hamilton pada graf 2-connected 4- regular berorder kurang dari 10.
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular