Judul: Seleksi Bakteri Asam Laktat dan Pemanfaatannya sebagai Starter Kering Menggunakan Matriks Tapioka Asam
Abstrak: Starter is a microbial preparation that will be added to the raw materials in production of fermented food products. It is used to accelerate the fermentation process and reduce the risk of failure during the fermentation. Although starter cultures could be in the liquid or dry forms, the dried culture is more advantageous due to its long stability without regenerated. The most widely used bacteria for starter cultures production is lactic acid bacteria (LAB). LAB as a starter should be safe for other natural microorganisms in human body and has a high fermentation productivity. Therefore, the strains selection of LAB which would be used as a starter is important to do. The important criterias for LAB selection are the ability of producing lactic acid and antibiotic sensitivity. LAB should also have a high cell viability after the drying process and during storage, meaning that drying techniques and proper matrix are also pivotal factors to produce a desirable starter cultures. Sour cassava starch is a modified starch which is produced from fermented tapioca. This material has promising properties for LAB encapsulation matrix because it is prepared using LAB-induced fermentation, and does not contain food chemical additives as well as contain fermented monosaccharides which can act as a protective agent (protectant) during drying and storage. Raw materials of sour cassava starch are widely available, economical and renewable. The aims this study were to produce LAB dried starter using sour cassava starch matrix and to study its viability after storage. Eleven local LAB isolates obtained from spontaneous fermentation of carbohydrate commodity were selected based on their acid production ability and antibiotic sensitivity. The initial selection of the acid production ability was conducted by measuring the total acid and pH level of culture media. The isolate sensitivity to antibiotics tetracycline, erythromycin and chloramphenicol were tested by disc diffusion method. The isolate that produce high level of acid and is vulnerable to antiobiotics was selected and subsequently evaluated its lactic acid production using high performance liquid chromatography (HPLC). The isolate that have a higher production of lactic acid was choosen for this study. Furthermore, its morphological character and growth curve were observed. Morphological characters have been observed using a light microscope including Gram staining and cell shape observation. Growth curve was observed by calculation of cell numbers (log CFU/mL) while the optical density (OD) using a spectrophotometer at a wavelength (λ) 620 nm. Cell numbers was calculated using total plate count (TPC) on de Man Rogosa Sharpe agar (MRSA) medium were incubated at 37°C for 48 hours. Observation was conducted every hour until the cells reached a maximum specific growth rate (μm,h-1). Dried starter of selected isolate was produced using freeze dryer (-50oC) and spray dryer (inlet 170°C, outlet 70°C). The matrix used was sour cassava starch and sour cassava starch enriched with 10 % skim milk were used as the positive control. Starter has been stored in an airtight aluminum foil for water content analysis (%), cell viability (log CFU/g) and survival rate (%) after drying. Storage stability of the best starter was evaluated in four
Keyword: dried starter, lactic acid bacteria, sour cassava starch, freeze drying, spray drying

Judul: Penambahan Starter Padat Bakteri Asam Laktat Untuk Meningkatkan Keamanan Pangan Tapioka.
Abstrak: Tapioka merupakan salah satu produk agroindustri yang potensial dan memiliki prospek untuk dikembangkan di Indonesia. Namun proses pengolahan yang ada saat ini memiliki kelemahan yaitu proses pengolahan tapioka masih dilakukan secara tradisional karena sebagian besar industri tapioka yang ada di Indonesia adalah industri skala kecil dan rumah tangga. Hal ini menyebabkan mutu tapioka yang dihasilkan masih rendah serta keamanan pangan masih kurang terjamin. Bakteri asam laktat dapat menghasilkan asam organik yang dapat menghambat pertumbuhan bakteri pembusuk/patogen pada pembuatan tapioka. Penambahan bakteri asam laktat dilakukan pada tahap ekstraksi khususnya saat pengendapan karena pada tahap ini kemungkinan kontaminasi bakteri patogen dari air sangat besar. Penelitian ini bertujuan untuk merancang proses produksi starter padat BAL melalui proses enkapsulasi menggunakan matriks berbasis pati termodifikasi yang meliputi sour cassava starch, lintnerized cassava starch dan pati nanokristalin; dan pemanfaatan starter dalam menekan pertumbuhan bakteri patogen pada proses produksi tapioka. Enkapsulasi BAL dilakukan dengan cara pengeringan beku (freeze dryer) dengan suhu -50 0C selama 48 jam. Jumlah sel starter padat BAL yang bertahan hidup setelah pengeringan beku dengan matriks sour cassava starch adalah 92%, matriks lintnerized cassava starch 93%, matriks nanokristalin 96%. Setelah penyimpanan selama 6 bulan dari tapioka yang dihasilkan, menunjukkan bahwa pada tapioka tanpa penambahan starter BAL terdeteksi pertumbuhan E. coli, Salmonella dan Shigella, sedangkan pada pati yang ditambahkan BAL tidak terdeteksi bakteri tersebut. Hal ini menunjukkan bahwa penambahan BAL selama proses ektraksi mampu menekan pertumbuhan bakteri patogen pada tapioka yang dihasilkan. Hasil pengujian menunjukkan bahwa matriks lintnerized cassava starch adalah matriks terbaik karena setelah 6 bulan penyimpanan masih terdeteksi pertumbuhan BAL tertinggi dibandingkan dengan starter cair dan matriks lainnya.
Keyword: bakteri asam laktat, enkapsulasi, lintnerized cassava starch, nanokristalin, sour cassava starch, tapioka

Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf