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: Pembuatan Tapioka Asam dengan Penambahan Starter Cair Bakteri Asam Laktat Indigenous
Abstrak: Sour cassava starch is a modified cassava starch produced through submerged fermentation for several weeks followed by sun drying. Lactic acid bacteria is the dominant microorganism and has important role in the fermentation process. The use of indigenous LAB isolate as starter is expected to shorten the fermentation time and maintain its quality. The purposes of this research were to prepare a liquid starter of lactic acid bacteria for the fermentation process, investigate the effect of liquid starter in accelerating the fermentation process and investigate the effect of fermentation time (0, 5, 10, 15, 20 and 25 days) to quality and functional properties of sour cassava starch. A randomized block design was used with fermentation time factor. The addition of liquid starter could accelerate the fermentation process to only 15 days, with the highest expanding capability. Acidifying of cassava starch led to an increase in peak viscosity, but decrease final viscosity of the paste. Acid accumulation could suppress undesirable microorganisms growth, so that it can extend the shelf life of the products.
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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