Seleksi Bakteri Asam Laktat dan Pemanfaatannya sebagai Starter Kering Menggunakan Matriks Tapioka Asam

Abstract

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 weeks storage at a cold temperature (4°C) and room temperature (28°C). Cell viability was measured at 0, 7, 14, 21 and 28 days after storage. Cell viability was measured using spread-plate method on MRSA medium and incubated at 37°C for 48 hours. Results from the initial selection of the total acid titrated and sensitivity to antibiotics tetracycline, erythromycin and chloramphenicol showed that isolates E1222 and D4 were not resistant to all antibiotics tested and had higher total acid titrated. The selection result using HPLC showed that E1222 isolate produced higher lactic acid (16581.88 mg/L) than D4 isolate (14609.24 mg/L). E1222 isolate that showed the best result was identified as Pediococcus pentosaceus. Morphological characterization showed that E1222 isolate was Gram-positive and cocci. E1222 isolate achieved the maximum specific growth rate (μm = 0.027 h-1) at the 6th hour, thus E1222 isolate culture which was processed using spray dryer and freeze dryer was sixth hours culture. The results showed that freeze dried starter resulted in higher cell viability (10.34 log CFU/g) than spray dried starter (8.91 log CFU/g). Sour cassava starch matrix was also able to maintain cell viability during drying reaches 89% after freeze drying and 76% after spray drying. Tested result of storage stability of freeze dried starter showed that during the four weeks of storage, cell viability could be maintained up to 89.38% at cold temperature (4°C) and reaches 0% at room temperature (28°C). The results suggested that the dried starter E1222 isolate was best produced using freeze dryer and stored at cold temperature (4°C).