Lactic Acid Bacteria and Fermentation by group one: Lactic Acid Bacteria and Fermentation by group one table of content: table of content Lactobacillus delbrueckii subsp. Bulgaricus Streptococcus salivarius subsp. Thermophilus The fermentation cycle Lactobacillus delbrueckii subsp. bulgaricus: Lactobacillus delbrueckii subsp. bulgaricus Kingdom : Monera Filum : Firmicutes Class : Bacilli Ordo : Lactobacillales Famili : Lactobacillaceae Genus : Lactobacillus Species : Lactobacillus delbrueckii Subspecies : Lactobacillus delbrueckii subsp. bulgaricus Characteristic: Characteristic Have Rod shape Have Flagella Have thick peptidoglikan (gram-positive) Slide 5: Lactobacillus delbrueckii subspecies bulgaricus (until 1984 known as Lactobacillus bulgaricus ) is one of several bacteria used for the production of yogurt. It is also found in other naturally fermented products. First identified in 1905 by the Bulgarian doctor Stamen Grigorov , the bacterium feeds on lactose to produce lactic acid, which is used to preserve milk. It is a Gram-positive rod that may appear long and filamentous. It is also non-motile, and it does not form spores. This bacterium is regarded as aciduric or acidophilic, since it requires a low pH (around 5.4-4.6) to grow effectively. The bacterium has complex nutritional requirements, including the inability to ferment any sugar except lactose. Streptococcus salivarius subsp. thermophilus: Streptococcus salivarius subsp. thermophilus Kingdom : Monera Filum : Firmicutes Kelas : Bacilli Ordo : Lactobacillales Famili : Streptococcaceae Genus : Streptococcus Species : Streptococcus salivarus Subspecies : Streptococcus salivarius subsp . thermophilus Slide 8: Streptococcus salivarius subsp. Thermophilus (previous name Streptococcus thermophilus ) is a Gram-positive bacteria and a homofermentative facultative anaerobe, of the viridans group. It tests negative for cytochrome , oxidase and catalase , and positive for alpha-hemolytic activity. It is non-motile and does not form endospores . It is also classified as a lactic acid bacterium. S. thermophilus is found in fermented milk products. It is not a probiotic (it does not survive the stomach in healthy humans) and is generally used in the production of yogurt, alongside Lactobacillus delbrueckii subsp. bulgaricus . The two species are synergistic, and S. thermophilus probably provides L. bulgaricus with folic acid and formic acid which it uses for purine synthesis. As long ago as the early 1900s, S. thermophilus has been used to make yogurt. Many of the yogurts sold in grocery stores today do not contain many live cultures of S. thermophilus because pasteurization destroys these beneficial organisms. Nonetheless, S. thermophilus is required by law to be present in yogurt. Its purpose is to turn lactose, the sugar in milk, into lactic acid. The increase in lactic acid turns milk into the gel-like structure characteristic of yogurt. Slide 10: Lactose (glucose) Acetic acid THE FERMENTATION CYCLE Make Yoghurt: Make Yoghurt Provide fresh UHT milk instead of milk powder, not sweetened condensed milk. Pasteurized milk only undergoes a process of heating not boiling. If you use bottled milk not pasteurized milk then the resulting yogurt will drip like gravy soup thickened using tapioca flour Provide Plain Yogurt, with no sugar and without essences Prepare a glass jar that has been poured hot water to be sterile. Sterilize hands and all the tools that will be used with alcohol Pour yogurt 5 percent of the total milk used, into the jar, then pour the milk has been slightly warmed and mix. Close the jar tightly, and place the container near the magic jar. Cover the jar and magic jar with a cloth so the heat will not come out. We use a magic jar so we will not have to use complicated tools like an incubator Wait for 8 hours. Don’t open the jar before 8 hours. If it thickens then it means that it is successful.