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[1] [2] During fermentation, organic molecules (e.g., glucose) are catabolized and donate electrons to other organic molecules. In the process, ATP and organic end products (e.g., lactate) are formed. Because oxygen is not required, it is an alternative to aerobic respiration. Over 25% of bacteria and archaea carry out fermentation.
These bacteria produce lactic acid in the milk culture, decreasing its pH and causing it to congeal. The bacteria also produce compounds that give yogurt its distinctive flavor. An additional effect of the lowered pH is the incompatibility of the acidic environment with many other types of harmful bacteria. [10] [18]
Thermal decomposition, or thermolysis, is a chemical decomposition of a substance caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing
First, glucose metabolism is faster through ethanol fermentation because it involves fewer enzymes and limits all reactions to the cytoplasm. Second, ethanol has bactericidal activity by causing damage to the cell membrane and protein denaturing, allowing yeast fungus to outcompete environmental bacteria for resources. [6]
The effects of temperature on enzyme activity. Top - increasing temperature increases the rate of reaction (Q 10 coefficient). Middle - the fraction of folded and functional enzyme decreases above its denaturation temperature. Bottom - consequently, an enzyme's optimal rate of reaction is at an intermediate temperature.
For example, if E. coli is placed on an agar plate containing only glucose and lactose, the bacteria will use glucose first and lactose second. When glucose is available in the environment, the synthesis of β-galactosidase is under repression due to the effect of catabolite repression caused by glucose.
Glucose uptake is believed to be a major rate-limiting step in glycolysis and replacing S. cerevisiae's HXT1-17 genes with a single chimera HXT gene results in decreased ethanol production or fully respiratory metabolism. [12] Thus, having an efficient glucose uptake system appears to be essential to ability of aerobic fermentation. [20]
It is regulated by moisture, temperature, and bacteria. [5] This process does not occur at a uniform rate and thus some proteins are degraded during early decomposition, while others are degraded during later stages of decomposition. During the early stages of decomposition, soft tissue proteins are broken down. These include proteins that: