Module 5: Fermentation

• glycolytic pathway: break glucose down to smaller molecules
• embden-meyerhoff (glycolysis) occurs in many bacteria and archaea
• entner-douderoff pathway occurs in mostly aerobic bacteria
• 3 steps of glycolysis: activation, hexose splitting, energy generation
• activation: atp donates phosphates to destabalize glucose
• hexose splitting: activated glucose is split, rxn pulled toward GAP
• energy generation: phosphate addition coupled with oxidation doesn't require energy, substate level phosphorylation to generate ATP
• what are the end products of glycolysis?

  pyruvate (carbon source) and NADH
• NADH is removed in fermentation
• entner-duodoroff pathway: net 1 ATP and 2 NADH and NADPH
• fermentation: reduction of NAD+ to NADH with pyruvate intermediate
• where does energy come from in fermentation?

  substrate level phosphorylation
• fermentation produces low energy yields
• fermentation is anaerobic
• fermentation substrates: sugar, amino acids
• fermentation products: organic acids, alcohols, gases
• alcohol fermentation: yeast grows on sugar, initially aerobic
• steps of alcohol fermentation:

  1. pyruvate decarboxylated to acetaldehyde
  2. reduced to ethanol by NADH
• what causes low alcohol content in alcohol fermentation?

  contamination by bacteria that ferments sugar before yeast
• what causes acetaldehyde build up (green apple taste) in alcohol fermentation?

  high ethanol concentration will reverse reaction
• what happens when there is high starting sugar concentration in alcohol fermentation?

  yeast will synthesize other compounds
• homofermentation: only produces lactic acid
• heterofermentation: produces lactate, CO2 and ethanol
• kimchi fermentation produces lactic acid
• steps of kimchi fermentation:

  1. coliforms ferment sugar to ph 5
  2. lactic acid bacteria heterferment to ph 4.5
  3. lactic acid bacteria homoferment to ph 4
• chocolate fermentation: natural microbes ferment seeds
• peak ethanol concentration occurs 1 day after yeast is introduced in chocolate fermentation
• peak lactic acid concentration occurs 2 days after lactic acid is introduced in chocolate fermentation
• peak acetic acid concentration occurs 2 days after acetic acid bacteria is introduced
• peak temperature occurs one day after spore-formers are introduced
• fermentation ends 1 day after mold is introduced