1 / 34

PDC

Ethanolic Fermentation - Electron and carbon flow -. 2. 2. 0. 0. 2. 10. 10. 12. 12. 12. 24. 10. 10. 10. 24. 10. 1. 0. 1. 0. 0. 2. 2. 2. 2. 2. 3. 6. 6. 2. 3. 3. glucose. ATP. ATP. PDC. PDC. EDH. EDH. = glucose. ethanol. = 2 red. equiv. = pyruvate.

alia
Télécharger la présentation

PDC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ethanolic Fermentation - Electron and carbon flow - 2 2 0 0 2 10 10 12 12 12 24 10 10 10 24 10 1 0 1 0 0 2 2 2 2 2 3 6 6 2 3 3 glucose ATP ATP PDC PDC EDH EDH = glucose ethanol = 2 red. equiv. = pyruvate Key enzymes: PDC = pyruvate decarboxylase EDH = Ethanol dehydrogenase = acetaldehyde = ethanol

  2. Ethanolic Fermentation - Electron and carbon flow - OH H C H H C H H O.S.: -1 → 5 electrons O.S.: -3 → 7 electrons • Energy conserved: • 2 ATP from glycolysis (PGK, PK) • Key enzymes: • Pyruvate Decarboxylase, • Ethanol Dehydrogenase • (could also be called ethanol oxidase or acetaldehyde reductase)

  3. The Entner Doudoroff (KDPG) pathway of ethanolic fermentation 2 2 0 0 0 10 24 10 10 12 12 12 12 12 24 24 10 22 10 10 0 0 1 1 1 2 6 3 3 3 6 2 6 3 2 2 2 3 2 2 Organism: Zymonas mobilis (not examined) = glucose = gluconate = GAP = pyruvate ATP = CO2. = acetaldehyde = ethanol

  4. Special features of Entner Doudoroff pathway • 1 NADH, 1 NADPH • Only 1 ATP (less biomass as byproduct) • Only one pyruvate through GAP (bottleneck) → faster? Special features of Zymomoanas • Higher glucose tolerance • Higher product yield (less ATP → less biomass) (100 g ethanol / 250 g glucose)= 78% molar conv. eff • Not higher ethanol tolerance

  5. Special features of Entner Doudoroff pathway (not examined) • 1 NADH, 1 NADPH • Only 1 ATP (less biomass as byproduct) • Only one pyruvate through GAP (bottleneck) → faster? Special features of Zymomoanas • Higher glucose tolerance • Higher product yield (less ATP → less biomass) (100 g ethanol / 250 g glucose)= 78% molar conv. eff • Not higher ethanol tolerance

  6. Ethanol as fuel in Brasil • Distillation costs more energy than ethanol fuel value • Separation costs higher than fermentation costs Research • Thermophilic strains (Clostridium using cellulose) • Finding more ethanol resistant strains

  7. Lactic Fermentation - Occurrence - • If plant or animal material containing sugars and complex nitrogen sources is left in the absence of oxygen → lactic acid bacteria take over  • Selective enrichment • Natural fermentation (since prehistoric times) • Why do lactic acid bacteria take over sugar conversion on rich media? : • Simple metabolism → fast degradation • 2) Amino acids are not synthesized but taken up from the medium → faster growth • 3) Strains are existing on substrate (e.g. milk, vegetables) • 4) O2 tolerance of strains • 5) Production of inhibitory acid (ph <5) • Examples: Milk, whole meal flour, vegetables,

  8. Lactic Fermentation - Organisms - • Lactic acid bacteria (Lactobateriacease) • gram positive • non motile • obligate anaerobics • no spores • aerotolerant • no cytochromes and catalase • fermentation of lactose • no growth on minimal glucose media • requirement of nutritional supplements (vitamins, amino acids, etc.) • when supplied with porphyrins → they form cytochromes !?! (indicating that they were originally aerobic organisms that have lost the capacity of respiration, metabolic cripples)

  9. 2 2 2 12 12 12 10 24 10 24 10 0 0 0 3 3 6 3 3 3 6 3 Homolactic Fermentation - Electron and carbon flow - ATP ATP LDH LDH lactate = glucose LDH = lactate dehydrogenase = 2 red. equiv. = pyruvate = lactate

  10. Homo-lactic Fermentation - Electron and carbon flow - O CH C H C H H C H H O.S.: +3 → 1 electron O.S.: 0 → 4 electrons O.S.: -3 → 7 electrons Strategy: 1) Aerotolerant → can ferment with strict anaerobes are still inhibited by oxygen 2) Simple quick metabolism and usage of carbohydrates 3) Production of acid, inhibiting competitors

  11. Significance: • Why do lactic acid bacteria not spoil food but preserve it? • Only ferment sugars (24 e-) to lactate (2* 12 e-)  nutritional value not significantly altered • Don’t degrade proteins • Don’t degrade fats • Acidity suppresses growth of food spoiling organisms (eg. Clostridia) • enhances nutritional value of organic material (example sauerkraut, Vit. C, scurvy) • Complex flavour development (diacetyl) • Examples: • Yogurt, sauerkraut, buttermilk, soy sauce, sour cream, cheese, pickled vegetables, • technical lactic acid for the production of bio-plastic (hydroxy acids allow chain linkages via ester bonds between hydroxy and carboxy group).

  12. 2 2 8 2 2 8 0 0 12 24 10 24 12 20 12 12 20 10 0 0 2 0 1 0 1 2 6 6 3 2 5 3 3 3 5 2 Heterolactic Fermentation Phosphoketolase pathway = glucose = ribose = 2 red. equiv. = pyruvate ATP = lactate = ethanol =acetate = CO2. Phosphoketolase pathway = combination of Pentosephosphate cycle and FBP pathway

  13. 2 2 8 2 2 8 0 0 12 24 10 24 12 20 12 12 20 10 0 0 2 0 1 0 1 2 6 6 3 2 5 3 3 3 5 2 Heterolactic Fermentation Phosphoketolase pathway = glucose = ribose = 2 red. equiv. = pyruvate ATP = lactate = ethanol =acetate = CO2. Presence of oxygen → lactate, acetate and CO2 production → 1 additional ATP from acetokinase. No ETP

  14. Heterolactic Fermentation Organisms: E.g. Leuconostoc spp. Lactobacillus brevis • Strategy: • Use of parts of the pentose phosphate cycle which is designed for synthesis of pentose (DNA, RNA). → • Aerotolerant, simple pathway, quick metabolism, suited for substrate saturation. Application: Sourdough bread, Silage, Kefir, Sauerkraut, Gauda cheese (eyes) In the presence of oxygen, reducing equivalents from glucose oxidation are transferred to oxygen, allowing the gain of an additional ATP via acetate excretion Key enzymes of FBP pathway missing (Aldolase, Triosephosphate isomerase).

  15. Application of Lactic Fermentation • Silage: Lactic acid fermentation of fodder material • Process: • 1) partial drying of fodder • 2) shredding • 3) Rapid filling of silo (1 or 2 days) • 4) packing as densely as possible • 5) Compressing • 6) Sealing airtight • 7) Additives (germination inhibitors, sugars, organic acids) • 8) Avoid contamination with decaying fodder (Clostridia, proteolytic bacteria) • Nutrient loss: • drying of fodder  hay (25%), • ensilaging (10%) (2ATP out of 38)

  16. Applications of Lactic Fermentation Sauerkraut In principle identical to silage with following modifications: 1) White cabbage as the only plant material 2) Cabbage mixed with NaCl (2 – 2.5%) 3) Capacity of vessels (concrete, wood) up to 100 tons 4) Incubation (18oC to 20oC) for 4 weeks 5) Recirculation of brine by pumping for process monitoring (acids) 6) About 1.5% lactic acid produced 7) Sterilisation of product to have cooked sauerkraut (German). Raw (fresh sauerkraut used in salads) 8) Problem: 1 to 15 tons of highly polluted effluent per ton of cabbage

  17. Applications of Lactic Fermentation Sauerkraut • Similar to silage with following modifications: • White cabbage as the only plant material • 2) Cabbage mixed with NaCl (2 – 2.5%) • 3) Capacity of vessels (concrete, wood) up to 100 tons • 4) Incubation (18oC to 20oC) for 4 weeks • 5) Recirculation of brine by pumping for process monitoring (acids) • 6) About 1.5% lactic acid produced • 7) Sterilisation of product to have cooked sauerkraut (German). Raw (fresh sauerkraut used in salads) • 8) Problem: 1 to 15 tons of highly polluted effluent per ton of cabbage Brine Recycle

  18. Applications of Lactic Fermentation Brine Recycle

  19. Applications of Lactic Fermentation Olives 1) Black (ripe) or green (unripe) olives 2) Pretreatment with 1.5% NaOH saline (reducing bitterness) 3) Washing 4) Place fruit (still alcaline) in brime of 10% NaCl + 3% lactic acid (to neutralise pH) 5) Sugar addition to accelerate fermentation (Lactobacillus plantarum) 6) Incubate for several months until lactic acid >0.5% 7) Wooden barrels or plastic tanks

  20. Pickled Gherkins 1. Cover gherkins in 3% salt brine (NaCl) 2. Add spices, herbs, dill 3. Irradiate surface (UV) and close vessel 4. After 3 – 6 weeks 3% lactic acid is produced 5. Fermentation pattern like silage

  21. Applications of Lactic Fermentation Technical lactic acid Use: Leather – Textile – and Pharmaceutical Industry Bioplastics (Polylactic acid, biodegradable) Food acid (flavourless, non volatile) e.g. in sausages Product yield: 900 g per g of sugar Substrate: whey, cornsteep liquor, malt extract, ideally: sugars (15% cane or beets) Strains: Lactobacillus bulgaricus, Lactobacillus delbrueckii Duration: 5 days batch culture

  22. Applications of Lactic Fermentation Sourdough bread Biological raising agent (homo- and heterolactic fermentation) CO2 produced from heterolactic bacteria Necessary for rye bread to increase digestibility Health bread (lipid, proteins unchanged, vitamins produced) Pre-acidified (stomach friendly) Complex flavour development Increased shelf life

  23. Cheese Production Milk Homogenise Add starter culture (S. cremoris, S. lactis, L. bulgaricus, S. thermophilus Pasteurise Add Rennet* Curdling** Stirring Settling Yougurt (430°) Scolding*** Cooling Washing Salting Heat treatment (600°) Kneading Whey Quark Fromage frais (acidic paste) Whey Cottage cheese (granular) Pressuring Maturing * Proteolytic enzyme ** Coagulating *** Heated stirring Brie Edamer Cheddar

  24. 2 2 0 8 12 14 12 12 14 0 2 0 1 3 3 3 3 3 Propanoate Formation From Lactate • Acryloyl pathway (Clostridium propionicum) • The 4 reducing equivalents from lactate oxidation to acetate • are merely “dumped” onto two further moles of lactate • (dismutation, disproportionation) LDH PrDH PDH ATP Enzymes: Lactate DH, Pyruvate DH, Propionate DH (PrDH)

  25. 2 2 0 8 12 14 12 12 14 0 2 0 1 3 3 3 3 3 Propanoate Formation From Lactate • Acryloyl pathway (Clostridium propionicum) Energetic benefit? The excretion of acetate gains 1 ATP (acetate kniase), Thus 1/3 ATP/lactate metabolised. LDH PrDH PDH ATP How to generate ATP from acetate excretion Phosphate Acetyl transferase: Acetate~CoA + Pi → Acetyl-P + CoA Acetokinase: Acetyl-P + ADP → Acetate + ATP

  26. Propanoate Formation From Lactate 2. Methyl-Malonyl-Pathway (Propionibacteria) • 2 reducing equivalents from lactate oxidation (exactly: PDH and ferredoxin as e- carrier) are transferred via electron transport phosphorylation to fumarate (fumarate respiration) resulting in one extra ATP (2/3 ATP/lactate metabolised). • Reverse TCA cycle. Fumarate reduction is an example of anaerobic respiration Homoacetogenesis is another example

  27. 14 2 2 0 8 0 2 10 14 14 12 12 14 12 12 12 14 10 10 10 12 4 1 1 0 0 0 2 4 3 3 3 3 4 3 3 3 4 3 4 3 4 Fd ETC Vit B12 Propanoate Formation From Lactate 2. Methyl-Malonyl-Pathway (Propionibacteria) = lactate LDH = propionate PDH ATP = succinate = fumarate (malate) ATP = OAA = pyruvate

  28. Propionic Fermentation of Glucose

  29. Propionic Fermentation of Glucose

  30. Propionic Fermentation of Glucose

  31. Butyric Fermentation

  32. Acetone Butanol fermentation

  33. Homoacetogenesis The homoacetogenesis starts like the butyric acid fermentation: 1) Use of the fructose bisphosphate pathway (FBP) leading to 2 puruvate and 2 NADH. 2) Oxidative decarboxylation of pyruvate to acetyl-CoA, hydrogen gas and CO2. 3) In contrast to the butyric fermentation no acetoacetyl-CoA is formed. Instead two acetyl-CoA are intermediate products.

  34. Homoacetogenesis

More Related