Food Microbiology &
Helen Billman-Jacobe
Microbial metabolism Fermentation
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Ray and Bhunia Ed 5 Ch8
Intended learning outcomes
Explain how monosaccharides are fermented by microorganisms via different pathways and product different end products
Explain that some metabolic end products are desirable and others are considered undesirable and are considered as spoilage
Explain the difference between homolactic and heterolactic fermentation Explain the process of alcoholic fermentation
End products of carbohydrate metabolism
microorganism
fermentation
endproducts
Ethanol, carbon dioxide
Lactic acid bacteria (LAB)
Homo fermentative
Lactic acid bacteria (LAB)
Hetero fermentative
Lactate, acetate, ethanol, carbon dioxide, diacetyl, acetoin
Propionic acid, acetate, CO2
Enterobacteriaceae
Mixed acid
Lactate, acetate, formate, succinate, CO2, H2
Lactate, acetate, formate,2,3 butanediol, CO2, H2
Butyrate, acetate, CO2, H2, butanol, ethanol, acetone, isopropanol
Fermentation
Fermentation is metabolism in which energy is derived from the partial oxidation of an organic compound using organic intermediates as electron donors and electron acceptors.
No outside electron acceptors are involved; no membrane or electron transport
Fermentation
Monosaccharides are fermented by anaerobic and facultative anaerobic microorganisms by one or more of Five major pathways for degradation of monosaccharides
1. Embden-Meyerhoff-Parnas (EMP) pathway
2. Hexose monophosphate shunt (HMP) pathway
3. Entner-Doudroff (ED) pathway
4. 2 Phosphoketolase (PK) pathways (pentose phosphoketolase and hexose phosphoketolase)
Embden-Meyerhoff-Parnas (EMP) pathway
This is the pathway of glycolysis glucosepyruvic acid + ATP
Lactic acid bacteria reduce the pyruvate to lactic acid (lactate)
Yeast reduce the pyruvate to alcohol (ethanol) and CO2
2 ways of reducing pyruvate so different endproducts
Embden-Meyerhoff-Parnas (EMP) pathway
This is the pathway of glycolysis glucosepyruvic acid + ATP
Lactic acid bacteria reduce the pyruvate to lactic acid (lactate)
Yeast reduce the pyruvate to alcohol (ethanol) and CO2 2 ways of reducing pyruvate so different endproducts
Embden-Meyerhof fermentations in bacteria can lead to a wide array of end products depending on the pathways taken in the reductive steps after the formation of pyruvic acid.
Alcoholic fermentation
Yeasts produce ethanol and CO2 by alcoholic fermentation product in the manufacture of beer, wine, bread and variety of fermented products.
Homolactic Fermentation
Lactic acid is the sole end product. Pathway of the homolactic acid bacteria (Lactobacillus, Lactococcus and most streptococci). The bacteria are used to ferment milk and milk products in the manufacture of yogurt, buttermilk, sour cream, cottage cheese, cheddar cheese, and most fermented dairy products.
Heterolactic vs homolactic fermentation
Heterolactic vs homolactic fermentation
Heterolactic vs homolactic fermentation
Pyruvate is a key metabolite. Diff endproducts
Embden-Meyerhoff-Parnas pathway
Used by homofermentative LAB, yeasts and some Bacillus sp
Hexose monophosphate shunt pathway
Used by heterofermentative LAB, Bacillus sp and Pseudomonas
Ray and Bhunia
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