84  ◾  Fundamental Food Microbiology
Pentose Phosphoketolase Pathway
This pathway is used by Escherichia coli, Enterobacter aerogenes, Bacillus spp., and some lactic acid
bacteria.
Ribose phosphate Xylulose phosphate
Acetyl-Phos
→
→
p phate Pyruvate
Acetate or Ethanol Lactate
+
→
+
Hexose Phosphoketolase Pathway
This pathway is also called the Bifidus pathway and is used by Bifidobacterium spp.
2
2
Glucose phosphate Acetyl phosphate
Xylulose
→
+
phosphate
Acetate
Pyruvate
3 Acetate 2 La
→
+
→
+
3
2
c ctate
Some Specific Pathways
Mixed Acid Fermentation
Mixed acid fermentation is characteristic of members of Enterobacteriaceae. Pyruvate produced
from monosaccharide fermentation can be used to produce different end products.
Pyruvate Lactate
Pyruvate Formate Acetyl CoA
Form
→
→
+
∼
a ate H CO
Acetyl CoA
Acetate and Ethanol
Pyruva
→
+
→
2
2
∼
t te Succinate
→
Propionic Acid Fermentation
This type of fermentation is carried out by propionic bacteria and Clostridium spp.
Lactate Pyruvate Propionyl CoA Propionate (prop
→
→
→
∼
i ionibacteria)
Lactate Acrylyl CoA Propionyl CoA
→
→
∼
∼
→ → Propionate (
s pp).
Clostridium
Butyrate, Butanol, and Acetone Fermentation
This type of fermentation is carried out by Clostridium spp.