TCA cycle (Krebs cycle / Citric acid cycle)
TCA cycle / Krebs cycle
Japanese: TCA回路（クエン酸回路・クレブス回路）
A metabolic pathway that fully oxidizes pyruvate under aerobic conditions, producing large amounts of ATP. The core of 'respiration,' distinct from fermentation.
The TCA cycle is a metabolic pathway operating under aerobic conditions. Pyruvate from glycolysis is converted to acetyl-CoA and enters this cycle. Each turn produces CO₂, NADH, and FADH₂, ultimately generating large amounts of ATP through the electron transport chain.
Aerobic microorganisms like koji mold actively run the TCA cycle for efficient energy production. Under anaerobic conditions, the TCA cycle cannot function fully, and yeast secures ATP through the 'detour' of alcoholic fermentation.
Citric acid, a TCA cycle intermediate, is the organic acid that white and black koji molds accumulate in abundance. The citric acid production in shochu-making is deeply connected to TCA cycle metabolism. Understanding metabolic pathways is the gateway to understanding fermentation's 'why.'