Citrate synthases

Citrate synthases are the enzymes that open the citric acid cycle, condensing acetyl-CoA with oxaloacetate to form citric acid. Two versions exist — EC 2.3.3.1 and EC 2.3.3.3 — with opposite stereospecificities, a subtlety that matters to biochemists tracing metabolic pathways. Though rarely added to foods directly, they sit at the heart of the fermentation microbiology behind commercial citric acid production, the versatile organic acid used as an acidulant, antioxidant, flavouring, antimicrobial, and chelating agent across the food and beverage industries.