Metabolism of propanoate begins with its conversion to propionyl coenzyme A (propionyl-CoA), the usual first step in the metabolism of carboxylic acids. Since propanoic acid has three carbons, propionyl-CoA can directly enter neither beta oxidation nor the citric acid cycles. In most vertebrates, propionyl-CoA is carboxylated to D-methylmalonyl-CoA, which is isomerised to L-methylmalonyl-CoA. A vitamin B 12 -dependent enzyme catalyzes rearrangement of L-methylmalonyl-CoA to succinyl-CoA, which is an intermediate of the citric acid cycle and can be readily incorporated there.
Chelating or sequestering agents are added to foods to bind trace metals which can act as catalysts in food spoilage. These agents play an important role in preventing clouding of what should be a clear soft drink. The prevention of fruit discolorations is aided by the addition of small amounts of these preservatives. Calcium disodium ethylene diamine tetracetate, otherwise known as EDT A, is gaining popularity for its ability to prevent or reduce discoloration, clouding and rancidity. It is used in a variety of products such as cream style corn, black-eyed peas, salad dressings and beer.