Propionic acid functions as a key short-chain fatty acid (SCFA) in microbial fermentation and metabolic regulation. It plays important roles in inhibiting histone deacetylases (HDACs) and serving as a gluconeogenic substrate in both ruminant and human gut physiology.
Chemical Properties
Propionic acid (CH₃CH₂COOH, MW 74.08 g/mol) is a colorless liquid with a pungent odor (density 0.993 g/cm³, bp 141°C, mp -21°C) that fully ionizes as a medium-strength carboxylic acid (pKa 4.87). It undergoes typical reactions including esterification, HVZ α-bromination (PBr₃ catalyst → 2-bromopropanoic acid), and salt formation (Ca, Na propionates). Propionic acid is miscible with water and ethanol and is steam volatile.
Biochemical Applications
In gut microbiome metabolism, propionate is produced via acrylate and succinate pathways (Propionibacterium, Bacteroides), activating GPR41/43 receptors to suppress lipolysis and stimulate leptin release via colonic L-cells. Hepatic gluconeogenesis converts propionyl-CoA → succinyl-CoA → oxaloacetate (yielding 9 kcal/mol ATP compared to glucose). Analytical laboratories use 0.1–1% propionic acid in GC mobile phases for SCFA profiling. Additionally, propionibacteria fermentation yields calcium propionate (0.3% in bread), which inhibits Aspergillus and Penicillium growth.
