Caproate fermentation
Caproate fermentation is a metabolic process used by different bacteria to utilize different organic substrates for the production of caproic acid as well as other valuable byproducts. Caproic acid is a valuable compound in food industries as a flavor additive, feedstock for chemical industries, antimicrobial agents in the pharmaceutical industry, and more. Though this process is used by varying bacterial species, the most common species utilizing caproate fermentation in its metabolic process is Clostridium kluyveri. This species, as well as others, utilize caproate fermentation through the breakdown of varying substrates for energy production, waste management and increased ability for survival in different environments.
Chemical structures and properties
Chemical Structure
Caproic acid is otherwise known as hexanoic acid. In solid state, the acid appears as a white crystalline structure, while when liquid, it appears clear with a yellow tint. Any contact with caproic acid will cause irritation to various parts of the body and is toxic to humans. The acid is formed through β-oxidation which elongates a short chain carboxylic acid origin using lactic acid as the electron donor to drive the process. This is done through a series of reactions driven by varying enzymes.Chemical methods
Carboxylic acids and alcohols are required as substrates for caproate fermentation. Due to the danger of high concentrations in these substrates, they must be diluted. This danger factor results in more materials needed and a more meticulous process to perform fermentation, which is costly. Recent studies suggest that food waste can serve as an alternative source for these substrates, potentially reducing cost and waste. The interest in creating more efficient methods for producing caproates—specifically n-caproate and n-caprylate —has been challenged by the natural efficiency of C. kluyveri. There are many different ways to produce caproate fermentation however, it is difficult to avoid disruption of the cell and effectively produce caproate. To efficiently produce caproate, optimal conditions are required including: pH, temperature, and environmental concentration.Process of Fermentation
Certain bacterial species convert carbohydrates into caproate, a six-carbon fatty acid.Throughout this process of fermentation, bacteria anaerobically break down carbohydrates like glucose through a series of biochemical reactions producing caproate. Furthermore, chain elongation of ethanol and acetate is also needed to create caproate. Ethanol is toxic to many bacterial species, so the ethanol must be pretty balanced in the process to ensure caproate production. Studies have found that with an ethanol/acetate ratio higher than 7:3 require no extra electron donors and a 10:1 ratio produced 8.42g/L of caproate. Additional byproducts are formed like hydrogen gas, carbon dioxide, and sometimes butyrate or acetate. Caproate is the main product, hence the name of caproate fermentation.