Effect of pH, yeast extract and inorganic carbon on chain elongation for hexanoic acid production

• Published in: Bioresource technology 2020-03, Vol.300, p.122659-122659, Article 122659
• Main Authors: San-Valero, Pau, Abubackar, Haris Nalakath, Veiga, María C., Kennes, Christian
• Format: Article
• Language: English
• Subjects: Bioreactors; Caproates; Caproic acid; Carbon; Chain elongation; Clostridium kluyveri; Fermentation; Hydrogen-Ion Concentration; Medium chain fatty acids; Plant Extracts
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2019.122659

[Display omitted] •Optimal acetate/butyrate conversion to hexanoate (>20 g/L) in C. kluyveri is shown.•Near neutral pH values, rather than pH 6.4, improve chain elongation in C. kluyveri.•The supply of inorganic carbon, i.e. NaHCO3, stimulates hexanoic acid production.•Yeast extract omission reduces growth and the final concentration of hexanoic acid. Several anaerobic bioconversion technologies produce short chain volatile fatty acids and sometimes ethanol, which can together be elongated to hexanoic acid (C6 acid) by Clostridium kluyveri in a secondary fermentation process. Initiatives are needed to further optimize the process. Therefore, five strategies were tested aiming at elucidating their influence on hexanoic acid production from mixtures of acetic acid, butyric acid and ethanol. pH-regulated bioreactors, maintained at pH 7.5, 6.8 or 6.4 led to maximum C6 acid concentrations of, respectively, 19.4, 18.3 and 13.3 g L−1. At pH 6.8, yeast extract omission resulted in a decrease of the hexanoic acid concentration to 12.0 g L−1 while the addition of an inorganic carbon source, such as bicarbonate, for pH control, increased the C6 acid concentration up to 21.4 g L−1. This research provides guidelines for efficient improved production of hexanoic acid by pure cultures of C. kluyveri, contributing to the state of art.