Journal
PROCESS BIOCHEMISTRY
Volume 54, Issue -, Pages 106-119Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.procbio.2016.12.024
Keywords
Carboxylic acid chain elongation; Hexanoic acid; Reverse beta-oxidation; Anaerobic fermentation
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Funding
- Brazilian Agricultural Research Corporation - Embrapa Tropical Agroindustry [11/2012-MP 3]
- Brazilian National Council for Science and Technology - CNPq [72420/2013-5, 401394/2014-0]
- University of Sao Paulo (USP)
- Federal University of Ceara (UFC)
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Anaerobic fermentation-based technologies are used for treating organic residues, and producing high value-added products, such as solvents, gases, and organic acids. Among several organic acids, n-caproic acid can be used as antimicrobial agent, additive in animal feed, flavor additive, and feedstock for chemical and biofuel industries. n-Caproic acid formation occurs through a carboxylic acid chain elongation process, which uses reverse beta-oxidation of acetic and/or n-butyric acid, and ethanol or lactic acid as an electron donor. This review addresses important issues in commercial n-caproic acid production: metabolic pathways, kinetics and thermodynamics, substrates, reactors, inhibition of competing biological activities, pH, and acid extraction. Additionally, a mathematical model to describe the reverse beta-oxidation kinetics was evaluated from existing literature. Current investigations show a wide range of n-caproic acid production rates (3.0-55.8 g/(L.d)), using different open cultures, fermentation conditions, and methods for inhibiting the methanogenesis. Clostridium kluyveri presence and a dominance of the Clostridium spp. were identified as determinant when ethanol was provided as electron donor. Continuous n-caproic acid extraction through pertraction is a promising technology, which combines selective extraction and enhanced production rates. However, confirming the industrial feasibility of this process requires further investigation.(C) 2016 Elsevier Ltd. All rights reserved.
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