title: Optimum alcohol concentration for chain elongation in mixed-culture fermentation of cellulosic substrate.
abstract: Medium-chain fatty acids (MCFA, e.g., caproic, heptanoic, caprylic acid) are more valuable than short-chain fatty acids (SCFA, e.g., acetic, propionic, butyric, valeric acid). SCFAs are major products in methane-inhibited mixed-culture anaerobic fermentation. By feeding ethanol to the fermentor, MCFA formation is enhanced through chain elongation. Microorganisms such as Clostridium kluyveri elongate short-chain acids by combining them with alcohol. Very low ethanol concentration reduces chain elongation rates, whereas very high ethanol concentrations inhibit microorganisms. To maximize MCFA production, different ethanol concentrations were investigated in the mixed-culture fermentation of office paper and chicken manure. At 10 g/L ethanol concentration, 10 g/L MCFA was formed. High ethanol concentrations (above 40 g/L) inhibit microorganisms resulting in no chain elongation. For chain elongation, propanol was found to be more inhibitory than ethanol. The data suggest that MCFA production will increase by continuously extracting MCFA and maintaining 5-10 g/L ethanol concentration by periodic addition. Biotechnol. Bioeng. 2016;113: 2597-2604. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843. sklonkar@tamu.edu.
authors.forename: Sagar
authors.initials: S
authors.lastname: Lonkar
authors.affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Fu
authors.affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843.
authors.forename: Mark
authors.initials: M
authors.lastname: Holtzapple
mesh_terms: D000818:Animals; D019149:Bioreactors / Q000382:microbiology; D002482:Cellulose / Q000378:metabolism*; D002645:Chickens; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism; D000431:Ethanol / Q000008:administration & dosage / Q000378:metabolism*; D005227:Fatty Acids / Q000096:biosynthesis* / Q000737:chemistry; D005285:Fermentation / Q000502:physiology; D019015:Geologic Sediments / Q000382:microbiology*; D008372:Manure / Q000382:microbiology*; D010209:Paper
chemical_list: D003470:Culture Media; D005227:Fatty Acids; D008372:Manure; D000431:Ethanol; D002482:Cellulose
keywords: chain elongation; medium-chain fatty acids; mixed-culture fermentation; the MixAlco process