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Effects of pH and acetic acid on homoacetic fermentation of lactate by Clostridium formicoaceticum
Author(s) -
Tang IChing,
Okos Martin R.,
Yang ShangTian
Publication year - 1989
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260340807
Subject(s) - acetic acid , fermentation , chemistry , kinetics , biochemistry , sodium acetate , salt (chemistry) , clostridium , mixed acid fermentation , nuclear chemistry , chromatography , lactic acid , organic chemistry , bacteria , lactic acid fermentation , biology , quantum mechanics , genetics , physics
Clostridium formicoaceticum homofermentatively converts lactate to acetate at 37°C and pH 6.6–9.6. However, this fermentation is strongly inhibited by acetic acid at acidic pH. The specific growth rate of this organism decreased from a maximum at pH 7.6 to zero at pH 6.6. This inhibition effect was found to be attributed to both H + and undissociated acetic acid. At pH values below 7.6, the H + inhibited the fermentation following non‐competitive inhibition kinetics. The acetic acid inhibition was found to be stronger at a lower medium pH. At pH 6.45–6.8, cell growth was found to be primarily limited by a maximum undissociated acetic acid concentration of 0.358 g/L (6m M ). This indicates that the undissociated acid, not the dissociated acid, is the major acid inhibitor. At pH 7.6 or higher, this organism could tolerate acetate concentrations of higher than 0.8 M , but salt (Na + ) became a strong inhibitor at concentrations of higher than 0.4 M . Acetic acid inhibition also can be represented by noncompetitive inhibition kinetics. A mathematical model for this homoacetic fermentation was also developed. This model can be used to simulate batch fermentation at any pH between 6.9 and 7.6.