Optimization of the initial levels of acetate, butyrate, pH, and sugars in the fermentation of blackstrap molasses by Clostridium acetobutylicum BIOTECH 1533

Date

6-1991

Degree

Bachelor of Science in Chemistry

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

William G. Padolina

Abstract

Scott, Rizaldy P., B.S. Chemistry, University of the Philippines Los Banos, June 1991. "Optimization of the initial levels of acetate, butyrate, pH, and sugars in the fermentation of blackstrap molasses to solvents by Clostridium acetobutylicum BIOTECH 1533."

Adviser: Dr. William G. Padolina

The influence of the initial levels of acetate, butyrate, pH, and total sugars on the batch fermentation of blackstrap molasses to acetone, 1-butanol, and ethanol by Clostridium acetobutylioum BIOTECH 1533 (NRRL B-643) was investigated. Factor effects and optimum factor levels in relation to solvent production and substrate consumption were studied thru response surface analysis based on a quadratic polynomial model with experiments performed according to the fractional factorial Box-Behnken design.

Fermentation studies on a molasses-rice bran medium done at 35°C for 60 h without continuous pH control have demonstrated a strong correlation between solvent yields and the levels of butyrate, pH, and total sugars. Solvent yields were apparently unaffected by acetate level. However, carbohydrate consumption rate was shown to be influenced by the four factors considered.

Maximum butanol and overall solvent production of 0.2506 and 0.3676, respectively, based on the amount of carbohydrate consumed were estimated to be obtainable under the following factor levels: acetic acid, 0.4424-0.7627 g/L; butyric acid, 0.6775-0.8027 g/L; initial pH, 5.00-5.07; and fermentable sugars, 29.0728-30.9808 g/L. Solvent concentrations were calculated to be maximal within the range 7.28-7.72 g/L for butanol and 10.62-11.39 g/L for total solvents. Complete carbohydrate consumption were predeicted under the defined optimal conditions. An increase in the present inoculation rate of 3% is suggested for the further improvement of substrate utilization and final solvent concentrations. Optimal conditions were predicted to provide yield enhancements of 30.80-32.62% for butanol and 38.76-39.38% for total solvents relative to a fermentation unsupplemented with acetate and butyrate at pH 6.00 and equivalent substrate feed rates. A phosphoenolpyruvate-dependent mechanism for the assimilation of sugars has been suggested to account for the effect of acetate on carbohydrate consumption. Solvent production enhancements caused by acid supplementations were discussed according to the putative physiological basis of the solventogenic shift. The insignificant effect of acetate level on the production of solvents has been hypothesized to be linked to the presence in C. acetobutylicum BIOTECH 1533 of a coenzyme A transferase involved in acid reassimilation that is more specific for butyrate instead of acetate uptake.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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