Conversion of volatile fatty acids into polyhydroxyalkanoate by Ralstonia eutropha

The aims of this study were to optimize condensed corn solubles (CCS) as a medium for growth of Ralstonia eutropha and to determine the effects of individual volatile fatty acids (VFAs) on polyhydroxyalkanoate (PHA) production.

A CCS medium of concentration 240 g l(-1) with a carbon : nitrogen ratio of 50 : 1 was developed as the optimal medium. Cultures were grown in 1-l aerated flasks at 250 rev min(-1) at 30 degrees C for 120 h. Comparable growth rates were observed in CCS vs a defined medium. At 48 h, VFAs were fed individually at different levels. Optimal levels of all the acids were determined to maximize PHA production. An overall comparison of the VFAs indicated that butyric and propionic acids provided the best results.

An optimized CCS medium supported growth of R. eutropha. Butyric and propionic acids were the most efficient carbon sources to maximize PHA production when added at the 5 g l(-1) level.

The study shows that a byproduct of ethanol industry can be effectively used as a low cost medium for PHA production, thus partly reducing the cost of commercialization of biopolymers.