Production of Medium-Chain-Length Poly(3-Hydroxyalkanoates) from Saponified Palm Kernel Oil by Pseudomonas putida: Kinetics of Batch and Fed-Batch Fermentations

The kinetics of medium-chain-length poly(3-hydroxyalkanoates), PHA(MCL) production by Pseudomonas putida PGA1 in batch and fed-batch fermentations were studied. With saponified palm kernel oil (SPKO) supplying the free fatty acids mixture as the sole carbon and energy source, PHA(MCL) accumulation is encouraged under ammonium-limited condition, which is a nitrogen stress environment. The amount of PHA(MCL) accumulated and its specific production rate, q(PHA) were influenced by the residual ammonium concentration level in the culture medium. It was observed that in both fermentation modes, when the residual ammonium was exhausted (<0.05 gL(-1)), the PHA(MCL) accumulation (11.9%) and q(PHA) (0.0062 h(-1)) were significantly reduced. However, this effect can be reversed by feeding low amount of ammonium to the culture, resulting in significantly improved PHA(MCL) yield (71.4%) and specific productivity (0.6 h(-1)). It is concluded that the feeding of low ammonium concentration to the culture medium during the PHA(MCL) accumulation has a positive effect on sustaining the PHA(MCL) biosynthetic capability of the organism. It was also found that increasing SPKO concentration in the medium significantly reduced (up to 50%) the volumetric oxygen transfer coefficient (K(L)a) of the fermentation system.