Abstract

The influence of a biosurfactant (rhamnolipids) on the effectiveness of citric acid production by Yarrowia lipolytica from sunflower oil was studied. The surfactant-mediated solubilization of the hydrophobic substrate was assessed by particle size distribution characteristics with and without the presence of sunflower oil hydrolization products. The presence of rhamnolipids contributed to a decrease of the oil droplet size, most notably for samples containing sunflower oil and its hydrolization products. The citric acid yield for cultures not supplemented with rhamnolipids was at 82.9 g/l, with a 1:0.04 citric acid to isocitric acid ratio (CA:ICA). The addition of rhamnolipids at 1 g/l resulted in a 5% increased citric acid yield (87.1 g/l), however a decrease (79.0 g/l) was observed for samples containing 5 g/l of rhamnolipids. The rhamnolipids-induced emulsification of sunflower oil did not seem to influence the citric acid production efficiency. Additional research revealed that the biosurfactant was degraded by yeast cells during the bioconversion process. The possible explanations of this phenomenon include the utilization of rhamnolipids as an alternative carbon source or microbial destabilization of micelles formed by this biosurfactant due to potential bioavailability issues.

Key words: Yarrowia lipolytica, citric acid, rhamnolipids, sunflower oil.