Sophorolipids (SL) are a promising biosurfactant due to their biodegradability and broad range of application in cleaning, cosmetics or agriculture. Downstream processing of biotechnological products is often challenging because of the complex mixture of many components in low concentrations, unknown thermodynamic data and high water content. With regard to sophorolipids, mainly poorly water-soluble lactonic SL can be produced in high concentrations of up to 400 g/L so that a product-rich phase is formed during cultivation. Consequently product isolation and purification can be achieved very easily by phase separation and subsequent washing steps. To optimize those process steps, the solubility of SL in water and protein removal was measured and implemented in an equilibrium stage model. The solubility of SL decreases with higher temperature, whereas the separation of proteins could not be investigated at high temperatures due to denaturation. Instead the distribution of proteins was determined at lower temperatures and used for the whole temperature range in the model. Based on this data, the optimal washing process to remove 90 % of protein consists of three stages and a product-phase to water ratio of 4:1 (w:w) per stage.
