A new approach for downstream purification of rhamnolipid biosurfactants

Abstract

Downstream purification processes often determine the manufacturing costs of biotechnological products, particularly for those with high yields in the upstream synthesis processes. Rhamnolipids are important biosurfactants with promising industrial applications. Significant research has been focused on optimizing rhamnolipid production in the upstream fermentation but there are very few studies on downstream processing. The objective of this study is to fill this critical technological gap by (1) tracking the recovery and purity of rhamnolipids processed through different unit operations and (2) developing new and more environmentally friendly downstream processing methods. A biopolymer removal step using alcohol precipitation was found effective in improving the recovery, from 66% to 78%, and giving about 87% purity in the product collected by acid precipitation without further solvent extraction. A reverse aqueous extraction method, which was optimized to recover 97% rhamnolipids from the solvent (ethyl acetate) extract, was examined as an alternative to the commonly used but costly, energy-intensive solvent vaporization. As a polishing step, calcium precipitation was optimized to selectively remove residual impurities while keeping all major rhamnolipid congeners in solution. The study also identified the presence of excess oil substrate/derivatives in the fermentation broth as a strongly negative factor to the downstream processing. The feeding strategy of oil substrate in fermentation should be carefully designed.