A novel approach for the production and purification of mannosylerythritol lipids (MEL) by Pseudozyma tsukubaensis using cassava wastewater as substrate

Abstract

P. tsukubaensis is a yeast-like microorganism that synthesized the biosurfactant mannosylerythritol lipids-B (MEL-B). Production cost can be one of the drawbacks of biosurfactants production. Therefore the development of efficient and cost effective purification strategies and the use of by-products in the culture medium could serve as important strategies to reduce overall process cost. The aim of this work was to evaluate the production of MEL using cassava wastewater, a hydrophilic medium composed of a low-cost substrate which is a by-product of cassava processing, followed by foam fractionation and ultrafiltration of MEL. Cassava wastewater proved to be a feasible culture medium for P. tsukubaensis and MEL-B production as the yield (1.26 g L−1) was similar to that reported by others using water-soluble carbon sources (up to 2 g L−1). Interestingly ultrafiltration with 100 kDa MWCO membranes (using 20 mL centrifugal devices) led to the purification of MEL-B in one step since ≈ 80% of MEL was recovered, while more than 95% of proteins were found in the permeate. The scale up of the ultrafiltration (up to 500 mL) using a cross flow filtration unit led to very similar results. Overall the ultrafiltration led to a threefold increase in MEL purity in terms of protein (at both scales). The chemical characterization by NMR confirmed the production of MEL-B homologue and also the production of a second stereoisomer ≈9%, while the CG-MS and MALDI-TOFMS analysis confirmed the main fatty acids within the structure of MEL-B (C8:0 and 12:0 and C8:0 and C14:1). Therefore, the process developed here was found to be a good alternative to the conventional production of MEL which uses synthetic culture medium, solvent extraction (ethyl acetate) and column chromatography (silica) for its purification.