Optimization of the primary purification process of extracting sphorolipid from the fermentation broth to achieve a higher yield and purity

Abstract

Sophorolipid (SL) is a surface-active glycolipid biosurfactant with promising industrial applications. It is synthesised by fermentation of hydrophobic and hydrophilic substrates using selected non-pathogenic yeasts. However, its applications are limited by high production costs and ineffective product recovery in downstream purification stages. Natural sophorolipids are produced in six to nine different hydrophobic sophorosides, where the carboxyl end of the fatty acid is either free, which is known as the acidic or open form, or it can be esterified internally to produce the lactonic form. The present study deals with the screening and selection of suitable solvents for the extraction of acidic and lactonic SL from fermentation broth. The optimisation study involves exhaustive extraction with the six different immiscible solvents ethyl acetate, butyl acetate, methylene dichloride, methyl tert.-butyl ether, methyl iso-butyl ketone and methyl ethyl ketone. The partition coefficient (K_d), which is the ratio of the solute concentration in the organic layer compared to the aqueous layer, determines the performance measurement of the extraction process in terms of yield and purity of the desired solute. The factors that influence exhaustive extraction were the broth to solvent ratio and the extraction stages. The optimal extraction conditions for the highest possible yield were a broth to solvent ratio of 1:1 and a number of extraction steps of 2. Methylene dichloride showed better results in terms of yield and selectivity in the extraction of acidic and lactonic SL from the fermentation broth compared to the other solvents investigated. For lactonic SL, the highest K_d value determined was 36.6 and for acidic SL the highest K_d value was 1.14.