Production, purification, and enzymatic polymerization of sophorolipids

Biosurfactants and sugar-containing polymers have a wide range of potential applications. Attaining the recognized potential, however, requires lower production costs of biosurfactants and more effective polymerization methods. Among the most important biosurfactants are sophorolipids (SLs), which are produced by the yeast Torulopsis bombicola in both acidic and lactonic forms. Consequently, we investigated the production, purification, and enzymatic polymerization of the lactonic SLs in this research.; The production of SLs by Torulopsis bombicola was studied using glucose as the primary C-source with or without n-hexadecane or soybean oil as the second C-source. An HPLC-MSn system was employed for structure identification and quantification of all the major SL components produced. The quantitative impact on the productivity from the different substrates was examined. The study clearly identified hexadecane as the preferred second C-source for sophorolipid production, giving the highest productivity and selectivity toward lactonic SLs. In addition, a close structure correspondence was observed between the SL's lipid moiety and the lipid precursor used in the fermentation. The biodegradability of SLs by T. bombicola cells during the prolonged cultivation was also examined.; Various experimental methods were carried out to study and optimize the purification of lactonic SLs. Aqueous buffer solutions were found much more suitable than the commonly used ethanol as the crystallization medium. A new and effective method was developed, which could purify the lactonic SLs to higher than 99% purity.; For synthesizing sugar-containing polymers from lactonic SLs, the lipase-catalyzed ring-opening polymerization in organic solvent was explored. The reactant conversion and product formation were monitored using HPLC-MSn, to understand the reaction mechanism. Various lipases and organic solvents were evaluated for their suitability. The effects of temperature and enzyme concentration were examined. Salt-activation was found beneficial to the lipase activity in organic solvents, especially the polar ones. While the formation of polymers was demonstrated in the study, the products formed were insoluble in a wide range of solvents tested. Future research is recommended to address the cause(s) of this undesirable property and develop more effective polymerization methods.