Biotechnological strategies to produce levan: Mass transfer and techno-economical evaluation

Abstract

Levan is a fructose polysaccharide with potential as a carrier for drug delivery systems due to its ability to form nanoparticles in water by a self-assembly phenomenon. In order to overcome drawbacks concerning its production by fermentative processes (long time for growing bacteria and downstreaming and purification steps), different enzymatic processes are studied. Specifically, a packed bed reactor with the enzyme in alginate beads, a monolithic reactor (with the immobilized enzyme) and a homogenous batch stirred tank (without enzyme immobilization) are proposed. The last one is used to determine the kinetics and to compare the efficacy of the heterogeneous reactors. Techno-economical evaluations show that, for packed bed reactor and monolithic reactor, fixed capital costs (around 500,000 €) and production costs are similar (around 6000 €/kg) in spite of the processes differences. Nanoparticles obtained by levan from alginate beads (2 mm) have a size around 230 nm whereas nanoparticles of 150 nm were obtained from the monolithic reactor and from the batch reactor. Finally, mass transfer models for those heterogeneous reactors highlight that monolithic reactor provides a low resistance to mass transport (0.031 s−1), whereas packed bed reactor increases that resistance (0.301 s−1) due to tortuosity and internal transport through beads.