Suspension and transformation performance of poly(2-hydroxyethyl methacrylate)-based anion exchange cryogel beads with immobilized Lactobacillus paracasei cells as biocatalysts towards biosynthesis of phenyllactic acid in stirred tank bioreactors

Abstract

Suspension hydrodynamics of poly(2-hydroxyethyl methacrylate)-based anion-exchange cryogel beads in stirred-tank bioreactors were investigated by high-speed imaging and the scale-up suspension behaviors were simulated by computational fluid dynamics methods. Lactobacillus paracasei cell-loaded cryogel beads were prepared and employed as biocatalysts for biotransformation of phenylalanine to phenyllactic acid (PLA). The results showed that with the increase of agitation rate, the cryogel beads underwent the transition from partial to complete suspension and finally to uniform suspension. The experimental and simulated just suspended impeller speeds were in good agreement with Zwietering’s correlation at the cryogel-bead concentrations from 1% to 8%. Non-uniform suspension behaviors and more heterogeneous turbulent flow fields especially in regions near impellers, baffles and bottom wall occurred in the simulated scaling-up of the bioreactors from the working volume of 5–200 L. The yield and productivity of PLA increased with the increase of the fraction of cell-loaded cryogel beads. The maximum PLA concentration of 202 mg L−1 and the productivity of 7.1 mg L−1 h−1 were obtained for 8% cell-loaded cryogel beads in 100 mM phosphate containing 1 mg mL−1 of phenylalanine and 2 mg mL−1 glucose at the agitation rate of 80 rpm and temperature of 35 °C, indicating that cell-loaded cryogel beads could be new biocatalysts for direct conversion of cheap substrate phenylalanine to high-value product, PLA.