Batch- and continuous propionic acid production from glycerol using free and immobilized cells of Propionibacterium acidipropionici

Propionicacid production from glycerol was studied using Propionibacterium acidipropionici DSM 4900 cells immobilized on polyethylenimine-treated Poraver (PEI-Poraver) and Luffa (PEI-Luffa), respectively. Using PEI-Luffa, the average productivity, yield and concentration of propionicacid from 40 g.L-1 glycerol were 0.29 g.L-1.h-1, 0.74 mol.mol-1 and 20.09 g.L-1, respectively, after four consecutive recycle-batches. PEI-Poraver supported attachment of 31 times higher amount of cells than PEI-Luffa and produced 20, 28 and 35 g.L-1propionicacid from 40, 65 and 85 g.L-1 glycerol, respectively (0.61 molPA.molGly-1). The corresponding production rates were 0.86, 0.43 and 0.35 g.L-1.h-1, which are the highest reported from glycerol via batch or fed-batch fermentations for equivalent propionicacid concentrations. Using a continuous mode of operation at a dilution rate of 0.1 h-1, cell washout was observed in the bioreactor with free cells; however, propionicacid productivity, yield and concentration were 1.4 g.L-1.h-1, 0.86 molPA.molGly-1, and 14.5 g.L-1, respectively, using immobilized cells in the PEI-Poraver bioreactor. The choice of the immobilization matrix can thus significantly influence the fermentation efficiency and -profile. The bioreactor using cells immobilized on PEI-Poraver allowed the fermentation of higher glycerol concentrations and provided stable and higher fermentation rates than that using free cells or the cells immobilized on PEI-Luffa.