초록
Propionic acid 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 propionic acid from 40gL<SUP>-1</SUP> glycerol were 0.29gL<SUP>-1</SUP>h<SUP>-1</SUP>, 0.74mol<SUB>PA</SUB>mol<SUB>Gly</SUB><SUP>-1</SUP> and 20gL<SUP>-1</SUP>, respectively, after four consecutive recycle-batches. PEI-Poraver supported attachment of 31 times higher amounts of cells than PEI-Luffa and produced 20, 28 and 35gL<SUP>-1</SUP> propionic acid from 40, 65 and 85gL<SUP>-1</SUP> glycerol, respectively (0.61mol<SUB>PA</SUB>mol<SUB>Gly</SUB><SUP>-1</SUP>). The corresponding production rates were 0.86, 0.43 and 0.35gL<SUP>-1</SUP>h<SUP>-1</SUP>, which are the highest reported from glycerol via batch or fed-batch fermentations for equivalent propionic acid concentrations. Using a continuous mode of operation at a dilution rate of 0.1h<SUP>-1</SUP>, cell washout was observed in the bioreactor with free cells; however, propionic acid productivity, yield and concentration were 1.40gL<SUP>-1</SUP>h<SUP>-1</SUP>, 0.86mol<SUB>PA</SUB>mol<SUB>Gly</SUB><SUP>-1</SUP>, and 15gL<SUP>-1</SUP>, 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.