Batch and continuous production of propionic acid from whey permeate by Propionibacterium acidi-propionici in a three-electrode amperometric culture system

Summary Growth of Propionibacterium acidi-propionici was studied on lactose as substrate and in acid whey permeate in a three-electrode poised-potential system with cobalt sepulchrate as artificial electron donor. In batch culture experiments in a stirred-tank reactor the substrate was fermented completely to propionic acid up to 6.5 g 1^–1 lactose in a supplemented whey permeate medium. No acetic acid was produced during the growth of P. acidi-propionici. An electron flow of 80–100 mA was obtained and the electron balance was 101%. In continuously growing cultures with 3 g 1^–1 of lactose as the substrate, propionate was formed as the only fermentation product up to a dilution rate (D) of 0.04 h^–1. With D>0.04 h^–1 the bacteria immobilized on the working electrode surface. It was examined whether an electron transfer occurred between the platinum working electrode and the immobilized cells. Correspondence to: W. Trösch