Fed-batch and continuous fermentation ofSelenomonas ruminantium for natural propionic, acetic and succinic acids

Abstract

An anaerobic fermentation process was developed for production of natural propionic, acetic and succinic acids froml-lactic acid usingSelenomonas ruminantium. Thel-lactic acid was quickly converted to a racemic mixture and there was no enantiomeric preference for further metabolism. The lactic acid was metabolized to propionic, acetic and succinic acids typically in a molar ratio of about 5∶3∶1. However, the ratio of propionate: succinate started high (as much as 22∶1), before declining to as low as 5∶1 after the first 48 h. Nutrients in corn steep liquor and yeast extract were necessary for optimal production of propionic acid. The corn steep liquor and yeast extract were heat stable at neutral pH, but some nutritional qualities were lost when heated at pH 2.4. In fed-batch fermentation on lactic acid 2.0% propionic acid was produced in 48 h and 2.3% in 68 h. A continuous culture operated at a dilution rate of 0.055 h−1 and a lactic acid feed concentration of 30 gL−1 had a propionic acid productivity of 0.59 gL−1h−1. The steady state results were: lactic acid 0.6%, propionic acid 1.1%, acetic acid 0.50%, and succinic acid 0.33%.