Abstract
Different nutritional and process parameters influencing lactic acid production by Lactobacillus casei, adsorbed to
Poraver beads in a recycle batch reactor system, were studied in an attempt to set up a system having a long
operational lifetime and permitting use of high substrate concentrations for maximal conversion to the product. The
presence of lactose, even as a minor fraction of the total sugar amount, was necessary for complete utilization by the
organism for growth and conversion to lactate. Hydrolysed whey protein constituted a richer source of nitrogen
compared to yeast extract. Addition of lactate to the medium at the start of the process resulted in severe inhibition
compared with the normal process. For a homofermentative process, pH 6.0 was found to be optimal. The overall
productivity of the recycle system was higher under all conditions studied in comparison with the batch process using
free cells. Enhancement in productivity in the recycle batch reactor was also accompanied by an increase in density
of suspended cells. However, the contribution of the suspended cells to the overall reactor productivity was not
noticeable. The bead size of the matrix was found to be important for operational stability of the reactor. © 1999
Published by Elsevier Science B.V. All rights reserved.