Lactic acid production by immobilized Lactobacillus casei in recycle batchreactor: a step towards optimization

Different nutritional and process parameters influencing lactic acid produc tion by Lactobacillus casei, adsorbed to Poraver beads in a recycle batch r eactor system, were studied in an attempt to set up a system having a long operational lifetime and permitting use of high substrate concentrations fo r maximal conversion to the product. The presence of lactose, even as a min or fraction of the total sugar amount, was necessary for complete utilizati on by the organism for growth and conversion to lactate. Hydrolysed whey pr otein constituted a richer source of nitrogen compared to yeast extract. Ad dition of lactate to the medium at the start of the process resulted in sev ere inhibition compared with the normal process. For a homofermentative pro cess, pH 6.0 was found to be optimal. The overall productivity of the recyc le system was higher under all conditions studied in comparison with the ba tch process using free cells. Enhancement in productivity in the recycle ba tch reactor was also accompanied by an increase in density of suspended cel ls. 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. (C) 1999 Published b y Elsevier Science B.V. All rights reserved.