Ik-Keun Yoo

Lactic acid recovery using two-stage electrodialysis and its modelling

An experimental study was carried out on a two-stage process for lactic acid recovery, which consisted of desalting electrodialysis and water-splitting electrodialysis. Limiting current densities were measured at various lactate concentrations in the feed solution for the determination of the condition for switching from constant-current mode to constant-voltage mode in the desalting electrodialysis. The relationship between the electrical resistance of membrane stack and the lactate concentration was identified. The amount of water transferred due to electroosmosis which caused volume change in the feed and permeate solution was also experimentally determined. Based on the experimental results, mathematical models were developed, in which time changes in the feed and permeate volumes and the electrical resistance were considered. Model predictions of lactate concentration, volume changes, switching time and energy consumption were in good agreement with the experimental data. The prediction of total operating time for desalting electrodialysis showed some errors. However, it was considered to be due to the difficulties involved in determining the termination time in actual operation.

Encapsulation of Lactobacillus casei cells in liquid-core alginate capsules for lactic acid production

Abstract The immobilization method of Lactobacillus casei cells was investigated using alginate capsules that possess an interphasic membrane and a liquid core. The capsules were found to offer more space for cellular growth than gel-core beads, which resulted in 1.5-fold higher cell concentration than in the latter; however, the Ca-alginate structure was unstable during repeated batch fermentations for lactic acid production. Ba-alginate capsules were chemically and physically more stable than the Ca-alginate capsules in phosphate and lactate solutions. Attempts were also made to use various hardening agents to stabilize the structure of the Ba-alginate capsules. It was found that the treatment with a mixture of chitosan and BaCl2 solution gave the best results for hardening. Finally, stable lactic acid production was possible with a productivity of more than 2.7 g l−1h−1 by L. casei cells immobilized in chitosan-coated Ba-alginate capsules. The cell leakage from the capsules was maintained relatively low during repeated batch fermentations.

Microencapsulation of recombinant Saccharomyces cerevisiae cells with invertase activity in liquid‐core alginate capsules

As a means of integrating cell growth and immobilization, recombinant Saccharomyces cerevisiae cells with invertase activity were immobilized in liquid‐core alginate capsules and cultured to a high density. S. cerevisiae cells of SEY 2102 (MAT α ura3–52 leu2–3, 112 his4–519) harboring plasmid pRB58 with the SUC2 gene coding for invertase were grown to 83 g/L of liquid‐core volume inside the capsule on a dry weight basis. The cloned invertase was expressed well in the immobilized cells with slightly higher activity than the free cells in a batch culture. Invertase in the immobilized cells showed slightly more improved thermal stability than in the free cells. Storage in a Na‐acetate buffer at 4°C and 10°C for 1 month resulted in 7% and 8% loss in activity, respectively. The sucrose hydrolysis reaction was stably maintained for 25 repeated batches for 7 days at 30°C. Continuous hydrolysis of 0.3 M sucrose was carried out in a packed bed reactor with a conversion of more than 90% at a maximum productivity of 55.5 g glucose/L per hour for 7 days. In a continuous stirred tank reactor, the maximum productivity of 80.8 g glucose/L per hour was achieved at a conversion of 59.1% using 1.0 M sucrose solution, and 0.5 M sucrose solution was hydrolyzed for 1 week with a 95% conversion at a productivity of 48.8 g/L per hour.

High density cell culture by membrane-based cell recycle

Enhancement of productivity of a bioprocess necessitates continuous operation of bioreactors with high biomass concentrations than are possible in conventional batch, fedbatch or continuous modes of culture. Membrane-based cell recycle has been effectively used to maintain high cell concentrations in bioreactors. This review compares membranebased cell recycle operation with other such high density cell culture systems as immobilized cell reactors and reactors with cell recycle by centrifugation or gravity sedimentation. A theoretical of production of primary and secondary metabolites in membrane-based recycle systems is presented. Operation of this type of system is discussed with examples from aerobic and anaerobic fermentations.

Effect of B vitamin supplementation on lactic acid production by Lactobacillus casei

Abstract Various nitrogen sources were compared with yeast extract (YE) in terms of their usefulness for efficient lactic acid production by Lactobacillus casei subsp. rhamnosus. None of these nitrogen sources gave lactic acid concentrations as high as that for YE during 48 h of fermentation. On the basis of the amount of B vitamins in YE, various amounts of five essential B vitamins known to support the growth of L. casei were supplemented together with the nitrogen sources. The addition of B vitamins at less than 25 mg/l enhanced the lactic acid production to some extent in all cases except for the media supplemented with nitrogen sources of casein origin. The most significant increase was obtained with the N-Z-Soy peptone medium, in which the production of lactic acid after 48 h of fermentation was 2.2-fold higher than that without vitamin supplementation. Half of the YE in a medium supplemented with 10 g/l YE could be replaced by B vitamins at less than 25 mg/l and 3.3 g/l N-Z-Soy peptone without a significant decrease in the rate of lactic acid production.

By-product formation in cell-recycled continuous culture of Lactobacillus casei

While the volumetric productivity of lactic acid increased in continuous culture of Lactobacillus casei with cell recycle, enhanced formation of by-products such as acetate, formate, ethanol, and D-lactate was observed in the cell-recycled fermenter compared with a simple chemostat at a similar range of dilution rate. The increased formation of by-product which was significantly dependent on substrate limitation resulted from a lower dilution rate rather than a high cell concentration in the cell-recycled fermenter.