**5. Conclusions**

Lactic acid production in LAB has both cell mass and growth dependent portions. Typically LAB require several nutrient components for their growth increasing the fermentation and down-stream processing costs. Down-stream processing is especially important in the production of lactic acid for PLA. As RP is the a major investment factor affecting costs, the minimization of medium and product purification costs should be accompanied by methods increasing cell mass concentration without excess growth. For this several different strategies have been applied so far mainly in academia (cell immobilization, cell-recycling and cell-retention). As history shows some of these could be applicable in industrial production as well, however pilot and demonstration plant studies and some risk-taking are required.

The Current Status and Future Expectations in Industrial Production of Lactic Acid by Lactic Acid Bacteria 625

**Abbreviations** 

D-LDH - D-lactate dehydrogenase

L-LDH - L-lactate dehydrogenase

RP - Volumetric productivity g/l\*h

PPP - Pentose phosphate pathway PKP - Phosphoketolase pathway

YP/X – Yield of lactic acid per cell mass g/g

Biotechnology 2011;156 286-301.

in Microbiology 2002;28 281-370.

Archives of Microbiology 1984;138 44-48.

SSF – Simultaneous saccharification and fermentation

YP/S – Yield of lactic acid per substrate consumed g/g

LAB – lactic acid bacteria

NTG – Nitrosoguanidine

PLA – poly lactic acid

**6. References** 

1995;16 221-231.

η % - Efficiency, i.e. the ratio of YP/S to the maximum theoretical value

[1] Wee YJ, Kim JN, Ryu HW. Biotechnological production of lactic acid and its recent

[2] Datta R, Tsai SP, Bonsignore P, Moon SH, Frank JR. Technological and Economic-Potential of Poly(Lactic Acid) and Lactic-Acid Derivatives. Fems Microbiology Reviews

[3] Fukushima K, Sogo K, Miura S, Kimura Y. Production of D-lactic acid by bacterial

[4] Jem JK, van der Pol JF, de Vos S. Microbial lactic acid, its polymer poly(lactic acid), and

[5] Vink ETH, Davies S, Kolstad JJ. The eco-profile for current Ingeo® polylactide

[6] Shah AA, Hasan F, Hameed A, Ahmed S. Biological degradation of plastics: A

[7] Nampoothiri KM, Nair NR, John RP. An overview of the recent developments in

[8] Abdel-Rahman MA, Tashiro Y, Sonomoto K. Lactic acid production from lignocellulose-derived sugars using lactic acid bacteria: Overview and limits. Journal of

[9] Carr FJ, Chill D, Maida N. The lactic acid bacteria: A literature survey. Critical Reviews

[10] Murphy MG, Condon S. Correlation of Oxygen Utilization and Hydrogen-Peroxide Accumulation with Oxygen Induced Enzymes in Lactobacillus-Plantarum Cultures.

[11] Sedewitz B, Schleifer KH, Gotz F. Physiological role of pyruvate oxidase in the aerobic metabolism of *Lactobacillus plantarum*. Journal of Bacteriology 1984;160 462-465.

applications. Food Technology and Biotechnology 2006;44 163-172.

fermentation of rice starch. Macromolecular Bioscience 2004;4 1021-1027.

their industrial applications. Microbiology Monographs 2010;14 323-346.

polylactide (PLA) research. Bioresource Technology 2010;101 8493-8501.

comprehensive review. Biotechnology Advances 2008;26 246-265.

production. Industrial Biotechnology 2010;6 212-224.

The main C/energy source spectrum available for LAB has been widened significantly. Reports of new possible substrates are frequently published, and the utilization of industrial side streams is a growing trend. Into this direction major successes have also been achieved with metabolic engineering providing strains for efficient production of lactic acid from pentoses as well, which is to promote sustainable use of renewables.

In an ideal fermentation process product inhibition should be minimized so that high RP would be achieved even at high lactic acid concentrations resulting in feasible average productivities. For this purpose both acclimatization and mutagenesis has been applied successfully. However, it has to be considered how far can we go in respect to fermentation pH and lactic acid concentration. There are already remarkable alternatives to LAB with naturally better properties in this sense. Some success has been achieved with in-situ product recovery, but also these procedures lack experiences in any larger scale.

Conventional lactic acid production process with LAB is accompanied with the formation of large amounts of gypsum in the product recovery stage. Fermentation at lower pH diminishes this amount, but does not prevent its formation. Electrodialysis has been considered too expensive technique for the recovery of such cheap, bulk products as lactic acid. However, recent reports claim promising results with this technology. Forecasted figures for lactic acid market show up to one million tons per year. The growth would come mainly from the growth of PLA as a biodegradable polymer based on renewable raw materials. Economies of scale should decrease the production costs, but new technical approaches are also needed to reach these figures.
