Poly-lactic acid synthesis for application in biomedical devices — A review

Factors affecting the fermentative lactic acid production from renewable resources1

Recent advances in lactic acid production by microbial fermentation processes

Microbial production of organic acids: expanding the markets.

Summary Lactic acid is widely used in the food, cosmetic, pharmaceutical, and chemical industries and has received increased attention for use as a monomer for the production of biodegradable poly(lactic acid). It can be produced by either biotechnological fermentation or chemical synthesis, but the former route has received considerable interest recently, due to environmental concerns and the limited nature of petrochemical feedstocks. There have been various attempts to produce lactic acid efficiently from inexpensive raw materials. We present a review of lactic acid-producing microorganisms, raw materials for lactic acid production, fermentation approaches for lactic acid production, and various applications of lactic acid, with a particular focus on recent investigations. In addition, the future potentials and economic impacts of lactic acid are discussed.

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Biotechnological Production of Lactic Acid and Its Recent Applications

A kinetic model of the fermentative production of lactic acid from glucose by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour has been developed. The model consists of terms for substrate and product inhibition as well as for the influence of pH and temperature. Experimental data from fermentation experiments under different physical conditions were used to fit and verify the model. Temperatures above 30 °C and pH levels below 6 enhanced the formation of by-products and d-lactic acid. By-products were formed in the presence of maltose only, whereas d-lactic acid was formed independently of the presence of maltose although the amount formed was greater when maltose was present. The lactic acid productivity was highest between 33 °C and 35 °C and at pH 6. In the concentration interval studied (up to 180 g l−1 glucose and 89 g l−1 lactic acid) simulations showed that both substances were inhibiting. Glucose inhibition was small compared with the inhibition due to lactic acid.

Modelling the influence of pH, temperature, glucose and lactic acid concentrations on the kinetics of lactic acid production by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour

l-lactic acid production from whole wheat flour hydrolysate using strains of Lactobacilli and Lactococci

A semidefined medium based on Casamino Acids allowed Lactococcus lactis ATCC 19435 to grow in the presence of oxygen at a slow rate (0.015 h−1). Accumulation of H2O2 in the culture prevented a higher growth rate. Addition of asparagine to the medium increased the growth rate, whereby H2O2 accumulated only temporarily during the lag phase. H2O2 is an inhibitor for several glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase being the most sensitive. Strain ATCC 19435 contained NADH oxidase (maximum specific rate under aerobic conditions, 426 nmol of NADH min−1 mg of protein−1), which reduced oxygen to water, whereby superoxide was formed as a by-product. H2O2 originated from the dismutation of superoxide by superoxide dismutase. Although H2O2 was rapidly destroyed under high metabolic fluxes, neither NADH peroxidase nor any other enzymatic H2O2-reducing activity was detected. However, pyruvate, the end product of glycolysis, reacted nonenzymatically and rapidly with H2O2 and hence was a potential alternative for scavenging of this oxygen metabolite intracellularly. Indeed, intracellular concentrations of up to 93 mM pyruvate were detected in aerobic cultures growing at high rates. It is hypothesized that self-generated pyruvate may serve to protect L. lactis strain ATCC 19435 from H2O2.

Formation and conversion of oxygen metabolites by Lactococcus lactis subsp. lactis ATCC 19435 under different growth conditions

Simultaneous saccharification of starch from whole-wheat flour and fermentation to lactic acid (SSF) was investigated. For saccharification the commercial enzyme mixture SAN Super 240 L, having α-amylase, amyloglucosidase and protease activity, was used, and Lactococcus lactis ssp. lactis ATCC 19435 was used for the fermentation. SSF was studied at flour concentrations corresponding to starch concentrations of 90 g/l and 180 g/l and SAN Super concentrations between 3 μl/g and 8 μl/g starch. Kinetic models, developed for the saccharification and fermentation, respectively, were used for simulation and data from SSF experiments were used for model verification. The model simulated SSF when sufficient amounts of nutrients were available during fermentation. This was achieved with high wheat flour concentrations or with addition of yeast extract or amino acids. Nutrient release was dependent on the level of enzyme activity.

Karin Hofvendahl

Papers

Factors affecting the fermentative lactic acid production from renewable resources1

Modelling the influence of pH, temperature, glucose and lactic acid concentrations on the kinetics of lactic acid production by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour

l-lactic acid production from whole wheat flour hydrolysate using strains of Lactobacilli and Lactococci

Formation and conversion of oxygen metabolites by Lactococcus lactis subsp. lactis ATCC 19435 under different growth conditions

Simultaneous enzymatic wheat starch saccharification and fermentation to lactic acid by Lactococcus lactis