L-Lactic acid production by combined utilization of agricultural bioresources as renewable and economical substrates through batch and repeated-batch fermentation of Enterococcus faecalis RKY1.

Enterococcus faecalis RKY1 was used to produce l-lactic acid from hydrol, soybean curd residues (SCR), and malt. Hydrol was efficiently metabolized to l-lactic acid with optical purity of >97.5%, though hydrol contained mixed sugars such as glucose, maltose, maltotriose, and maltodextrin. Combined utilization of hydrol, SCR, and malt was enough to sustain lactic acid fermentation by E. faecalis RKY1. In order to reduce the amount of nitrogen sources and product inhibition, cell-recycle repeated-batch fermentation was employed, where a high cell mass (26.3g/L) was obtained. Lactic acid productivity was improved by removal of lactic acid from fermentation broth by membrane filtration and by linearly increased cell density. When the total of 10 repeated-batch fermentations were carried out using 100g/L hydrol, 150g/L SCR hydrolyzate, and 20g/L malt hydrolyzate as the main nutrients, lactic acid productivity was increased significantly from 3.20g/L/h to 6.37g/L/h.

Optimization of alkaline protease production by batch culture of Bacillus sp. RKY3 through Plackett-Burman and response surface methodological approaches.

The proteolytic enzymes are the most important group of commercially produced enzymes. The production of alkaline protease was optimized using a newly isolated Bacillus sp. RKY3. The fermentation variables were selected in accordance with the Plackett-Burman design and were further optimized via response surface methodological approach. Four significant variables (corn starch, yeast extract, corn steep liquor, and inoculum size) were selected for the optimization studies. The statistical model was constructed via central composite design (CCD) using three screened variables (corn starch, corn steep liquor, and inoculum size). An overall 2.3-fold increase in protease production was achieved in the optimized medium as compared with the unoptimized basal medium. Enzyme activity increased significantly with optimized medium (939 u ml(-1)) when compared with unoptimized medium (417 u ml(-1)).

Production of lactic acid from cheese whey by batch and repeated batch cultures of Lactobacillus sp. RKY2.

The fermentative production of lactic acid from cheese whey and corn steep liquor (CSL) as cheap raw materials was investigated by using Lactobacillus sp. RKY2 in order to develop a cost-effective fermentation medium. Lactic acid yields based on consumed lactose were obtained at more than 0.98 g/g from the medium containing whey lactose. Lactic acid productivities and yields obtained from whey lactose medium were slightly higher than those obtained from pure lactose medium. The lactic acid productivity gradually decreased with increase in substrate concentration owing to substrate and product inhibitions. The fermentation efficiencies were improved by the addition of more CSL to the medium. Moreover, through the cell-recycle repeated batch fermentation, lactic acid productivity was maximized to 6.34 g/L/h, which was 6.2 times higher than that of the batch fermentation.

Production of lactic acid from cheese whey by batch and repeated batch cultures of Lactobacillus sp. RKY2.

The fermentative production of lactic acid from cheese whey and corn steep liquor (CSL) as cheap raw materials was investigated by using Lactobacillus sp. RKY2 in order to develop a cost-effective fermentation medium. Lactic acid yields based on consumed lactose were obtained at more than 0.98 g/g from the medium containing whey lactose. Lactic acid productivities and yields obtained from whey lactose medium were slightly higher than those obtained from pure lactose medium. The lactic acid productivity gradually decreased with increase in substrate concentration owing to substrate and product inhibitions. The fermentation efficiencies were improved by the addition of more CSL to the medium. Moreover, through the cell-recycle repeated batch fermentation, lactic acid productivity was maximized to 6.34 g/L/h, which was 6.2 times higher than that of the batch fermentation.

Recovery of lactic acid by repeated batch electrodialysis and lactic acid production using electrodialysis wastewater.

Repeated batch electrodialysis for lactic acid recovery was investigated using lactic acid solution and fermentation broth. In both cases, lactate fluxes averaged more than 7.0 moles/m2.h, lactate recovery reached more than 99% for all the batch runs, and specific energy consumption per unit lactate transported was lower than 0.25 kWh/kg-lactate. When electrodialysis wastewater was used as a fermentation medium, supplemented with 100 g/l glucose, up to 92.4 g/l lactic acid was produced with a productivity of 0.67 g/l.h. In addition, when electrodialysis wastewater was supplemented with 150 g/l whole-corn flour hydrolyzate and 5 g/l corn steep liquor, 2.5-fold and 1.8-fold increases in lactic acid productivity and maximum cell growth, respectively, were achieved, as compared with lactic acid fermentation using electrodialysis wastewater supplemented with glucose only.

Lactic acid production from agricultural resources as cheap raw materials.

Agricultural resources such as barley, wheat, and corn were hydrolyzed by commercial amylolytic enzymes and fermented into lactic acid by Enterococcus faecalis RKY1. Although no additional nutrients were supplemented to those resources, lactic acid productivities were obtained at >0.8 g/l h from barley and wheat. When 200 g/l of whole wheat flour was hydrolyzed by amylolytic enzymes after the pre-treatment with 0.3% (v/v) sulfuric acid and sterilized by filtration, E. faecalis RKY1 efficiently produced lactic acid with 2.6 g/l h of lactic acid productivity and 5.90 g/l of maximal dry cell weight without additional nutrients. Lactic acid productivity and cell growth could be enhanced to 31% and 12% higher values than those of non-adapted RKY1, by adaptation of E. faecalis RKY1 to CSL-based medium. When the medium contained 200 g/l of whole wheat flour hydrolyzate, 15 g/l of corn steep liquor, and 1.5 g/l of yeast extract, lactic acid productivity and maximal dry cell weight were obtained at 5.36 g/l h and 14.08 g/l, respectively. This result represented an improvement of up to 106% of lactic acid productivity and 138% of maximal dry cell weight in comparison to the fermentation from whole wheat flour hydrolyzate only.

Culture medium optimization for acetic acid production by a persimmon vinegar-derived bacterium.

A new acetic acid-producing microorganism, Acetobacter sp. RKY4, was isolated from Korean traditional persimmon vinegar, and we optimized the culture medium for acetic acid production from ethanol using the newly isolated Acetobacter sp. RKY4. The optimized culture medium for acetic acid production using this microorganism was found to be 40 g/L ethanol, 10 g/L glycerol, 10 g/L corn steep liquor, 0.5 g/L MgSO4.7H2O, and 1.0 g/L (NH4)H2PO4. Acetobacter sp. RKY4 produced 47.1 g/L of acetic acid after 48 h of fermentation in a 250 mL Erlenmeyer flask containing 50 mL of the optimized medium.

Fermentative production of DL-lactic acid from amylase-treated rice and wheat brans hydrolyzate by a novel lactic acid bacterium, Lactobacillus sp.

Rice and wheat brans, without additional nutrients and hydrolyzed by alpha-amylase and amyloglucosidase, were fermented to DL-lactic acid using a newly isolated strain of Lactobacillus sp. RKY2. In batch fermentations at 36 degrees C and pH 6, the amount of lactic acid in fermentation broth reached 129 g l(-1) by supplementation of rice bran with whole rice flour. The maximum productivity was 3.1 g lactic acid l(-1) h(-1) in rice bran medium supplemented with whole rice flour or whole wheat flour.

Production of fumaric acid using rice bran and subsequent conversion to succinic acid through a two-step process.

The fungal production of fumaric acid using rice bran and subsequent bacterial conversion of succinic acid using fungal culture broth were investigated. Since the rice bran contains abundant proteins, amino acids, vitamins, and minerals, it is suitable material that fungi use as a nitrogen source. The effective concentration of rice bran to produce fumaric acid was 5 g/L. A large amount of rice bran caused excessive fungal growth rather than enhance fumaric acid production. In addition, we could produce fumaric acid without the addition of zinc and iron. Fungal culture broth containing approx 25 g/L of fumaric acid was directly employed for succinic acid conversion. The amount of glycerol and yeast extract required for succinic acid conversion was reduced to 70 and 30%, respectively, compared with the amounts cited in previous studies.

Biotechnological production of L(+)-lactic acid from wood hydrolyzate by batch fermentation of Enterococcus faecalis.

The inhibition of lactic acid fermentation by wood hydrolyzate was decreased (approx. 20%) by adaptation of Enterococcus faecalis RKY1 to wood hydrolyzate-based medium whereby lactic acid productivity and cell growth were enhanced by 0.5 g l(-1) h(-1) and 2.1 g l(-1), respectively. When the diluted or concentrated wood hydrolyzate (equivalent to 25-100 g glucose l(-1)) was supplemented with 15 g yeast extract l(-1), 24-93 g lactic acid l(-1) was produced at a rate between 1.7 g l(-1) h(-1) and 3.2 g l(-1) h(-1).

Lactic acid production through cell-recycle repeated-batch bioreactor.

The effect of various nitrogen sources on cell growth and lactic acid production was investigated. The most effective nitrogen source was yeast extract; more yeast extract gave higher cell growth and lactic acid productivity. Yeast extract dosage and cell growth were proportional up to a yeast extract concentration of 30 g/L, and lactic acid productivity was linearly correlated up to a yeast extract dosage of 25 g/L. However, increasing the yeast extract content raises the total production cost of lactic acid. Therefore, we attempted to find the optimum yeast extract dosage for a repeated-batch operation with cell recycling. The results show that when using Enterococcus faecalis RKY1 only 26% of the yeast extract dosage for a conventional batch fermentation was sufficient to produce the same amount of lactic acid, whereas the lactic acid concentration in the product stream (92-94 g/L) and lactic acid productivity (6.03-6.20 g/[L x h]) were similar to those of a batch operation. Furthermore, long-term stability was established.

Continuous production of succinic acid by a fumarate-reducing bacterium immobilized in a hollow-fiber bioreactor.

Enterococcus faecalis RKY1, a fumarate-reducing bacterium, was immobilized in an asymmetric hollow-fiber bioreactor (HFBR) for the continuous production of succinic acid. The cells were inoculated into the shell side of the HFBR, which was operated in transverse mode. Since the pH values in the HFBR declined during continuous operation to about 5.7, it was necessary to change the feed pH from 7.0 to 8.0 after 24 h of operation in order to enhance production of succinic acid. During continuous operation with a medium containing fumarate and glycerol, the productivity of succinate was 3.0-10.9 g/(L x h) with an initial concentration of 30 g/L of fumarate, 4.9-14.9 g/(L x h) with 50 g/L of fumarate, and 7.2-17.1 g/(L x h) with 80 g/L of fumarate for dilution rates between 0.1 and 0.4 h(-1). The maximum productivity of succinate obtained by the HFBR (17.1 g of succinate/[L x h]) was 1.7 times higher than that of the batch bioconversions (9.9 g of succinate/ [L x h]) with 80 g/L of fumarate. Furthermore, the long-term stability of the HFBR was demonstrated with a continuously efficient production of succinate for more than 15 d (360 h).