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.     

Simultaneous saccharification and extractive fermentation of lignocellulosic materials into lactic acid in a two-zone fermentor-extractor system

Simultaneous saccharification and extractive fermentation of lignocellulosic materials into lactic acid was investigated using a two-zone bioreactor. The system is composed of an immobilized cell reactor, a separate column reactor containing the lignocellulosic substrate and a hollow-fiber membrane. It is operated by recirculating the cell free enzyme (cellulase) solution from the immobilized cell reactor to the column reactor through the membrane. The enzyme and microbial reactions thus occur at separate locations, yet simultaneously. This design provides flexibility in reactor operation as it allows easy separation of the solid substrate from the microorganism, in situ removal of the product and, if desired, different temperatures in the two reactor sections. This reactor system was tested using pretreated switchgrass as the substrate. It was operated under a fed-batch mode with continuous removal of lactic acid by solvent extraction. The overall lactic acid yield obtainable from this bioreactor system is 77% of the theoretical.     

Simultaneous fermentation and separation of lactic acid in a biparticle fluidized-bed bioreactor

A bioreactor configuration has been tested for simultaneous fermentation and separation of the desired inhibitory product, lactic acid. The bioreactor is a fluidized bed of immobilized Lactobacillus delbreuckii. Another solid phase of denser sorbent particles (a poly-vinyl pyridine resin) was added to this fluidized bed. These sorbent particles fell through the bed, absorbed the product, and were removed. In test fermentations, the addition of the sorbent enhanced the fermentation and moderated the fall of the pH. The biparticle fluidized-bed bioreactor utilizing immobilized microorganisms and adsorbent particles has been shown to enhance the production of lactic acid fourfold in this nonoptimized system.

     

Continuous production of lactic acid in a cell recycle reactor

The production of lactic acid from glucose has been demonstrated using a CSTR (continuous stirred-tank reactor) with cell recycle. Studies were conducted withLactobacillus delbrueckii at a fermentation temperature of 42°C and a pH of 6.25. A cell density of 140 g dry weight/L and a volumetric productivity of 150 g/L.h, with complete glucose consumption, were obtained. It was not possible to obtain a lactic acid concentration above 60 g/L because of product inhibition. A cell purge was not necessary to maintain high viability bacteria culture or to obtain a steady state. At steady state the net cell growth appeared to be negligible. The specific glucose consumption for cell maintenance was 0.33 g glucose/g cells-h.     

Semicontinuous production of lactic acid from cheese whey using integrated membrane reactor

Semicontinuous production of lactic acid from cheese whey using free cells of Bifidobacterium longum with and without nanofiltration was studied. For the semicontinuous fermentation without membrane separation, the lactic acid productivity of the second and third runs is much lower than the first run. The semicontinuous fermentation with nanoseparation was run semicontinuously for 72 h with lactic acid to be harvested every 24 h using a nanofiltration membrane unit. The cells and unutilized lactose were kept in the reactor and mixed with newly added cheese whey in the subsequent runs. Slight increase in the lactic acid productivity was observed in the second and third runs during the semicontinuous fermentation with nanofiltration. It can be concluded that nanoseparation could improve the lactic acid productivity of the semicontinuous fermentation process.     

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.     

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·h]) were similar to those of a batch operation. Furthermore, long-term stability was established.     

Resin selection and single-step production and recovery of lactic acid from pretreated wood

Four ion-exchange resins (Amberlite IRA 900, IRA 400, IRA 96, and IRA 67) were employed for lactic acid recovery from simultaneous saccharification and fermentation (SSF) media. The best resins (Amberlite IRA 900 and IRA 400) were assayed for capacity, regenerant consumption, percentage of lactic acid recovery, and product concentration. Almost quantitative lactic acid recoveries at constant capacities were achieved in four sequential loading/regeneration cycles. A strong-base resin (Amberlite IRA 400) was selected for intermittent lactic acid separation in a typical SSF process, in which pretreated wood was saccharified by cellulases in the presence of Lactobacillus delbrueckii. The dynamics of lactic acid generation and lactic acid recovery were established.     

Separate and Concentrate Lactic Acid Using Combination of Nanofiltration and Reverse Osmosis Membranes

The processes of lactic acid production include two key stages, which are (a) fermentation and (b) product recovery. In this study, free cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutoff of 100–400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step. The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics has the highest lactose retention (97 ± 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic acid was also reported in this paper.     

Release of Polyphenols Is the Major Factor Influencing the Bioconversion of Rice Straw to Lactic Acid

In this study, we found that p-coumaric acid (p-CA), ferulic acid (FA), and condensed tannins were released from rice straw during saccharification. The presence of polyphenols prolonged the lag phase and lowered the productivity of lactic acid. p-CA was identified as a key inhibitor. Tannins had a lower inhibitory effect than p-CA; FA had little inhibitory effect. Acid, alkaline, and ball milling pretreatments elicited different levels of polyphenol release from rice straw. Due to the different levels of polyphenol release in the pretreatment step, the enzymatic hydrolysates contained different concentrations of polyphenols. Compared with fermentation with a synthetic medium, fermentation with the hydrolysates of ball-milled rice straw provided much lower productivity and yield of lactic acid due to the presence of polyphenols. Removal of these compounds played an important role in lactic acid fermentation. When rice straw was alkaline pretreated, the hydrolysates contained few phenolic compounds, resulting in high productivity and yield of lactic acid (1.8 g/L/h and 26.7 g/100 g straw), which were comparable to those in a synthetic medium. This indicates that there is a correlation between removal of phenolic compounds and efficiency in lactic acid fermentation.     

Production of lactic acid from food wastes

Conversion of food wastes into lactic acid by simultaneous saccharification and fermentation (SSF) was investigated. The process involves saccharification of the starch component in food wastes by a commercial amylolytic enzyme preparation (a mixture of amyloglucosidase, α-amylase, and protease) and fermentation by Lactobacillus delbrueckii. The highest observed overall yield of lactic acid in the SSF was 91% of theoretical. Lactic acid concentration as high as 80 g/L was attainable in 48 h of the SSF. The optimum operating conditions for the maximum productivity were found to be 42°C and pH 6.0. Without supplementation of nitrogen-containing nutrients, the lactic acid yield in the SSF decreased to 60%: 27 g/L of lactic acid from 60 g/L of food waste. The overall performance of the SSF, however, was not significantly affected by the elimination of mineral supplements.     

Production of lactic acid from pulp mill solid waste and xylose using Lactobacillus delbrueckii (NRRL B445)

Using the simultaneoussaccharification and fermentation (SSF) technique, pulp mill solid waste cellulose was converted into glucose using cellulase enzyme and glucose into lacticacid using NRRL B445. SSF experiments were conducted at various pH levels, temperatures, and nutrient concentrations, and the lactic acid yield ranged from 86 to 97%. The depletion of xylose in SSF was further investigated by inoculating NRRL B445 into a xylose-only medium. On prolonged incubation, depletion of xylose with lactic acid production was observed. An experimental procedure with a nonglucose medium was developed to eliminate the lag phase. From xylose fermentation, Lactobacillus delbrueckii yielded 88–92% lactic acid and 2–12% acetic acid.     

Lactic acid fermentation in cell-recycle membrane bioreactor

Traditional lactic acid fermentation suffers from low productivity and low product purity. Cell-recycle fermentation has become one of the methods to obtain high cell density, which results in higher productivity. Lactic acid fermentation was investigated in a cell-recycle membrane bioreactor at higher substrate concentrations of 100 and 120 g/dm³. A maximum cell density of 145 g/dm³ and a maximum productivity of 34 g/(dm³…h) were achieved in cell-recycle fermentation. In spite of complete consumption of substrate, there was a continuous increase in cell density in cell-recycle fermentation. Control of cell density in cell-recycle fermentation was attempted by cell bleeding and reduction in yeast extract concentration.     

Simultaneous saccharification and fermentation of cassava bagasse for l-(+)-lactic acid production using Lactobacilli

Saccharification and fermentation of cassava (Manihot esculenta) bagasse was carried out in a single step for the production of L-(+)-lactic acid by Lactobacillus casei and Lactobacillus delbrueckii. Using 15.5% w/v of cassava bagasse as the raw material, a maximum starch to lactic acid conversion of 96% was obtained with L. casei with a productivity rate of 1.40mg/mL·h and maximum yield of 83.8 mg/mL. It was 94% with L. delbrueckii with a productivity rate of 1.36 mg/mL·h. and maximum yeild of 81.9 mg/mL. Supplementation of bagasse with 0.01% w/v MnCl₂ showed positive influence on the lactic acid production by L. casei.     

High-yield fermentation of pentoses into lactic acid

Lactobacillus species capable of fermenting glucose are generally incapable of utilizing xylose for growth or fermentation. In this study, a novel aspect of a well-known Lactobacillus strain, L. casei subsp. rhamnous (ATCC 10863), was uncovered: it can ferment xylose as efficiently as glucose. This strain is a registered organism, extremely stable on long-term operation. Fermentation by this strain is characterized by an initial lag phase lasting 24–72 h before xylose consumption takes place. The yield (grams/gram) of lactic acid from xylose is in excess of 80% with initial volumetric productivity of 0.38 g/(L-h). Acetic acid is the primary byproduct formed at the level of about 10% of the lactic acid. In addition to xylose, it can ferment all other minor sugars in hemicellulose except arabinose. Subjected to mixed sugar fermentation, this strain consumes glucose first, then mannose, followed by almost simultaneous utilization of xylose and galactose. It shows high tolerance for lactic acid as well as extraneous toxins. It can ferment the mixed sugars present in acid-treated hydrolysate of softwood, giving yields similar to that of pure sugar but at a slower rate. Author to whom all correspondence and reprint requests should be addressed.     

Stimulation of Nisin production from whey by a mixed culture of Lactococcus lactis and Saccharomyces cerevisiae

The production of nisin, a natural food preservative, by Lactococcus lactis subsp. lactis (ATCC 11454) is associated with the simultaneous formation of lactic acid during fermentation in a whey-based medium. As a result of the low concentration and high separation cost of lactic acid, recovering lactic acid as a product may not be economical, but its removal from the fermentation broth is important because the accumulation of lactic acid inhibits nisin biosynthesis. In this study, lactic acid removal was accomplished by biological means. A mixed culture of L. lactis and Saccharomyces cerevisiae was established in order to stimulate the production of nisin via the in situ consumption of lactic acid by the yeast strain, which is capable of utilizing lactic acid as carbon source. The S. cerevisiae in the mixed culture did not compete with the nisin-producing bacteria because the yeast does not utilize lactose, the major carbohydrate in whey for bacterial growth and nisin production. The results showed that lactic acid produced by the bacteria was almost totally utilized by the yeast and the pH of the mixed culture could be maintained at around 6.0. Nisin production by the mixed culture system reached 150.3 mg/L, which was 0.85 times higher than that by a pure culture of L. lactis.     

Continuous Production of Thermostable α-Amylase by Immobilized Bacillus Cells in a Fluidized-Bed Reactor

The exponential cells ofBacillus cereus immobilized in calcium alginate and spun into microcylindrical particles were used in a fluidized-bed reactor for continuous synthesis of thermostable α-amylase. The reactor was operated over a period of 30 d with a dilution rate of 0.33 h^-1, producing 1000–1200 U/mL of enzyme. The productivity of the reactor was in the range of 330–396 kU/h. A 20-fold increase in the productivity with respect to batch fermentation with free cells was attained.     

Continuous production of butanol from starch-based packing peanuts

Acetone, butanol, ethanol (ABE, or solvents) were produced from starch-based packing peanuts in batch and continuous reactors. In a batch reactor, 18.9 g/L of total ABE was produced from 80 g/L packing peanuts in 110 h of fermentation. The initial and final starch concentrations were 69.6 and 11.1 g/L, respectively. In this fermentation, ABE yield and productivity of 0.32 and 0.17 g/(L·h) were obtained, respectively. Compared to the batch fermentation, continuous fermentation of 40 g/L of starch-based packing peanuts in P2 medium resulted in a maximum solvent production of 8.4 g/L at a dilution rate of 0.033 h⁻¹. This resulted in a productivity of 0.27 g/(L·h). However, the reactor was not stable and fermentation deteriorated with time. Continuous fermentation of 35 g/L of starch solution resulted in a similar performance. These studies were performed in a vertical column reactor using Clostridium beijerinckii BA101 and P2 medium. It is anticipated that prolonged exposure of culture to acrylamide, which is formed during boiling/autoclaving of starch, affects the fermentation negatively.