Process development and optimisation of lactic acid purification using electrodialysis

Cell free sodium lactate solutions were subjected to purification based on mono- and bi-polar electrodialysis. Lactate concentration in the product stream increased to a maximum of 15% during mono-polar electrodialysis. Stack energy consumption averaged 0.6 kW h kg(-1) lactate transported at current efficiencies in the 90% range. Under optimum feed concentration (125 g l(-1)) and process conditions (auto-current mode with conductivity setpoints of minimum 5 and maximum 40 mS cm(-1)), lactate flux reached 300 g m(-2) h(-1) and water flux were low for mono-polar electrodialysis averaging 0.3 kg H(2)O per M lactate transported. Glucose in the concentrate stream solutions was reduced to < 2 g l(-1). Acetate impurities enriched from about 0.5 g l(-1) in the feed stream to 1.5 g l(-1) in the concentrate stream solutions. After mono-polar electrodialysis, the concentrated sodium lactate solutions were further purified using bi-polar electrodialysis. Water transport during bi-polar electrodialysis reached figures of 0.070 - 0.222 kg H(2)O per M lactate. Free lactic acid concentration reached 16% with lactate flux of up to 300 g m(-2) h(-1). Stack energy consumption ranged from 0.6 to 1 kW h per kg lactate. Under optimised process conditions current efficiency during bi-polar electrodialysis was consistently around 90%. Glucose was further reduced from 2 to <1 g l(-1) in the free lactic acid solution. Acetic acid impurity remained at around 1 g l(-1). Significant reduction in colour and minerals in the product streams was observed during electrodialysis purification.     

Optimisation of media and cultivation conditions for L(+)(S)-lactic acid production by Lactobacillus casei NRRL B-441

Process variables and concentration of carbon in media were optimised for lactic acid production by Lactobacillus casei NRRL B-441. Lactic acid yield was inversely proportional to initial glucose concentration within the experimental area (80-160 g l(-1)). The highest lactic acid concentration in batch fermentation, 118.6 g l(-1), was obtained with 160 g 1(-1) glucose. The maximum volumetric productivity, 4.4 g 1(-1) h(-1) at 15 h, was achieved at an initial glucose concentration of 100 g l(-1). Similar lactic acid concentrations were reached with a fedbatch approach using growing cells, in which case the fermentation time was much shorter. Statistical experimental design and response surface methodology were used for optimising the process variables. The temperature and pH optima for lactic acid production were 35 degrees C, pH 6.3. Malt sprout extract supplemented with yeast extract (4 g l(-1)) appeared to be an economical alternative to yeast extract alone (22 g l(-1)) although the fermentation time was a little longer. The results demonstrated both the separation of the growth and lactic acid production phases and lactic acid production by non-growing cells without any nutrient supplements. Resting L. casei cells converted 120 g l(-1) glucose to lactic acid with 100% yield and a maximum volumetric productivity of 3.5 g l(-1) h(-1).     

Effect of RQ and pre-seed conditions on biomass and galactosyl transferase production during fed-batch culture of S. cerevisiae BT150

A feedback RQ controlled fed-batch process for the recombinant production of a soluble human N-deglycosylated recombinant beta-1, 4-galactosyltransferase (NdrGal-T) with Saccharomyces cerevisiae BT150 was investigated. Several RQ values were tested for optimal production of NdrGal-T. Four times higher volumetric activity was reached at RQ=1.0 (32 U l(-1)) than at all higher RQ values (about 8 U l(-1)). RQ, 1.0 was the best choice for both, biomass and enzyme production. Optimal concentration of glucose in preculture was 25 g l(-1). At higher values slightly more ethanol was produced than at lower values of preculture glucose concentrations, moreover no positive effect on biomass and enzyme production was found. Lower values caused not only decrease of ethanol but also decrease of biomass formation (from 1.69 g h(-1) to 0.81 g h(-1)) and enzyme overall productivity (from 2.2 U h(-1) to 0.63 U h(-1)). Successfully performed cultivation with three precultures predicted scale-up possibility of feedback RQ-controlled NdrGal-T production with S. cerevisiae BT150 from lab to pilot-scale fermentor.     

Performance assessment of two patent strains ofZymomonas mobilis in batch and continuous fermentations

Summary The performance ofZymomonas mobilis strains ATCC 31821 and ATCC 31823 was assessed in batch and continuous culture. In batch culture using a medium containing 250 g/l glucose, identical maximum specific growth rates of 0.16/h were found, though final biomass concentration and growth yield were significantly lower for ATCC 31 823 than for ATCC 31 821. Final ethanol concentrations in this medium were about 110 g/l vor both organisms. In continuous culture at increasing dilution rates using a medium containing 100 g/l glucose, no significant differences were seen between the two strains with respect to the fermentation parameters studied. For ATCC 31 821, maximum rates of glucose uptake (Q_s) and ethanol produktion (Q_p) of 8.7 g glu/g/h and 4.4 g eth/g/h, respectively, were found. Both strains showed a similar performance at a fixed dilution rate of 0.1/h, where maximum ethanol concentrations of about 68 g/l were reached at a feed glucose concentration of about 139 g/l. At this dilution rate the maximum values of Q_s and Q_p were about 5.8 g glu/g/h and 2.8 g eth/g/h, respectively. Test tube experiments showed that growth, measured as optical density, decreased with increasing concentrations of exogenous ethanol with complete inhibition of growth at ethanol concentrations >8% (v/v). As evidenced by the results presented here, we have been unable to practice the invention as described in U.S. Patent 4,403,034 (Rogers and Tribe 1983).Nomenclature D Dilution rate, 1/h - _max maximum specific growth rate, 1/h - S_R Initial substrate concentration, g glucose/1 - S Residual substrate concentration, g glucose/1 - S₀ Effluent substrate concentration, g glucose/1 - X Blomass concentration; g cells/l - OD₆₂₀ Optical density at 620 nm, dimensionless - [P] Product concentration, g ethanol/1 - Y_x/s Growth yield, g cells/g glucose used - Y_p/s Product yield, g ethanol/g glucose used - %, Yield Percentage yield, Y_p/sx100/Y _p ^s/max =Y_p/sx100/0.51 - Q_s Specific rate of glucose uptake, g glucose/g cells/h - Q_p Specific rate of ethanol formation, g ethanol/g cells/h - m_e Maintenance energy coefficient, g glucose/g cells/h - VP Volumetric productivity, g ethanol/l/h - t Fermentation time, h     

A continuous lactic acid production system using an immobilized packed bed of Lactobacillus helveticus

A 5 l packed bed bioreactor was used to study the effect of initial lactose concentration and hydraulic retention time (HRT) on cell growth, lactose utilization and lactic acid production. Up to 95% of the initial lactose concentration was utilized at longer HRTs (30-36 h). The study showed that lactic acid production increased with increases in HRT (12-36 h) and initial lactose concentrations. The highest lactic acid production rate (3.90 g l(-1) h(-1)) was obtained with an initial lactose concentration of 100 g/l and an HRT of 18 h, whereas the lowest lactic acid production rate (1.35 g l(-1) h(-1)) was obtained with an initial lactose concentration of 50 g/l and an HRT of 36 h. This suggested that optimal lactic acid production can be achieved at an HRT of 18 h and initial lactose concentration of 100 g/l.     

Cell reuse in submerged lactic acid batch fermentation

The reusability of biomass in lactic acid batch fermentation with free cells of Lactobacillus paracasei was studied in a 2–1 fermenter and in a 50-1 fermenter. In lab-scale fermentation experiments, 33 to 100% of the cell mass formed was reused in the subsequent batch in each case. In a series of seven consecutive batches, maximum values of lactate formation productivity of 6.32 to 11.54 g/l × h were observed at initial cell concentrations of 2.1 to 24.6 g/l. In all of the experiments, the initial cell viability was 78% or greater than 78%, and the final cell viability did not fall below 70%. At cell concentrations above 20 g/l, the productivity of lactic acid formation did not increase further, but remained constant. Because its level could be influenced by varying the proportions between the content of yeast extract, peptone and initial cell mass (1:1:2, 1:1:1 and 3.3.1) in the medium and no inhibitory effects were observed, this finding can be attributed to nutrient limitation. A low degree of cell reuse was reached in an analogous series of experiments carried out in a 50-1 fermenter. In this case, the initial cell concentration varied between 0.5 and 1.1 g/l, and therefore cell growth was not limited by nutrients in the first period of fermentation. Lactate production was still stable after six cell-reuse operations. The lactic acid yield did not fall below 90%. Temporary storage of the biomass in a refrigerator for a time interval of one to two weeks caused no significant impairment of overall lactate production, but a proportional prolongation of the lag phase occurred with increasing duration of storage.     

Application of bipolar electrodialysis on recovery of free lactic acid after simultaneous saccharification and fermentation of cassava starch

The efficiency of bipolar electrodialysis (BED) for the recovery of lactic acid from fermentation broth was evaluated. Three systems of BED (bipolar-anion, bipolar-cation and bipolar-anion-cation) at fixed voltage (20 V) were compared using a model solution of ammonium lactate (100 g l(-1)). Results showed that bipolar-anion (BED-anion) was the most beneficial in terms of lactate flux, current efficiency, energy consumption and recovery ratio. Consequently, BED-anion was used to purify lactic acid from fermentation broth which had been pre-treated with mono-polar electrodialysis (MED). The final lactic acid concentration and lactate flux obtained were 144 g l(-1) and 393 g m(-2) h(-1), respectively. Using the two-step process (MED and BED-anion) the concentration of fermentation broth was increased by 33% and the total energy consumption was 2.76 kW h kg(-1).     

Production of <Emphasis Type="SmallCaps">l</Emphasis>-lactic acid from a mixture of xylose and glucose by co-cultivation of lactic acid bacteria

The production of optically pure lactic acid in a high yield from xylose or a mixture of xylose and glucose, which is a model hydrolysate of lignocellulose, is described. In a single cultivation, Enterococcus casseliflavus produced 38 g/l of lactic acid with an optical purity of 96% enantiomeric excess (ee) and 6.4 g/l of acetic acid from 50 g/l of xylose when MRS medium was used. When a mixture of 50 g/l of xylose and 100 g/l of glucose was used as the carbon source in a cultivation of E. casseliflavus alone, glucose was converted to lactic acid in the early phase of the cultivation but xylose was hardly consumed. In a co-cultivation where E. casseliflavus and Lactobacillus casei specific for glucose were simultaneously inoculated, little or no lactic acid was produced after the glucose was almost consumed. A co-cultivation with two-stage inoculation (in which E. casseliflavus was added at a cultivation time of 40 h after L. casei cells were inoculated) resulted in complete consumption of 50 g/l of xylose and 100 g/l of glucose. In the co-cultivation, 95 g/l of lactic acid with a high optical purity of 96% ee was obtained at 192 h. Such a co-cultivation using two microorganisms specific for each sugar is considered to be one promising cultivation technique for the efficient production of lactic acid from a sugar mixture derived from lignocellulose.     

<Emphasis Type="Italic">Brettanomyces bruxellensis</Emphasis>: effect of oxygen on growth and acetic acid production

The influence of the oxygen supply on the growth, acetic acid and ethanol production by Brettanomyces bruxellensis in a glucose medium was investigated with different air flow rates in the range 0-300 l h(-1 ) x (0-0.5 vvm). This study shows that growth of this yeast is stimulated by moderate aeration. The optimal oxygen supply for cellular synthesis was an oxygen transfer rate (OTR) of 43 mg O(2) l(-1) x h(-1). In this case, there was an air flow rate of 60 l h(-1) (0.1 vvm). Above this value, the maximum biomass concentration decreased. Ethanol and acetic acid production was also dependent on the level of aeration: the higher the oxygen supply, the greater the acetic acid production and the lower the ethanol production. At the highest aeration rates, we observed a strong inhibition of the ethanol yield. Over 180 l h(-1) x (0.3 vvm, OTR =105 mg O(2) l(-1) x h(-1)), glucose consumption was inhibited and a high concentration of acetic acid (6.0 g x l(-1)) was produced. The ratio of "ethanol + acetic acid" produced per mole of consumed glucose using carbon balance calculations was analyzed. It was shown that this ratio remained constant in all cases. This makes it possible to establish a stoichiometric equation between oxygen supply and metabolite production.     

Lactate as substrate for glycogen resynthesis after exercise

Muscle glycogen levels in the perfused rat hemicorpus preparation were reduced two-thirds by electrical stimulation plus exposure to epinephrine (10(-7) M) for 30 min. During the contraction period muscle lactate concentrations increased from a control level of 3.6 +/- 0.6 to a final value of 24.1 +/- 1.6 mumol/g muscle. To determine whether the lactate that had accumulated in muscle during contraction could be used to resynthesize glycogen, glycogen levels were determined after 1-3 h of recovery from the contraction period during which time the perfusion medium (flow-through system) contained low (1.3 mmol/l) or high (10.5 or 18 mmol/l) lactate concentrations but no glucose. With the low perfusate lactate concentration, muscle lactate levels declined to 7.2 +/- 0.8 mumol/g muscle by 3 h after the contraction period and muscle glycogen levels did not increase (1.28 +/- 0.07 at 3 h vs. 1.35 +/- 0.09 mg glucosyl U/g at end of exercise). Lactate disappearance from muscle was accounted for entirely by output into the venous effluent. With the high perfusate lactate concentrations, muscle lactate levels remained high (13.7 +/- 1.7 and 19.3 +/- 2.0 mumol/g) and glycogen levels increased by 1.11 and 0.86 mg glucosyl U/g, respectively, after 1 h of recovery from exercise. No more glycogen was synthesized when the recovery period was extended. Therefore, it appears that limited resynthesis of glycogen from lactate can occur after the contraction period but only when arterial lactate concentrations are high; otherwise the lactate that builds up in muscle during contraction will diffuse into the bloodstream.     

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).     

Accumulation of pyruvate by changing the redox status in Escherichia coli

Pyruvate was produced from glucose by Escherichia coli BW25113 that contained formate dehydrogenase (FDH) from Mycobacterium vaccae. In aerobic shake-flask culture (K (L) a?=?4.9?min(-1)), the recombinant strain produced 6.7?g pyruvate?l(-1) after 24?h with 4?g sodium formate?l(-1) and a yield of 0.34?g pyruvate?g?glucose(-1). These values were higher than those of the original strain (0.2?g?l(-1) pyruvate and 0.02?g pyruvate?g?glucose(-1)). Based on the reaction mechanism of FDH, the introduction of FDH into E. coli enhances the accumulation of pyruvate by the regeneration of NADH from NAD(+) since NAD(+) is a shared cosubstrate with the pyruvate dehydrogenase complex, which decarboxylates pyruvate to acetyl-CoA and CO(2). The oxygenation level was enough high to inactivate lactate dehydrogenase, which was of benefit to pyruvate accumulation without lactate as a by-product.     

Coupled lactic acid fermentation and adsorption

Polyvinylpyridine (PVP) and activated carbon were evaluated for coupled lactic acid fermentation and adsorption, to prevent the product concentration from reaching inhibitory levels. The lactic acid production doubled as a result of periodical circulation of the fermentation broth through a PVP adsorption column. The adsorbent was then regenerated and the adsorbed lactate harvested, by passing 0.1 N NaOH through the column. However, each adsorption-regeneration cycle caused about 14% loss of the adsorption capacity, thus limiting the practical use of this rather expensive adsorbent. Activated carbon was found much more effective than PVP in lactic acid and lactate adsorption. The cells of Lactobacillus delbrueckii subsp. delbrueckii (LDD) also had strong tendency to adsorb on the carbon. A study was therefore conducted using an activated carbon column for simultaneous cell immobilization and lactate adsorption, in a semi-batch process with periodical medium replacement. The process produced lactate steadily at about 1.3 g l(-1)h(-1) when the replacement medium contained at least 2 g l(-1) of yeast extract. The production, however, stopped after switching to a medium without yeast extract. Active lactic acid production by LDD appeared to require yeast extract above a certain critical level (<2 g l(-1)).     

Efficient homolactic fermentation by Kluyveromyces lactis strains defective in pyruvate utilization and transformed with the heterologous LDH gene.

A high yield of lactic acid per gram of glucose consumed and the absence of additional metabolites in the fermentation broth are two important goals of lactic acid production by microrganisms. Both purposes have been previously approached by using a Kluyveromyces lactis yeast strain lacking the single pyruvate decarboxylase gene (KlPDC1) and transformed with the heterologous lactate dehydrogenase gene (LDH). The LDH gene was placed under the control the KlPDC1 promoter, which has allowed very high levels of lactate dehydrogenase (LDH) activity, due to the absence of autoregulation by KlPdc1p. The maximal yield obtained was 0.58 g g(-1), suggesting that a large fraction of the glucose consumed was not converted into pyruvate. In a different attempt to redirect pyruvate flux toward homolactic fermentation, we used K. lactis LDH transformant strains deleted of the pyruvate dehydrogenase (PDH) E1alpha subunit gene. A great process improvement was obtained by the use of producing strains lacking both PDH and pyruvate decarboxylase activities, which showed yield levels of as high as 0.85 g g(-1) (maximum theoretical yield, 1 g g(-1)), and with high LDH activity.     

Evaluation of plastic-composite supports in repeated fed-batch biofilm lactic acid fermentation by Lactobacillus casei

A customized stirred-tank biofilm reactor was designed for plastic-composite supports (PCS). In repeated-batch studies, the PCS-biofilm reactors outperformed the suspended-cell reactors by demonstrating higher lactic acid productivities (2.45 g l(-1) h(-1) vs 1.75 g l(-1) h(-1)) and greater glucose consumption rates (3.27 g l(-1) h(-1) vs 2.09 g l(-1) h(-1)). In the repeated fed-batch studies, reactors were spiked periodically with concentrated glucose (75%) to maintain a concentration of approximately 80 g of glucose l(-1) in the bioreactor. In suspended-cell fermentations with 10 g of yeast extract (YE) l(-1) and zero, one, two, and three glucose spikes, the lactic acid productivities were 2.64, 1.58, 0.80, and 0.62 g l(-1) h(-1), respectively. In comparison, biofilm reactors with 7 g of YE l(-1) and zero, one, two, and three glucose spikes achieved lactic acid productivities of 4.20, 2.78, 0.66, and 0.94 g l(-1) h(-1), respectively. The use of nystatin (30 U ml(-1)) subdued the contaminating yeast population with no effect on the lactic acid productivity of the biofilm reactors, but it did affect productivity in the suspended-cell bioreactor. Overall, in repeated fed-batch fermentations, the biofilm reactors consistently outperformed the suspended-cell bioreactors, required less YE, and produced up to 146 g of lactic acid l(-1) with 7 g of YE l(-1), whereas the suspended-cell reactor produced 132 g l(-1) with 10 g of YE l(-1).     

Strain improvement and metabolic flux analysis in the wild-type and a mutant Lactobacillus lactis strain for L(+)-lactic acid production

The effects of initial glucose concentration and calcium lactate concentration on the lactic acid production by the parent strain, Lactobacillus lactis BME5-18, were studied. The results of the experiments indicated that glucose and lactate repressed the cell growth and the lactic acid production by Lactobacillus lactis BME5-18. A L(+)-lactic acid overproducing strain, Lactobacillus lactis BME5-18M, was screened by mutagenizing the parent strain with ultraviolet (UV) light irradiation and selecting the high glucose and lactate calcium concentration repression resistant mutant. Starting with a concentration of 100g L(-1) glucose, the mutant produced 98.6 g L(-1) lactic acid after 60 h in flasks, 73.9% higher than that of the parent strain. The L(+)-lactic acid purity was 98.1% by weight based on the amount of total lactic acid. The culture of the parent strain could not be analyzed well by conventional metabolic flux analysis techniques, since some pyruvate were accumulated intracellularly. Therefore, a revised flux analysis method was proposed by introducing intracellular pyruvate pool. Further studies demonstrate that there is a high level of NADH oxidase activity (12.11 mmol mg(-1) min(-1)) in the parent strain. The molecular mechanisms of the strain improvement were proposed, i.e., the high level of NADH oxidase activity was eliminated and the uptake rate of glucose was increased from 82.1 C-mmol (g DW h)(-1) to 98.9 C-mmol (g DW h)(-1) by mutagenizing the parent strain with UV, and therefore the mutant strain converts mostly pyruvate to lactic acid with a higher productivity (1.76 g L(-1) h(-1)) than the parent strain (0.95 g L(-1) h(-1)).     

High production of acetone-butanol-ethanol with high cell density culture by cell-recycling and bleeding

A continuous acetone-butanol-ethanol (ABE) production system with high cell density obtained by cell-recycling of Clostridium saccharoperbutylacetonicum N1-4 has been studied. In conventional continuous culture of ABE without cell-recycling, the cell concentration was below 5.2 g l(-1) and the maximum ABE productivity was only 1.85 g l(-1)h(-1) at a dilution rate of 0.20 h(-1). To obtain a high cell density at a faster rate, we concentrated the solventogenic cells of the broth 10 times by membrane filtration and were able to obtain approximately 20 g l(-1) of active cells after only 12h of cultivation. Continuous culture with cell-recycling was then started, and the cell concentration increased gradually through cultivation to a value greater than 100 g l(-1). The maximum ABE productivity of 11.0 gl(-1)h(-1) was obtained at a dilution rate of 0.85 h(-1). However, a cell concentration greater than 100 gl(-1) resulted in heavy bubbling and broth outflow, which made it impossible to carry out continuous culture. Therefore, to maintain a stable cell concentration, cell-bleeding was performed together with cell-recycling. At dilution rates of 0.11h(-1) and above for cell-bleeding, continuous culture with cell-recycling could be operated for more than 200 h without strain degeneration and the overall volumetric ABE productivity of 7.55 gl(-1)h(-1) was achieved at an ABE concentration of 8.58 gl(-1).     

Physiological stress in decapod crustaceans (Munida rugosa and Liocarcinus depurator) discarded in the Clyde Nephrops fishery

Crustacean discards experience stress during commercial fishing operations, due to increased exercise while in the trawl and aerial exposure during sorting of the catch. Physiological stress and recovery were assessed following trawling of two ecologically important decapod species, regularly discarded in the Clyde Nephrops fishery. Haemolymph samples taken from trawled swimming crabs, Liocarcinus depurator, and squat lobsters, Munida rugosa, had significantly higher concentrations of ammonia (0.308 and 0.519 mmol l(-1)), D-glucose (0.14 and 0.097 mmol l(-1)) and L-lactate (6.2 and 0.87 mmol l(-1)) compared with controls, indicating an impairment of ammonia excretion and a switch to anaerobic metabolism. Concurrently, the haemolymph pH of trawled squat lobsters was low (7.47) compared with controls (7.75); however, the reverse trend was found in L. depurator. Initially elevated lactate (7.98 mmol l(-1)) and glucose (0.73 mmol l(-1)) concentrations of trawled and emersed (1 h) L. depurator were restored, 4 h after re-immersion along with pH (7.54). Crabs that had been emersed for 1 h had significantly higher concentrations of glucose (0.2 mmol l(-1)) and lactate (5.14 mmol l(-1)), and had more acidic blood (7.64) than L. depurator subject to 1 h of exercise, indicating that anoxia was the main cause of physiological stress. Crabs and squat lobsters lost 7% and 9% of their initial body wet weight following 1 h of emersion, although blood osmolarities did not change significantly. While all animals survived aerial exposure in our experiments, sorting of the catch on commercial boats takes up to 300 min, which could lead to mortality or sub-lethal chronic biochemical changes that could compromise fitness.     

High concentration cultivation of Bifidobacterium longum in fermenter with cross-flow filtration

Summary High concentration cultivation of Bifidobacterium longum in a fermenter with cross-flow filtration using a ceramic filter is described. Continuous cross-flow filtration allowed complete recycling of the cells to the fermenter and also continuous separation of inhibitory metabolites. The final cell concentration attained in the cultivation was 54.4 g dry wt./l; this was seven times as high as that without cross-flow filtration. The time course of the cultivation with cross-flow filtration was predicted, based on the assumption that the specific growth rate can be expressed only as a function of concentrations of metabolites (acetate and lactate) in a culture broth.Nomenclature D dilution rate (h^-1) - m maintenance coefficient (h^-1) - OD ₅₇₀ optimal density at 570 nm - P _A acetate concentration (g/l) - P _A0 initial acetate concentration (g/l) - P _L lactate concentration (g/l) - P _L0 initial lactate concentration (g/l) - S lactose (substrate) concentration (g/l) - S ₀ initial lactose (substrate) concentration (g/l) - t cultivation time (h) - Y _x/s growth yield (g/g) - X dry cell concentration (g/l) - X ₀ initial dry cell concentration (g/l) - constant - constant     

Production of lactic acid and fructose from media with cane sugar using mutant of Lactobacillus delbrueckii NCIM 2365

AIMS: To examine the potential of Lactobacillus delbrueckii mutant, Uc-3 to produce lactic acid and fructose from sucrose-based media. METHODS AND RESULTS: The mutant of L. delbrueckii NCIM 2365 was cultivated in shake flask containing hydrolysed cane sugar (sucrose)-based medium. The lactic acid yield and volumetric productivity with hydrolysed cane concentration up to 200 g l(-1) were in the range of 92-97% of the theoretical value and between 2.7 and 3.8 g l(-1) h(-1), respectively. The fructose fraction of the syrup produced was more than 95% when the total initial sugar concentration in the medium was higher (150-200 g l(-1)). There are no unwanted byproducts detected in the fermentation broth. CONCLUSIONS: We demonstrated that L. delbrueckii mutant Uc-3 was able to utilize glucose preferentially to produce lactic acid and fructose from hydrolysed cane sugar in batch fermentation process. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings will be useful in the production of lactic acid and high fructose syrups using media with high concentrations of sucrose-based raw materials. This approach can lead to modification of the traditional fermentation processes to obtain value-added byproducts, attaining better process economics.