Continuous Lactic Acid Fermentation Research Articles

Multi-criteria analysis of cell-recycle based continuous lactic acid production process

ABSTRACT This study focuses on the optimization of the cell-recycle based continuous lactic acid (LA) fermentation production process with the estimation of improved kinetic parameters. The non-dominated sorting genetic algorithm II (NSGA-II) is used considering seven variables and five imposed constraints for multi-objective optimization (MOO) study. Three objectives namely LA productivity, substrate conversion, and yield are formed for the maximization purpose. Three different cases are constructed by using a combination of two bi-objectives and one tri-objective optimization problem, and the modified differential evolution (MDE) algorithm is used to individually optimize each case. Pareto ranking is carried out for MOO, and the best optimal solution is determined using the technique for order preference by similarity to the ideal solution (TOPSIS) method. The highest value of volumetric productivity of LA (184.363 kg/m3.h) is reported in case-4a. The highest yield (1.176) is reported in case-2, while the highest substrate conversion (0.963) is reported in case-1.

Effect of honeycomb, granular, and powder activated carbon additives on continuous lactic acid fermentation of complex food waste with mixed inoculation

To accelerate and stabilize lactic acid fermentation from food waste, three types of activated carbon, including honeycomb activated carbon, granular activated carbon, and powder activated carbon, were tested as additives in continuous food waste fermentation processes. The results showed that carbohydrate was the primary substrate for lactic acid production, but its conversion reached a high, stable level after a long period of microbial acclimation in the control system. Activated carbon, especially honeycomb activated carbon accelerated the stabilization of lactic acid fermentation and enhanced the tolerance of fermentation systems to a hostile and fluctuating environment. The addition of activated carbon increased the oxidation-reduction potential to approximately 100mV and altered the microbial communities. Homolactic fermentation bacteria were dominant in all the systems, and the honeycomb activated carbon addition stimulated the growth of unclassified Lactobacillus and immobilized Lactobacillus panis with strong carbohydrate metabolism. In addition, powder activated carbon enhanced the degradation of protein due to the multiplying Pseudomonas. At the stable stage, the organic conversion rates were close in the control system and the systems with the activated carbon addition, and the lactic acid concentrations in these systems remained at 8000-10,000mg/L. Considering the cost of the additives, honeycomb activated carbon is a good choice to stabilize lactic acid production from food waste.

Batch and Continuous Lactic Acid Fermentation Based on A Multi-Substrate Approach.

The utilisation of waste materials and industrial residues became a priority within the bioeconomy concept and the production of biobased chemicals. The aim of this study was to evaluate the feasibility to continuously produce L-lactic acid from different renewable substrates, in a multi-substrate strategy mode. Based on batch experiments observations, Bacillus coagulans A534 strain was able to continuously metabolise acid whey, sugar beet molasses, sugar bread, alfalfa press green juice and tapioca starch. Additionally, reference experiments showed its behaviour in standard medium. Continuous fermentations indicated that the highest productivity was achieved when molasses was employed with a value of 10.34 g·L−1·h−1, while the lactic acid to sugar conversion yield was 0.86 g·g−1. This study demonstrated that LA can be efficiently produced in continuous mode regardless the substrate, which is a huge advantage in comparison to other platform chemicals.

A review on the current developments in continuous lactic acid fermentations and case studies utilising inexpensive raw materials

Abstract The numerous applications of lactic acid have made it one of the most important platform chemicals and, for many years, its biotechnological production has been the topic of intensive research. Currently, most of the lactic acid is manufactured in batch mode; however, continuous mode could offer various advantages, especially in terms of productivity. This review provides a summary of the most recent studies on continuous lactic acid production. Potential advantages of continuous over batch mode, the improvements that high cell densities can represent, utilisation of low cost substrates and some economic aspects of continuous mode are discussed. The review is complemented by 3 experimental case studies utilising inexpensive substrates: tapioca starch hydrolysate, molasses combined with rapeseed meal hydrolysate and acid whey. In all cases, continuous cultivation was coupled with cell recycling using hollow-fibre membranes for l - or d -lactic acid production. Lactic acid productivities higher than 5 g l−1 h−1 and substrate conversion yields above 80% were achieved for all the cases. Final lactic acid concentrations were 50.3, 59.6 and 45.9 g l−1 for the tapioca starch hydrolysate, molasses and acid whey respectively. These results support the claim that continuous cultivation using cell recycling is a promising approach for high lactic acid productivities.

Anaerobic Membrane Bioreactor for Continuous Lactic Acid Fermentation.

Membrane bioreactor systems can enhance anaerobic lactic acid fermentation by reducing product inhibition, thus increasing productivity. In batch fermentations, the bioconversion of glucose is strongly inhibited in the presence of more than 100 g·L−1 lactic acid and is only possible when the product is simultaneously removed, which can be achieved by ceramic membrane filtration. The crossflow velocity is a more important determinant of flux than the transmembrane pressure. Therefore, to stabilize the performance of the membrane bioreactor system during continuous fermentation, the crossflow velocity was controlled by varying the biomass concentration, which was monitored in real-time using an optical sensor. Continuous fermentation under these conditions, thus, achieved a stable productivity of ~8 g·L−1·h−1 and the concentration of lactic acid was maintained at ~40 g·L−1 at a dilution rate of 0.2 h−1. No residual sugar was detected in the steady state with a feed concentration of 50 g·L−1.

Effect of temperature on continuous fermentative lactic acid (LA) production and bacterial community, and development of LA-producing UASB reactor

A frequently used fermentation manner in lactic acid (LA) production, batch fermentation by pure cultures, has a limited practicability: low volumetric productivity and high energy consumption. In this study, continuous LA fermentation was performed in a completely stirred tank reactor at 12h HRT, inoculated with anaerobic digester sludge. Glucose (25g COD/L) was used as a feedstock and temperature was increased from 35 to 60°C. LA production significantly increased from 50°C, which was negligible up to 45°C, with obvious bacterial community change. At 50 and 55°C, LA production was maximized, reaching 23g COD/L, corresponding to 92% LA conversion efficiency. Pyrosequencing analysis showed that microbial diversity was simplified at 50–60°C, and the sequences closely related with Bacillus coagulans became predominant, followed by Lactobacillus fermentum. An LA-producing upflow ananerobic sludge blanket reactor was successfully developed, which enhanced the productivity up to 4.8gLA/L/h by shortening HRT to 4h.

Lactic acid production by Lactobacillus sp. RKY2 in a cell-recycle continuous fermentation using lignocellulosic hydrolyzates as inexpensive raw materials

Continuous lactic acid fermentations were conducted using lignocellulosic hydrolyzates and corn steep liquor as inexpensive raw materials. Lactic acid concentrations decreased with increases in the dilution rate, whereas the residual substrate concentrations increased. However, lactic acid yields were maintained at more than 0.90 g g −1 over all cases experimented. The cell-recycle cultivation system exerted positive effects on fermentation efficiency, including volumetric productivity, which is attributable to the retention of cells in the bioreactor. The cell-recycle continuous fermentation of lignocellulosic hydrolyzates yielded a lactic acid productivity of 6.7 g l −1 h −1 for a dilution rate of 0.16 h −1 using 30 g l −1 of corn steep liquor and 1.5 g l −1 of yeast extract as nutrients. The productivity (6.7 g l −1 h −1) acquired by the cell-recycle continuous fermentation of lignocellulosic hydrolyzates was 1.6 times higher than the lactic acid productivity yielded in the continuous fermentation without cell-recycle system.

An Empiric Steady State Model of Lactate Production in Continuous Fermentation with Total Cell Retention

AbstractContinuous lactic acid fermentation with total cell recycling was carried out with the strain Lactobacillus paracasei ATB 160111 in a membrane reactor system. The aim of this study was to examine the dependence of lactic acid production and cell mass formation on the hydraulic dilution rate, D, and the availability of both yeast extract and peptone in a modified glucose medium. An experimental design was used and experimental data were obtained, which could be fitted by sigmoidal equations with a high accuracy within the parameter ranges investigated of 0.1 h–1 ≤ D ≤ 0.5 h–1 and 2.5 g/L ≤ peptone/yeast extract ≤ 50 g/L. A steady‐state lactate concentration was established in all tests and a maximum lactate productivity of 26 g/(L × h) was reached at a dilution rate of 0.5 h–1 and a nutrient concentration of 15 g/L. Increasing the concentrations of peptone and yeast extract beyond a value of 15.9 g/L did not lead to an increase in productivity, although total cell mass was accumulated up to 200 g/L. Further examinations showed that only a certain part of the biomass was always active and balanced cell growth was clearly not limited by the lack of any nutrient component in the medium, however, it was affected strongly by product inhibition. A significant decrease in lactic acid yield occurred when the biomass concentration exceeded a value of about 80 g/L. The empiric models used in this study allowed the performance behavior of different strains, for which no biologically well‐founded data are yet known, to be compared. Whether empirical sigmoidal models can be also used for the description of process states in continuous fermentation processes should also be looked into.

Continuous lactic acid fermentation using a plastic composite support biofilm reactor.

An immobilized-cell biofilm reactor was used for the continuous production of lactic acid by Lactobacillus casei subsp. rhamnosus (ATCC 11443). At Iowa State University, a unique plastic composite support (PCS) that stimulates biofilm formation has been developed. The optimized PCS blend for Lactobacillus contains 50% (wt/wt) agricultural products [35% (wt/wt) ground soy hulls, 5% (wt/wt) soy flour, 5% (wt/wt) yeast extract, 5% (wt/wt) dried bovine albumin, and mineral salts] and 50% (wt/wt) polypropylene (PP) produced by high-temperature extrusion. The PCS tubes have a wall thickness of 3.5 mm, outer diameter of 10.5 mm, and were cut into 10-cm lengths. Six PCS tubes, three rows of two parallel tubes, were bound in a grid fashion to the agitator shaft of a 1.2-1 vessel for a New Brunswick Bioflo 3000 fermentor. PCS stimulates biofilm formation, supplies nutrients to attached and suspended cells, and increases lactic acid production. Biofilm thickness on the PCS tubes was controlled by the agitation speed. The PCS biofilm reactor and PP control reactor achieved optimal average production rates of 9.0 and 5.8 g l(-1) h(-1), respectively, at 0.4 h(-1) dilution rate and 125-rpm agitation with yields of approximately 70%.

PH-Dependent Continuous Lactic Acid Fermentation by Lactococcus lactis IO-1 Using Hydrolyzed Sago Starch.

pH-Dependent Continuous Lactic Acid Fermentation by Lactococcus lactis IO-1 Using Hydrolyzed Sago Starch.

Physiological aspects of continuous lactic acid fermentations at high dilution rates

The effects of the substrate conditions on the volumetric productivity of Lactobacillus helveticus at different cell densities up to 60 g l−1 in a continuous stirred-tank reactor with microfiltration to retain the biomass were investigated. At low dilution rates, D, the steady-state volumetric productivity, rp, gradually increased to a maximum at D = 1.2–1.5 h−1, because of reduced product inhibition. At higher D values, rp unexpectedly decreased, although the substrate conditions further improved. The maxima of rp at different cell densities coincided with a critical specific substrate utilization rate beyond which the cell metabolism seems to be controlled through a catabolic modulator factor, and rp decreases.

RHEOLOGY OF PURE AND MIXED KAPPA‐CARRAGEENAN GELS IN LACTIC ACID FERMENTATION CONDITIONS

ABSTRACTTexture profile analysis and rupture tests, respectively, at a deformation of 5 and 80%, were carried out on commercial kappa‐carrageenan gel cylinders (3% w/v concentration) and on mixed gel cylinders (kappa‐carrageenan/iotacarrageenan or locust bean gum [LBG], in different proportions), to select the best gel composition as an immobilization matrix for continuous lactic acid fermentations of dairy media. Mixed gel cylinders were soaked in a model system for lactic fermentations consisting of 36 dairy media: milk, whey and whey permeate, with 4 lactate concentrations (5, 20, 35 and 50 g/L of medium), combined with 3 pH values (6.5, 6.0, 5.5). GENUGEL X‐0909 n°5180850 was the most resistant of all commercial kappa‐carrageenans available; mixing this kappacarrageenan with LBG in the respective proportions of 2.75%/0.25% gave the best rheological properties to the resulting mixed gel. Our study of the impact of fermentation parameters showed that pH has a significant effect on hardness, cohesion and percentage of deformation at rupture in milk (but not in the other 2 media). A pH drop of milk from 6.5 to 5.5 resulted in more brittle gels which may be explained by an increase in the amount of soluble calcium cations. Generally, soaking in milk produced the most brittle gels due to its calcium content, whey produced the hardest gels and whey permeate, the softest. An increase in the amomonium lactate concentmtion significantly improved hardness, rupture force and percentage of deformation at rupture, while reducing cohesion and resilience: NH4+ cations would account for this effect. The differences in rheological behuviour of immobilization gel beads during continuous Eactic fermentations of milk and whey permeate would be due to the cation content and more specijically to the higher calcium concentmtion in milk.

Uptake of lactose and continuous lactic acid fermentation by entrapped non-growing Lactobacillus helveticus in whey permeate

Continuous production of lactic acid from lactose has been carried out in a stirred-tank reactor with non-growing Lactobacillus helveticus entrapped in calcium alginate beads. A considerably longer operation half-life was obtained in a continuously operated reactor than in a batch-operated reactor. It is possible to simulate the action of entrapped non-growing cells on the basis of information from diffusion and kinetic experiments with suspended free cells. The simulation fit the experimental data over a broad range of substrate concentrations if the specific lactic acid production rate, q P, was used as a variable parameter in the model. The dynamic mathematical model used is divided into three parts: the reactor model, which describes the mass balance in a continuously operated stirred-tank reactor with immobilized biomass, the mass-transfer model including both external diffusion and internal mass transfer, and the kinetic model for uptake of substrate on the basis of a Michaelis-Menten-type mechanism. From kinetic data obtained for free biomass experiments it was found, with the use of non-linear parameter estimation techniques, that the conversion rate of lactose by L. helveticus followed a Michaelis-Menten-type mechanism with K S at half-saturation=0.22±0.01 g/l. The maximum specific lactose uptake rate for growing cells, q S,max, varied between 4.32±0.02 g lactose g cells-1 h-1 and 4.89 ±0.02 g lactose g cells-1 h-1. The initial specific lactose uptake rate for non-growing cells, q S,0, was found to be approximately 40% of the maximum specific lactose uptake rate for growing cells.

Batch and continuous production of lactic acid from salt whey using free and immobilized cultures of lactobacilli

Salt whey permeate was used as a substrate for lactic acid production by different strains of homofermentative lactobacilli. An isolate from Egyptian Cheddar cheese proved to be the most effective lactic acid producer. The salt whey permeate was optimized by addition of yeast extract and minerals to enable exponential growth of organisms. The lactic acid productivity of free and immobilized cells was compared and fermentation conditions were improved. Continuous lactic acid fermentation from salt whey permeate with cells immobilized in agarose beads was successfully carried out in a chemostat with a steady lactic acid concentration of 33.4 mg/ml.

Rapid continuous lactic acid fermentation by immobilised lactic acid bacteria for soy sauce production

Continuous lactic acid fermentation was carried out to produce an appropriate feed solution for rapid ethanol fermentation in soy sauce production. Lactic acid bacteria were immobilised physically within porous alumina ceramic beads and the fermentation substrate was a filtered extract of soy sauce mash. Lactic acid concentration was controlled by dilution rate. The volumetric production rate was dependent on the dilution rate and was much higher than that in batch fermentation. The lactic acid productivity was mathematically modelled from the basic material balance and the rate equation. The simulated results agreed with the experimental ones.

Lactic Acid Production in a Mixed-Culture Biofilm Reactor

Novel solid supports, consisting of polypropylene blended with various agricultural materials (pp composite), were evaluated as supports for pure- and mixed-culture continuous lactic acid fermentations in biofilm reactors. Streptomyces viridosporus T7A (ATCC 39115) was used to form a biofilm, and Lactobacillus casei subsp. rhamnosus (ATCC 11443) was used for lactic acid production. For mixed-culture fermentations, a 15-day continuous fermentation of S. viridosporus was performed initially to establish the biofilm. The culture medium was then inoculated with L. casei subsp. rhamnosus. For pure-culture fermentation, L. casei subsp. rhamnosus was inoculated directly into the reactors containing sterile pp composite chips. The biofilm reactors containing various pp composite chips were compared with a biofilm reactor containing pure polypropylene chips and with a reactor containing a suspension culture. Continuous fermentation was started, and each flow rate (0.06 to 1.92 ml/min) was held constant for 24 h; steady state was achieved after 10 h. Lactic acid production was determined throughout the 24-h period by high-performance liquid chromatography. Production rates that were two to five times faster than those of the suspension culture (control) were observed for the pure- and mixed-culture bioreactors. Both lactic acid production rates and lactic acid concentrations in the culture medium were consistently higher in mixed-culture than in pure-culture fermentations. Biofilm formation on the chips was detected at harvest by chip clumping and Gram staining.

Adaptive on-line optimizing control for lactic acid fermentation

The adaptive on-line optimization strategy was applied for continuous lactic acid fermentation. The control objective was to maximize the lactate production rate while keeping the lactate concentration at a specified value. The control task was divided into two. The task of the upper layer in the hierarchical control scheme was to search for the optimal operating point for cell concentration, while the task of the lower layer was to make the cell and lactate concentrations follow the respective set points which were either specified or given from the upper layer. The cell and lactate concentrations were either measured on-line or estimated every 2 min. The bioreactor was equipped with a hollow-fiber module, and control was implemented by manipulating the draw-off rate through the filter and the bleed stream flow rate in an on-off manner. It was experimentally shown that productivity as high as 20 kg/m 3·h could be attained and maintained for about 40–50 h when the lactate concentration was kept at either 20 kg/m 3 or 30 kg/m 3.

Optimal conditions for production of lactic acid from cheese whey permeate by Ca-alginate-entrapped Lactobacillus helveticus

Whole cells of Lactobacillus helveticus were immobilized in calcium-alginate beads to produce lactic acid from cheese whey ultrafiltrate. Ca-alginate-entrapped cells were characterized by higher fermentation rates and optimum pH than free cells. No difference could be observed in the profile of cell activity against temperature for either type of cells. After a heat treatment, cell activity was higher for free cells than for immobilized cells. Continuous lactic acid fermentation using a packed bed reactor was investigated.

Continuous lactic acid fermentation with concentrated product recovery by ultrafiltration and electrodialysis

Lactose of sweet whey permeate was converted into sodium lactate byLactobacillus helveticus. To increase the, productivity of the lactic acid fermentation and to reduce the amounts of effluents, the bioreactor was coupled with an ultrafiltration module and an electrodialysis unit. Without the electrodialyzer, with total cell recycling and at a dilution rate of 0.88 h−1, a cellular concentration of 64 gl−1 and a productivity of 22 gl−1 h−1 were obtained. When the electrodialysis unit is coupled, the outlet concentration of lactate was stabilized at 85±5 gl−1.

Continuous lactic acid fermentation of whey to produce a ruminant feed supplement high in crude protein

AbstractA mathematical model was developed to simulate, on a digital computer, the continuous fermentation of whey lactose to lactic acid with neutralization by ammonia. The simulation predicted the retention times for experimental test and the use of two stages for greatest efficiency. In the experimental tests, Lactobacillus bulgaricus was inoculated into whey in a 14‐liter continuous fermentor at 44°C and with automatic pH control. A series of steady‐state conditions was managed nonaseptically for 42 days without evident contamination and with an actual increase in the efficiency of conversion. Lactic acid was produced predominately' throughout the period, with less than 0.2% of other compounds. The product contained approximately 8 times as much crude protein (N × 6.25) as the original whey. In a single‐stage fermentation at pH 5.5, a retention time of 15 hr resulted in a residual lactose concentration of 0.7%; and little improvement was realized by increasing the retention time. Increasing the pH to 5.8 resulted in a significant improvement, but further increasing the pH to 6.0 resulted in only a small additional gain. By the employment of two fermentors in series at pH 5.5 with a total retention time of 31 hr, the residual lactose was reduced to less than 0.1%. Lactic acid was produced as a function mainly of maintenance rather than growth metabolism.