Industrial Production Of Lactic Acid Research Articles

Biofilm formation by agave epiphytic lactic acid bacteria fed with agave fructans.

The aim of this work was to find out if biofilms can be made by lactic acid bacteria (LAB) isolated from agave plants using agave fructans as sole carbohydrate substrates or if it was necessary to use fructose as a breakdown product of such polymers. This is part of a research project geared to develop industrial lactic acid production from agave fructans, an abundant raw material in Mexico's agave plantations. Present results showed that nine strains of LAB isolated from Agave salmiana and belonging to genus Lacticaseibacillus and Enterococcus produced exopolysaccharides directly from agave fructans to a greater extent than with fructose. The best polysaccharide productions in planktonic cultures were Lacticaseibacillus paracasei strains DG2, DG3, DG4 and DG8. Furthermore, all nine LAB strains produced biofilms on polystyrene microplates, much better with agave fructans than with fructose. In most strains, biofilm formation was favored at pH from 6.0 to 6.5, except for strains DG7 and DG9 where pH 5.5 was optimal. Biofilm formation required between 3 and 5 days of incubation in all Lacticaseibacillus paracasei strains, whereas Enterococcus faecium required a little less of 3 days. Present results support the straight use of agave fructans to develop LAB biofilms using agave epiphytic bacteria. This finding simplifies upstream processing of agave fructans to be used for future lactic acid fermentation in LAB biofilm reactors.

Microbial Fermentation Processes of Lactic Acid: Challenges, Solutions, and Future Prospects.

The demand for lactic acid and lactic acid-derived products in the food, pharmaceutical, and cosmetic industries is increasing year by year. In recent decades, the synthesis of lactic acid by microbials has gained much attention from scientists due to the superior optical purity of the product, its low production costs, and its higher production efficiency compared to chemical synthesis. Microbial fermentation involves the selection of feedstock, strains, and fermentation modes. Each step can potentially affect the yield and purity of the final product. Therefore, there are still many critical challenges in lactic acid production. The costs of feedstocks and energy; the inhibition of substrates and end-product; the sensitivity to the inhibitory compounds released during pretreatment; and the lower optical purity are the main obstacles hindering the fermentation of lactic acid. This review highlights the limitations and challenges of applying microbial fermentation in lactic acid production. In addition, corresponding solutions to these difficulties are summarized in order to provide some guidance for the industrial production of lactic acid.

Rapid adaptive evolution of Bacillus coagulans to undetoxified corncob hydrolysates for lactic acid production and new insights into its high phenolic degradation

Here, an adapted Bacillus coagulans (Weizmannia coagulans) strain CC17B-1 was developed for lignocellulosic lactic acid production through a short and rapid adaptive laboratory evolution technique. Without any detoxification, two actual corn cob hydrolysates from the factory were effectively fermented to lactic acid within 60 h. Strain CC17B-1 is capable of degrading all nine determined phenolic compounds in the hydrolysate, with the only exception being vanillic acid. Notably, its tolerances for ferulic acid and p-coumaric acid are the highest doses reported in anaerobic microbes. A proposed degradation pathway showed that strain CC17B-1 could convert phenolic aldehydes to phenolic alcohol and then further degrade them completely. This work provides new ideas for the microbe phenolic degradation pathway and paves the way for industrial lactic acid production from lignocellulosic biomass.

Bioconversion of Corn Crop Residues: Lactic Acid Production through Simultaneous Saccharification and Fermentation

Lactic acid (LA) is a chemical building block with wide applications in the food, cosmetics, and chemical industries. Its polymer polylactic acid further increases this range of applications as a green and biocompatible alternative to petrol-based plastics. Corn is the fourth largest crop in the world, and its residues represent a potentially renewable feedstock for industrial lactic acid production through simultaneous saccharification and fermentation (SSF). The main goal of this work is to summarize and compare the pretreatment methods, enzymatic formulations and microbial strains that have been combined in a SSF setup for bioconversion of corn crop residues into LA. Additionally, the main concerns of scaling-up and the innovation readiness level towards commercial implementation of this technology are also discussed. The analysis on commercial implementation renders the current state of SSF technology unsustainable, mainly due to high wastewater generation and saccharification costs. Nonetheless, there are promising strategies that are being tested and are focused on addressing these issues. The present work proves that the study and optimization of SSF as a biorefinery framework represents a step towards the adoption of potentially sustainable waste management practices.

Photocatalytic Biorefinery to Lactic Acid: A Carbon Nitride Framework with O Atoms Replacing the Graphitic N Linkers Shows Fast Migration/Separation of Charge

AbstractThe rational regulation of the structure of photocatalysts with an enhanced visible‐light absorption property and rapid charge dynamics is promising and challenging. Here, a facile method was developed for preparing oxygen‐doped carbon nitride bundles with porous hollow trunk‐shaped structures (Ox@CNB) using melamine with assistance of hydrochloric acid. Experimental results and density functional theory (DFT) calculations indicated that Ox@CNB exhibited controllable bandgaps (2.20–2.60 eV) and a low photoluminescence intensity. Interestingly, Ox@CNB displayed excellent photocatalytic activity for the synthesis of lactic acid (81.4 %) and universality for the reforming of biomass‐derived monosaccharides to lactic acid. The oxidation active species of h+, ⋅OH, ⋅O2− and 1O2 all promoted the lactic acid production, and h+ played a major role. A possible reaction mechanism of lactic acid synthesis was proposed by combining the experimental with the DFT results. A one‐thousand‐fold up‐scaled experiment demonstrated the significant application potential of the system for the industrial production of lactic acid.

Selection of optimal conditions for the lactic acid biosynthesis

Lactic acid is used in various industries: chemical, food, cosmetic, pharmaceutical, agriculture and polymer production. 40% of the domestic market demand for lactic acid is met through imports, while the main methods for producing lactic acid are microbiological or synthetic. The most rational is microbiological synthesis, however, when it is implemented, valuable sugar-containing substrates (crystalline sucrose, molasses, sugar syrup) are used, which significantly affects the cost of the final product. There was an obvious need to search for new technologies for the production of lactic acid. Prospective and cost-effective is the processing of whey into lactic acid using bacterial fermentation of the lactose contained in the whey. The aim of the study is to screen cultures of microorganisms capable of fermenting lactose contained in milk whey and to select the composition of the medium that provides the maximum yield of lactic acid. Strains of lactic acid bacteria were used in the experiment: Leuconostocmesenteroides subsp. mesenteroides 122 (B1699), Lactobacillus brevis B78 (B5728), Lactobacillus plantarum K9 (B5466), Lactobacillus casei C1 (B5726), Lactobacillus acidophilus (B9012), Lactobacillus paracasei BT 24/88 (B6253), Lactobacillus paracasei 139 (B2430), obtained from the Russian National Collection of Industrial Microorganisms (Scientific Center "Kurchatov Institute" -Research Institute for Genetics and Selection of Industrial Microorganisms). The authors determined the optimal composition of the medium for the biosynthesis of lactic acid by selecting the concentrations of yeast autolysate and salt solution that provide the maximum yield of lactic acid. The authors also selected the optimal duration of lactic acid biosynthesis. The study of the acid-forming ability of strains of lactic acid bacteria showed that of the strains studied, Lactobacillus casei C1 (B5726) showed the greatest ability to ferment lactose by synthesizing lactic acid, which correlates with the data on assimilation of lactose by the culture. The optimal cultivation time (132 h) and the concentration of yeast lysate (5%) in a nutrient medium based on curd whey were selected. With optimal parameters, the maximum concentration of lactic acid in the culture liquid of Lactobacillus casei C1 (B5726) was 54.77 g / L, which is comparable with the currently used producers in the industrial production of lactic acid.

Isolation and Characterization of Pediococcus sp. HLV1 from Fermented Idly Batter

The aim of the present study is the isolation and characterization of the lactic acid bacteria from idly batter, a traditional Indian fermented product. To achieve the aim, 10 idly batter samples were selected from different regions of Kadapa district. In the primary isolation and screening process, 50 lactic-acid-producing bacteria were isolated, and from them, six strains were selected based on their lactic acid yielding capacity for further evaluation. The selected cultures were studied for their phenotypic characters, and all cultures were Gram positive, cocci, and catalase negative. All the six strains were tested for their growth and lactic acid production at above 35 °C, and finally, one strain that showed good growth at 50 °C was selected for further characterization. Molecular characterization by 16S rRNA gene analysis and BLAST analysis revealed 99% similarity with Pediococcus pentosaceus Ni1142. The isolated culture was named as Pediococcus sp. HLV1, and the sequence was submitted to the NCBI databank as accession number MH921241. The isolated strain is able to utilize a wide range of carbohydrate substrates including glucose, fructose, sucrose, lactose, maltose, and xylose. The major fermentation product from glucose is lactic acid. Pediococcus sp. HLV1 showed optimum growth and production of lactic acid with glucose as carbon source (10%) and yeast extract as nitrogen source (0.3%) at pH 7.0 and 40 °C. As well-known probiotic bacteria, the isolated Pediococcus spp. also showed antimicrobial activity against both Gram-positive and Gram-negative bacteria and more specifically inhibited Gram-positive Bacillus. Using the above optimal conditions, lactic acid from a fresh mango peel extract was studied, and at the end of the fermentation, 5.2% (v/v) of lactic acid was produced. In conclusion, the isolated LAB Pediococcus sp. strain HLV1 is able to grow and produce lactic acid at a high temperature (45 °C) and to survive at 50 °C. Mango peel, a by-product of mango pulp industries, can be utilized as one of the economically cheap feedstocks for industrial production of lactic acid by the Pediococcus sp. strain HLV1.

In vivo evolution of lactic acid hyper-tolerant Clostridium thermocellum

Lactic acid (LA) has several applications in the food, cosmetics and pharmaceutical industries, as well as in the production of biodegradable plastic polymers, namely polylactides. Industrial production of LA is essentially based on microbial fermentation. Recent reports have shown the potential of the cellulolytic bacterium Clostridium thermocellum for direct LA production from inexpensive lignocellulosic biomass. However, C. thermocellum is highly sensitive to acids and does not grow at pH < 6.0. Improvement of LA tolerance of this microorganism is pivotal for its application in cost-efficient production of LA. In the present study, the LA tolerance of C. thermocellum strains LL345 (wild-type fermentation profile) and LL1111 (high LA yield) was increased by adaptive laboratory evolution. At large inoculum size (10 %), the maximum tolerated LA concentration of strain LL1111 was more than doubled, from 15 g/L to 35 g/L, while subcultures evolved from LL345 showed 50–85 % faster growth in medium containing 45 g/L LA. Gene mutations (pyruvate phosphate dikinase, histidine protein kinase/phosphorylase) possibly affecting carbohydrate and/or phosphate metabolism have been detected in most LA-adapted populations. Although improvement of LA tolerance may sometimes also enable higher LA production in microorganisms, C. thermocellum LA-adapted cultures showed a yield of LA, and generally of other organic acids, similar to or lower than parental strains. Based on its improved LA tolerance and LA titer similar to its parent strain (LL1111), mixed adapted culture LL1630 showed the highest performing phenotype and could serve as a framework for improving LA production by further metabolic engineering.

L-Lactic Acid Production Using Engineered Saccharomyces cerevisiae with Improved Organic Acid Tolerance.

Lactic acid is mainly used to produce bio-based, bio-degradable polylactic acid. For industrial production of lactic acid, engineered Saccharomyces cerevisiae can be used. To avoid cellular toxicity caused by lactic acid accumulation, pH-neutralizing agents are used, leading to increased production costs. In this study, lactic acid-producing S. cerevisiae BK01 was developed with improved lactic acid tolerance through adaptive laboratory evolution (ALE) on 8% lactic acid. The genetic basis of BK01 could not be determined, suggesting complex mechanisms associated with lactic acid tolerance. However, BK01 had distinctive metabolomic traits clearly separated from the parental strain, and lactic acid production was improved by 17% (from 102 g/L to 119 g/L). To the best of our knowledge, this is the highest lactic acid titer produced by engineered S. cerevisiae without the use of pH neutralizers. Moreover, cellulosic lactic acid production by BK01 was demonstrated using acetate-rich buckwheat husk hydrolysates. Particularly, BK01 revealed improved tolerance against acetic acid of the hydrolysates, a major fermentation inhibitor of lignocellulosic biomass. In short, ALE with a high concentration of lactic acid improved lactic acid production as well as acetic acid tolerance of BK01, suggesting a potential for economically viable cellulosic lactic acid production.

Reasonable regulation of carbon/nitride ratio in carbon nitride for efficient photocatalytic reforming of biomass-derived feedstocks to lactic acid

Photocatalysis provides a promising opportunity for selective oxidation of biomass to high-value chemicals under mild conditions. The key to realize this transformation is to design a cost-effective and environmentally friendly photocatalyst. Here, we report the preparation of a carbon nitride photocatalyst with controllable carbon/nitride (C/N) ratio and its application in the selective photocatalytic synthesis of lactic acid from biomass-derived monosaccharides. Reasonable C/N ratio in the catalyst can significantly enhance the visible light absorption range and accelerate the mobility of photogenerated carriers. The obtained photocatalyst exhibited excellent photocatalytic activity, yielding 76.8% lactic acid. All of the h+,·O2-,·OH and 1O2 are beneficial for lactic acid production, and the·O2- plays a major role. Furthermore, the photocatalyst exhibited excellent reusability and universality. The 1000-fold scale-up experiments indicated that the system has potential for industrial production of lactic acid. Therefore, the present work offers a promising example for photocatalytic reforming of biomass.

Upscale fermenter design for lactic acid production from cheese whey permeate focusing on impeller selection and energy optimization

This study focusses on the design and scale-up of industrial lactic acid production by fermentation of dairy cheese whey permeate based on standard methodological parameters. The aim was to address the shortcomings of standard scale-up methodologies and provide a framework for fermenter scale-up that enables the accurate estimation of energy consumption by suitable selection of turbine and speed for industrial deployment. Moreover, life cycle assessment (LCA) was carried out to identify the potential impacts and possibilities to reduce the operation associated emissions at an early stage. The findings showed that a 3000 times scale-up strategy assuming constant geometric dimensions and specific energy consumption (P/Vw) resulted in lower impeller speed and energy demand. The Rushton turbine blade (RTB) and LightninA315 four-blade hydrofoil (LA315) were found to have the highest and lowest torque output, respectively, at a similar P/Vw of 2.8 kWm−3, with agitation speeds of 1.33 and 2.5 s−1, respectively. RTB demonstrating lower shear damage towards cells (up to 1.33 s−1) was selected because it permits high torque, low-power and acceptable turbulence. The LCA results showed a strong relation between the number of impellers installed and associated emissions suggesting a trade-off between mixing performance and environmental impacts.

Copper oxide functionalized chitosan hybrid hydrogels for highly efficient photocatalytic-reforming of biomass-based monosaccharides to lactic acid

Much attention has been focused on the photocatalytic-reforming of biomass to produce high-value chemicals due to their unique merits. In this study, we report a freezing-thawing strategy for the preparation of an alkaline CuO-chitosan hybrid hydrogel (CuO@CS-H). The synergism between CuO and alkaline chitosan hydrogel led to a highly efficient photocatalytic-reforming of xylose to lactic acid under a weak alkaline system, and the highest lactic acid yield is 81.6 %. The retained lactic acid yield was about 91.2 % after being used nine times. The reaction system is universal for the production of lactic acid from biomass-derived pentoses and hexoses, and O2− plays a major role in the synthesis of lactic acid. Industrial production of lactic acid via the as-proposed system was shown to be feasible according to a two-thousand-fold scale-up experiment. This work initiates a novel strategy of photocatalytic synthesis of lactic acid from biomass-based monosaccharides.

Combination of Cell Growth Dependent and Independent Modes for Efficient L-Lactic Acid Production by Lactobacillus paracasei

In this study,on the basis of L-lactic acid production by Lactobacillus paracasei,a high cell density strategy with the combination of cell growth dependent and independent modes was developed through investigating the optimal initial glucose concentration and the metabolic capacity of resting cells. The results indicated that the cells grew well under 140 g/L of initial glucose concentration,and all the glucose could be rapidly exhausted to produce L-lactic acid. Moreover,the cells could still maintain high metabolic activity within 6~7 h after the end of fermentation. Finally,based on the above results,the L-lactic acid productivity of high cell density phase was enhanced by 1.4-fold compared with that of normal batch fermentation,and the L-lactic acid yield was also improved significantly to 0.985 g/g. This study extended the highly efficient production period so as to improve the production efficiency of L-lactic acid. Otherwise,the auxiliary time required in the fermentation process could be effectively reduced,including seed preparation and cell growth. Thus,it would be potentially applied for future industrial lactic acid production.

Efficient two-step lactic acid production from cassava biomass using thermostable enzyme cocktail and lactic acid bacteria: insights from hydrolysis optimization and proteomics analysis.

Lactic acid is an intermediate-volume specialty chemical, used in the production of biodegradable polymers and other chemicals. Although lactic acid production process is well established, however, the cost of production is very high. Therefore, in this study; starchy biomass (cassava) was hydrolyzed with in-house enzyme cocktail prepared from Aspergillus foetidus MTCC508 and Bacillus subtilis RA10. Process optimization using Taguchi experimental design helped to optimize the most effective ratio of fungal and bacterial amylase for effective saccharification of cassava. A higher sugar yield of 379.63mg/gds was obtained under optimized conditions, using 30U/gds of bacterial enzyme and 90U/gds of the fungal enzyme at pH 4 within 48h of saccharification. Among 11 lactic acid bacteria isolated, Lactobacillus fermentum S1A and Lactobacillus farraginis SS3A produced the highest amount of lactic acid 0.81g/g and 0.77g/g, respectively, from the cassava hydrolysate. The study proved the potential renewable source of cassava biomass as a source for fermentable sugars that can be fermented to lactic acid with high yield. In future, this cost-effective and environmental-friendly bioprocess can be upscaled for industrial lactic acid production.

Capnophilic Lactic Fermentation from Thermotoga neapolitana: A Resourceful Pathway to Obtain Almost Enantiopure L-lactic Acid

The industrial production of lactic acid (LA) is mainly based on bacterial fermentation. This process can result in enantiopure or racemic mixture according to the producing organism. Between the enantiomers, L-lactic acid shows superior market value. Recently, we reported a novel anaplerotic pathway called capnophilic lactic fermentation (CLF) that produces a high concentration of LA by fermentation of sugar in the anaerobic thermophilic bacterium Thermotoga neapolitana. The aim of this work was the identification of the enantiomeric characterization of the LA produced by T. neapolitana and identification of the lactate dehydrogenase in T. neapolitana (TnLDH) and related bacteria of the order Thermotogales. Chemical derivatization and GC/MS analysis were applied to define the stereochemistry of LA from T. neapolitana. A bioinformatics study on TnLDH was carried out for the characterization of the enzyme. Chemical analysis showed a 95.2% enantiomeric excess of L-LA produced by T. neapolitana. A phylogenetic approach clearly clustered the TnLDH together with the L-LDH from lactic acid bacteria. We report for the first time that T. neapolitana is able to produce almost enantiopure L-lactic acid. The result was confirmed by bioinformatics analysis on TnLDH, which is a member of the L-LDH sub-family.

Production of optically pure L(+)-lactic acid from waste plywood chips using an isolated thermotolerant Enterococcus faecalis SI at a pilot scale.

Utilization of renewable and low-cost lignocellulosic wastes has received major focus in industrial lactic acid production. The use of high solid loadings in biomass pretreatment potentially offers advantages over low solid loadings including higher lactic acid concentration with decreased production and capital costs. In this study, an isolated Enterococcus faecalis SI with optimal temperature 42°C was used to produce optically pure L-lactic acid (> 99%) from enzyme-saccharified hydrolysates of acid-impregnated steam explosion (AISE)-treated plywood chips. The L-lactic acid production increased by 10% at 5L scale compared to the similar fermentation scheme reported by Wee et al. The fermentation with a high solid loading of 20% and 35% (w/v) AISE-pretreated plywood chips had been successfully scaled up to process development unit scale (100L) and pilot scale (9m3), respectively. This is the first report of pilot-scale lignocellulosic lactic acid fermentation by E. faecalis with high lactic acid titer (nearly 92gL-1) and yield (0.97kgkg-1). Therefore, large-scale L-lactic acid production by E. faecalis SI shows the potential application for industries.

Electrochemical production of lactic acid from glycerol oxidation catalyzed by AuPt nanoparticles

The production of valuable chemicals from relatively inexpensive feedstocks utilizing electrochemical methods has been attracting widespread attention in recent years since it is highly efficient, decentralized, environmental-friendly and can operate in room temperature and pressure. Currently, the industrial production of lactic acid is mainly based on bio-fermentation, leading to drawbacks including severe conditions, unfriendliness to environment, low efficiency and requirement of expensive equipment, which can potentially overcome by electrochemical methods. Herein, we report for the first time the preparation of lactic acid at room temperature and pressure from the one-pot electro-oxidation of glycerol, a byproduct from biodiesel production. AuPt nanoparticles with different surface compositions were employed in this work to optimize the catalysis performance, and the glycerol oxidation was operated at a series of applied potentials, pH and glycerol concentration. The optimal lactic acid selectivity was 73%, obtained with Au-enriched surface at applied potential of 0.45 V vs. RHE.

Novel homologous lactate transporter improves l-lactic acid production from glycerol in recombinant strains of Pichia pastoris

BackgroundCrude glycerol is the main byproduct of the biodiesel industry. Although it can have different applications, its purification is costly. Therefore, in this study a biotechnological route has been proposed for further utilization of crude glycerol in the fermentative production of lactic acid. This acid is largely utilized in food, pharmaceutical, textile, and chemical industries, making it the hydroxycarboxylic acid with the highest market potential worldwide. Currently, industrial production of lactic acid is done mainly using sugar as the substrate. Thus here, for the first time, Pichia pastoris has been engineered for heterologous l-lactic acid production using glycerol as a single carbon source. For that, the Bos taurus lactate dehydrogenase gene was introduced into P. pastoris. Moreover, a heterologous and a novel homologous lactate transporter have been evaluated for l-lactic acid production.ResultsBatch fermentation of the P. pastoris X-33 strain producing LDHb allowed for lactic acid production in this yeast. Although P. pastoris is known for its respiratory metabolism, batch fermentations were performed with different oxygenation levels, indicating that lower oxygen availability increased lactic acid production by 20 %, pushing the yeast towards a fermentative metabolism. Furthermore, a newly putative lactate transporter from P. pastoris named PAS has been identified by search similarity with the lactate transporter from Saccharomyces cerevisiae Jen1p. Both heterologous and homologous transporters, Jen1p and PAS, were evaluated in one strain already containing LDH activity. Fed-batch experiments of P. pastoris strains carrying the lactate transporter were performed with the batch phase at aerobic conditions followed by an aerobic oxygen-limited phase where production of lactic acid was favored. The results showed that the strain containing PAS presented the highest lactic acid titer, reaching a yield of approximately 0.7 g/g.ConclusionsWe showed that P. pastoris has a great potential as a fermentative organism for producing l-lactic acid using glycerol as the carbon source at limited oxygenation conditions (below 0.05 % DO in the bioreactor). The best strain had both the LDHb and the homologous lactate transporter encoding genes expressed, and reached a titer 1.5 times higher than the strain with the S. cerevisiae transporter. Finally, it was also shown that increased lactic acid production was concomitant to reduction of acetic acid formation by half.

PROSPECTS FOR THE APPLICATION OF ULTRASONIC MEMBRANE EXTRACTORS IN THE SUBMERGED CULTIVATION OF LACTIC ACID AND PROPIONIC ACID BACTERIA

The industrial production of lactic acid and propionic acid bacteria , which produce lactic, acetic and propionic acids and used as the components of biological preservatives of feed and fodder, requires to maintain a total concentration of organic acids in fermentation broth at a level of one percent during the whole fermentation process. The higher concentration inhibits the growth and development of these microorganisms, so their cell concentration in fermentation broth does not exceed 0.6·10 9 ml -1 . Under laboratory conditions, pH of cultivation medium can be regulated by the neutralization of organic acids with alkaline, but under the large-scale production, the loss of produced lactic, acetic, and propionic acids is inexpedient, since they are widely used in various industrial segments including the conservation of rich fodder. One of the possible solutions is the use of a membrane extractor to remove organic acids, which represent valuable metabolites, from the cultural broth directly during the cultivation process. In this study, the efficiency of a specially designed membrane extractor equipped with additional ultrasonic transducers, which reduced diffusion limitations near the membrane surface, has been assessed in the process of submerged cultivation of three bacterial cultures: Lactococcus lactis VPKM B-2092 , Lactobacillus plantarum VPKM B-4173 , and Propionibacterium acidipropionici VPKM B-5723 . The extractor was connected to the fermenter as external device and consisted of a cartridge filter preventing the biomass uptake into the extractor and a membrane extractor of a “liquid-liquid”type equipped with pH-state and hydrodynamic ultrasonic transducers. Whereas classic pH-states feed a pH-correcting solution into a fermenter according to a signal from a pH sensor, the developed pH-state construction turned on the US membrane extractor to remove excess organic acids from the fermentation broth. Due to the maintenance of optimum pH, the final concentration of L. lactis, L. plantarum, and P. acidipropionici cells increased in 5.8, 3.6, and 3.2 times, respectively. The equipping of a membrane extractor with ultrasonic transducers accelerated the removal of organic acids from fermentation broth of L. lactis, L. plantarum, and P. acidipropionici in 5.25, 5, and 6.25 times, respectively, i.e., provided a more rapid and efficient fermentation. The proposed technology improves the economical efficiency of the process and provides the required diversity of technical solutions for its use in a microbiological production.

Improvement of lactic acid production in Saccharomyces cerevisiae by a deletion of ssb1.

Polylactic acid (PLA) is an important renewable polymer, but current processes for producing its precursor, lactic acid, suffer from process inefficiencies related to the use of bacterial hosts. Therefore, improving the capacity of Saccharomyces cerevisiae to produce lactic acid is a promising approach to improve industrial production of lactic acid. As one such improvement required, the lactic acid tolerance of yeast must be significantly increased. To enable improved tolerance, we employed an RNAi-mediated genome-wide expression knockdown approach as a means to rapidly identify potential genetic targets. In this approach, several gene knockdown targets were identified which confer increased acid tolerance to S. cerevisiae BY4741, of which knockdown of the ribosome-associated chaperone SSB1 conferred the highest increase (52%). This target was then transferred into a lactic acid-overproducing strain of S. cerevisiae CEN.PK in the form of a knockout and the resulting strain demonstrated up to 33% increased cell growth, 58% increased glucose consumption, and 60% increased L-lactic acid production. As SSB1 contains a close functional homolog SSB2 in yeast, this result was counterintuitive and may point to as-yet-undefined functional differences between SSB1 and SSB2 related to lactic acid production. The final strain produced over 50 g/L of lactic acid in under 60 h of fermentation.