Lactic acid production from pretreated corn stover with recycled streams

In order to overcome bottlenecks of the high amount of cellulase consumption in lignocellulosic l-Lactic acid (LA) production, a non-sterilized fed-batch simultaneous saccharification and fermentation (SSF) -membrane separation integration process was established in this current work. During the process, residual cellulase that remaining in the waste aqueous solution and solid residuals of corn stover (CS) were recycled and reused in subsequent fermentations. A total 6 rounds of operation were performed. Averagely, LA yield of 0.389 g g⁻¹ (pretreated CS) was achieved, which was 1.20 times higher than that of the conventional process without waste stream recycling. Moreover, the wastewater discharge and the cost of nutrients for fermentation can also hugely decrease. Results indicated that cellulase, wastewater discharge and nutrients consumption of the process reduced by 47.4 %, 73.7 % and 86.1 %, respectively. This study opens a promising way for the reduction of second-generation LA production cost, which could significantly change the economic feasibility of the LA biorefineries.     

Continuous 2-keto-gluconic acid (2KGA) production from corn starch hydrolysate by Pseudomonas fluorescens AR4

A continuous fermentation process for 2-keto-gluconic acid (2KGA) production from cheap raw material corn starch hydrolysate was developed using the strain Pseudomonas fluorescens AR4. The dilution rate and feeding glucose concentration had a significant effect on the cell concentrations, glucose utilization and 2KGA production performance. The optimal operating factors were obtained as: 0.065 h⁻¹ of dilution rate, 180 g/L of feeding glucose concentration, and 16 h of batch fermentation time as the starting point. Under these conditions, the steady state had the 135.92 g/L of produced 2KGA concentration, 8.83 g/L.h of average volumetric productivity, and 0.9510 g/g of yield. In conclusion, the proposed efficient and stable continuous fermentation process for 2KGA production by the strain P. fluorescens AR4 is potentially competitive for industrial production from corn starch hydrolysate in terms of 2KGA productivity and yield.     

Lactic acid production with Lactobacillus casei ssp. rhamnosus NBIMCC 1013: Modeling and optimization of the nutrient medium

The medium needed to perform a fermentation process with viable cells of Lactobacillus casei ssp. rhamnosus NBIMCC 1013 for the production of lactic acid was modeled and optimized. On the basis of single‐factor experiments and statistical analysis, the significant factors affecting the fermentation process, i.e. the concentration of carbon source, concentrations of both yeast and meat extracts, and the range of variability of these components were determined. Modeling and optimization of the medium contents were performed using central composite design. The composition of the medium used for the production of lactic acid (g/L) was as follows: glucose 69.8, meat extract 17.07, yeast extract 10.9, CH₃COONa 10, K₂HPO₄ 0.25, KH₂PO₄ 0.25, MgSO₄·7H₂O 0.05, and FeSO₄ 0.05. The maximum specific growth rate of the lactic acid bacteria (μ=0.51 h⁻¹) and other kinetic parameters were determined during cultivation in a laboratory bioreactor using the logistic equation and the Luedeking–Piret model. The obtained medium allows the production of lactic acid under optimum conditions, at high specific sugar assimilation rates and high lactic acid accumulation rates. The positive results of the paper are the new nutrient medium for lactic acid production and the process kinetic model, enabling scaling up and switching to a continuous process.     

Lactic acid and animal feeds production from Sophora flavescens residues by Rhizopus oryzae fermentation

In this study, the feasibility of producing lactic acid and animal feeds from Sophora flavescens residues (SFR) by Rhizopus oryzae was explored. Results showed that the simultaneous saccharification and fermentation (SSF) is the optimal fermentation mode, which was simple and high-efficiency. When the inoculation volume of R. oryzae was 10 % and the pH value was adjusted by adding CaCO₃ in stages during SSF, the maximum concentration of lactic acid was 46.78 g/L, and the maximum lactic acid productivity reached 0.97 g/L/h. Results also showed that the protein content of the solid residues after fermentation of R. oryzae reached 12.15 %. This content was 46 times higher than that by the original SFRs and nearly 4.3 times the protein content of the solid residues after fermentation by Enterococcus faecium. In addition, the solid residues after fermentation rich in Fe and Zn could be used as animal feeds or feed additives. Thus, it is expected that this study may provide a novel approach for Chinese medicine residues treatment towards full resource recovery.     

Direct fermentation of starch to lactic acid byLactobacillus amylovorus

Summary Fermentation production of lactic acid directly from starch was studied in a batch fermentor usingLactobacillus amylovorus. At an initial concentration of 120 g/L starch, 96.2 g/L of lactic acid was produced from liquefied starch in 20 hours while 92.5 g/L of lactate was produced from the raw starch in 39 hours. High initial glucose levels (100 g/L) in the medium inhibited the organism, unless it had been adapted by growing it in a low-glucose medium. The direct production of lactic acid from starch could reduce overall production costs significantly.     

Lactic acid production directly from starch in a starch-controlled fed-batch operation using Lactobacillus amylophilus

Based on the batch results, we constructed a simplified simultaneous saccharification and fermentation (SSF) model for the simulation of lactic acid production directly from unhydrolyzed potato starch using Lactobacillus amylophilus. The results of batch operation at different initial starch concentrations (20, 40 and 60 g/l) indicated that a higher initial starch concentration would lead to a slightly lower productivity, but would largely decrease the yield. Among that, the batch with 20 g/l of initial starch had the maximum productivity and the maximum yield, which would be 0.31 g/(l h) and 98% (g/g), respectively. In view of increasing the productivity and the final lactic acid concentration, a starch-controlled fed-batch operation with 20 g/l of initial starch was performed. It showed the fed-batch operation with starch controlled at 8 ± 1 g/l by adjusting the starch-feeding rate led to the maximum productivity of 0.75 g/(l h) and the yield of 69%.     

Lactic acid production from agriculture residues

Various agriculture feedstock residues were evaluated for lactic acid production by simultaneous saccharification and fermentation (SSF) using Lactobacillus delbrueckii and Lactobacillus plantarum, without any additional nutrients. Lactic acid production was higher in alfalfa fiber and soya fiber compared to corncob (soft) and wheat straw. In Lactobacillus plantarum, the amount of lactic acid obtained from alfalfa fiber and soya fiber was 46 and 44 g/100 g fiber, respectively. However, in Lactobacillus delbrueckii, the lactic acid production in soya fiber was 44 g/100 g fiber and that of alfalfa was 32 g/100 g fiber. Small amounts of acetic acid were also produced from SSF of agricultural feedstocks residues. During SSF of alfalfa fiber, lactic acid production in both L. delbrueckii and L. plantarum was enhanced by adding pectinases and cellulases. Lactic acid production from alfalfa fiber did not change with increasing O₂ transfer rates in the fermentation medium, whereas acetic acid production in both Lactobacillus cultures increased with increasing O₂ transfer rates.     

均匀设计法对产几丁质酶细菌C4发酵条件的优化

系统研究了碳源,氮源,起始pH值、培养基装量、培养温度和时间等因素对细菌C4产几丁质酶的影响。结果表明,碳、氮源分别以胶体几丁质、KNO和蛋白胨最好;在起始pH值7．6—8．5,培养基装量为三角瓶体积的12％,培养温度28℃,振荡培养(180r／min)5d时最有利于几丁质酶的产生。在此基础上通过均匀设计法优化了发酵培养基配方。优化后的培养基配方为：胶体几丁质1．5％,蛋白胨0．55％,KNO3 0．3％,MgSO4 0．09％,Tween80 0．005％。在该条件下,几丁质酶活力达2．68U／mL,比在原基础培养条件下的酶活力提高90．1％。     

Lactic acid production from corn stover using mixed cultures of Lactobacillus rhamnosus and Lactobacillus brevis

Mixed cultures of Lactobacillus rhamnosus and Lactobacillus brevis was studied for improving utilization of both cellulose- and hemicellulose-derived sugars from corn stover for lactic acid production. During simultaneous saccharification and fermentation (SSF) of NaOH-treated corn stover by the mixed cultures, a lactic acid yield of 0.70 g/g was obtained, which was about 18.6% and 29.6% higher than that by single cultures of L. rhamnosus and L. brevis, respectively. Our results indicated that lactic acid yield from NaOH-pretreated corn stover by mixed cultures of L. rhamnosus and L. brevis was comparable to that from pure sugar mixtures (0.73 g/g of glucose/xylose mixture at 3:1 w/w).     

Lactic acid bacteria strains selected from fermented total mixed rations improve ensiling and in vitro rumen fermentation characteristics of corn stover silage

ObjectiveThis study identified the major lactic acid bacteria (LAB) strains from different fermented total mixed rations (FTMRs) via metataxonomic analysis and evaluated the ability of their standard strain as ensiling inoculants for corn stover silage.MethodsThe bacterial composition of eight FTMRs were analyzed by 16S rDNA sequencing. Corn stover was ensiled without LAB inoculation (control) or with 1×10⁶ cfu/g LAB standard strain (Lactobacillus vaginalis, Lactobacillus reuteri, Lactobacillus helveticus, or Lactobacillus paralimentarius) selected from the FTMRs or 10 g/t commercial silage inoculant (CSI) around 25°C for 56 days. For each inoculation, a portion of the silage was sampled to analyze ensiling characteristics at time intervals of 0, 1, 3, 7, 14, 28, and 56 days, gas production (GP), microbial crude protein and volatile fatty acids as the measurements of rumen fermentation characteristics were evaluated in vitro with the silages of 56 days after 72 h incubation.ResultsLactobacillus covered >85% relative abundance of all FTMRs, in which L. pontis, L. vaginalis, L. reuteri, L. helveticus, and L. paralimentarius showed >4% in specific FTMRs. CSI, L. helveticus, and L. paralimentarius accelerated the decline of silage pH. Silage inoculated with L. paralimentarius and CSI produced more lactic acid the early 14 days. Silage inoculated with L. paralimentarius produced less acetic acid and butyric acid. For the in vitro rumen fermentation, silage inoculated with CSI produced more potential GP, isobutyric acid, and isovaleric acid; silage inoculated with L. helveticus produced more potential GP and isovaleric acid, silage inoculated with L. paralimentarius or L. reuteri produced more potential GP only.ConclusionThe standard strain L. paralimentarius (DSM 13238) is a promising ensiling inoculant for corn stover silage. The findings provide clues on strategies to select LAB to improve the quality of silage.     

Growth and butyric acid production by Clostridium populeti

The growth of Clostridium populeti in 2% (w/v) glucose medium containing 0.2% (w/v) yeast extract was optimal with 10 mM NH₄Cl as the nitrogen source. Although the maximum specific growth rate (=0.32 h^-1) with 5 mM NH₄Cl was similar, the biomass yield was about 30% lower than that at the optimum. Either sodium sulphide or cysteine-HCl at an optimum concentration of 0.33 mM and 5.0 mM respectively, could serve as the sole sulphur source for growth. The growth rate was unaffected by initial glucose concentrations of up to 10% (w/v), but in the presence of 15% glucose it declined by about 35%. The molar yield of butyric acid (mol/mol glucose) declined from 0.70 in 1% (w/v) initial glucose medium to 0.39 in 10% glucose medium. In 5.7% initial glucose medium, butyric acid levels of 6.3 g/l were obtained (0.56 mol butyrate/mol glucose) after 72 h of incubation in 2.5 l batch cultures. A decrease of about 50% in the maximum specific growth rate of C. populeti was observed in the presence of an initial concentration of either 1.2 g/l of butyric acid or 18.9 g/l of acetic acid.This paper is issued as NRCC No. 29032     

Lactic acid production by loofah-immobilized Rhizopus oryzae through one-step fermentation process using starch substrate

Rhizopus oryzae PTCC 5263 capacity in synthesis of lactic acid (LA) from 10 g/l of soluble potato starch was determined using one-step fermentation process. Pellets were the favorable growing form of the free cells. The extent of the natural ability of the test fungus on biofilm formation on loofah sponge was examined by immobilizing R. oryzae (LIRO). The maximum LA concentration for the free cells and LIRO within 96 h was 3 and 4 g/l, respectively. In terms of specific starch utilization rate (\(q_{\text{s}}\)) and specific LA formation (\(q_{\text{p}}\)), LIRO performed more favorably compared to the free cells (\(q_{{{\text{s}}_{\text{F}} }} > q_{{{\text{s}}_{\text{LIRO}} }}\) and \(q_{{{\text{p}}_{\text{F}} }} < q_{{{\text{p}}_{\text{LIRO}} }}\)). Cell immobilization strategy was undertaken for the column reactor studies based on the statistically optimized levels of the inoculum size and temperature. Maximum production of the LA by the LIRO using an airlift reactor with net draft tube was 5 g/l obtainable within 48 h.

     

Enzymatic production of cyclodextrins from unliquefied corn starch in an attrition bioreactor

A novel enzymatic process for the production of cyclodextrins from unliquefied starch was developed. Cyclodextrins were produced in an attrition bioreactor in which simultaneous hydrolysis of starch and synthesis of cyclodextrins by cyclodextrin glycosyltransferase (CGTase) occur. The CGTase was obtained from isolated Bacillus sp. BE101, and maximum activity of the enzyme was observed at pH 6.0 and a temperature of 45 degrees C. The effect of milling media size and material on the performance of the attrition bioreactor was investigated, and operational parameters such as agitation speed, volume of milling media, ratio of enzyme to starch, and starch concentration were optimized. The production yield of cyclodextrins from unliquefied corn starch of 15% reached 35% at 24 h under optimized conditions. Energy consumption for the production of cyclodextrins in the attrition bioreactor system was estimated to be about 25% of that required for the liquefaction of starch in the conventional process.     

Anaerobic fermentative production of lactic acid using cheese whey and corn steep liquor

Cheese whey was the most suitable substrate for production of lactic acid under anaerobic conditions by Entercoccus flavescens which, on supplementating with corn steep liquor (5% v/v) and 10 mM CaCO₃ at pH 5.5, 37°C, yielded 12.6 g lactic acid/l in 36 h. Production was scaled up to a 10 l bioreactor under controlled pH and continuous CO₂ supply and gave 28 g lactic acid/l in 30 h resulting in a net 8.7-fold increase in production as compared to unoptimized conditions.     

Lactic acid production from whey permeate by immobilized Lactobacillus casei

Two matrices have been assessed for their ability to immobilize Lactobacillus casei cells for lactic acid fermentation in whey permeate medium. Agar at 2% concentration was found to be a better gel than polyacrylamide in its effectiveness to entrap the bacterial cells to carry out batch fermentation up to three repeat runs. Of the various physiological parameters studied, temperature and pH were observed to have no significant influence on the fermentation ability of the immobilized organism. A temperature range of 40–50°C and a pH range of 4.5–6.0 rather than specific values, were found to be optimum when fermentation was carried out under stationary conditions. In batch fermentation ～90% conversion of the substrate (lactose) was achieved in 48 h using immobilized cell gel cubes of 4 × 2 × 2 mm size, containing 400 mg dry bacterial cells per flask and 4.5% w/v (initial) whey lactose content as substrate. However, further increase in substrate levels tested (>4.5% w/v) did not improve the process efficiency. Supplementation of Mg²⁺ (1 mM) and agricultural by-products (mustard oil cake, 6%) in the whey permeate medium further improved the acid production ability of the immobilized cells under study.     

Lactic acid and biosurfactants production from hydrolyzed distilled grape marc

Acid hydrolysis of distilled grape marc, an useless agricultural residue from wineries, was carried out using dilute sulfuric acid (1–5%) at several reaction times and 130 °C, in order to obtain monomeric sugars which after supplementation with corn steep liquor (10 g/L) and yeast extract (10 g/L) were used to carry out the fermentation into lactic acid by Lactobacillus pentosus without detoxification stage. Xylose was the main sugar generated followed by glucose and arabinose. Possible inhibitor compounds such as acetic acid liberated from acetyl groups, and furfural and hydroxymethylfurfural generated by sugars dehydration, were produced as degradation byproducts. The hydrolysis stage was optimized by using an incomplete factorial design where the independent variables were the percentage of catalyzer, the reaction time and the temperature. The optima conditions in terms of xylose concentration were 3.3% H₂SO₄, 125 min and 130 °C, but due to the high furfural concentration, two other conditions using lower reaction times (30 and 77.5 min) were also selected to assay the fermentation. Although any condition was feasible to fully utilize the relatively broad spectra of sugars released by the acid hydrolysis, under the shorter reaction time the best results were achieved (Q_P = 0.476 g/L h; Y_P/S = 0.71 g/g) which represents a theoretical yield of 97%. Furthermore, L. pentosus produced 4.8 mg/L of intracellular biosurfactants, measured as biosurfactin, representing a yield of 0.60 mg of intracellular biosurfactant per g of sugars consumed.     

Lactic acid production from agricultural resources as cheap raw materials

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

Lactic acid production from xylose by the fungus Rhizopus oryzae

Lignocellulosic biomass is considered nowadays to be an economically attractive carbohydrate feedstock for large-scale fermentation of bulk chemicals such as lactic acid. The filamentous fungus Rhizopus oryzae is able to grow in mineral medium with glucose as sole carbon source and to produce optically pure l(+)-lactic acid. Less is known about the conversion by R. oryzae of pentose sugars such as xylose, which is abundantly present in lignocellulosic hydrolysates. This paper describes the conversion of xylose in synthetic media into lactic acid by ten R. oryzae strains resulting in yields between 0.41 and 0.71 g g⁻¹. By-products were fungal biomass, xylitol, glycerol, ethanol and carbon dioxide. The growth of R. oryzae CBS 112.07 in media with initial xylose concentrations above 40 g l⁻¹ showed inhibition of substrate consumption and lactic acid production rates. In case of mixed substrates, diauxic growth was observed where consumption of glucose and xylose occurred subsequently. Sugar consumption rate and lactic acid production rate were significantly higher during glucose consumption phase compared to xylose consumption phase. Available xylose (10.3 g l⁻¹) and glucose (19.2 g l⁻¹) present in a mild-temperature alkaline treated wheat straw hydrolysate was converted subsequently by R. oryzae with rates of 2.2 g glucose l⁻¹ h⁻¹ and 0.5 g xylose l⁻¹ h⁻¹. This resulted mainly into the product lactic acid (6.8 g l⁻¹) and ethanol (5.7 g l⁻¹).     

Modeling and optimization of fermentative hydrogen production

Biohydrogen is a sustainable energy resource due to its potentially higher efficiency of conversion to usable power, non-polluting nature and high energy density. The purpose of modeling and optimization is to improve, analyze and predict biohydrogen production. Biohydrogen production depends on a number of variables, including pH, temperature, substrate concentration and nutrient availability, among others. Mathematical modeling of several distinct processes such as kinetics of microbial growth and products formation, steady state behavior of organic substrate along with its utilization and inhibition have been presented. Present paper summarizes the experimental design methods used to investigate effects of various factors on fermentative hydrogen production, including one-factor-at-a-time design, full factorial and fractional factorial designs. Each design method is briefly outlined, followed by the introduction of its analysis. In addition, the applications of artificial neural network, genetic algorithm, principal component analysis and optimization process using desirability function have also been highlighted.     

Enhanced production of itaconic acid from corn starch and market refuse fruits by genetically manipulated Aspergillus terreus SKR10

A potent itaconic acid producing strain, Aspergillus terreus SKR10, was isolated from horticulture waste. Market refuse, apple and banana, were explored as novel substrates for itaconic acid production with yields of 20+/-2.0 and 20.0+/-1.0 g l(-1), respectively. Itaconic acid yields of 28.5+/-2.2 and 31.0+/-1.7 g l(-1) were obtained with acid and alpha-amylase hydrolyzed corn starch. The efficiency of itaconic acid production by this wild type strain was improved by ultraviolet, chemical and mixed mutagenic treatments. Two high itaconic acid yielding mutants, N45 and UNCS1 were obtained by gradient plating. These two mutants were capable of producing twice the yield of itaconic acid as the parent strain.