Continuous propionate production from whey permeate using a novel fibrous bed bioreactor

Changes in Chemical Composition and Fatty Acid Profile of Milk and Cheese and Sensory Profile of Milk via Supplementation of Goats' Diet with Marine Algae

The aim of the present study was to assess the effects of the low level of Schizochytrium limacinum marine algae (daily 5 g per animal) on the milk, cheese, and whey composition; fatty acid profile of milk and cheese; and the sensory profile of goat milk using an e-nose device. Thirty Alpine goats were randomly divided into two groups: the control group (C, n = 15)-fed grass with daily 600 g concentrate and the experimental group (MA, n = 15) who received the same forage and concentrate supplemented with 5 g/head/day marine algae. Animals were kept indoors and the investigation period lasted 52 days, including the first six weeks as the period of adaptation and the last 10 days as the treatment period. During the adaptation period, bulk milk samples from each group were collected once a week (0, 7, 14, 21, 28, 35, and 42 d), while during the treatment period (10 days), bulk milk samples from each group were taken every day, and cheese samples were processed from bulk milk each day from both groups. Marine algae supplementation had no negative effect on milk composition. In contrast, the marine algae inclusion significantly elevated the fat and protein content of whey and the protein content of cheese, as well as the recovery of fat and protein in the curd, while increasing the cheeses' moisture content on a fat-free basis. The marine algae supplementation significantly increased the docosahexaenoic acid (DHA) and the rumenic acid (CLA c9t11) concentrations and decreased the n-6/n-3 ratio in the milk and cheese. There were no significant differences between the C and the MA group with regard to the sensory profiles of the milk. It can be concluded that the milk obtained from goats given daily supplementation of 5g of MA has a fatty acid profile more beneficial to human health, without any negative effects on the milk's aromatic components.

High-rate continuous n-butanol production by Clostridium acetobutylicum from glucose and butyric acid in a single-pass fibrous bed bioreactor

Biobutanol produced in acetone-butanol-ethanol (ABE) fermentation at batch mode cannot compete with chemically derived butanol because of the low reactor productivity. Continuous fermentation can dramatically enhance productivity and lower capital and operating costs but are rarely used in industrial fermentation because of increased risks in culture degeneration, cell washout, and contamination. In this study, cells of the asporogenous Clostridium acetobutylicum ATCC55025 were immobilized in a single-pass fibrous-bed bioreactor (FBB) for continuous production of butanol from glucose and butyrate at various dilution rates. Butyric acid in the feed medium helped maintaining cells in the solventogenic phase for stable continuous butanol production. At the dilution rate of 1.88 h^-1 , butanol was produced at 9.55 g/L with a yield of 0.24 g/g and productivity of 16.8 g/L/h, which was the highest productivity ever achieved for biobutanol fermentation and an 80-fold improvement over the conventional ABE fermentation. The extremely high productivity was attributed to the high density of viable cells (~100 g/L at >70% viability) immobilized in the fibrous matrix, which also enabled the cells to better tolerate butanol and butyric acid. The FBB was stable for continuous operation for an extended period of over one month. This article is protected by copyright. All rights reserved.

Fermentation strategies to improve propionic acid production with propionibacterium ssp.: a review

Propionic acid (PA) is a carboxylic acid applied in a variety of processes, such as food and feed preservative, and as a chemical intermediate in the production of polymers, pesticides and drugs. PA production is predominantly performed by petrochemical routes, but environmental issues are making it necessary to use sustainable processes based on renewable materials. PA production by fermentation with the Propionibacterium genus is a promising option in this scenario, due to the ability of this genus to consume a variety of renewable carbon sources with higher productivity than other native microorganisms. However, Propionibacterium fermentation processes present important challenges that must be faced to make this route competitive, such as: a high fermentation time, product inhibition and low PA final titer, which increase the cost of product recovery. This article summarizes the state of the art regarding strategies to improve PA production by fermentation with the Propionibacterium genus. Firstly, strategies associated with environmental fermentation conditions and nutrition requirements are discussed. Subsequently, advantages and disadvantages of various strategies proposed to improve process performance (high cell concentration by immobilization or recycle, co-culture fermentation, genome shuffling, evolutive and metabolic engineering, and in situ recovery) are evaluated.

Fermentative production of propionic acid: prospects and limitations of microorganisms and substrates

Propionic acid is an important organic acid with wide industrial applications, especially in the food industry. It is currently produced from petrochemicals via chemical routes. Increasing concerns about greenhouse gas emissions from fossil fuels and a growing consumer preference for bio-based products have led to interest in fermentative production of propionic acid, but it is not yet competitive with chemical production. To improve the economic feasibility and sustainability of bio-propionic acid, fermentation performance in terms of concentration, yield, and productivity must be improved and the cost of raw materials must be reduced. These goals require robust microbial producers and inexpensive renewable feedstocks, so the present review focuses on bacterial producers of propionic acid and promising sources of substrates as carbon sources. Emphasis is placed on assessing the capacity of propionibacteria and the various approaches pursued in an effort to improve their performance through metabolic engineering. A wide range of substrates employed in propionic acid fermentation is analyzed with particular interest in the prospects of inexpensive renewable feedstocks, such as cellulosic biomass and industrial residues, to produce cost-competitive bio-propionic acid. KEY POINTS: • Fermentative propionic acid production emerges as competitor to chemical synthesis. • Various bacteria synthesize propionic acid, but propionibacteria are the best producers. • Biomass substrates hold promise to reduce propionic acid fermentation cost.

Use of Calcium Amino Acid Chelate in the Production of Acid-Curd Goat Cheese

Amino acid chelates are a new group of compounds approved for food enrichment, however there is no previous research using calcium amino acid chelate to enrich goat's milk products. The purpose of this research was to evaluate the possibility of using calcium amino acid chelate to produce goat's acid-curd cheese. In this study, four types of acid-curd cheeses from goat's milk subjected to 85 °C/5 min treatment were produced: control cheeses-made from milk without calcium addition and cheeses from milk enriched with 30, 35 and 40 mg of Ca (in 100 g of milk) in the form of calcium amino acid chelate. Goat cheese with calcium amino acid chelate had a higher moisture content, and a lower fat content. More fat was separated with the whey. In cheeses made from the milk with calcium amino acid chelate there was no goaty taste. Enrichment with 35 mg of Ca in 100 g of goat milk increased the calcium content in cheese by 60.5% in comparison to the control sample. However, the enrichment of goat milk with 40 mg Ca (in 100 g of processed milk) increased the calcium content in cheese by only 63.29%.

The effect of graphene-poly(methyl methacrylate) fibres on microbial growth

A novel class of ultra-thin fibres, which affect microbial growth, were explored. The microbial properties of poly(methyl methacrylate) fibres containing 2, 4 and 8 wt% of graphene nanoplatelets (GNPs) were studied. GNPs were dispersed in a polymeric solution and processed using pressurized gyration. Electron microscopy was used to characterize GNP and fibre morphology. Scanning electron microscopy revealed the formation of beaded porous fibres. GNP concentration was found to dictate fibre morphology. As the GNP concentration increased, the average fibre diameter increased from 0.75 to 2.71 µm, while fibre porosity decreased. Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa were used to investigate the properties of 2, 4 and 8 wt% GNP-loaded fibres. GNP-loaded fibres (0 wt%) were used as the negative control. The fibres were incubated for 24 h with the bacteria; bacterial colony-forming units were enumerated by adopting the colony-counting method. The presence of 2 and 4 wt% GNP-loaded fibres promoted microbial growth, while 8 wt% GNP-loaded fibres showed antimicrobial activity. These results indicate that the minimum inhibitory concentration of GNPs required within a fibre is 8 wt%.

Propionic acid production from corn stover hydrolysate by Propionibacterium acidipropionici

BACKGROUND

The production of value-added chemicals alongside biofuels from lignocellulosic hydrolysates is critical for developing economically viable biorefineries. Here, the production of propionic acid (PA), a potential building block for C3-based chemicals, from corn stover hydrolysate is investigated using the native PA-producing bacterium Propionibacterium acidipropionici.

RESULTS

A wide range of culture conditions and process parameters were examined and experimentally optimized to maximize titer, rate, and yield of PA. The effect of gas sparging during fermentation was first examined, and N2 was found to exhibit improved performance over CO2. Subsequently, the effects of different hydrolysate concentrations, nitrogen sources, and neutralization agents were investigated. One of the best combinations found during batch experiments used yeast extract (YE) as the primary nitrogen source and NH4OH for pH control. This combination enabled PA titers of 30.8 g/L with a productivity of 0.40 g/L h from 76.8 g/L biomass sugars, while successfully minimizing lactic acid production. Due to the economic significance of downstream separations, increasing titers using fed-batch fermentation was examined by changing both feeding media and strategy. Continuous feeding of hydrolysate was found to be superior to pulsed feeding and combined with high YE concentrations increased PA titers to 62.7 g/L and improved the simultaneous utilization of different biomass sugars. Additionally, applying high YE supplementation maintains the lactic acid concentration below 4 g/L for the duration of the fermentation. Finally, with the aim of increasing productivity, high cell density fed-batch fermentations were conducted. PA titers increased to 64.7 g/L with a productivity of 2.35 g/L h for the batch stage and 0.77 g/L h for the overall process.

CONCLUSION

These results highlight the importance of media and fermentation strategy to improve PA production. Overall, this work demonstrates the feasibility of producing PA from corn stover hydrolysate.

High efficiency succinic acid production from glycerol via in situ fibrous bed bioreactor with an engineered Yarrowia lipolytica

In this study, in situ fibrous bed bioreactor (isFBB) was developed at the first time for efficient succinic acid (SA) production by Yarrowia lipolytica. After optimization, SA titer, productivity and yield of 51.9g/L, 1.46g/L/h and 0.42g/g were obtained respectively via isFBB fermentation under conditions of 750cm² cotton towel, 120g/L initial glycerol and 3L/min aeration rate. By fed batch strategy, SA titer raised up to 198.2g/L was achieved, which was the highest value ever reported. In operation stability study, SA productivity showed no obvious decrease after 12 repeated batches of 460h fermentation, and cell viability even recovered within two repeated batches after intentional interruption. This study successfully attained a highly efficient and stable isFBB for enhanced SA production by Y. lipolytica.

Recent trends in bioethanol production from food processing byproducts

The widespread use of corn starch and sugarcane as sources of sugar for the production of ethanol via fermentation may negatively impact the use of farmland for production of food. Thus, alternative sources of fermentable sugars, particularly from lignocellulosic sources, have been extensively investigated. Another source of fermentable sugars with substantial potential for ethanol production is the waste from the food growing and processing industry. Reviewed here is the use of waste from potato processing, molasses from processing of sugar beets into sugar, whey from cheese production, byproducts of rice and coffee bean processing, and other food processing wastes as sugar sources for fermentation to ethanol. Specific topics discussed include the organisms used for fermentation, strategies, such as co-culturing and cell immobilization, used to improve the fermentation process, and the use of genetic engineering to improve the performance of ethanol producing fermenters.

Volatile fatty acids production from anaerobic treatment of cassava waste water: effect of temperature and alkalinity

The production of volatile fatty acids (VFAs), intermediates in the anaerobic degradation process of organic matter from waste water, was evaluated in this work. A batch reactor was used to investigate the effect of temperature, and alkalinity in the production of VFAs, from the fermentation of industrial cassava waste water. Peak production of total volatile fatty acids (TVFAs) was observed in the first two days of acidogenesis. A central composite design was performed, and the highest yield (3400 mg L(-1) of TVFA) was obtained with 30°C and 3 g L(-1) of sodium bicarbonate. The peak of VFA was in 45 h (pH 5.9) with a predominance of acetic (63%) and butyric acid (22%), followed by propionic acid (12%). Decreases in amounts of cyanide (12.9%) and chemical oxygen demand (21.6%) were observed, in addition to the production of biogas (0.53 cm(3) h(-1)). The process was validated experimentally and 3400 g L(-1) of TVFA were obtained with a low relative standard deviation.

Improved ethanol production from cheese whey, whey powder, and sugar beet molasses by "Vitreoscilla hemoglobin expressing" Escherichia coli

This work investigated the improvement of ethanol production by engineered ethanologenic Escherichia coli to express the hemoglobin from the bacterium Vitreoscilla (VHb). Ethanologenic E. coli strain FBR5 and FBR5 transformed with the VHb gene in two constructs (strains TS3 and TS4) were grown in cheese whey (CW) medium at small and large scales, at both high and low aeration, or with whey powder (WP) or sugar beet molasses hydrolysate (SBMH) media at large scale and low aeration. Culture pH, cell growth, VHb levels, and ethanol production were evaluated after 48 h. VHb expression in TS3 and TS4 enhanced their ethanol production in CW (21-419%), in WP (17-362%), or in SBMH (48-118%) media. This work extends the findings that "VHb technology" may be useful for improving the production of ethanol from waste and byproducts of various sources.

An economical biorefinery process for propionic acid production from glycerol and potato juice using high cell density fermentation

An economically sustainable process was developed for propionic acid production by fermentation of glycerol using Propionibacterium acidipropionici and potato juice, a by-product of starch processing, as a nitrogen/vitamin source. The fermentation was done as high-cell-density sequential batches with cell recycle. Propionic acid production and glycerol consumption rates were dependent on initial biomass concentration, and reached a maximum of 1.42 and 2.30 g L(-1) h(-1), respectively, from 50 g L(-1) glycerol at initial cell density of 23.7 gCDW L(-1). Halving the concentration of nitrogen/vitamin source resulted in reduction of acetic and succinic acids yields by ~39% each. At glycerol concentrations of 85 and 120 g L(-1), respectively, 43.8 and 50.8 g L(-1) propionic acid were obtained at a rate of 0.88 and 0.29 g L(-1) h(-1) and yield of 84 and 78 mol%. Succinic acid was 13 g% of propionic acid and could represent a potential co-product covering the cost of nitrogen/vitamin source.

Long-term Continuous Production of Monoclonal Antibody by Hybridoma Cells Immobilized in a Fibrous-Bed Bioreactor

The kinetics and long-term stability of continuous production of monoclonal antibody IgG2b by hybridoma HD-24 cells immobilized in a fibrous-bed bioreactor (FBB) were studied for a period of approximately 8 months. The cells were immobilized in the fibrous bed by surface attachment of cells and entrapment of large cell clumps in the void space of the fibrous matrix. A high viable cell density of 1.01 x 10(8)/ml was attained in the bioreactor, which was about 63 times higher than those in conventional T-flask and spinner flask cultures. The continuous FBB produced IgG at a concentration of approximately 0.5 g/l, with reactor productivity of approximately 7 mg/h.l, which was about 23 times higher than those from conventional T-flask and spinner flask cultures. The IgG concentration can be further increased to approximately 0.67 g/l by using higher feed (glucose and glutamine) concentrations and running the reactor at a recycle batch or fed-batch mode. The long-term performance of this bioreactor was also evaluated. For a period of 36 days monitored, the MAb produced in the continuous well-mixed bioreactor at 50 h retention time (0.02/h dilution rate) was maintained at a steady concentration level of approximately 0.3 g/l with less than 8% drift. At the end of the study, it was found that approximately 25% of the cells were strongly attached to the fiber surfaces and the other approximately 75% entrapped or weakly immobilized in the fibrous matrix. The strongly attached cells had a high viability of approximately 90%, compared to approximately 75% for cells weakly immobilized and only approximately 1.4% for freely suspended cells, suggesting that the fibrous matrix preferentially retained and protected the viable (productive) cells. The FBB thus was able to maintain its long-term productivity because nonviable and dead cells were continuously washed off from the fibrous matrix. The high MAb concentration and production rate and excellent stability for continuous long-term production obtained in this study compare favorably to other bioreactor studies reported in the literature. The reactor performance can be further improved by providing better pH and aeration controls at higher feed concentrations. The FBB is easy to operate and scale-up, and thus can be used economically for industrial production of MAb.

Multifaceted attributes of dairy propionibacteria: a review

Dairy propionibacteria are Generally Recognized as Safe (GRAS) status microorganisms which have been traditionally used for the manufacture of Swiss type cheeses. In the last two decades various added features and functionalities have been discovered and developed from these bacteria. Propionibacteria are robust organisms with remarkable adaptability to technological and physiological stress conditions. Besides, they also display a multitude of health promoting properties like modulation of gut microbiota, improved gut physiology and immunomodulation suggesting their promising probiotic potential. Propionibacteria produce an interestingly wide range of functional biomolecules like B group vitamins, trehalose, conjugated linoleic acid, propionic acid, bacteriocins, bifidogenic factors etc. These bacteria are thus now being explored for designing novel functional foods as well as for industrial production of nutraceuticals. Growing interest in these bacteria is fueled by the first whole genome sequencing of a Propionibacterium freudenreichii strain providing a platform for better understanding of various pathways and further improvement in related process technologies.

Microbial production of propionic acid from propionibacteria: current state, challenges and perspectives

Propionic acid (PA) is an important building block chemical and finds a variety of applications in organic synthesis, food, feeding stuffs, perfume, paint and pharmaceutical industries. Presently, PA is mainly produced by petrochemical route. With the continuous increase in oil prices, public concern about environmental pollution, and the consumers' desire for bio-based natural and green ingredients in foods and pharmaceuticals, PA production from propionibacteria has attracted considerable attention, and substantial progresses have been made on microbial PA production. However, production of PA by propionibacteria is facing challenges such as severe inhibition of end-products during cell growth and the formation of by-products (acetic acid and succinic acid). The integration of reverse metabolic engineering and systematic metabolic engineering provides an opportunity to significantly improve the acid tolerance of propionibacteria and reduce the formation of by-products, and makes it feasible to strengthen the commercial competition of biotechnological PA production from propionibacteria to be comparable to the petrochemical route.

Canonical Analysis Technique as an Approach to Determine Optimal Conditions for Lactic Acid Production byLactobacillus helveticusATCC 15009

The response surface methodology and canonical analysis were employed to find the most suitable conditions forLactobacillus helveticusto produce lactic acid from cheese whey in batch fermentation. The analyzed variables were temperature, pH, and the concentrations of lactose and yeast extract. The experiments were carried out according to a central composite design with three center points. An empiric equation that correlated the concentration of lactic acid with the independent variables was proposed. The optimal conditions determined by the canonical analysis of the fitted model were 40°C, pH 6.8, 82 g/L of lactose, and 23.36 g/L of yeast extract. At this point, the lactic acid concentration reached 59.38 g/L. A subsequent fermentation, carried out under optimal conditions, confirmed the product concentration predicted by the adjusted model. This concentration of lactic acid is the highest ever reported forLactobacillus helveticusATCC 15009 in batch process using cheese whey as substrate.

Efficient production of butyric acid from Jerusalem artichoke by immobilized Clostridium tyrobutyricum in a fibrous-bed bioreactor

Butyric acid is an important specialty chemical with wide industrial applications. The feasible large-scale fermentation for the economical production of butyric acid requires low-cost substrate and efficient process. In the present study, butyric acid production by immobilized Clostridium tyrobutyricum was successfully performed in a fibrous-bed bioreactor using Jerusalem artichoke as the substrate. Repeated-batch fermentation was carried out to produce butyric acid with a high butyrate yield (0.44 g/g), high productivity (2.75 g/L/h) and a butyrate concentration of 27.5 g/L. Furthermore, fed-batch fermentation using sulfuric acid pretreated Jerusalem artichoke hydrolysate resulted in a high butyric acid concentration of 60.4 g/L, with the yield of 0.38 g/g and the selectivity of ∼ 85.1 (85.1g butyric acid/g acetic acid). Thus, the production of butyric acid from Jerusalem artichoke on a commercial scale could be achieved based on the system developed in this work.

A novel recycle batch immobilized cell bioreactor for propionate production from whey lactose

Recycle batch fermentations using immobilized cells of Propionibacterium acidipropionici were studied for propionate production from whey permeate, de-lactose whey permeate, and acid whey. Cells were immobilized in a spirally wound fibrous sheet packed in a 0.5-L column reactor, which was connected to a 5-L stirred tank batch fermentor with recirculation. The immobilized cells bioreactor served as a breeder for these recycle batch fermentations. High fermentation rates and conversions were obtained with these whey media without nutrient supplementation. It took approximately 55 h to ferment whey permeate containing approximately 45 g/L lactose to approximately 20 g/L propionic acid. Higher propionate concentrations can be produced with various concentrated whey media containing more lactose. The highest propionic acid concentration obtained with the recycle batch reactor was 65 g/L, which is much higher than the normal maximum concentration of 35 to 45 g/L reported in the literature. The volumetric productivity ranged from 0.22 g/L x h to 0.47 g/L x h, depending on the propionate concentration and whey medium used. The corresponding specific cell productivity was 0.033 to 0.07 g/L x g cell. The productivity increased to 0.68 g/L x h when whey permeate was supplemented with 1% (w/v) yeast extract. Compared with conventional batch fermentation, the recycle batch fermentation with the immobilized cell bioreactor allows faster fermentation, produces a higher concentration of product, and can be run continually without significant downtime. The process also produced similar fermentation results with nonsterile whey media.

Engineering Propionibacterium acidipropionici for enhanced propionic acid tolerance and fermentation

Propionibacterium acidipropionici, a Gram-positive, anaerobic bacterium, has been the most used species for propionic acid production from sugars. In this study, the metabolically engineered mutant ACK-Tet, which has its acetate kinase gene knocked out from the chromosome, was immobilized and adapted in a fibrous bed bioreactor (FBB) to increase its acid tolerance and ability to produce propionic acid at a high final concentration in fed-batch fermentation. After about 3 months adaptation in the FBB, the propionic acid concentration in the fermentation broth reached approximately 100 g/L, which was much higher than the highest concentration of approximately 71 g/L previously attained with the wild-type in the FBB. To understand the mechanism and factors contributing to the enhanced acid tolerance, adapted mutant cells were harvested from the FBB and characterized for their morphology, growth inhibition by propionic acid, protein expression profiles as observed in SDS-PAGE, and H+-ATPase activity, which is related to the proton pumping and cell's ability to control its intracellular pH gradient. The adapted mutant obtained from the FBB showed significantly reduced growth sensitivity to propionic acid inhibition, increased H+-ATPase expression and activity, and significantly elongated rod morphology.

Butyric acid fermentation in a fibrous bed bioreactor with immobilized Clostridium tyrobutyricum from cane molasses

Butyrate fermentation by immobilized Clostridium tyrobutyricum was successfully carried out in a fibrous bed bioreactor using cane molasses. Batch fermentations were conducted to investigate the influence of pH on the metabolism of the strain, and the results showed that the fermentation gave a highest butyrate production of 26.2 g l(-1) with yield of 0.47 g g(-1) and reactor productivity up to 4.13 g l(-1)h(-1) at pH 6.0. When repeated-batch fermentation was carried out, long-term operation with high butyrate yield, volumetric productivity was achieved. Several cane molasses pretreatment techniques were investigated, and it was found that sulfuric acid treatment gave better results regarding butyrate concentration (34.6+/-0.8 g l(-1)), yield (0.58+/-0.01 g g(-1)), and sugar utilization (90.8+/-0.9%). Also, fed-batch fermentation from cane molasses pretreated with sulfuric acid was performed to further increase the concentration of butyrate up to 55.2 g l(-1).

Airlift-driven fibrous-bed bioreactor for continuous production of glucoamylase using immobilized recombinant yeast cells

Continuous production of a fungal glucoamylase by immobilized recombinant Saccharomyces cerevisiae strain C468 containing plasmid pGAC9. Yeast cells were immobilized on hydrophilic cotton cloth in an inverse internal loop airlift-driven bioreactor. Free-cell culture in the airlift and stirred tank bioreactors confirmed the plasmid instability of the recombinant yeast. Enhanced glucoamylase productivity and plasmid stability were observed both in the free and immobilized cell cultures in the airlift bioreactor system. The glucoamylase level of the free-cell culture in the airlift bioreactor was approximately 20% higher than that in the in stirred tank bioreactor due to high cell density (cell dry weight/volume of bioreactor) and fraction of the plasmid-carrying cells. A potentially high glucoamylase activity of 161U/L and a corresponding volumetric productivity of 3.5U/Lh were achieved when a cell density of approximately 85g/L (or 12.3g/g fiber) was attained in the fibrous-bed immobilized cell bioreactor system. The stable glucoamylase production was achieved after five generations, at which time a fraction of approximately 62% of the plasmid-carrying cells was realized in the immobilized cell system. Plasmid stability was increased for the immobilized cells during continuous culture at the operating dilution rate. The volumetric and specific productivities and fraction of plasmid-carrying cells in the immobilized cell system were higher than in the free-cell counterpart, however. This was in part due to the high viability (approximately 80%) in the immobilized cell system and the selective immobilization of the plasmid-carrying cells in the fibrous bed, and perhaps increased plasmid copy number.

Study on solvent extraction of propionic acid from simulated discharged water in vitamin B12 production by anaerobic fermentation

The potential of recovering propionic acid from discharged water in vitamin B(12) production by anaerobic fermentation was investigated in this paper. A primary amine, N(1923), was used as the extractant, kerosene as diluter and n-octanol as modifier. The influences of the content of N(1923) in the organic phase, the phase ratio and the pH of aqueous phase on the extraction yield of propionic acid were studied. The organic phase composition with the volume ratio was proposed of N(1923):kerosene:n-octanol as 45:35:20. Under conditions of the phase ratio (o/w) as 1:4, the pH of aqueous phase of 3.0 and after 5 min extraction, the extraction yield of propionic acid can be over 97%.

Kinetic analysis and pH-shift control strategy for propionic acid production with Propionibacterium Freudenreichii CCTCC M207015

The production of propionic acid by Propionibacterium freudenreichii CCTCC M207015 was investigated in a 7.5-l stirred-tank fermentor. Batch fermentations by P. freudenreichii CCTCC M207015 at various pH values ranging from 5.5 to 7.0 were studied. Based on the analysis of the time course of specific cell growth rate (mu (x)) and specific propionic acid formation rate (mu (p)), a two-stage pH-shift control strategy was proposed. At first 48 h, pH was controlled at 6.5 to obtain the maximal mu (x), subsequently pH 6.0 was used to maintain high mu (p) to enhance the production of propionic acid. By applying this pH-shift control strategy in propionic acid fermentation, the maximal propionic acid and glucose conversion efficiency had a significant improvement and reached 19.21 g/l and 48.03%, respectively, compared with those of constant pH operation (14.58 g/l and 36.45%). Fed-batch fermentation with pH-shift control strategy was also applied to produce propionic acid; the maximal propionic acid yield and glucose conversion efficiency reached 25.23 g/l and 47.76%, respectively.

Antibacterial and antilarval activity of deep-sea bacteria from sediments of the West Pacific Ocean

Deep-sea microorganisms are a new source of bioactive compounds. In this study, crude ethyl acetate extracts of 176 strains of deep-sea bacteria, isolated from sediments of the West Pacific Ocean, were screened for their antibacterial activity against four test bacterial strains isolated from marine biofilms. Of these, 28 deep-sea bacterial strains exhibited antibacterial activity against one or more of the bacteria tested. Active deep-sea bacterial strains belonged mainly to the genera of Pseudomonas, Psychrobacter and Halomonas. Additionally, antilarval activity of 56 deep-sea bacterial strains was screened using Balanus amphitrite larvae. Seven bacterial strains produced metabolites that had strong inhibitive effects on larval settlement. None of these metabolites showed significant toxicity. The crude extract of one deep-sea Streptomyces strain could completely inhibit larval settlement at a concentration of 25 microg ml(-1).

Construction and characterization of ack knock-out mutants of Propionibacterium acidipropionici for enhanced propionic acid fermentation

Propionibacterium acidipropionici produces propionic acid from glucose with acetic acid, succinic acid, and CO2 as byproducts. In this work, inactivation of ack gene, encoding acetate kinase (AK), by gene disruption and integrational mutagenesis was studied as a method to reduce acetate formation in propionic acid fermentation. The partial ack gene of approximately 750 bp in P. acidipropionici was cloned using a PCR-based method with degenerate primers and sequenced. The deduced amino acid sequence had 88% similarity and 76% identity with the amino acid sequence of AK from Bacillus subtilis. The partial ack gene was used to construct a linear DNA fragment with an inserted tetracycline resistance cassette and a nonreplicative integrational plasmid containing a tetracycline resistance gene cassette. These DNA constructs were then introduced into P. acidipropionici by electroporation, resulting in two mutants, ACK-Tet and TAT-ACK-Tet, respectively. Southern hybridization confirmed that the ack gene in the mutant ACK-Tet was disrupted by the inserted tetracycline resistance gene. As compared to the wild-type, the activities of AK were reduced by 26% and 43% in ACK-Tet and TAT-ACK-Tet mutants, respectively. The specific growth rate of these mutants was reduced by approximately 25% to 0.10/h (0.13/h for the wild-type), probably because of reduced acetate and ATP production. Both mutants produced approximately 14% less acetate from glucose. Although ack disruption alone did not completely eliminate acetate production, the propionate yield was increased by approximately 13%.

Enhanced propionic acid fermentation by Propionibacterium acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor

Fed-batch fermentations of glucose by P. acidipropionici ATCC 4875 in free-cell suspension culture and immobilized in a fibrous-bed bioreactor (FBB) were studied. The latter produced a much higher propionic acid concentration (71.8 +/- 0.8 g/L vs. 52.2 +/- 1.1 g/L), indicating enhanced tolerance to propionic acid inhibition by cells adapted in the FBB. Compared to the free-cell fermentation, the FBB culture produced 20-59% more propionate (0.40-0.65 +/- 0.02 g/g vs. 0.41 +/- 0.02 g/g), 17% less acetate (0.10 +/- 0.01 g/g vs. 0.12 +/- 0.02 g/g), and 50% less succinate (0.09 +/- 0.02 g/g vs. 0.18 +/- 0.03 g/g) from glucose. The higher propionate production in the FBB was attributed to mutations in two key enzymes, oxaloacetate transcarboxylase and propionyl CoA: succinyl CoA transferase, leading to the production of propionic acid from pyruvate. Both showed higher specific activity and lower sensitivity to propionic acid inhibition in the mutant than in the wild type. In contrast, the activity of PEP carboxylase, which converts PEP directly to oxaloacetate and leads to the production of succinate from glucose, was generally lower in the mutant than in the wild type. For phosphotransacetylase and acetate kinase in the acetate formation pathway, however, there was no significant difference between the mutant and the wild type. In addition, the mutant had a striking change in its morphology. With a threefold increase in its length and approximately 24% decrease in its diameter, the mutant cell had an approximately 10% higher specific surface area that should have made the mutant more efficient in transporting substrates and metabolites across the cell membrane. A slightly lower membrane-bound ATPase activity found in the mutant also indicated that the mutant might have a more efficient proton pump to allow it to better tolerate propionic acid. In addition, the mutant had more longer-chain saturated fatty acids (C17:0) and less unsaturated fatty acids (C18:1), both of which could decrease membrane fluidity and might have contributed to the increased propionate tolerance. The enhanced propionic acid production from glucose by P. acidipropionici was thus attributed to both a high viable cell density maintained in the reactor and favorable mutations resulted from adaptation by cell immobilization in the FBB.

Production of L(+)-lactic acid from glucose and starch by immobilized cells of Rhizopus oryzae in a rotating fibrous bed bioreactor

A rotating fibrous-bed bioreactor (RFB) was developed for fermentation to produce L(+)-lactic acid from glucose and cornstarch by Rhizopus oryzae. Fungal mycelia were immobilized on cotton cloth in the RFB for a prolonged period to study the fermentation kinetics and process stability. The pH and dissolved oxygen concentration (DO) were found to have significant effects on lactic acid productivity and yield, with pH 6 and 90% DO being the optimal conditions. A high lactic acid yield of 90% (w/w) and productivity of 2.5 g/L.h (467 g/h.m(2)) was obtained from glucose in fed-batch fermentation. When cornstarch was used as the substrate, the lactic acid yield was close to 100% (w/w) and the productivity was 1.65 g/L.h (300 g/h.m(2)). The highest concentration of lactic acid achieved in these fed-batch fermentations was 127 g/L. The immobilized-cells fermentation in the RFB gave a virtually cell-free fermentation broth and provided many advantages over conventional fermentation processes, especially those with freely suspended fungal cells. Without immobilization with the cotton cloth, mycelia grew everywhere in the fermentor and caused serious problems in reactor control and operation and consequently the fermentation was poor in lactic acid production. Oxygen transfer in the RFB was also studied and the volumetric oxygen transfer coefficients under various aeration and agitation conditions were determined and then used to estimate the oxygen transfer rate and uptake rate during the fermentation. The results showed that the oxygen uptake rate increased with increasing DO, indicating that oxygen transfer was limited by the diffusion inside the mycelial layer.

Production of carboxylic acids from hydrolyzed corn meal by immobilized cell fermentation in a fibrous-bed bioreactor

Corn meal hydrolyzed with amylases was used as the carbon source for producing acetic, propionic, and butyric acids via anaerobic fermentations. In this study, corn meal, containing 75% (w/w) starch, 20% (w/w) fibers, and 1.5% (w/w) protein, was first hydrolyzed using amylases at 60 degrees C. The hydrolysis yielded approximately 100% recovery of starch converted to glucose and 17.9% recovery of protein. The resulting corn meal hydrolyzate was then used, after sterilization, for fermentation studies. A co-culture of Lactococcus lactis and Clostridium formicoaceticum was used to produce acetic acid from glucose. Propionibacterium acidipropionici was used for propionic acid fermentation, and Clostridium tyrobutylicum was used for butyric acid production. These cells were immobilized on a spirally wound fibrous matrix packed in a fibrous-bed bioreactor (FBB) developed for multi-phase biological reactions or fermentation. The bioreactor was connected to a stirred-tank fermentor that provided pH and temperature controls via medium circulation. The fermentation system was operated at the recycle batch mode. Temperature and pH were controlled at 37 degrees C and 7.6, respectively, for acetic acid fermentation, 32 degrees C and 6.0, respectively, for propionic acid fermentation, and 37 degrees C and 6.0, respectively, for butyric acid production. The fermentation demonstrated a yield of approximately 100% and a volumetric productivity of approximately 1 g/(1 h) for acetic acid production. The propionic acid fermentation achieved an approximately 60% yield and a productivity of 2.12 g/(1 h), whereas the butyric acid fermentation obtained an approximately 50% yield and a productivity of 6.78 g/(1 h). These results were comparable to, or better than those fermentations using chemically defined media containing glucose as the substrate, suggesting that these carboxylic acids can be efficiently produced from direct fermentation of corn meal hydrolyzate. The corn fiber present as suspended solids in the corn meal hydrolyzate did not cause operating problem to the immobilized cell bioreactor as is usually encountered by conventional immobilized cell bioreactor systems. It is concluded that the FBB technology is suitable for producing value-added biochemicals directly from agricultural residues or commodities such as corn meal.

Exopolysaccharide production by Propionibacterium acidi-propionici on milk microfiltrate

AIMS

The aims of this work were to evaluate growth and exopolysaccharide (EPS) production properties of Propionibacterium acidi-propionici DSM 4900 on milk permeate.

METHODS AND RESULTS

Anaerobic growth on milk permeate was only possible if supplemented with yeast extract (YE). Fermentation capacities of the strain were significantly improved by further increasing the supplemented YE. At 5 g l(-1) YE, consumption of 45 g l(-1) lactose to produce 9 g l(-1) biomass, 34 g l(-1) organic acids and 0.65 g l(-1) EPS was observed. From a kinetic point of view, EPS production occurred during the bacteria growth phase. At the excreted polysaccharide level, the medium showed shear-thinning behaviour with a relatively high apparent viscosity of up to 30 mPa.s (milli.Pascal.second) at a shear rate of 17 s(-1).

CONCLUSION

EPS production by P. acidi-propionici DSM 4900 on milk permeate showed promising rheological behaviour of the milk-derived medium obtained, even at a low production level.

SIGNIFICANCE AND IMPACT OF THE STUDY

A kinetic study on EPS production by a food-grade bacterium that could be used in situ in alimentation was carried out.