Propionic acid production from soy molasses by Propionibacterium acidipropionici: Fermentation kinetics and economic analysis

Soybean molasses can be used as a substitute for corn in grazing beef cattle supplements during the rainy season

Soybean molasses (SBMO) is a byproduct derived from the production of soy protein concentrate, obtained through solubilization in water and alcohol. The utilization of SBMO as an animal feed ingredient shows promising potential, primarily due to its low cost and as a potential energy concentrate. This study aimed to assess the intake, digestibility, ruminal parameters (pH and ruminal ammonia - NH3), nitrogen retention (NR) and microbial protein synthesis in grazing beef cattle supplemented with SBMO as a substitute for corn during the rainy season. Five Nellore (10-month-old) bulls with an average initial weight of 246 ± 11.2 kg were utilized in a 5 × 5 Latin square design. The animals were housed in five paddocks, each consisting of 0.34 ha of Marandu grass (Urochloa brizantha). Five isonitrogenous protein-energy supplements (300 g crude protein [CP]/kg supplement) were formulated, with SBMO replacing corn at varying levels (0, 0.25, 0.50, 0.75, or 1.00 g-1 g). The supplements were provided daily at a quantity of 2.0 kg-1 animal. The inclusion of SBMO at any level of corn substitution did not significantly affect the intake of pasture dry matter or total dry matter (P > 0.10). Likewise, the intake of CP and, consequently, the ruminal concentration of NH3 did not differ among the SBMO levels. Increasing the inclusion of SBMO did not have a significant impact on NR (P > 0.10), indicating that animals receiving supplements containing 100% SBMO as a substitute for corn may perform similarly to animals receiving supplements with 100% corn (0% SBMO). Soybean molasses represents a viable alternative energy source for grazing beef cattle during the rainy season and can entirely replace corn without adversely affecting animal nutritional performance.

From waste management to circular economy: Leveraging thermophiles for sustainable growth and global resource optimization

Waste of any origin is one of the most serious global and man-made concerns of our day. It causes climate change, environmental degradation, and human health problems. Proper waste management practices, including waste reduction, safe handling, and appropriate treatment, are essential to mitigate these consequences. It is thus essential to implement effective waste management strategies that reduce waste at the source, promote recycling and reuse, and safely dispose of waste. Transitioning to a circular economy with policies involving governments, industries, and individuals is essential for sustainable growth and waste management. The review focuses on diverse kinds of environmental waste sources around the world, such as residential, industrial, commercial, municipal services, electronic wastes, wastewater sewerage, and agricultural wastes, and their challenges in efficiently valorizing them into useful products. It highlights the need for rational waste management, circularity, and sustainable growth, and the potential of a circular economy to address these challenges. The article has explored the role of thermophilic microbes in the bioremediation of waste. Thermophiles known for their thermostability and thermostable enzymes, have emerged to have diverse applications in biotechnology and various industrial processes. Several approaches have been explored to unlock the potential of thermophiles in achieving the objective of establishing a zero-carbon sustainable bio-economy and minimizing waste generation. Various thermophiles have demonstrated substantial potential in addressing different waste challenges. The review findings affirm that thermophilic microbes have emerged as pivotal and indispensable candidates for harnessing and valorizing a range of environmental wastes into valuable products, thereby fostering the bio-circular economy.

Utilization of propionic acid bacteria in the biotransformation of soy (tofu) whey: Growth and metabolite changes

Soy whey, a by-product from the tofu and soy protein isolate industry was evaluated as a substrate for a biofortified beverage using several propionic acid bacteria (PAB). PAB growth and changes in sugars, organic acids, amino acids and isoflavones were investigated. Vitamin B12 and short-chain fatty acid (SCFA) production were measured over time. Acidipropionibacterium acidipropionici (DSM 20272) showed the highest growth, compared to the other three PABs (Propionibacterium freudenreichii [DSM 20271 and DSM 4902], A. jensenii [DSM 20535]). Acidipropionibacterium (DSM 20272 and DSM 20535) showed the best propionic acid and acetic acid production, while P. freudenreichii produced the most succinic acid. Propionibacterium freudenreichii exhibited significant vitamin B12 production at 4.06 ± 0.28 µg/L for DSM 20271, followed by 2.58 ± 0.22 µg/L for DSM 4902. Notably, all PAB displayed strong β-glycosidase activities evidenced by the conversion of isoflavone glycosides to isoflavone aglycones. The stark differences between Acidipropionibacterium spp. and Propionibacterium spp. indicate that the former PAB is specialized in SCFA production, while the latter PAB is better at vitamin B12 bioenrichment. This study demonstrated the possibility of employing PAB fermentation to improve SCFA and vitamin B12 content. This can open avenues for a beverage or functional ingredient development.

Bandgap engineering control bifunctional MnxCd1-xS photocatalysts selectively reforming xylose to C3 organic acids and efficient hydrogen production

The simultaneous reforming of biomass into high value-added chemicals and H2 production by water splitting in a green and environmentally clean way is a very challenging task. Herein, we demonstrate the design of bifunctional MnxCd1-xS photocatalyst with a controllable band gap by bandgap engineering. Bandgap engineering effectively regulates the oxidation and reduction capacity of materials. The design of photocatalysts with suitable conduction bands and valence bands makes the targeted conversion of xylose possible. Innovative conversion of xylose to glyceric acid, lactic acid, and propanoic acid. The optimized Mn0.7Cd0.3S catalyst showed excellent performance in the production of H2 (14.06 mmol·gcat-1·h-1, 29.9 times more than CdS and 351.5 times more than MnS), xylose conversion (90%), and C3 organic acid yield (59.2%) without cocatalyst and any scavengers under visible light irradiation. This work shows that a rational photocatalyst design can achieve efficient simultaneous production of high value-added chemicals and clean energy.

Reprocessing of side-streams towards obtaining valuable bacterial metabolites

Every year, all over the world, the industry generates huge amounts of residues. Side-streams are most often used as feed, landfilled, incinerated, or discharged into sewage. These disposal methods are far from perfect. Taking into account the composition of the side-streams, it seems that they should be used as raw materials for further processing, in accordance with the zero-waste policy and sustainable development. The article describes the latest achievements in biotechnology in the context of bacterial reprocessing of residues with the simultaneous acquisition of their metabolites. The article focuses on four metabolites - bacterial cellulose, propionic acid, vitamin B12 and PHAs. Taking into account global trends (e.g. food, packaging, medicine), it seems that in the near future there will be a sharp increase in demand for this type of compounds. In order for their production to be profitable and commercialised, cheap methods of its obtaining must be developed. The article, in addition to obtaining these bacterial metabolites from side-streams, also discusses e.g. factors affecting their production, metabolic pathways and potential and current applications. The presented chapters provide a complete overview of the current knowledge on above metabolites, which can be helpful for the academic and scientific communities and the several industries. KEY POINTS: • The industry generates millions of tons of organic side-streams each year. • Generated residues burden the natural environment. • A good and cost-effective method of side-streams management seems to be biotechnology - reprocessing with the use of bacteria. • Biotechnological disposal of side-streams gives the opportunity to obtain valuable compounds in cheaper ways: BC, PA, vitmain B12, PHAs.

High-Yield Production of Propionate from 1,2-Propanediol by Engineered Pseudomonas putida KT2440, a Robust Strain with Highly Oxidative Capacity

Bio-based propionate attracts increasing attention owing to its green nature and specific food additive market. To date, the time-consuming and costly fermentation process by strict anaerobes makes propionate production not ideal. In this study, we designed a new route for propionate production, in which 1,2-propanediol was first dehydrated to propionaldehyde and then to propionate by taking advantage of the robust oxidization capacity of the Pseudomonas putida KT2440 strain. The high atom economy (0.97 g/g) in this proposed pathway is more advantageous than the previous l-threonine-derived route (0.62 g/g). The molecular mechanism of the extraordinary oxidation capacity of P. putida KT2440 was first deciphered. The propionate production was realized in P. putida KT2440 by screening suitable glycerol dehydratases and optimizing the expression to eliminate the formation of 1-propanol and the accumulation of the intermediate propionaldehyde. The engineered strain produced propionate with a molar conversion rate of >99% from 1,2-propanediol. A high titer of 46.5 g/L pure propionic acid with a productivity of 1.55 g/L/h and a mass yield of 0.96 g/g was achieved in fed-batch biotransformation. Thus, this study provides another idea for the production of high-purity bio-based propionate from renewable materials with high atom economy.

Metagenomics insight into bioaugmentation mechanism of Propionibacterium acidipropionici during anaerobic acidification of kitchen waste

In the present study, a biochemical strategy for improving propionic acid production from kitchen waste acidification by bioaugmentation with Propionibacterium acidipropionici (P. acidipropionici) was investigated. When the inoculum of P. acidipropionici was 30% (w/w) of the seeding sludge, the propionic acid production increased by 79.57%. Further, bioaugmentation improved the relative abundance of Firmicute and Actinobacteria. The results of metagenomic analysis further reveal that the ATP-binding cassette (ABC) transporters and all related pathways of Propanoate metabolism (ko00640) were enriched when P. acidipropionici was added. For Propanoate metabolism, most functional genes involved in the conversion from Glycolysis / Gluconeogenesis (ko00010) to Propanoyl-CoA and conversion from Propanoyl-CoA to propionic acid were enhanced after bioaugmentation with P. acidipropionici, thereby promoting propionic acid production. As such, bioaugmentation with P. acidipropionici was effective in the anaerobic acidification of kitchen waste for propionic acid production.

Use of apple pomace, glycerine, and potato wastewater for the production of propionic acid and vitamin B12

Abstract

Propionic acid bacteria (PAB) are a source of valuable metabolites, including propionic acid and vitamin B12. Propionic acid, a food preservative, is synthesized from petroleum refining by-products, giving rise to ecological concerns. Due to changing food trends, the demand for vitamin B12 has been expected to increase in the future. Therefore, it is necessary to look for new, alternative methods of obtaining these compounds. This study was conducted with an aim of optimizing the production of PAB metabolites using only residues (apple pomace, waste glycerine, and potato wastewater), without any enzymatic or chemical pretreatment and enrichment. Media consisting of one, two, or three industrial side-streams were used for the production of PAB metabolites. The highest production of propionic acid was observed in the medium containing all three residues (8.15 g/L, yield: 0.48 g/g). In the same medium, the highest production of acetic acid was found — 2.31 g/L (0.13 g/g). The presence of waste glycerine in the media had a positive effect on the efficiency of propionic acid production and P/A ratio. The concentration of vitamin B12 obtained in the wet biomass of Propionibacterium freudenreichii DSM 20271 ranged from 90 to 290 µg/100 g. The highest production of cobalamin was achieved in potato wastewater and apple pomace, which may be a source of the precursors of vitamin B12 — cobalt and riboflavin. The results obtained show both propionic acid and vitamin B12 can be produced in a more sustainable manner through the fermentation of residues which are often not properly managed.

Key points

• The tested strain has been showed metabolic activity in the analyzed industrial side-streams (apple pomace, waste glycerine, potato wastewater).

• All the side-streams were relevant for the production of propinic acid.

• The addition of waste glycerine increases the propionic acid production efficiency and P/A ratio.

• B12 was produced the most in the media containing potato wastewater and apple pomace as dominant ingredients.

Microbial cell factories for the production of three-carbon backbone organic acids from agro-industrial wastes

At present, mass production of basic and valuable commodities is dependent on linear petroleum-based industries, which ultimately makes the depletion of finite natural reserves and accumulation of non-biodegradable and hazardous wastes. Therefore, an ecofriendly and sustainable solution should be established for a circular economy where infinite resources, such as agro-industrial wastes, are fully utilized as substrates in the production of target value-added chemicals. Hereby, recent advances in metabolic engineering strategies and techniques used in the development of microbial cell factories for enhanced production of three-carbon platform chemicals such as lactic acid, propionic acid, and 3-hydroxypropionic acid are discussed. Further developments and future perspectives in the production of these organic acids from agro-industrial wastes from the dairy, sugar, and biodiesel industries are also highlighted to demonstrate the importance of waste-based biorefineries for organic acid production.

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.

High Cell Density Culture of Dairy Propionibacterium sp. and Acidipropionibacterium sp.: A Review for Food Industry Applications

The dairy bacteria Propionibacterium sp. and Acidipropionibacterium sp. are versatile and potentially probiotic microorganisms showing outstanding functionalities for the food industry, such as the production of propionic acid and vitamin B12 biosynthesis. They are the only food grade microorganisms able to produce vitamin B12. However, the fermentation batch process using these bacteria present some bioprocess limitations due to strong end-product inhibition, cells slow-growing rates, low product titer, yields and productivities, which reduces the bioprocess prospects for industrial applications. The high cell density culture (HCDC) bioprocess system is known as an efficient approach to overcome most of those problems. The main techniques applied to achieve HCDC of dairy Propionibacterium are the fed-batch cultivation, cell recycling, perfusion, extractive fermentation, and immobilization. In this review, the techniques available and reported to achieve HCDC of Propionibacterium sp. and Acidipropionibacterium sp. are discussed, and the advantages and drawbacks of this system of cultivation in relation to biomass formation, vitamin B12 biosynthesis, and propionic acid production are evaluated.

Microbial α-galactosidases: Efficient biocatalysts for bioprocess technology

Galactomannans, abundantly present in plant biomass, can be used as renewable fermentation feedstock for biorefineries working for the production of bioethanol and other value-added products. The complete and efficient bioconversion of biomass to fermentable sugars for the generation of biofuels and other value-added products require the concerted action of accessory enzymes like α-galactosidases, which can work in cohesion with other carbohydrases in an enzyme cocktail. In the paper industry, α-galactosidases enhance the bleaching effect of endo-β-1,4-mannanases on softwood kraft pulp. Microbial α-galactosidases also find applications in the treatment of legume foods, recovery of sucrose from sugar beet syrup, improving the rheological properties of galactomannans, and synthesis of α-galactooligosaccharides to be used as functional food ingredients. Owing to their industrial applications, there is a surge in the research focused on α-galactosidases. The current review illustrates the diverse industrial applications of microbial α-galactosidases and their challenges and prospects.

Propionic acid-rich fermentation (PARF) production from organic wastes: A review

Nowadays, increasing attention has been drawn to biological valorization of organic wastes. Wherein, propionic acid-rich fermentation (PARF) has become a focal point of research. The objective of this review is to make a thorough investigation on the potential of PARF production and give future outlook. By discussing the key factors affecting PARF including substrate types, pH, temperature, retention time, etc., and various improving methods to enhance PARF including different pretreatments, inoculation optimization and immobilization, a comprehensive summary on how to achieve PARF from organic waste is presented. Then, current application of PARF liquid is concluded, which is found to play an essential role in the efficient denitrification and phosphorus removal of wastewater and preparation of microbial lipids. Finally, the environmental performance of PARF production is reviewed through life cycle assessment studies, and environmentally sensitive sectors are summarized for process optimization, providing a reference for waste management in low carbon scenarios.

Bioaugmentation as a strategy for tailor-made volatile fatty acid production

This study aimed to develop a novel strategy for tailor-made volatile fatty acid (VFA) composition. For this purpose, the mixed microbial culture was bioaugmented by Propionibacterium acidipropionici. Anaerobic sequencing batch reactors were operated with cheese wastewater under alkali pH. While the maximum propionic acid production almost four times increased (3779 ± 201 mgCOD_eq propionic acid/L in the bioaugmented reactor and 942 ± 172 mgCOD_eq propionic acid/L in the control reactor), there was no significant difference in VFA composition. The gene copy number of P.acidipropionici increased 20 times after the bioaugmentation. Furthermore, the gene copy number of P.acidipropionici was positively correlated with total VFA and isovaleric acid concentration. The relative abundance of family Flavobacteriaceae increased in the bioaugmented reactor, which might be caused by the syntrophic relation between Flavobacteriaceae and P. acidipropionici. The cycle analysis results showed that the shorter cycle (6h) could ensure the same efficiency.

Whole conversion of agro-industrial wastes rich in galactose-based carbohydrates into lipid using oleaginous yeast Aureobasidium namibiae

BACKGROUND

Raw materials composed of easily assimilated monosaccharides have been employed as carbon source for production of microbial lipids. Nevertheless, agro-industrial wastes rich in galactose-based carbohydrates have not been introduced as feedstocks for oleaginous yeasts.

RESULTS

In this study, Aureobasidium namibiae A12 was found to efficiently accumulate lipid from soy molasses and whey powder containing galactose-based carbohydrates, with lipid productions of 5.30 g/L and 5.23 g/L, respectively. Over 80% of the fatty acids was C_16:0, C_18:0, C_18:1, and C_18:2. All kinds of single sugar components in the two byproducts were readily converted into lipids, with yields ranging between 0.116 g/g and 0.138 g/g. Three α-galactosidases and five β-galactosidases in the strain were cloned and analyzed. Changes of transcriptional levels indicated GalB and GalC were key α-galactosidases, and GalG was key β-galactosidase. In 10 L fermentor, lipid production from SM and WP achieved 6.45 g/L and 6.13 g/L, respectively. β-galactosidase was responsible for lactose hydrolysis; sucrase and α-galactosidase both contributed to the efficient hydrolysis of raffinose and stachyose in a cooperation manner.

CONCLUSIONS

This is a new way to produce lipids from raw materials containing galactose-based carbohydrates. This finding revealed the significance of sucrase in the direct hydrolysis of galactose-based carbohydrates in raw materials for the first time and facilitated the understanding of the efficient utilization of galactose-based carbohydrates to manufacture lipid or other chemicals in bioprocess.

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 Propionibacterium freudenreichii T82 Strain for Effective Biosynthesis of Propionic Acid and Trehalose in a Medium with Apple Pomace Extract and Potato Wastewater

Propionic acid bacteria are the source of many metabolites, e.g., propionic acid and trehalose. Compared to microbiological synthesis, the production of these metabolites by petrochemical means or enzymatic conversion is more profitable. The components of microbiological media account for a large part of the costs associated with propionic fermentation, due to the high nutritional requirements of Propionibacterium. This problem can be overcome by formulating a medium based on the by-products of technological processes, which can act as nutritional sources and at the same time replace expensive laboratory preparations (e.g., peptone and yeast extract). The metabolic activity of P. freudenreichii was investigated in two different breeding environments: in a medium containing peptone, yeast extract, and biotin, and in a waste-based medium consisting of only apple pomace and potato wastewater. The highest production of propionic acid amounting to 14.54 g/L was obtained in the medium containing apple pomace and pure laboratory supplements with a yield of 0.44 g/g. Importantly, the acid production parameters in the waste medium reached almost the same level (12.71 g/L, 0.42 g/g) as the medium containing pure supplements. Acetic acid synthesis was more efficient in the waste medium; it was also characterized by a higher level of accumulated trehalose (59.8 mg/g d.s.). Thus, the obtained results show that P. freudenreichii bacteria exhibited relatively high metabolic activity in an environment with apple pomace used as a carbon source and potato wastewater used as a nitrogen source. This method of propioniate production could be cheaper and more sustainable than the chemical manner.

Propionic acid production from apple pomace in bioreactor using Propionibacterium freudenreichii: an economic analysis of the process

Propionic acid and its salts are widely used as food and feed preservative. Currently, these compounds are chemically produced, which is more profitable compared to biotechnological production using bacteria of the Propionibacterium genus. Appropriate steps can enable reducing the production costs; for example, cheap industrial byproducts can be used as culture media. One such cost-effective raw material is apple pomace, a low-value byproduct from the food industry. It contains sugars such as glucose and fructose which can serve as potential carbon sources for microorganisms. This paper discusses the possibility of using apple pomace in the production of propionic acid and presents an economic analysis of the production process. The tested strain produced 8.01 g/L of propionic acid (yield 0.40 g/g) and 2.29 g/L of acetic acid (yield 0.11 g/g) from apple pomace extract. The economic analysis showed that the production of 1 kg of propionic acid (considering only waste) from 1000 kg of apple pomace would cost approximately 1.25 USD. The manufacturing cost (consumables, including feedstock, labor, and utilities) would be approximately 2.35 USD/kg, and the total cost including taxes would be approximately 3.05 USD/kg. From the economic point of view, it is necessary to improve the production of propionic acid from apple pomace, to increase the yield of fermentation and thus decrease the total production costs. This can be achieved, for example, using industrial byproducts as nitrogen and vitamin sources, instead of high-cost substrates such as yeast extract or peptone.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02582-x.

Propionic acid production from food waste in batch reactors: Effect of pH, types of inoculum, and thermal pre-treatment

In this study, lab-scale batch fermentation tests were carried out at mesophilic temperature (30 °C) to examine the influence of inoculum type, pH-value, and thermal pretreatment of substrate on propionic acid (PA) production from dog food. The selected inocula comprised a mixed bacterial culture, milk, and soft goat cheese. The batch tests were performed at pH 4, pH 6, and pH 8 for both, untreated and thermally pretreated food. Results show that the production of PA and volatile fatty acids (VFAs) in general were significantly dependent on the chosen inoculum and adjusted pH value. The maximum PA production rates and yields were determined for the cheese inoculum at pH 6 using untreated and pretreated dog food. PA concentration reached 10 gL^-1and 26.5 gL^-1, respectively. Our findings show that by selecting optimal process parameters, an efficient PA production from model food waste can be achieved.

Sustainable production of propionic acid: catalytic deoxygenation of lactic acid over MoOx/Fe

The synergistic effect between MoOx and Fe markedly promoted the activity on deoxygenation of lactic acid to bio-propionic acid.

Effect of different vegetable wastes on the performance of volatile fatty acids production by anaerobic fermentation

Volatile fatty acids (VFAs) are intermediates of anaerobic fermentation with high value and wide range of usage. VFA production from vegetable wastes (VW) is an effective way to dispose of wastes and recover resources. The organic matter composition of the substrate influences VFA yield and distribution, which is related to the separation and purification of the downstream steps and the application of the product. Hence, potato peels, carrots, celery, and Chinese cabbage were selected to investigate the effect of VW types on the performance of the VFA production in a batch anaerobic fermentation reactor with continuous stirring at 37 °C, total solid (TS) of 4.5%. A VFA yield of 452 mg COD/g VS_feed (chemical oxygen demand (COD); volatile solids (VS)) was achieved from potato peels, which was 40.1%, 21.5%, and 124.9% higher than that of carrots, celery, and Chinese cabbage, respectively. The rapid acidification of carrots caused a sharp decline in pH and led to inhibition of VFA production. The acidification of celery started slowly, and the yield of hexanoic acid increased rapidly in the later stage of fermentation. The VFA yield of Chinese cabbage was inhibited due to the low initial pH, but the ethanol concentration reached 7577.04 mg COD/L. According to the VFA profile, the fermentation of potato peels, carrots, celery, and Chinese cabbage can be classified as propionate-type, butyrate-type, mixed-acid type, and ethanol-acetate type metabolic pathway, respectively. The results of this study suggest that a suitable combination of vegetable waste types is important for selective VFA production.

Improving propionic acid production from a hemicellulosic hydrolysate of sorghum bagasse by means of cell immobilization and sequential batch operation

Propionic acid (PA) is an important organic compound with extensive application in different industrial sectors and is currently produced by petrochemical processes. The production of PA by large-scale fermentation processes presents a bottleneck, particularly due to low volumetric productivity. In this context, the present work aimed to produce PA by a biochemical route from a hemicellulosic hydrolysate of sorghum bagasse using the strain Propionibacterium acidipropionici CIP 53164. Conditions were optimized to increase volumetric productivity and process efficiency. Initially, in simple batch fermentation, a final concentration of PA of 17.5 g⋅L^-1 was obtained. Next, fed batch operation with free cells was adopted to minimize substrate inhibition. Although a higher concentration of PA was achieved (38.0 g⋅L^-1 ), the response variables (Y_P/S = 0.409 g⋅g^-1 and Q_P = 0.198 g⋅L^-1 ⋅H^-1 ) were close to those of the simple batch experiment. Finally, the fermentability of the hemicellulosic hydrolysate was investigated in a sequential batch with immobilized cells. The PA concentration achieved a maximum of 35.3 g⋅L^-1 in the third cycle; moreover, the volumetric productivity was almost sixfold higher (1.17 g⋅L^-1 ⋅H^-1 ) in sequential batch than in simple batch fermentation. The results are highly promising, providing preliminary data for studies on scaling up the production of this organic acid.

Transcriptomics and Proteomics Analyses of the Responses of Propionibacterium acidipropionici to Metabolic and Evolutionary Manipulation

We first performed a combination of metabolic engineering (deletion of ldh and poxB and overexpression of mmc) with evolutionary engineering (selection under oxygen stress, acid stress and osmotic stress) in Propionibacterium acidipropionici. The results indicated that the mutants had superior physiological activity, especially the mutant III obtained from P. acidipropionici-Δldh-ΔpoxB+mmc by evolutionary engineering, with 1.5-3.5 times higher growth rates, as well as a 37.1% increase of propionic acid (PA) titer and a 37.8% increase PA productivity compared to the wild type. Moreover, the integrative transcriptomics and proteomics analyses revealed that the differentially expressed genes (DEGs) and proteins (DEPs) in the mutant III were involved in energy metabolism, including the glycolysis pathway and tricarboxylic acid cycle (TCA cycle). These genes were up-regulated to supply increased amounts of energy and precursors for PA synthesis compared to the wild type. In addition, the down-regulation of fatty acid biosynthesis and fatty acid metabolism may indicate that the repressed metabolic flux was related to the production of PA. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to verify the differential expression levels of 16 selected key genes. The results offer deep insights into the mechanism of high PA production, which provides the theoretical foundation for the construction of advanced microbial cell factories.

Propionic Acid: Method of Production, Current State and Perspectives

During the past years, there has been a growing interest in the bioproduction of propionic acid by Propionibacterium. One of the major limitations of the existing models lies in their low productivity yield. Hence, many strategies have been proposed in order to circumvent this obstacle. This article provides a comprehensive synthesis and review of important biotechnological aspects of propionic acid production as a common ingredient in food and biotechnology industries. We first discuss some of the most important production processes, mainly focusing on biological production. Then, we provide a summary of important propionic acid producers, including Propionibacterium freudenreichii and Propionibacterium acidipropionici, as well as a wide range of reported growth/production media. Furthermore, we describe bioprocess variables that can have impact on the production yield. Finally, we propose methods for the extraction and analysis of propionic acid and put forward strategies for overcoming the limitations of competitive microbial production from the economical point of view. Several factors influence the propionic acid concentration and productivity such as culture conditions, type and bioreactor scale; however, the pH value and temperature are the most important ones. Given that there are many reports about propionic acid production from glucose, whey permeate, glycerol, lactic acid, hemicelluloses, hydrolyzed corn meal, lactose, sugarcane molasses and enzymatically hydrolyzed whole wheat flour, only few review articles evaluate biotechnological aspects, i.e. bioprocess variables.

Co-cultures with integrated in situ product removal for lactate-based propionic acid production

Propionic acid (PA) is a valuable organic acid for the food and feed industry, but no bioproduction at industrial scale exists so far. As product inhibition is a major burden for bioprocesses producing organic acids, in situ product removal (ISPR) is desirable. Here, we demonstrate a new strategy to produce PA with a co-culture coupled with ISPR using electrodialysis. Specifically, Bacillus coagulans first produces lactic acid (LA) from sugar(s) and LA is converted to PA using Veillonella criceti. Applying ISPR to the mentioned co-culture, the specific PA yield was increased from 0.35 to 0.39 g g⁻¹ compared to no ISPR usage. Furthermore, the productivity was increased from 0.63 to 0.7 g L⁻¹ h⁻¹ by applying ISPR. Additionally, it was shown that co-consumption of xylose and glucose led to a higher PA productivity of 0.73 g L⁻¹ h⁻¹, although PA yield was only increased slightly up to 0.36 g g⁻¹.

Fruity flavors from waste: A novel process to upgrade crude glycerol to ethyl valerate

Valeric acid and its ester derivatives are chemical compounds with a high industrial interest. Here we report a new approach to produce them from crude glycerol, by combining propionic acid fermentation with chain elongation. Propionic acid was produced by Propionibacterium acidipropionici (8.49 ± 1.40 g·L^-1). In the subsequent mixed population chain elongation, valeric acid was the dominant product (5.3 ± 0.69 g·L^-1) of the chain elongation process. Residual glycerol negatively impacted the selectivity of mixed culture chain elongation towards valeric acid, whereas this was unaffected when Clostridium kluyveri was used as bio-catalyst. Valeric acid could be selectively isolated and upgraded to ethyl valerate by using dodecane as extractant and medium for esterification, whereas shorter-chain carboxylic acids could be recovered by using a 10 wt% solution of trioctylphosphine oxide (TOPO) in dodecane. Overall, our work shows that the combined fermentation, electrochemistry and homogeneous catalysis enables fine chemical production from side streams.

Optimization of propionic acid production in apple pomace extract with Propionibacterium freudenreichii

Sequential optimization of propionate production using apple pomace was studied. All experiments were performed in a static flask in anaerobic conditions. Effect of apple pomace as nitrogen source against conventional N sources (yeast extract, peptone) was studied. The double increase was observed in propionic acid production while using yeast extract and peptone (0.29 ± 0.01 g/g), as against the use of only apple pomace extract (APE) (0.14 ± 0.01 g/g). Intensification of propionic acid fermentation was also achieved by increasing the pH control frequency of the culture medium from 24-(0.29 ± 0.01 g/g) to 12-hour intervals (30 °C) (0.30 ± 0.02 g/g) and by increasing the temperature of the culture from 30 to 37 °C (12-hour intervals of pH control) (0.32 ± 0.01 g/g). An important factor in improving the parameters of fermentation was the addition of biotin to the medium. The 0.2 mg/L dose of biotin allowed to attain 7.66 g/L propionate with a yield of 0.38 ± 0.03 g/g (12-hour intervals of pH control, 37 °C).

Whole Conversion of Soybean Molasses into Isomaltulose and Ethanol by Combining Enzymatic Hydrolysis and Successive Selective Fermentations

Isomaltulose is mainly produced from sucrose by microbial fermentation, when the utilization of sucrose contributes a high production cost. To achieve a low-cost isomaltulose production, soy molasses was introduced as an alternative substrate. Firstly, α-galactosidase gene from Rhizomucor miehei was expressed in Yarrowia lipolytica, which then showed a galactosidase activity of 121.6 U/mL. Under the effects of the recombinant α-galactosidase, most of the raffinose-family oligosaccharides in soy molasses were hydrolyzed into sucrose. Then the soy molasses hydrolysate with high sucrose content (22.04%, w/w) was supplemented into the medium, with an isomaltulose production of 209.4 g/L, and the yield of 0.95 g/g. Finally, by virtue of the bioremoval process using Pichia stipitis, sugar byproducts in broth were transformed into ethanol at the end of fermentation, thus resulting in high isomaltulose purity (97.8%). The bioprocess employed in this study provides a novel strategy for low-cost and efficient isomaltulose production from soybean molasses.

Harnessing Nature's Anaerobes for Biotechnology and Bioprocessing

Industrial biotechnology has the potential to decrease our reliance on petroleum for fuel and bio-based chemical production and also enable valorization of waste streams. Anaerobic microorganisms thrive in resource-limited environments and offer an array of novel bioactivities in this regard that could revolutionize biomanufacturing. However, they have not been adopted for widespread industrial use owing to their strict growth requirements, limited number of available strains, difficulty in scale-up, and genetic intractability. This review provides an overview of current and future uses for anaerobes in biotechnology and bioprocessing in the postgenomic era. We focus on the recently characterized anaerobic fungi (Neocallimastigomycota) native to the digestive tract of large herbivores, which possess a trove of enzymes, pathways, transporters, and other biomolecules that can be harnessed for numerous biotechnological applications. Resolving current genetic intractability, scale-up, and cultivation challenges will unlock the potential of these lignocellulolytic fungi and other nonmodel micro-organisms to accelerate bio-based production.

Butyric acid: Applications and recent advances in its bioproduction

Butyric acid is an important C4 organic acid with broad applications. It is currently produced by chemosynthesis from petroleum-based feedstocks. However, the fermentative production of butyric acid from renewable feedstocks has received growing attention because of consumer demand for green products and natural ingredients in foods, pharmaceuticals, animal feed supplements, and cosmetics. In this review, strategies for improving microbial butyric acid production, including strain engineering and novel fermentation process development are discussed and compared regarding product yield, titer, purity and productivity. Future perspectives on strain and process improvements for butyric acid production are also discussed.