J Crit Rev, Vol 1, Issue 1, 29-35 Review Article


BIOCONVERSION OF GLYCEROL

MANDAR KARVE, JAY J. PATEL, NIRMAL K. PATEL*

Department of Industrial Chemistry, Institute of Science & Technology for Advanced Studies and Research (ISTAR), Vallabh Vidyanagar 388120, Gujarat, India.
Email: drnirmalpatel@yahoo.com

Received: 21 Aug 2014 Revised and Accepted: 15 Sep 2014


ABSTRACT

The availability of petroleum sources in the near future is limited, so nowadays search for renewable energy sources are maximized. Biodiesel is one of the most important substituted for this problem. During biodiesel production, excessive glycerol is generated asbyproducts which contains impurities such as methanol, free fatty acid and salt. Thedisposal of glycerol leads to environmental problems. Alternatively glycerol can be utilized to obtain various valuable products viz.1,3-propanediol (1,3-PDO), 1,2-propanediol (1,2-PDO), ethanol, 2,3-butanediol, dihydroxyacetone, succinic acid, propionic acid and citric acid. Utilization of crude glycerol by means of chemical synthesis requires expensive catalysts like Ir, Cr, Ag etc. Comparatively biological method for utilizing crude glycerol is best to avoid environmental problems. Bioconversion of glycerol is carried out at 30- 400C temperature and atmospheric pressure pressure which gives different products. Different microorganisms viz. Escherichia coli, Pseudomonas, Enterobacter aerogen, Klebsiella pneumoniae, Clostridium butaricum and Clostridium pasterium are reported to grow on glycerol to produce valuable chemicals. In this review article, bioconversion of glycerol to speciality chemicals such as ethanol, 1,3-PDO, 1,2-PDO, 2,3-butanediol, dihydroxyacetone, succinic acid, propionic acid and citric acid etc. Are discussed.

Keywords: Bioconversion, Glycerol, Biodiesel, Microorganisms, 1,3-propanediol.


INTRODUCTION

Glycerol was first discovered by Karl Wilhelm Scheele. He synthesized and characterized many other chemical compounds such as tartaric acid, citric acid and lactic acid. Glycerol is also known as 1,2,3-propanetriol as it contains three hydroxyl groups there so, it is also termed as polyol compound. It is the principal by-product obtained during transesterification of vegetable oils[1,2,3]. Glycerol is completely soluble in water and alcohol and slightly soluble in ether, ethyl acetate, and dioxane. It is insoluble in hydrocarbons. It has useful solvent properties which is similar water and simple aliphatic alcohols[4,5]. About 1.3 billion gallons glycerol was produced in the USA while 0.8 billion gallons glycerol was produced in India till 2013[6]. It is obtained from various sources viz. via acrolein route, via allyl chloride route, in fat splitting, saponification, ethanolic fermentation of glucose and major in biodiesel production.

Biodiesel is produced by transesterification of vegetable oils with methanol using sodium hydroxide as catalyst. Biodiesel is a mixture of methyl ester and fatty acids. Biodiesel can be used in the diesel engine motors. Germany is the largest producer and consumer of biodiesel in the world, which produces more than 2.5 billion liters annually[7]. Many countries use biodiesel as an admixture to diesel with different proportions. Brazil used 2% biodiesel till January 2008, which is now increasing to 5%. There are two reasons on the basis of which Brazil will become a major producer and consumer of biodiesel: Brazilian used alcohol in fuel cars since long and second, the conditions for cultivating oleaginous plants are extremely favorable in many areas of the Brazil [8]. The availability of petroleum is limited in the future, so biodiesel use will continually grow. In 2010, the gradual declining of petroleum production was started, and it assumes petroleum reserves may completely deplete by 2050. On the other hand, the demand of biofuel is rising worldwide[9].

Crude glycerol obtained from the biodiesel industry contains impurity such as methanol, fatty acid and salt. Purification of crude glycerol can be done by distillation method. But this method is quite costly if it is compared to the production cost required for traditional synthesis of glycerol. This technology produces high purity glycerol at high yields. But the distillation of glycerol is an energy intensive process because of its high heat capacity and required a high supply of energy for vaporization[10]. Ion exchange has also been used to purify raw glycerol, but this technique is not economically viable from an industrial view of point due to the high content of salts present in crude glycerol [11].

Pure glycerol is required for utilizing in different application viz. in food, drugs, creams, tobacco processing, wrapping and packaging of materials, pharmaceutical industry, gaskets and cork products, as lubricants. As glycerol is obtained as a by-product in the production of biodiesel and it is assumed that by the year of 2020, production of glycerol will reach six times more [12]. The massive glycerol production forces a collapse in its market price and currently the market price of glycerol is reached to 60Rs per Kg.

A company like Dow Chemicals, Procter and Gamble closes their glycerol producing facilities. Therefore, alternative uses of glycerol are required. It can be utilized for combustion, animal feeding, thermo-chemical conversions, composting and biological conversion methods. The combustion of crude glycerol has been used for disposal. But, this method is not economical for large producers of biodiesel [13]. The process also generates the toxic greenhouse gases like CO and CO2, which also have an adverse effect to the atmosphere and living organisms. It has also been suggested that glycerol can be composted or used to increase the biogas production of anaerobic digesters but it requires only 1% glycerol so this method is not solution for disposal[14]. Biodiesel-derived glycerol was fed to dairy cows in order to prevent ketosis, but found that it was not useful[15]. Glycerol can be thermochemically converted into propylene glycol. In which Raney nickel catalyst was used at 2300C[16]. Glycerol is also used in the bioconversion process to obtain various products such as1,3-propanediol[17], ethanol[18], citric acid[19] and succinic acid[20]. These products also obtained by chemical synthesis too [21].

When the desired product is 1,3-PDO, it can be produced chemically by two methods: the hydration of acrolein and the hydroformylation of ethylene [22-24]. Chemical synthesis of 1,3-PDO requires high energy consumption, toxic intermediates like 3-hydroxypropyonaldehyde, expensive catalysts like Ir, Cr and Ag which leads to high costs of 1,3-PDO production[25-27]. More then 0.1 million tons of 1,3-PDO are produced yearly [28,29]. Currently, more than 2 million tons 1,3-PDO produced[30]. Consequently, chemical synthesis is expensive, thus, 1,3-PDO still has a low market volume[31]. Due to the environmental benefits and use of a renewable feed stock, the bioconversion of glycerol to 1,3-PDO is an attractive alternative to chemical synthesis[23]. Bioconversion of crude glycerol from the biodiesel process to value-added products is a driver towards higher cost efficiency of biodiesel production.Glycerol can be used by different microorganisms as an energy source. Microorganisms have the potential use in bioconversion of crude glycerol produced from biodiesel [32]. During industrial fermentation processes, glycerol can be used as a substitute for carbohydrates, such as sucrose, glucose and starch. Bioconversion of glycerol adds significant value to the productivity of the biodiesel industry. In this review, examples of possible bioconversion of glycerol are discussed and it demonstrates that inspite of simple chemical, glycerol is an important carbon sourcefor industrial microbiology.

Microorganisms

There are number of microorganisms can use glycerol as the sole carbon and energy source, viz. Escherichia coli (E. coli)[33], Enterobacter aerogenes (E. aerogen)[34,35]and Lactobacillus reuteri[36,37], Pseudomonas[38],Clostridium acetobutylicum, Clostridium butylicum[39,40], Citrobacter freundli[41-44], Clostridium pasteurianum[45-47], Clostridium butyricum[48-50],Klebsiella pneumoniae[51-53]and Enterobacter agglomerans[54] which are used to grow aerobically and anaerobically on glycerol and converts the glycerol into various products.

Glycerol is metabolized by oxidative and reducing pathwayin Citrobacter, Clostridium, E. coli, Enterobacter and Klebsiella[55]. In the oxidative pathway, glycerol converts to dihydroxyacetone [46]while in the reducing pathway, glycerol convertsinthe 3-hydroxypropionaldehyde [56]. The use ofthe NADH+H+-dependent enzyme reduce the 3-hydroxypropionaldehyde to 1,3-PDO[57]. The 1,3-PDOis highly specific for glycerol fermentation.

In the K. pneumoniae, the genes functionally linked with activities of glycerol dehydratase, 1,3-PDO dehydrogenase, glycerol dehydrogenase [58]. Glycerol dehydratase is very oxygen sensitive and strongly associated with the cell membrane [59,60]. Glycerol is degraded via dihydroxyacetone using yeasts. Sometimes it is converted to glycerol-3-phosphate through glycerol kinase, which can be used as precursor for lipid biosynthesis and can serve as a substrate for the synthesis of other metabolites [61]. The aerobic degradation of glycerol was carried out using K. pneumonia [62]. Bioconversion of glycerol to ethanol or butanol does not depend on the by-products formed using Clostridium pasteurianum [52]. Another example is succinic acid obtained using the bioconversion of glycerol [63].

Bioconversion products

There are a number of products which are obtained through bioconversion of glycerol, which is shown in table 1.

Table 1: It shows the various products obtained from the bioconversion of glycerol

S. No.

Products

Microorganism

Application

1.

Ethanol

Bacillus, Klebsiella planticola, Escherichia coli and Enterobacter aerogene

Motor fuel, household heating, feedstock, antiseptic and as a fuel

2.

1,3-propanediol

Escherichia coli, Lactobacillus, Citrobacter freundii, Klebsiella pneumoniae, Clostridium pasteurianum, Pseudomonas andEnnterobacter agglomerans

Composites, adhesives, laminates, for coatings, moldings, manufacturing of polyesters and copolyesters, as a solvent, antifreeze

3.

1,2-propanediol

Escherichia coli, Bacteroides ruminicola, Thermoanaerobacterium, Thermosaccharolyticum, Klebsiella pneumoniaeand yeasts

Manufacturing of polyester, as humectant, solvent, food preservatives and as antifreeze agent

4.

2,3-butanediol

Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter aerogenes, Bacillus polymyxa and Bacillus

Used in the resolution of carbonyl compounds in gas chromatography, used as precursor for various chemical manufacturing, flavoring agent, converted to 1,3-butadiene which is used for synthetic rubber, antifreeze agents, solvents, plastics, liquid fuel additives, in cosmetic industry

5.

Dihydroxyacetone

Gluconobacter oxydans

Used in wine making, as a colouring agent, in cosmetic industry

6.

Succinic acid

Anaerobiospirillum succiniciproducens

As precursor for manufacturing of specialized polyester, as a acidity regulator in food bevarages and as a food additive

7.

Propionic acid

Propionibacterium acidipropionici, Propionibacterium acnesand Clostridium propionicum

As apreservatives and food additives, as an intermediate in thermoplastic production

8.

Citric acid

Aspergillus niger, Yarrowia lipolytica

As a emulsifying agent in ice cream, as a chelating agent, as a cleaning agent, in pharmaceutical and cosmetic industry, in industrial construction, photography and in dyeing

Ethanol

Ethanol is generally produced from sugar cane, corn starch and sugar beets. Ethanol is produced from a glycerol-enriched algal mixture using Bacillus with final concentration 7.0-9.6 gm/L[64]. Major ethanol and formate are produce using fermetataion of glycerol by Klebsiella planticola which was isolated from the rumen[65]. Escherichia coli was used as biocatalyst for converting glycerol into ethanol. Glycerol was consumed within 84 hrs, with 86% of ethanol and 7% of succinic acid as the products. While acetate were produced in minor amount. Glycerol from biodiesel production was converted to ethanol using E. aerogenes using synthetic medium. Glycerol was consumed in 24 hrs and yields ethanol at 1.0 mol/mol glycerol. The yield of ethanol from glycerol fermentation is very low and future development is required[34].

1,3-propanediol

Bacterial fermentation has been known for almost 120 years. in which glycerol is converted to 1,3-PDO[66]. The 1,3-PDO is the main product obtained through bioconversion of glycerol. 1,3-PDO is the oldest fermentation product and was first observed as a product in 1881 in fermentation of glycerol[67]. Then in 1914, production of 1,3-PDO by Bacillus sp. Was described. Microbiology School of Delft was analyzed 1,3-PDO using different Enterobacteriaceae in 1928[68]. The 1,3-PDO is an emerging speciality chemical. 1,3-PDO can be used to produce polyesters, polyethers and polyurethanes[69]. It is also used as asolvent and lubricant[70].

The bioconversion of glycerol to 1,3-PDO has been demonstrated for several bacteria, such as E. coli[33], Pseudomonas[38], Lactobacillus[71], Citrobacter freundii[41], Klebsiella pneumonia [72], Clostridium pasteurianum(C. pasteurianum)[73],Ennterobacter agglomerans (E. agglomerans)[74] and E. aerogen[35]. As an additional reducing equivalent required so complete conversion of glycerol to 1,3-PDO is notpossible[75]. Glycerol is converted to 1,3-PDO by two steps, using any of the microorganisms. The first one is the conversion of glycerol to 3-hydroxypropionaldehyde and water and then 3-hydroxypropionaldehyde is reduced to 1,3-PDO by NAD+-linked oxidoreductase [76]. The production of 1,3-PDO from glycerol is carried out under aerobic as well as anaerobic conditions where glycerol is used as a carbon source, In Citrobacter, Klebsiella and Clostridium strains, a parallel pathway for glycerol conversion is used. In which glycerol is oxidized to dihydroxyacetone (DHA) by NAD+ followed by phosphorylation of the dihydroxyacetone gives dihydroxyacetone phosphate. This is an oxidative pathway[55].

Bioconversion of glycerol by Enterobacter strain results in the 1,3-PDO while the secondary productslike formate, succinate and ethanol are produced in variable amounts[77]. Bacterium C. pasteurianumconverts glycerol into different products, such as n-butanol, 1,3-propanediol, ethanol,acetic acid, butyric acid and lactic acid[47].

The maximum concentrations that inhibit glycerolfermentation by C. butyricum are 60 gm/L for 1,3-PDO[48]. During batch fermentationsusingC. butyricum,112 gm/L glycerol was used to produce 63.4 gm/L 1,3-PDO[4]. The conversion yield was0.69 mol/mol and maximal 1,3-PDO productivity was 1.85 gm/L/h.

The highest 1,3-PDOconcentration obtained in continuous culture was 31-48 gm/L, with aconversion yield of 0.55 gm 1,3-PDO/gm glycerol. K. pneumoniae was used to ferment crude glycerol and obtained a concentration of51.3-53 gm/L of 1,3-PDO[78]. Waste glycerol was utilized to produce 1,3-PDO using Pseudomonas strain. 0.514 mol 1,3-PDO was obtained per mole of waste glycerol[38]. Bioconversion of glycerol was carried out using E. aerogen where 0.615 mole 1,3-PDO was obtained at 300C[35]. E. coli was grow on glycerol to yield 1,3-PDO which was further utilized for polyester manufacturing[33].

A recombinant E. coli strain produces glycerol fromD-glucose. Then glycerol is converted to 1,3-PDO by K. pneumoniae. This two-stage process renders up to 60-70 gm/L 1,3-PDO/L[51]. In the DuPont and Genencor patent, a process using a recombinant E. coli strain containing the genes from K. pneumoniae for 1,3-PDO production is described. This recombinant microorganism reached a final 1,3-PDO concentration of 135 gm/L using glucose as substrate. The efficiency of substrate conversion was 51%[79].

E. coli was used to convert glycerol to 1,3-PDO have been constructed by over expressing genes of the dihydroxy acetone from K. pneumoniae. But, the glycerol conversion is low due to toxic by-products, such as glycerol-3-phosphate[55]. A recombinant E. coli JM109 strain containing the genes (coding for 1,3-propanediol oxidoreductase from wild type E. coli)[29]. This recombinant strain produced up to 41.1 gm/L of 1,3-PDO in an optimized culture medium containing 61.8 gm glycerol/L. Several metabolic engineering approaches for 1,2 and 1,3-propanediol production[80].

1,2-propanediol

1,2-propanediol (1,2-PDO) is also known as propylenglycol, which is a commodity chemical with a wide range of applications, including polyester resins, plastics, antifreeze agents, detergents, paints[81].

There are number of microorganisms reported as natural producers of 1,2-PDOviz. E. coli[82,83], Bacteroides ruminicola[84], Thermoanaerobacterium thermosaccharolyticum[85], Klebsiella pneumonia [86] and yeasts. The 1,2-PDO may formed from lactaldehyde in which lactaldehyde is reduced to 1,2-PDO byNADH-dependent lactaldehyde reductase[87].

First approaches towards the metabolic engineering of E. coli strains for production of 1,2-PDOfrom glucose involved overexpression of genes for glycerol dehydrogenase and produce 0.7 gm/L using E. coli or K. pneumoniae together with the E. coli methylglyoxal synthase gene[80]. Additional overexpressionof yeast alcohol dehydrogenase further improved productionperformance of 1,2-PDO giving 4.5 gm/L which was achieved in a fed batch fermentation process[88]. Elimination of lactate dehydrogenase by gene deletion improved 1,2-PDO production by an E. coli strain[89]. As glycerol has a higher degree of reduction than glucose, 0.72 gm 1,2-PDO produce per gm of glycerol while 0.63 gm 1,2-PDO produces per gm of glucose. Also, 1,2-PDO has been reported to be a natural productof anaerobic fermentation of glycerol in E. coli[90].

Glycerol is converted to 1,2-PDO in a pathway consisting of glycerol dehydrogenase forthe oxidation of glycerol leads to dihydroxyacetone and phosphorylation of the dihydroxyacetone givesdihydroxyacetone-phosphate by dihydroxyacetonekinase. Subsequently, dihydroxyacetone-phosphate is reduced to 1,2-PDO[83].

During production of 1,2-PDO different by-products viz. succinate, acetate, ethanol, and formate were formed. To eliminate by-product formation genes was tested. However, removal of the genes for acetate kinase, phosphate acetyltransferase, and lactatedehydrogenase resulted in an increased product yield of 0.21 gm/gm, but increasedethanol, formate, and pyruvate formation. The use of raw glycerol by E. colireducedformate formation and increased the 1,2-PDO yield (0.24 gm/gm)[90]. Recombinant strains of S. cerevisiae and C. glutamicum have been developed forproduction of 1,2-PDOwhich produces 1.1 gm/L 1,2-PDO[91,92].

2,3-butanediol

2,3-butanediol is another glycol that can be produced from the bioconversion of glycerol[93,94]. 2,3-butanediol can be added as a flavoring agent in food products when converted to diacetyl through oxidation. 2,3-Butanediol can be converted to 1,3-butadiene, which is used in the production of synthetic rubber, antifreeze agents, solvents, plastics, liquid fuel additives, polyurethanes for drugs and cosmetic products [95]. The 2,3-butanediol production carried out at low pH and an excess of glycerol. It is used as a solvent, fuel and for the production of polymers and chemicals [96].

2,3-BDO production has been possible by using various strain viz. Klebsiella pneumoniae [97], Klebsiella oxytoca [98], Enterobacter aerogenes [99], Bacillus polymyxa [100]and Bacillus [101]. Glycerol is a good substrate for 2,3-BDO production. Bioproduction of 2,3-BDO is carried out from pyruvate in three steps. In the first step, acetolactate synthase catalyses the condensation of two pyruvate molecules to acetolactate with CO2 liberation. In thesecond step, acetolactate is decarboxylated by acetolactate decarboxylase to acetoin while third step consists reduction of acetoin to 2,3-butanediol[102]. In 2,3-BDO production, ethanol was produced as a by-product which could be eliminated by insertion mutagenesis of the aldehyde dehydrogenase gene and gives 0.48 gm 2,3-BDO per gm of glycerol[103].

Bioconversion of glycerol to 2,3-BDO was carried out using K. pneumoniae G31 which resulted in final concentrations of 49.2 gm/L. The medium pH had a large influence on 2,3-BDO production as 2,3-BDO production being favored at alkaline pH. By applying strong aeration, increased the 2,3-BDO production and reduced by-products[104].

Dihydroxyacetone

Dihydroxyacetone (DHA) is serves as a versatile building block for the organic synthesis of a fine chemicals and generally used in the cosmetic industry[105,106]. It can be produced by oxidation of glycerol by acetic acid bacterium Gluconobacter oxydansin a process that requires good oxygenation and a medium containing yeast extract[107-109]. The chemical production of DHA is so expensive as it requires higher safety. Thus, the production of DHA is performed more economically using a microbial process[110,111].

For glycerol catabolism, there are two pathways used in Gluconobacter oxydans[112]. Glycerol is phosphorylated to glycerol-3-phosphate and then dehydrogenated to DHA-phosphate, which is ATP- and NAD-dependent. DHA production occurs via a membrane bound glycerol dehydrogenase, which appears to be the only process responsible for DHA synthesis. Both the substrate and product have an inhibitory effect on bacterial growth is observed in aDHA microbial synthesis[113]. The culture was able to grow in up to 80 gm/L DHA concentration while the formation of the product was observed maximum up to 220 gm/L DHA concentration. The effect of the over expression of glycerol dehydrogenase on glycerol oxidation, demonstrating that growth on glycerol was significantly improved in the over expression strains which having optical density 2.8-2.9 compared to the control strains having optical density 1.8-2.0. The velocity of total glycerol dehydrogenase inactivation can be reduced by the higher concentration of enzyme and slowed down the inactivation of glycerol oxidation[114].

DHA was produced from glycerol using Gluconobacter oxydans which is belongs to the family of Acetobacteraceae. They are able to oxidize many carbohydrates and alcohols incompletely. Problems have occurred in the process of DHA production by G. oxydans was inhibition of the biotransformation process by the substrate glycerol and the product DHA. Both inhibit the growth and DHA production[115].

Succinic acid

Succinate has a great importance as speciality chemical in industries which produces food and pharmaceutical products, green solvents, biodegradable plastics, surfactants, detergents, and ingredients to stimulate plant growth. Due to its structure as a linear saturated dicarboxylic acid, succinate can be used as an intermediate chemical and can be converted to 1,4-butanediol[116], tetrahydrofuran, γ-butyrolactone and linear aliphatic esters[117]. An increasing demand for succinic acid is expected as its use is extended to the synthesis of biodegradable polymers such as polybutyrate succinate (PBS) and polyamides[118]. The synthesis of a new biodegradable polymer, poly(1,3-propylene succinate), obtained through the thermal polycondensation of succinic acid with 1,3-PDO[119]. Succinate is currently produced petrochemically from butane through maleic anhydride[120]; only natural succinic acid sold in the food market is produced by fermentation. Using several different metabolic pathways like pyruvate carboxylation, succinate is produced under anaerobic conditions. By utilizing anaerobiospirillum succiniciproducens (A. succiniciproducens), succinate can be produced using the carboxylation pathway, catalyzed by malate dehydrogenase, fumarase and fumarate dehydrogenase[121].

Glycerol can be converted to succinic acid using A. succiniciproducens[121]. Fermentation of glycerol as the sole carbon source using A. succiniciproducens gives 19 gm/L of succinic acid where medium is supplemented with yeast extract while glycerol was fed with glucose 29.6 gm/L of succinic acid wasobtained. Succinic acid production from glycerol have some advantages over glucose, like high succinic acid produces with low acetic acid as by-product. Acetic acid imposes difficulties during downstream process for the recovery of succinic acid. As looking to the separation cost of succinate from fermentation broth, the formation of by-products like acetic acid is a problem to be solved through fermentation process optimization[118]. Fumaric acid has several industrial applications, that it is used as an acidulant in the food industry and promising candidate for manufacturing the various polymers. It is a direct precursor of succinic acid, it can be obtained from glycerol fermentation[122].

Propionic acid

Propionic acid is derived directly from ametabolic pathway and it is synthesized in a similar pathway to that of succinic acid[2]. Propionate is used as an antifungal agent in food and feed and asa basic chemical to produce cellulose-based plastics, herbicides, solvents, perfumes, arthritis drugs, flavors andthermoplastics[123]. The numerous industrial applications of propionic acid account for an increasing interest in thedevelopment of a biotechnological production process based on therenewable resource glycerol[124]. The production of propionate fromglycerol can be carried out using three bacterial strains: Propionibacterium acidipropionici, Propionibacterium acnes and Clostridium propionicum[2]. Consideringfermentation time and conversion yield, the best strain for glycerolconversion to propionate was P. acidipropionici. The fermentationprofile of this bacterium revealed five end products, consisting of propionic acid as the major product (0.84 mol/mol), with the following minimal by-products: succinate,acetate and n-propanol. The maximal propionic acid concentrationwas 42 gm/L using 80 gm/L glycerol in the medium[125]. As the efficiency of propionic acid extractionthrough distillation is strongly limited by acetic acid, the extremely low acetic acid concentrationobtained by using glycerol as substrate should greatly increase the yield of propionic acid recovered through distillation and simplifythe distillation procedure. The authorsconclude that glycerol is a promising substrate for propionic acid production, both in terms of conversion yield and productivity (0.35 gm/L/h)[126,127].

Citric acid

Citric acid can be produced in large quantities by fermentation method. Citric acid is widely used to impart a pleasant, fruity flavor to foods and beverages and used as an additive in detergents, pharmaceuticals, cosmetics and toiletries[128]. Citric acid is produced by submerged microbial fermentation of molasses using Aspergillus Niger[129].

In recent years, considerable interest has arisen in finding less expensive carbon sources for citric acid production[130]. Yarrowia lipolytica (Y. lipolytica) grows on glycerol to produce citric acid, so concluding that raw glycerol may be a suitable substrate for citric acid production. This yeast produced up to 35 gm/L of citric acid when a high initial concentration of glycerol was used in the culture medium. Growth and citric acid production parameters on glycerol were similar to those obtained using glucose. The final concentration of citric acid was 77.4 gm/L in the fermentation broth when using raw glycerol as a substrate[130]. Using Y. lipolytica N15, higher citric acid concentrations of 112 gm/gm was obtained[131,132].

CONCLUSION

Glycerol availability increased extremely as it arises as by-product of the biodiesel process. As glycerol is a renewable resource, utilizing this renewable waste substrate is the choice of an environmentally friendly process. As we utilized waste glycerol from biodiesel industry for thebioconversionprocess to obtain value added products, it will help to reduce the cost of waste treatment and disposal problem. Bioconversion of crude glycerol gives speciality chemicals which are used for the manufacturing of biodegradable polymer. As well utilization of crude glycerol promotes the use of biodiesel and reduce the petroleumdependency. If the biodiesel production is more economical and it will help to establish more bio refineries which also helps to develop the bioconversion process for converting glycerol into higher value products. Different microorganisms were developed for the production of ethanol, 1,3-propanediol, 1,2-propanediol, 2,3-butanediol, succinic acid, citric acid, propionic acid. Glycerol is a versatile compound and important carbon source which produces different chemicals in industrial microbiology. Future research shall also concentrate their efforts for increasing the % conversion of glycerol to useful products by bioconversion route as well as develop the most efficient and economic techniques.

ACKNOWLEDGEMENT

The author is thankful to the Principal, ISTAR and the Head of Department of Industrial chemistry, ISTAR for giving constant support.

REFERENCES

  1. Solomon BO, Zeng AP, Biebl H, Schlieker H, Posten C, Deckwer WD. Comparison of the energetic efficiencies of hydrogen and oxychemicals formation in Klebsiella pneumoniae and Clostridium butyricum during anaerobic growth on glycerol. J Biotechnol 1995;39(2):107-17.
  2. Barbirato F, Bories A. Relationship between the physiology of Enterobacter agglomerans CNCM 1210 grown anaerobically on glycerol and the culture conditions. Res Microbiol 1997;148(6):475-84.
  3. Barbirato F, Chedaille D, Bories A. Propionic acid fermentation from glycerol: comparison with conventional substrates. Appl Microbiol Biotechnol 1997;47(4):441-6.
  4. Barbirato F, Himmi EH, Conte T, Bories A. 1,3-Propanediol production by fermentation: an interesting way to valorize glycerin from the ester and ethanol industries. Ind Crops Prod 1998;7(2):281-9.
  5. Colin T, Bories A, Lavigne C, Moulin G. Effects of acetate and butyrate during glycerol fermentation by Clostridium butyricum. Curr Microbiol 2001;43(4):238-43.
  6. Rittmann D, SN Lindner, VF Wendisch. Engineering of a glycerol utilization pathway for amino acid production by Corynebacterium glutamicum. Appl Environ Microbiol 2008;74(20):6216-22.
  7. MF Milazzo, F Spina, A Vinci, C Espro, JCJ Bart. Brassica biodiesels: past, present and future. Renew Sustain Ener Rev 2013;18(C):350-89.
  8. Zahira Yaakob, Masita Mohammada, Mohammad Alherbawi, Zahangir Alam, Kamaruzaman Sopian. Overview of the production of biodiesel from Waste cooking oil. Renew Sustain Ener Rev 2013;18(C):184-93.
  9. Demirbas MF, Balat M. Recent advances on the production and utilization trends of biofuels: a global perspective. Ener Convers Mgmt 2006;47(15):2371-81.
  10. Posada JA, Cardona CA, Rincón LE. Sustainable biodiesel production from palm
  11. using in situ produced glycerol and biomass for raw bioethanol. En: Society for Industrial Microbiology. 32nd symposium on biotechnology for fuels and chemicals. Clearwater Beach, Florida; 2010. p. 19-22.
  12. Berriosa M, Skelton RL. Comparison of purification methods for biodiesel. Chem Eng J 2008;144:459-65.
  13. Campbell CJ, Laherrère JH. The end of cheap oil. Sci Am 1998;3(2):78-83.
  14. Keerthi P Venkataramanan, Judy J Boatman, Yogi Kurniawan, Katherine A Taconi, Geoffrey D. Bothun and Carmen Scholz Impact of impurities in biodiesel-derived crude glycerol on the fermentation by Clostridium pasteurianum ATCC 6013. Appl Microbiol Biotechnol 2012;93(3):1325-35.
  15. Muna Albanna. Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste. Management of Microbial Resources in the Environment: Spring. Netherlands; 2013. p. 313-40.
  16. Hayirli. The role of exogenous insulin in the complex of hepatic lipidosis and ketosis associated with insulin resistance phenomenon in postpartum dairy cattle. Veterinary Res Communi 2006;30(7):749-74.
  17. N Mezhevoi, VG Badelin. Thermochemical investigation of interaction of L-serin with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions. Russi J Gen Chem 2010;80(1):27-30.
  18. González-Pajuelo M, Andrade JC, Vasconcelos I. Production of 1,3-propanediol by Clostridium butyricum VPI 3266 in continuous cultures with high yield and productivity. J Ind Microbiol Biotech 2005;32(9):391-6.
  19. Choi WJ, Hartono MR, Chan W H, Yeo SS. Ethanol production from biodiesel-derived crude glycerol by newly isolated Kluyvera cryocrescens. Appl Microbiol Biotechnol 2011;89(4):1255-64.
  20. Papanikolaou S, Muniglia L, Chevalot I, Aggelis G, Marc I. Yarrowia lipolytica as a potential producer of citric acid from raw glycerol. J Appl Microbiol 2002;92:737-44.
  21. Scholten E, Dägele D. Succinic acid production by a newly isolated bacterium. Biotechnol Lett 2008;30(12):2143-46.
  22. Malinowski J. Evaluation of liquid extraction potentials for downstream separation of 1,3-propanediol. Biot Tech 1999;13(2):127-30.
  23. Cameron DC, Altaras NE, Hoffman ML, Shaw AJ. Metabolic engineering of propanediol pathways. Biotechnol Prog 1998;14(1):116-25.
  24. Hao J, Xu F, Liu H, Liu D. Downstream processing of 1,3-propanediol fermentation broth. J Chem Technol Biotechnol 2006;81(1):102-08.
  25. Yang G, Tian J, LI J. Fermentation of 1,3-propanediol by a lactate deficient mutant of Klebsiella oxytoca under microaerobic conditions. Appl Microbiol Biotechnol 2007;73(5):1017-24.
  26. Lin R, Liu H, Hao J, Cheng K, Liu D. Enhancement of 1,3-propanediol production by Klebsiella pneumoniae with fumarate addition. Biotechnol Lett 2005;27(22):1755-59.
  27. Raynaud C, Sarçabal P, Meynial-Salles I, Croux C, Soucaille P. Molecular characterization of the 1,3-propanediol (1,3-PD) operon of Clostridium butyricum. Proc Natl Acad Sci 2003;100(9):5010-15.
  28. González-Pajuelo M, Andrade JC, Vasconcelos I. Production of 1,3-propanediol by Clostridium butyricum VPI 3266 using a synthetic medium and raw glycerol. J Ind Microbiol Biotech 2004;31(9):442-6.
  29. Németh A, Kupcsulik B, Sevella B. 1,3-Propanediol oxidoreductase production with Klebsiella pneumoniae DSM2026. World J Microbiol Biotechnol 2003;19(7):659-63.
  30. Zhang X, Li Y, Zhuge B, Tang X, ShenW, Rao Z, et al. Construction of a novel recombinant Escherichia coli strain capable of producing 1,3-propanediol and optimization of fermentation parameters by statistical design. World J Microbiol Biotechnol 2006;22(9):945-52.
  31. Daria Szymanowska-Powałowska, Agnieszka Drożdżyńska, Natalia Remszel. Isolation of new strains of bacteria able to synthesize 1,3-propanediol from glycerol. Adv Microbiol 2013;3(2):171-80.
  32. Deckwer WD. Microbial conversion of glycerol to 1,3-propanediol. FEMS Microbiol Rev 1995;16(2):143-9.
  33. Menzel K, Zeng AP, Deckwer WD. Enzymatic evidence for an involvement of pyruvate dehydrogenase in the anaerobic glycerol metabolism of Klebsiella pneumoniae. J Biotechnol 1997;56(2):135-42.
  34. Mandar Karve, Jay J Patel, Nirmal K Patel. Bioconverison of glycerol to 1,3-propanediol and its application. Proceedings of the ICETCS 2013 Confer., Spring. (In press).
  35. Ito T, Nakashimada Y, Senba K, Matsui T, Nishio N. Hydrogen and ethanol production from glycerol-containing wastes discharged after biodiesel manufacturing process. J Biosci Bioeng 2005;100(3):260-5.
  36. Mandar Karve, Jay J Patel, VK Sinha, Nirmal K Patel. A novel biological route for 1,3-propanediol synthesis through transesterification of cottonseed oil. Acc Biotechnol Res 2014. (In press)
  37. Talarico TL, Axelsson LT, Novotny J, Fiuzat M, Dobrogosz WJ. Utilization of glycerol as a hydrogen acceptor by Lactobacillus reuteri: purification of 1,3-propanediol: NAD+ oxidoreductase. Appl Env Microbiol 1990;56(4):943-8.
  38. Talarico TL, Casas IA, Chung TC, Dobrogosz WJ. Production and isolation of reuterin, a growth inhibitor produced by Lactobacillus reuteri. Antimicrob Agents Chemother 1988;32(12):1854-8.
  39. Mandar Karve, Jay J Patel, VK Sinha, Nirmal K Patel. Bioconverison of waste glycerol to 1,3-propanediol and its application. Acc Biotechnol Res 2014;1:(1). (In press)
  40. Hao J, W Wang, J Tian, J Li,  D Liu. Decrease of 3-hydroxypropionaldehyde accumulation in 1,3-propanediol production by over-expressing dhaT gene in Klebsiella pneumoniae TUAC01. J Ind Microbiol Biotechnol 2008;35(7):735-41.
  41. Youngleson JS, Jones WA, Jones DT, Woods DR. Molecular analysis and nucleotide sequence of the adh1 gene encoding an NADPH-dependent butanol dehydrogenase gene in the Gram-positive anaerobe Clostridium acetobutylicum. Gene 1998;78(2):355-64.
  42. Boenigk R, Bowien S, Gottschalk G. Fermentation of glycerol to 1,3-propanediol in continuous cultures of Citrobacter freundii. Appl Microbiol Biotechnol 1993;38(4):453-7.
  43. Malinowski J. Evaluation of liquid extraction potentials for downstream separation of 1,3-propanediol. Biot Tech 1990;13(2):127-30.
  44. Daniel R, Boenigk R, Gottschalk G. Purification of 1,3-Propanediol Dehydrogenase from citrobacter freundii and cloning sequencing and overexpression of the corresponding gene in escherichia coli. J Bacteriol 1995;177(8):2151-6.
  45. Seifert C, S Bowien, G Gottschalk, R Daniel. Identification and expression of the genes and purification and characterization of the gene products involved in reactivation of coenzyme B-12-dependent glycerol dehydratase of Citrobacter freundii. Eur J Biochem 2001;268(8):2369-78.
  46. Dabrock B, Bahl H, Gottschalk G. Parameters affecting solvent production by Clostridium pasteurianum. Appl Environ Microbiol 1992;58(4):1233-9.
  47. Macis L, Daniel R, Gottschalk G. Properties and sequence of the coenzyme B12-dependent glycerol dehydratase of Clostridium pasteurianum. FEMS Microbiol Lett 1998;164(1):21-8.
  48. Luers F, Seyfried M, Daniel R, Gottschalk G. Glycerol conversion to 1,3-propanediol by Clostridium pasteurianum: Cloning and expression of the gene encoding 1,3-propanediol dehydrogenase. FEMS Microbiol Lett 1997;154(2):337-45.
  49. Biebl H, Menzel K, Zeng AP, Deckwer WD. Microbial production of 1,3-propanediol. Appl Microbiol Biotechnol 1999;52(3):289-97.
  50. Biebl H, Marten S, Hippe H, Deckwer WD. Glycerol conversion to 1,3-propanediol by newly isolated clostridia. Appl Microbiol Biotechnol 1992;36(5):592-7.
  51. Abbad-Andaloussi S, Manginot-Dürr C, Amine J, Petitdemange E, Petitdemange H. Isolation and characterization of Clostridium butyricum DSM 5431 mutants with increased resistance to 1,3-propanediol and altered production of acids. Appl Env Microbiol 1995;61(12):4413-7.
  52. Tong IT, Cameron DC. Enhancement of 1,3-propanediol production by cofermentation in Escherichia coli expressing Klebsiella pneumoniae dha regulon genes. Appl Biochem Biotechnol 1992;34(1):149-59.
  53. Biebl H, Zeng AP, Menzel K, Deckwer WD. Fermentation of glycerol to 1,3-propanediol and 2,3-butanediol by Klebsiella pneumonia. Appl Microbiol Biotechnol 1998;50(1):24-9.
  54. Forage RG, Foster AM. Glycerol fermentation in Klebsiella pneumoniae: Functions of the coenzyme B12-dependent glycerol and diol dehydratases. J Bacteriol 1982;149(2):413-9.
  55. Barbirato F, Bories A. Relationship between the physiology of Enterobacter agglomerans CNCM 1210 grown anaerobically on glycerol and the culture conditions. Res Microbiol 1997;148(6):475-84.
  56. Zhu MM, Lawman PD, Cameron DC. Improving 1.3-propanediol production from glycerol in a metabolically engineered Escherichia coli by reducing accumulation of sn-glycerol-3-phosphate. Biotechnol Prog 2002;18(4):694-9.
  57. Toraya T, Honda S, Kuno S, Fukui S. Distribution of coenzyme B12-dependent diol dehydratase and Glycerol dehydratase in selected genera of Enterobacteriaceae and Propionibacteriaceae. J Bacteriol 1980;141(3):1439-42.
  58. Ahrens K, Menzel K, Zeng AP, Deckwer WD. Kinetic dynamic and pathway studies of glycerol metabolism by Klebsiella pneumoniae in anaerobic continuous culture: III Enzymes and fluxes of glycerol dissimilation and 13-propanediol formation. Biotechnol Bioeng 1998;59(5):544-52.
  59. Forage RG, Lin CC. dha System mediating aerobic and anaerobic dissimilation of glycerol in Klebsiella pneumoniae NCIB 418. J Bacteriol 1982;151(2):591-9.
  60. Saint-Amans S, Girbal L, Andrade J, Ahrens K, Soucaille P. Regulation of carbon and electron flow in Clostridium butyricum VPI 3266 grown on glucose-glycerol mixtures. J Bacteriol 2001;183(5):1748-54.
  61. González-Pajuelo M, Meynial-Salles I, Mendes F, Soucaille P, Vasconcelos I. Microbial conversion of glycerol to 1,3-propanediol: physiological comparison of a natural producer, Clostridium butyricum VPI 3266 and an engineered strain, Clostridium acetobutylicum DG1 (pSPD5). Appl Env Microbiol 2006;72(1):96-101.
  62. Wang ZX, Zhuge J, Fang H, Prior BA. Glycerol production by microbial fermentation: a review. Biotechnol Adv 2001;19(3):201-23.
  63. Ruch FE, Lengeler J, Lin CC. Regulation of glycerol catabolism in Klebsiella aerogenes. J Bacteriol 1974;119(1):50-6.
  64. Dharmadi Y, Murarka A, Gonzalez R. Anaerobic fermentation of glycerol by Escherichia coli: a new platform for metabolic engineering. Biotechnol Bioeng 2006;94(5):821-9.
  65. Nakas JP, Schaedle M, Parkinson CM, Coonley CE, Tanenbaum SW. System development of linked-fermentation production of solvents from algal biomass. Appl Environ Microbiol 1983;46(5):1017-23.
  66. Jarvis GN, Moore ERB, Thiele JH. Formate and ethanol are the major products of glycerol fermentation produced by a Klebsiella planticola strain isolated from red deer. J Appl Microbiol 1997;83(2):166-74.
  67. Zeng AP, Biebl H. Bulk chemicals from biotechnology: the case of 1,3-propanediol production and the new trends. Adv Biochem Eng Spring 2002;239-59.
  68. Werkman CH, GF Gillen. Bacteria producing trimethylene glycol. J Bacteriol 1932;23(2):167-82.
  69. Katrlík J, Vostiar I, Sefcovicová J, Tkác J, Mastihuba V, Valach M, Stefuca V, et al. A novel microbial biosensor based on cells of Gluconobacter oxydans for the selective determination of 1,3-propanediol in the presence of glycerol and its application to bioprocess monitoring. Analyt Bioanalyt Chem 2007;388(1):287-95.
  70. Colin T, Bories A, Moulin G. Inhibition of Clostridium butyricum by 1,3-propanediol and diols during glycerol fermentation. Appl Microbiol Biotechnol 2000; 54:201-5.
  71. Willke TH, Vorlop KD. Industrial bioconversion of renewable resources as an alternative to conventional chemistry. Appl Microbiol Biotechnol 2004; 66(2):131-42.
  72. Kang T, Korber DR, Tanaka T. Bioconversion of glycerol to 1,3-propanediol in thin stillage-based media by engineered Lactobacillus panis PM1. J Ind Microbiol Biotechnol 2014;41(4):629-35.
  73. Swati Khanna, Arun Goyala, Vijayanand S Moholkar. Effect of Fermentation parameters on Bio-alcohols production from glycerol using immobilized clostridium pasteurianum: an optimization study. Preparative Biochem Biotechnol 2013;43(8):828-47.
  74. Anand Hiremath, Mithra Kannabiran, Vidhya Rangaswamy. 1,3-propanediol production from crude glycerol from jatropha biodiesel process. New Biotechnol 2011;28(1):19-23.
  75. Cheng KK, Liu DH, Sun Y, Liu WB. 1,3-propanediol production by Klebsiella pneumoniae under different aeration strategies. Biotechnol Lett 2004;26(11):911-15.
  76. Chotani G, Dodge T, Hsu A, Kumar M, LaDuca R, Trimbur D, et al. The commercial production of chemicals using pathway engineering. Biochim Biophys  Acta 2000;1543(2):434-55.
  77. Nakamura CE, Whited GM. Metabolic engineering for the microbial production of 1,3-propanediol. Curr Opin Biotechnol 2003;14(5):454-9.
  78. Homann T, C Tag, H Biebl, WD Deckwer, B Schink. Fermentation of glycerol to 1,3-propanediol by klebsiella and citrobacter strains. Appl Microbiol Biot 1990;33(2):121-6.
  79. Mu Y, Teng H, Zhang DJ, Wang W, Xiu ZL. Microbial production of 1,3-propanediol by Klebsiella pneumoniae using crude glycerol biodiesel preparations. Biotechnol Lett 2006;28(21):1755-9.
  80. Haynie Sharon L, Wagner Lorraine W. Process for making 1,3-propanediol from carbohydrates using mixed microbial cultures. US Patent 1997;5;599-689.
  81. Cameron DC, Altaras NE, Hoffman ML, Shaw AJ. Metabolic engineering of propanediol pathways. Biotechnol Prog 1998;14(1):116-25.
  82. Shelley S. A renewable route to propylene glycol. Chem Eng Prog 2007;103:6-9.
  83. Hacking AJ, EC Lin. Disruption of the fucose pathway as a consequence of genetic adaptation to propanediol as a carbon source in Escherichia coli. J Bacteriol 1976;126(3):1166-72.
  84. Gonzalez R, A Murarka, Y Dharmadi, SS Yazdani. A new model for the anaerobic fermentation of glycerol in enteric bacteria: trunk and auxiliary pathways in Escherichia coli. Metab Eng 2008;10(5):234-45.
  85. Turner KW, AM Roberton. Xylose, arabinose, and rhamnose fermentation by Bacteroides ruminicola. Appl Environ Microbiol 1979;38(1):7-12.
  86. Cameron DC, CL Cooney. A novel fermentation-the production of r(-)-1,2-propanediol and acetol by clostridium thermosaccharolyticum. Bio-Technol 1986;4(1): 651-4.
  87. Badia J, J Ros, J Aguilar. Fermentation mechanism of fucose and rhamnose in Salmonella typhimurium and Klebsiella pneumoniae. J Bacteriol 1985;161(1): 435-7.
  88. Suzuki T, H Onishi. Aerobic dissimilation of l-rhamnose and production of lrhamnonic acid and 1,2-propanediol by yeasts. Agr Biol Chem 1968;32(7):888-93.
  89. Altaras NE, DC Cameron. Enhanced production of (R)-1,2-propanediol by metabolically engineered Escherichia coli. Biotechnol Prog 2000;16(6):940-6.
  90. Berrios-Rivera SJ, K. Y. San, GN Bennett. The effect of carbon sources and lactate dehydrogenase deletion on 1,2-propanediol production in Escherichia coli. J Ind Microbiol Biotechnol 2003;30(1):34-40.
  91. Clomburg JM, R Gonzalez. Metabolic engineering of Escherichia coli for the production of 1,2-propanediol from glycerol. Biotechnol Bioeng 2011;108(4): 867-79.
  92. Lee W, NA Dasilva. Application of sequential integration for metabolic engineering of 1,2-propanediol production in yeast. Metab Eng 2006;8(1):58-65.
  93. Jung JY, ES Choi, MK Oh. Enhanced production of 1,2-propanediol by tpi1 deletion in Saccharomyces cerevisiae. J Microbiol Biotechnol 2008;18(11):1797-02.
  94. S Afschar, CE Vaz Rossell, R Jonas, A Quesada Chanto, K Schaller. Microbial production and downstream processing of 2,3-butanediol. J Biotechnol 1996;27(3):317-29.
  95. C Saha, RJ Bothast. Production of 2,3-butanediol by newly isolated Enterobacter cloacae. Appl Microbiol Biotechnol 1999;52(3):321-6.
  96. Syu MJ. Biological production of 2,3-butanediol. Appl Microbiol Biotechnol 2001;55(1):10-8.
  97. Perego P, A Converti, M Del Borghi. Effects of temperature, inoculum size and starch hydrolyzate concentration on butanediol production by Bacillus licheniformis. Bioresour Technol 2003;89(2):125-31.
  98. Grover BP, SK Garg, J Verma. Production of 2,3-Butanediol from Wood Hydrolysate by Klebsiella-Pneumoniae. World J Microb Biot 1990;6(3):328-32.
  99. Perego P, A Converti, A Del Borghi, P Canepa. 2,3-butanediol production by Enterobacter aerogenes: selection of the optimal conditions and application to food industry residues. Bioprocess Eng 2000;23(6):613-20.
  100. De Mas C, NB Jansen, GT Tsao. Production of optically active 2,3-butanediol by Bacillus polymyxa. Biotechnol Bioeng 1988;31(4):366-77.
  101. Nilegaonkar SS, SB Bhosale, CN Dandage, AH Kapadi. Potential of Bacillus licheniformis for the production of 2,3-butanediol. J Ferment Bioeng 1996;82(4): 408-10.
  102. Jansen NB, MC Flickinger, GT Tsao. Production of 2,3-butanediol from Dxylose by Klebsiella oxytoca ATCC 8724. Biotechnol Bioeng 1984;26(4):362-9.
  103. Juni E. Mechanisms of formation of acetoin by bacteria. J Biolog Chem 1952;195(2):715-26.
  104. Ji X J, H Huang, J G Zhu, L J Ren, Z K Nie, J Du, S Li. Engineering Klebsiella oxytoca for efficient 2, 3-butanediol production through insertional inactivation of acetaldehyde dehydrogenase gene. Appl Microbiol Biotechnol 2010;85(6):1751-8.
  105. Petrov K, P Petrova. Enhanced production of 2,3-butanediol from glycerol by forced pH fluctuations. Appl Microbiol Biotechnol 2010;87(3):943-9.
  106. Hekmat D, R Bauer, J Fricke. Optimization of the microbial synthesis of dihydroxyacetone from glycerol with Gluconobacter oxydans. Bioprocess Biosyst Eng 2003;26(2):109-16.
  107. Bauer R, N Katsikis, S Varga, D Hekmat. Study of the inhibitory effect of the product dihydroxyacetone on Gluconobacter oxydans in a semi-continuous two-stage repeated-fed-batch process. Bioprocess Biosyst Eng 2005;28(1):37-43.
  108. Nabe K, N Izuo, S Yamada, I Chibata. Conversion of glycerol to dihydroxyacetone by immobilized whole cells of acetobacter xylinum. Appl Environ Microbiol 1979;38(6):1056-60.
  109. Wethmar M, WD Deckwer. Semisynthetic culture medium for growth and dihydroxyacetone production by Gluconobacter oxydans. Biotechnol Tech 1999;13(4):283-7.
  110. Flickinger MC, D Perlman. Application of Oxygen-Enriched aeration in the conversion of glycerol to dihydroxyacetone by gluconobacter melanogenus ifo3293. Appl Environ Microbiol 1977;33(3):706-12.
  111. Demirel S, Lehnert K, Lucas M, Claus, et al. Use of renewables for the production of chemicals: Glycerol oxidation over carbon supported gold catalysts. Applied Catalysis B: Environ 2007;70(1-4):637-43.
  112. Zope B, Davis R. Influence of reactor configuration on the selective oxidation of glycerol over Au/TiO2. Topics Cataly 2009;52(3):269-77.
  113. Bories A, C Claret, P Soucaille. Kinetic-Study and optimization of the production of dihydroxyacetone from glycerol using gluconobacter oxydans. Process Biochem 1991;26(1):243-8.
  114. Claret C, JM Salmon, C Romieu, A Bories. Physiology of gluconabacter oxydans during dihydroxyacetone production from glycerol. Appl Microbiol Biot 1994;41(3):359-65.
  115. Claret C, A Bories, P Soucaille. Glycerol inhibition of growth and dihydroxyacetone production by gluconobacter oxydans. Current Microbiol 1992;25(3):149-55.
  116. Matsushita K, H Toyama, O Adachi. Respiratory chains and bioenergetics of acetic acid bacteria. Adv Microb Physiol 1994;36(2):247-01.
  117. Yoshinori Hara, Hiroko Inagaki. Method for producing 1,4-butanediol. US5077442; 1991.
  118. Zeikus JG, Jain MK, Elankovan P. Biotechnology of succinic acid production and markets for derived industrial products. Appl Microbiol Biotechnol 1999;51(5):545-52.
  119. Song H, Lee SY. Production of succinic acid by bacterial fermentation. Enzyme Microb Technol 2006;39(3):352-61.
  120. Ranucci E, liu Y, Lindblad MS, Albertsson AC. New biodegradable polymers from renewable sources. High molecular weight poly(ester carbonate)s from succinic acid and 1,3-propanediol. Macromol Rapid Commun 2000;21(10):680-4.
  121. Bechthold K, Bretz S, Kabasci R, Kopitzky, A Springer. Succinic acid: a new platform chemical for biobased polymers from renewable resources. Chemi Engi  Technol 2008;31(5):647-54.
  122. Lee SY, Hong SH, Lee SH, Park SJ. Fermentative production of chemicals that can be used for polymer synthesis. Macromol Biosci 2004;4(3):157-64.
  123. Zhou Y, Du J, Tsao GT. Comparison of fumaric acid production by Rhizopus oryzae using different neutralizing agents. Bioprocess Biosyst Eng 2002;25(3):179-81.
  124. Himmi EH, Bories A, Boussaid A, Hassani L. Propionic acid fermentation of glycerol and glucose by Propionibacterium acidipropionici and Propionibacterium freudenreichii ssp. shermanii. Appl Microbiol Biotechnol 2000;53(4):435-40.
  125. Yang G, Tian J, LI J. Fermentation of 1,3-propanediol by a lactate deficient mutant of Klebsiella oxytoca under microaerobic conditions. Appl Microbiol Biotechnol 2007; 73(5):1017-24.
  126. Dae-Eun Cheonga, Hae-In Leeb, Jae-Seong So. Optimization of electrotransformation conditions for Propionibacterium acnes. J Microbiol Methods 2008;72(1):38-41.
  127. Wang ZX, Zhuge J, Fang H, Prior BA. Glycerol production by microbial fermentation: a review. Biotechnol Adv 2001;19(3):201-23.
  128. Zhong Gu, Bonita A Glatz, Charles E Glatz. Effects of propionic acid on propionibacteria fermentation. Enzym Microb Technol 1998;22(1):13-8.
  129. Soccol CR, Vandenberghe LPS, Rodrigues C, Pandey A. New perspectives for citric acid production and application. Food Technol Biotechnol 2006;44(2):141-9.
  130. Gurpreet Singh Dhillon, Satinder Kaur Brar, Surinder Kau. Rheological studies during submerged citric acid fermentation by aspergillus niger in stirred fermentor using apple pomace ultrafiltration sludge 2013;6(5):1240-50.
  131. Imandi SB, Bandaru VVR, Somalanka SR, Garapati HR. Optimization of medium constituents for the production of citric acid from byproduct glycerol using Doehlert experimental design. Enzyme Microb Technol 2007;40(5):1367-72.
  132. Abdulrahman M, Al-Shehri, Yasser S, Mostafa. Citric acid production from date syrup using immobilized cells of aspergillus niger. Biotechnol 2006;5(4):461-5.
  133. Ling-Fei Wang, Zhi-Peng Wang, Xiao-Yan Liu, Zhen-Ming Chi. Citric acid production from extract of Jerusalem artichoke tubers by the genetically engineered yeast Yarrowia lipolytica strain 30 and purification of citric acid. Bioprocess Biosy Engi 2013;36(11):1759-66.

Refbacks

  • There are currently no refbacks.