Oleochemical Industry Research Articles

A review on the important aspects of lipase immobilization on nanomaterials.

Lipase is one of the most widely used enzymes and plays an important role in biotechnological and industrial processes including food, paper, and oleochemical industries, as well as in pharmaceutical applications. However, its aqueous solubility and instability make its application relatively difficult and expensive. The immobilization technique is often used to improve lipase performance, and the strategy has turned out to be a promising method. Immobilized lipase on nanomaterials (NMs) has shown superiority to the free lipase, such as improved thermal and pH stability, longer stable time, and the capacity of being reused. However, immobilization of lipase on NMs also sometimes causes activity loss and protein loading is relatively lowered under some conditions. The overall performance of immobilized lipase on NMs is influenced by mechanisms of immobilization, type of NMs being used, and physicochemical features of the used NMs (such as particle size, aggregation behavior, NM dimension, and type of coupling/modifying agents being used). Based on the specific features of lipase and NMs, this review discusses the recent developments, some mechanisms, and influence of NMs on lipase immobilization and their activity. Multiple application potential of the immobilized lipases has also been considered.

Single cell oil production by Lipomyces starkeyi: Biphasic fed-batch fermentation strategy providing glucose for growth and xylose for oil production

The aim of this study was to produce single cell oil (SCO) from Lipomyces starkeyi ATCC 56304 using a biphasic fed-batch fermentation strategy. Fed-batch fermentations were performed to compare oil production using glucose, xylose, mixed-sugars (1:1 ratio of glucose:xylose), and a biphasic system supplying glucose for cell growth and xylose for oil production. The fermentation using xylose as the sole carbon source generated an oil yield of 0.16gg−1 and a productivity of 0.12gL−1h−1, two-times the oil yield (0.08gg−1) and productivity (0.06gL−1h−1) achieved with glucose. At 120h, the biphasic fermentation produced a greater oil productivity (0.13gL−1h−1) compared to the mixed-sugar fermentation (0.09gL−1h−1) but similar oil productivities (0.14gL−1h−1) were achieved for both at longer fermentation times. The biphasic fermentation generated a final oil yield of 0.17gg−1 and an oil content of 60.1% (w w−1), but oil productivity showed minor improvement at 0.14gL−1h−1 after 255h. Oleic acid accounted for at least 65% of the fatty acid content, suggesting that oil from L. starkeyi has potential for application in the biofuel and oleochemical industries.

PEMANFAATAN GLISERIN DARI RESIDU GLISERIN SEBAGAI PLASTICIZER UNTUK PEMBUATAN BIOPLASTIK DENGAN BAHAN BAKU PATI BONGGOL PISANG KEPOK

Glycerin residue is waste oleochemical industry that still contain glycerin. To produce quality and maximum quantity of glycerin, then research the effect of pH acidification using phosphoric acid. Glycerin analysis includes the analysis of pH, Fatty Acid and Ester (FAE), and analysis of the levels of glycerin. The maximum yield obtained at pH acidification 2 is grading 91,60% glycerin and Fatty Acid and Ester (FAE) 3,63 meq/100 g. Glycerin obtained is used as a plasticizer in the manufacture of bioplastics. Manufacture of bioplastics using the method of pouring a solution with varying concentrations of starch banana weevil (5% w/v and 7% w/v), variations of the addition of glycerin (1 ml, 3 ml, 5 ml and 7 ml), and a variety of gelatinization temperature (60°C, 70°C, and 80°C). Analysis of bioplastics include FTIR testing, tensile strength that is supported by SEM analysis. The results obtained in the analysis of FTIR does not form a new cluster on bioplastics starch banana weevil, but only a shift in the recharge area only, it is due to the addition of O-H groups originating from water molecules that enter the polysaccharide through a mechanism gelatinitation that generates interaction hydrogen bonding strengthened. The maximum tensile strength of bioplastics produced at a concentration of starch 7% w/v, 1 ml glycerine and gelatinization temperature of 80°C is 3,430 MPa. While the tensile strength bioplastic decreased with increasing glycerin which can be shown from the results of SEM where there is a crack, indentations and lumps of starch insoluble.

Solvent recovery and deacidification by organic solvent nanofiltration: Experimental investigation and mass transfer modeling

Non-edible oils, waste oils and animal fats are promising feedstocks for more economic and ecological production processes. However, the composition of these low-quality oils, especially the content of free fatty acids, strongly fluctuates requiring the development of flexible process concepts. Therefore, this study investigates the potential of organic solvent nanofiltration for important applications in the oleochemical industry. It is shown that an efficient recovery of non-polar extraction solvents is possible for a wide range of low-quality oils. Commercially available PDMS-based membranes enable high solvent fluxes and rejection of triglyceride and fatty acids. In deacidification experiments, high selective separation of free fatty acids from triglycerides for long-chain as well as medium-chain oils is achieved by using polar solvents and available polyimide-based membranes. The amount of solvent, which is added to the low-quality oils, is identified as crucial parameter for separation efficiency. Membrane performance is accurately described by a (reduced) solution-diffusion model with imperfections, for which mass transfer of solvents and fatty acids is described by the convective contribution, while mass transfer of triglycerides is described by the diffusive contribution.

Bioconversion of crude glycerol to microbial lipid using a robust oleaginous yeast Rhodosporidium toruloides ATCC 10788 capable of growing in the presence of impurities

In this work, crude glycerol, a by-product from a biodiesel industry was characterized and converted to microbial lipid. The sample of crude glycerol was found to contain 44.56wt.% glycerol, 13.86wt.% methanol, 10.74wt.% of ash and 32.97wt.% of soap. Rhodosporidium toruloides ATCC 10788 was studied for the first time to determine its ability to grow on crude glycerol as a carbon source. Methanol concentration as low as 0.5% (w/v) in the medium containing pure glycerol inhibited biomass and lipid production by this strain. However, higher concentration of methanol (i.e. 1.5% w/v) in crude glycerol containing media did not have the same effect on the organism, with double the biomass (21.16g/L), triple the lipid concentration (11.27g/L) and high lipid content (53.28wt.%) produced at the end of 168h. Unlike many other oleaginous microorganisms, the ability of this yeast to consume other impurities present in crude glycerol enhanced the growth and lipid production in such a way that the effect of methanol was masked or became insignificant. The lipid obtained contained 47.16% of oleic acid (a monounsaturated fatty acid), making it a very good feedstock for some oleochemical industries and the production of biodiesel. This bioconversion process which involves the production of lipid from crude glycerol waste stream will be of great interest to the biodiesel industry as it can be easily integrated into the existing biodiesel production plant. The use of such robust strains to produce other value added products can also be explored.

Selective Production of Acid-form Sophorolipids from Glycerol by Candida floricola.

Biosurfactants (BSs) are produced in abundance from various feedstocks by diverse microorganisms, and are used in various applications. In this paper, we describe a new yeast isolate that produces glycolipid-BSs from glycerol, with the aim of enhancing the utilization of the surplus glycerol produced by the oleo-chemical industry. As a result of the screening, strain ZM1502 was obtained as a potential producer of BS from glycerol. Based on TLC analysis, the strain produced glycolipid BSs. According to structural analyses (NMR, MALDI-TOF MS, and GC-MS), the main component of the glycolipids was 6',6"-di-O-acetylated acid-form sophorolipid (SL). Interestingly, the strain produced only acid-form SL, without lactone-form SLs, although the conventional SL-producing yeast, Starmerella bombicola, produces lactone-form SLs with small amounts of the acid-form. Based on taxonomy, the strain was identified as Candida floricola. It produced 3.5 g L-1 of acid-form SLs in 20% (w/v) glycerol. In addition, C. floricola CBS7290 and NBRC10700T also produced only acid-form SLs from glycerol. These results suggest that C. floricola would enhance the utilization of waste glycerol as a fermentation feedstock and facilitate a broad range of applications for SLs.

Esters of oligo-(glycerol carbonate-glycerol): New biobased oligomeric surfactants

Glycerol carbonate is one of the most potentially multifunction glycerol-derived compounds. Glycerol is an important by-product of the oleochemical industry. The oligomerization of glycerol carbonate, assisted by the glycerol, results in the production of polyhydroxylated oligomers rich in linear carbonate groups. The polar moieties of these oligomers (Mw<1000Da) were supplied by glycerol and glycerol carbonate rather than ethylene oxide as in most commercial surfactants. The insertion of linear carbonate groups into the glycerol-based skeleton rendered the oligomers amphiphilic, resulting in a decrease in air/water surface tension to 57mN/m. We improved the physical and chemical properties of the oligomers, by altering the type of acylation reaction and the nature of the acyl donor. The polar head is constituted of homo-oligomers and hetero-oligomers. Homo-oligomers are oligoglycerol and/or oligocarbonate, hetero-oligomers are oligo(glycerol-glycerol carbonate). Coprah oligoesters had the best surfactant properties (CMC<1mg/mL, πcmc<30mN/m), outperforming molecules of fossil origin, such as ethylene glycol monododecyl ether, glycol ethers and fatty acid esters of sorbitan polyethoxylates. The self-assembling properties of oligocarbonate esters were highlighted by their ability to stabilize inverse and multiple emulsions. The oligo-(glycerol carbonate-glycerol ether) with relatively low molecular weights showed properties of relatively high-molecular weight molecules, and constitute a viable “green” alternative to ethoxylated surfactants.

Fitting of broken and intact cell model to supercritical fluid extraction (SFE) of sunflower oil

Abstract The present work is focused on the supercritical extraction and kinetic study of sunflower oil. The effect of operating parameters, namely pressure (20–40 MPa), temperature (333–373 K), solvent mass flow (0.83 × 10 − 4 to 2.50 × 10 − 4 kg/s), particle size (0.50–1.00 mm) and ethanol as co-solvent (0–10%) have been studied by a set of experiments. The outcomes of work show, extraction yield increases with increasing pressure, solvent mass flow and co-solvent. The retrograde phenomenon is also observed between 333 and 353 K. The experimental data have been used to simulate the broken and intact cell model and fitting parameters are optimized by the global optimization method. The model successfully fitted the experimental data at high pressure with lower particle size. Industrial relevance The sunflower seeds are a major source of good quality, high oleic acid, vegetable oil and Vitamin E. Hence, largely used in beauty care products, production of vegetable oil based fuel oil and lubricants. There are also many other applications of rich–oleic acid oils such as food, cosmetics, pharmaceuticals, biodiesel production, and also as a feedstock for the oleo-chemical industry. In recent years, due to rigid environmental regulation and health concern, high pressure extraction of the vegetable oil with supercritical carbon dioxide has received considerable attention as a promising alternative to conventional solvent extraction and mechanical process. Hence, the present work is focused on extraction of seed oil by supercritical CO 2 . Moreover, for industrial application of supercritical fluid extraction, it is very important to study the kinetic model that gives large scale extraction curves with minimum error by using model fitting parameters with small scale experiment. There are large numbers of models based on different approach suggested by various researchers to fit experimental data of supercritical fluid extraction. Amongst them, the broken and intact cell model proposed by Sovova's (1994) is widely used to fit the experimental data of vegetable oil extraction. The broken and intact cell model has three fitting parameters and many authors have applied different optimization techniques to optimize these fitting parameters. Therefore, in the present work the optimized kinetic parameters of Sovova's model for sunflower oil extraction are obtained by applying the Box complex optimization method to study the influence of pressure, temperature, particle size, co-solvent and solvent flow rate of extraction yield.

Selective hydrogenation of fatty acids and methyl esters of fatty acids to obtain fatty alcohols–a review

AbstractIn this paper, a review is presented of the evolution of different catalytic systems and operating conditions used in the selective hydrogenation of acids and esters of fatty acids to obtain fatty alcohols, which have broad industrial applications in the oleochemical industry. In addition, the current status of the different technologies used industrially (Lurgi, Davy and Henkel) for obtaining fatty alcohols, as well as major global sources of raw materials for the oleochemical industry are put forward. Finally, the reaction mechanisms of the selective hydrogenation process of oleic acid and methyl oleate to obtain the corresponding unsaturated alcohol as well as the new catalysts proposed by researchers are described. © 2016 Society of Chemical Industry

Tuning Lipase Reaction for Production of Fatty Acids from Oil.

Fats or oils are split partially or completely to obtain fatty acids that find wide applications in oleo-chemical industries. Lipase-mediated complete splitting (hydrolysis) of oils is a green process having great potential to replace the traditional methods of oil splitting. However, cost of lipases, mechanistic kinetic equilibrium and associated operational limitations prove to be deterrents for scale up of the enzymatic oil splitting process. In the present study, we demonstrate the use of immobilised 1,3-regioselective lipase (HyLIP) for complete hydrolysis of oil in monophasic reaction medium. Incorporation of a polar organic solvent (tert-butanol, 1:5, v/v) homogenises the oil-water mixture and contributes positively towards complete hydrolysis. The monophasic oil hydrolysis reaction with optimised water concentration (0.05%, v/v) gave Free Fatty Acid (FFA) yield of 88% (HyLIP and Novozym-435) and 66% (TLIM and RMIM). Smart reaction engineering and modification of the reaction intermediates to favourable substrate lead to ∼99% degree of hydrolysis of triglycerides with ∼90% FFA yield using 1,3-regioselective lipase. The present work becomes basic platform for developing technologies for synthesis of fatty acids, monoglycerides, diglycerides and glycerol.

Room Temperature Ionic Liquids as Green Solvent Alternatives in the Metathesis of Oleochemical Feedstocks

One of the most important areas of green chemistry is the application of environmentally friendly solvents in catalysis and synthesis. Conventional organic solvents pose a threat to the environment due to the volatility, highly flammability, toxicity and carcinogenic properties they exhibit. The recently emerged room temperature ionic liquids (RTILs) are promising green solvent alternatives to the volatile organic solvents due to their ease of reuse, non-volatility, thermal stability and ability to dissolve a variety of organic and organometallic compounds. This review explores the use of RTILs as green solvent media in olefin metathesis for applications in the oleochemical industry.

Apocynaceae Seed Lipids: Characterization and Occurrence of Isoricinoleic Acid and Triacylglycerol Estolides

AbstractIsoricinoleic acid (9‐hydroxy‐cis‐12‐octadecenoic acid; IR) is a potential renewable feedstock for the oleochemical industry, a precursor for the synthesis of antimicrobial compounds and a component of the seed oil of certain plants in the Apocynaceae. For a more detailed survey of this plant family, seeds of 18 species representing different subfamilies were obtained and acyl composition and oil content was determined. IR was observed only in species of the tribes Wrightieae and Nerieae in the Apocynoideae subfamily and is reported for the first time in the seed oil of the desert rose Adenium obesum in which it is present at a level of around 26 %. In contrast to previous reports, IR was not found in oil from Holarrhena species, H. antidysenterica and H. pubescens, nor in oil from Annona squamosa. To examine the oil structure, samples were analyzed using MALDI‐TOF mass spectrometry. This technique proved to be a simple method to demonstrate the occurrence of the estolide 9‐acetoxy‐cis‐12‐octadecenoic acid in oil from Nerium oleander and gave further insight into the distribution of estolides within the oil, revealing the presence of tetra‐ and penta‐acyl‐TAG molecules, and molecules containing IR esterified to all three position of glycerol. For other species in which IR was observed, the HFA was found to be a component of seed TAG, but no secondary acylation of the hydroxyl groups was observed.

Candida rugosa Lipase Immobilized onto Acid-Functionalized Multi-walled Carbon Nanotubes for Sustainable Production of Methyl Oleate.

The chemical production of methyl oleate using chemically synthesized fatty acid alcohols and other toxic chemicals may lead to significant environmental hazards to mankind. Being a highly valuable fatty acid replacement raw material in oleochemical industry, the mass production of methyl oleate via environmentally favorable processes is of concern. In this context, an alternative technique utilizing Candida rugosa lipase (CRL) physically adsorbed on multi-walled carbon nanotubes (MWCNTs) has been suggested. In this study, the acid-functionalized MWCNTs prepared using a mixture of HNO3 and H2SO4 (1:3 v/v) was used as support for immobilizing CRL onto MWCNTs (CRL-MWCNTs) as biocatalysts. Enzymatic esterification was performed and the efficiency of CRL-MWCNTs was evaluated against the free CRL under varying conditions, viz. temperature, molar ratio of acid/alcohol, solvent log P, and enzyme loading. The CRL-MWCNTs resulted in 30-110 % improvement in the production of methyl oleate over the free CRL. The CRL-MWCNTs attained its highest yield (84.17 %) at 50 °C, molar ratio of acid/alcohol of 1:3, 3 mg/mL of enzyme loading, and iso-octane (log P 4.5) as solvent. Consequently, physical adsorption of CRL onto acid-functionalized MWCNTs has improved the activity and stability of CRL and hence provides an environmentally friendly means for the production of methyl oleate.

Application of Taguchi Optimization Method in Improving the Selectivity of Dihydroxystearic Acid

Dihydroxystearic acid (DHSA) is perceived to be of significant value to various types of industries, especially the oleochemical industry. It is produced by reacting palm-based crude oleic acid (OA) with formic acid and hydrogen peroxide through thein situepoxidation-dihydroxylation, a multistep reaction process. Optimization of the reaction’s operating conditions with respect to the selectivity of DHSA was conducted via the Taguchi method of optimization. The selectivity of DHSA was determined based on gas chromatography (GC) analysis. The signal-to-noise (S/N) ratio analysis procedure in Taguchi method revealed that the optimum operating conditions for the production of crude DHSA with respect to its selectivity were found to be: catalyst (sulphuric acid) loading at 0.5 gm, formic acid-to-oleic acid unsaturation mole ratio of 1:1, hydrogen peroxide-to-oleic acid unsaturation mole ratio of 0.75:1 and reaction temperature: 85°C. ANOVA tested at 90% confidence level revealed that reaction temperature and catalyst loading highly affect the selectivity of DHSA. The selectivity of DHSA was improved to 97.2% by applying the optimum operating conditions as obtained by Taguchi method.

A new energy source from the anaerobic co‐digestion (acd) treatment of oleo chemical effluent with glycerin pitch

AbstractThe high‐strength wastes generated from the oleo chemical industry, namely oleo chemical effluent (OCE) and glycerin pitch (GP), have raised a serious disposal problem. An aerobic digestion after chemical pre‐treatment and costly incineration/landfill disposal is the only currently available treatment method for OCE and GP, respectively. Due to the high alkalinity and organic content of GP, there is a potential to anaerobically co‐digest OCE with GP, which can be used to neutralise OCE's acidity while providing the required organic strength for biogas production. The objective of this study is to evaluate the feasibility of anaerobic co‐digestion (ACD) of OCE and GP based on their maximum available energy potential. This study was evaluated based on 85% chemical oxygen demand removal efficiency. The study disclosed that GP is able to generate maximum potential methane production of 6716 m3/d and energy of 0.097 MW/h, which are two times higher than that in OCE. The cost benefit analysis also revealed that with the establishment of ACD, a cost saving of USD 1 693 716/year from disposal and an earning profit of USD 54 544/year from energy generation can be achieved. Therefore, it could be concluded that ACD of OCE and GP is feasible to produce a reduced strength of final effluent with enhanced methane production. © 2015 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Optimization of Bauhinia monandra seed oil extraction via artificial neural network and response surface methodology: A potential biofuel candidate

The influence of sample weight, time, and solvent type and their reciprocal interactions on Bauhinia monandra seed oil (BMSO) yield using artificial neural network (ANN) and response surface methodology (RSM) was investigated. Also, the BMSO obtained was characterized to determine its aptness for oleochemical industry. Numerically predicted optimum values for the extraction process using RSM model were found to be the same for the developed ANN model. The optimum values were sample weight of 60g, time of 100min and petroleum ether with a corresponding BMSO yield of 14.8wt%. Performance evaluation of the models by multiple coefficient of correlation (R), coefficient of determination (R2) and absolute average deviation (AAD) showed that the ANN model was marginally better (R=0.9995, R2=0.9991, AAD=0.27%) than the RSM model (R=0.9993, R2=0.9986, AAD=0.49%) in predicting BMSO yield. Physicochemical properties of the BMSO such as acid value (7.56mg KOH/g), indicated that it is non-edible and the fatty acids profile showed that the oil was highly unsaturated (87.9%), which makes it a potential candidate for biodiesel production.

Immobilized lipase from Hypocrea pseudokoningii on hydrophobic and ionic supports: Determination of thermal and organic solvent stabilities for applications in the oleochemical industry

Hypocrea pseudokoningii purified lipase was immobilized on hydrophobic supports (phenyl-sepharose, butyl-sepharose, octyl-sepharose, Hexyl Toyopearl, Lewatit, Purolite, Decaoctyl sepabeads) and ionic supports (Duolite, DEAE-agarose, PEI-agarose, MANAE-agarose, and Q-sepharose). The immobilization processes resulted in derivatives with excellent thermal stabilities, increasing the half-life up to 500-fold. The derivatives had excellent stability to organic solvents compared to the crude lipase. In the presence of 50% ethanol, hexyl and Decaoctyl derivatives increased by about 6- and 3.5-fold their stability to organic solvents, respectively. When tested for methanol, phenyl-sepharose derivative also increased their stability to organic solvents in approximately 2-fold. Octyl-sepharose derivative was fully stable for 48h in the presence of propanol, which showed a half-life of about 7.5h. The greater activation of the derivatives occurred using 50% cyclohexane, in which the hexyl derivative obtained an increase in the activity of 9-fold and phenyl and octyl derivatives had their activity increased by 6-fold. The lipase showed activity on different oils. Therefore, the adsorption of lipases in low ionic strength and highly hydrophobic supports is shown to be a simple and rapid tool for the immobilization of H. pseudokoningii lipase. These derivatives strongly increase the chances of this biocatalyst for industrial application.

Modeling, identification, and control for the production of glycerol by the hydrolysis of tallow

AbstractMost of the oleochemical industries use glycerol as raw material for its adverse commercial applications in various fields. In spite of many available methods to produce glycerol from tallow, hydrolysis is one of the most feasible and widely used methods that draw the attention of doing more research for ensuring the safe operation, production level improvement, and accuracy of the synthesis process. The synthesis using biochemical methods in immobilized packed column lacks fastness compared to that of chemical means, which is enriched with more research problems. To attain inherent safety, improved process control methods need to be designed, which requires the knowledge of transient dynamics and sensitivity analysis of the process. This paper gives a state-of-the-art review of experimental analysis, mathematical modeling, parametric identification, and integrated control systems using sensors, actuators, and respective multiloop controllers for the production of glycerol and fatty acids from tallow fat through chemical/biochemical hydrolysis.

Engineering a Streptomyces coelicolor biosynthesis pathway into Escherichia coli for high yield triglyceride production.

BackgroundMicrobial lipid production represents a potential alternative feedstock for the biofuel and oleochemical industries. Since Escherichia coli exhibits many genetic, technical, and biotechnological advantages over native oleaginous bacteria, we aimed to construct a metabolically engineered E. coli strain capable of accumulating high levels of triacylglycerol (TAG) and evaluate its neutral lipid productivity during high cell density fed-batch fermentations.ResultsThe Streptomyces coelicolor TAG biosynthesis pathway, defined by the acyl-CoA:diacylglycerol acyltransferase (DGAT) Sco0958 and the phosphatidic acid phosphatase (PAP) Lppβ, was successfully reconstructed in an E. coli diacylglycerol kinase (dgkA) mutant strain. TAG production in this genetic background was optimized by increasing the levels of the TAG precursors, diacylglycerol and long-chain acyl-CoAs. For this we carried out a series of stepwise optimizations of the chassis by 1) fine-tuning the expression of the heterologous SCO0958 and lppβ genes, 2) overexpression of the S. coelicolor acetyl-CoA carboxylase complex, and 3) mutation of fadE, the gene encoding for the acyl-CoA dehydrogenase that catalyzes the first step of the β-oxidation cycle in E. coli. The best producing strain, MPS13/pET28-0958-ACC/pBAD-LPPβ rendered a cellular content of 4.85% cell dry weight (CDW) TAG in batch cultivation. Process optimization of fed-batch fermentation in a 1-L stirred-tank bioreactor resulted in cultures with an OD600nm of 80 and a product titer of 722.1 mg TAG L-1 at the end of the process.ConclusionsThis study represents the highest reported fed-batch productivity of TAG reached by a model non-oleaginous bacterium. The organism used as a platform was an E. coli BL21 derivative strain containing a deletion in the dgkA gene and containing the TAG biosynthesis genes from S. coelicolor. The genetic studies carried out with this strain indicate that diacylglycerol (DAG) availability appears to be one of the main limiting factors to achieve higher yields of the storage compound. Therefore, in order to develop a competitive process for neutral lipid production in E. coli, it is still necessary to better understand the native regulation of the carbon flow metabolism of this organism, and in particular, to improve the levels of DAG biosynthesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0172-0) contains supplementary material, which is available to authorized users.

Carbon accumulation in Rhodotorula glutinis induced by nitrogen limitation.

BackgroundOleaginous microorganisms, such as bacterium, yeast and algal species, can represent an alternative oil source for biodiesel production. The composition of their accumulated lipid is similar to the lipid of an oleaginous plant with a predominance of unsaturated fatty acid. Moreover this alternative to conventional biodiesel production does not create competition for land use between food and oleo-chemical industry supplies. Despite this promising potential, development of microbial production processes are at an early stage. Nutritional limited conditions, such as nitrogen limitation, with an excess of carbon substrate is commonly used to induce lipid accumulation metabolism. Nitrogen limitation implies modification of the carbon-to-nitrogen ratio in culture medium, which impacts on carbon flow distribution in the metabolic network.ResultsThe goal of the present study is to improve our knowledge of carbon flow distribution in oleaginous yeast metabolism by focusing carbon distribution between carbohydrate and lipid pools in order to optimize microbial lipid production. The dynamic effects of limiting nitrogen consumption flux according to carbon flow were studied to trigger lipid accumulation in the oleaginous yeast Rhodotorula glutinis. With a decrease of the specific nitrogen consumption rate from 0.052 Nmol.CmolX−1.h−1 to 0.003 Nmol.CmolX−1.h−1, a short and transitory intracellular carbohydrate accumulation occurred before the lipid accumulation phase. This phenomenon was studied in fed-batch culture under optimal operating conditions, with a mineral medium and using glucose as carbon source. Two different strategies of decreasing nitrogen flow on carbohydrate accumulation were investigated: an instantaneous decrease and a progressive decrease of nitrogen flow.ConclusionsLipid production performance in these fed-batch culture strategies with R. glutinis were higher than those reported in the previous literature; the catalytic specific lipid production rate was 0.07 Cmollip.CmolX*−1.h−1. Experimental results suggested that carbohydrate accumulation was an intrinsic phenomenon connected to the limitation of growth by nitrogen when the nitrogen-to-carbon ratio in the feed flow was lower than 0.045 Nmol.Cmol−1. Carbohydrate accumulation corresponded to a 440% increase of carbohydrate content. These results suggest that microbial lipid production can be optimized by culture strategy and that carbohydrate accumulation must be taken account for process design.