A new method for preparing raw material for biodiesel production

Culturing rhodotorula glutinis in fermentation-friendly deep eutectic solvent extraction liquor of lignin for producing microbial lipid

Currently, deep eutectic solvents (DES) have attracted increasing attention due to their excellent performance in delignification. However, few studies focused on the treatment of DES waste liquid after extraction of lignin. In this work, the fermentation-friendly DES comprised of glycerol, choline chloride (ChCl) and acetic acid (AA) was applied for delignification of lignocellulose. Subsequently, the extraction effects of different DES were investigated, and the DES extraction liquor was used for lipid production. Results shows ChCl made little difference to lipid synthesis, while excessive AA exerted inhibitory effect on the growth of cells. Following pretreatment, the delignification exceeded 63%. When the DES liquid obtained after lignin extraction was used to produce lipid, the delay period was obvious, while the lipid yield and content were unaffected. Not only is the DES prepared in this study effective in delignification of lignocellulose, it is also applicable as raw material to produce lipid.

A Review on Machine Learning Application in Biodiesel Production Studies

The consumption of fossil fuels has exponentially increased in recent decades, despite significant air pollution, environmental deterioration challenges, health problems, and limited resources. Biofuel can be used instead of fossil fuel due to environmental benefits and availability to produce various energy sorts like electricity, power, and heating or to sustain transportation fuels. Biodiesel production is an intricate process that requires identifying unknown nonlinear relationships between the system input and output data; therefore, accurate and swift modeling instruments like machine learning (ML) or artificial intelligence (AI) are necessary to design, handle, control, optimize, and monitor the system. Among the biodiesel production modeling methods, machine learning provides better predictions with the highest accuracy, inspired by the brain’s autolearning and self-improving capability to solve the study’s complicated questions; therefore, it is beneficial for modeling (trans) esterification processes, physicochemical properties, and monitoring biodiesel systems in real-time. Machine learning applications in the production phase include quality optimization and estimation, process conditions, and quantity. Emissions composition and temperature estimation and motor performance analysis investigate in the consumption phase. Fatty methyl acid ester stands as the output parameter, and the input parameters include oil and catalyst type, methanol-to-oil ratio, catalyst concentration, reaction time, domain, and frequency. This paper will present a review and discuss various ML technology advantages, disadvantages, and applications in biodiesel production, mainly focused on recently published articles from 2010 to 2021, to make decisions and optimize, model, control, monitor, and forecast biodiesel production.

Modeling and optimization of microbial lipid fermentation from cellulosic ethanol wastewater by Rhodotorula glutinis based on the support vector machine

To establish the models of microbial lipid production from cellulosic ethanol wastewater by R. glutinis, the biomass, lipid yield, and COD removal rate were investigated under different conditions. Subsequently, the genetic algorithm based on SVM was adopted to optimize parameters for obtaining the maximum biomass. The results demonstrated that the initial COD and glucose content had a significant effect on lipids synthesis. Most of the organic matter in the wastewater was consumed with the production of lipid. Compared with BP-ANN, SVM had better fitting and generalization ability for small amount of experimental data. By genetic algorithm optimization based on SVM, the maximum biomass and lipid yield could reach 11.87 g/L and 2.18 g/L, respectively. The results suggest that the SVM model could be used as an effective tool to optimize fermentation conditions.

Simultaneous lipid production for biodiesel feedstock and decontamination of sago processing wastewater using Candida tropicalis ASY2

BACKGROUND

Without sufficient alternatives to crude oil, as demand continues to rise, the global economy will undergo a drastic decline as oil prices explode. Dependence on crude oil and growing environmental impairment must eventually be overcome by creating a sustainable and profitable alternative based on renewable and accessible feedstock. One of the promising solutions for the current and near-future is the substitution of fossil fuels with sustainable liquid feedstock for biofuel production. Among the different renewable liquid feedstock's studied, wastewater is the least explored one for biodiesel production. Sago wastewater is the byproduct of the cassava processing industry and has starch content ranging from 4 to 7%. The present investigation was aimed to produce microbial lipids from oleaginous yeast, Candida tropicalis ASY2 for use as biodiesel feedstock and simultaneously decontaminate the sago processing wastewater for reuse. Initial screening of oleaginous yeast to find an efficient amylolytic with maximum lipid productivity resulted in a potent oleaginous yeast strain, C. tropicalis ASY2, that utilizes SWW as a substrate. Shake flask experiments are conducted over a fermentation time of 240 h to determine a suitable fatty acid composition using GC-FID for biodiesel production with simultaneous removal of SWW pollutants using ASY2.

RESULTS

The maximum biomass of 0.021 g L^-1 h^-1 and lipid productivity of 0.010 g L^-1 h^-1 was recorded in SWW with lipid content of 49%. The yeast strain degraded cyanide in SWW (79%) and also removed chemical oxygen demand (COD), biological oxygen demand (BOD), nitrate (NO₃), ammoniacal (NH₄), and phosphate (PO₄) ions (84%, 92%, 100%, 98%, and 85%, respectively). GC-FID analysis of fatty acid methyl esters (FAME) revealed high oleic acid content (41.33%), which is one of the primary fatty acids for biodiesel production.

CONCLUSIONS

It is evident that the present study provides an innovative and ecologically sustainable technology that generates valuable fuel, biodiesel using SWW as a substrate and decontaminates for reuse.

Microbial lipid production and organic matters removal from cellulosic ethanol wastewater through coupling oleaginous yeasts and activated sludge biological method

In this paper, a novel strategy for lipid production through coupling oleaginous yeasts and activated sludge biological methods by cultivation of Rhodotorula glutinis in cellulosic ethanol wastewater was studied. Under optimal conditions in wastewater medium (dilution ratio of 1:2 and glucose supplement of 40 g/L), the maximum biomass and lipid content as well as the lipid yield reached 11.31 g/L, 18.35% and 2.08 g/L, with the associated removal rates of COD, TOC, NH₄⁺-N, TN and TP reaching 83.15%, 81.81%, 85.49%, 70.52% and 67.46%, respectively. Cellulosic ethanol wastewater treated by the anaerobic-aerobic biological process resulted in removal of COD, NH₄⁺-N, TP and TN reaching 67.55%, 94.17%, 90.16% and 48.89%, respectively. The reused water was used to dilute medium of R. glutinis for microbial lipid production reaching 2.38 g/L and caused positive effects on the accumulation of biomass and lipid.

Effect of sludge features and extraction-esterification technology on the synthesis of biodiesel from secondary wastewater treatment sludges

Secondary sludge from municipal wastewater treatment plant is proposed as a promising alternative lipid feedstock for biodiesel production. A deep study combining different type of raw materials (sludge coming from the oxic, anoxic and anaerobic steps of the biological treatment) with different technologies (liquid-liquid and solid-liquid extractions followed by acid catalysed transesterification and in situ extraction-transesterification procedure) allows a complete comparison of available technologies. Different parameters - contact time, catalyst concentration, pretreatments - were considered, obtaining more than 17% FAMEs yield after 50min of sonication with the in situ procedure and 5% of H₂SO₄. This result corresponds to an increment of more than 65% respect to the best results reported at typical conditions. Experimental data were used to propose a mathematical model for this process, demonstrating that the mass transfer of lipids from the sludge to the liquid is the limiting step.

Recent advances and industrial viewpoint for biological treatment of wastewaters by oleaginous microorganisms

Recently, technology of using oleaginous microorganisms for biological treatment of wastewaters has become one hot topic in biochemical and environmental engineering for its advantages such as easy for operation in basic bioreactor, having potential to produce valuable bio-products, efficient wastewaters treatment in short period, etc. To promote its industrialization, this article provides some comprehensive analysis of this technology such as its advances, issues, and outlook especially from industrial viewpoint. In detail, the types of wastewaters can be treated and the kinds of oleaginous microorganisms used for biological treatment are introduced, the potential of industrial application and issues (relatively low COD removal, low lipid yield, cost of operation, and lack of scale up application) of this technology are presented, and some critical outlook mainly on co-culture method, combination with other treatments, process controlling and adjusting are discussed systematically. By this article, some important information to develop this technology can be obtained.

The effect of amino acids on lipid production and nutrient removal by Rhodotorula glutinis cultivation in starch wastewater

In this paper, the components of amino acids in mixed starch wastewater (corn steep water/corn gluten water=1/3, v/v) were analyzed by GC-MS. Effects of amino acids on lipid production by Rhodotorula glutinis and COD removal were studied. The results showed that mixed starch wastewater contained 9 kinds of amino acids and these amino acids significantly improved the biomass (13.63g/L), lipid yield (2.48g/L) and COD removal compared to the basic medium (6.23g/L and 1.56g/L). In a 5L fermentor containing mixed starch wastewater as substrate to culture R. glutinis, the maximum biomass, lipid content and lipid yield reached 26.38g/L, 28.90% and 7.62g/L, with the associated removal rates of COD, TN and TP reaching 77.41%, 69.12% and 73.85%, respectively. The results revealed a promising approach for lipid production with using amino acids present in starch wastewater as an alternative nitrogen source.

Co-generation of microbial lipid and bio-butanol from corn cob bagasse in an environmentally friendly biorefinery process

Biorefinery process of corn cob bagasse was investigated by integrating microbial lipid and ABE fermentation. The effects of NaOH concentration on the fermentations performance were evaluated. The black liquor after pretreatment was used as substrate for microbial lipid fermentation, while the enzymatic hydrolysates of the bagasse were used for ABE fermentation. The results demonstrated that under the optimized condition, the cellulose and hemicellulose in raw material could be effectively utilized. Approximate 87.7% of the polysaccharides were converted into valuable biobased products (∼175.7g/kg of ABE along with ∼36.6g/kg of lipid). At the same time, almost half of the initial COD (∼48.9%) in the black liquor could be degraded. The environmentally friendly biorefinery process showed promising in maximizing the utilization of biomass for future biofuels production.

Technological trends and market perspectives for production of microbial oils rich in omega-3

In recent years, foods that contain omega-3 lipids have emerged as important promoters of human health. These lipids are essential for the functional development of the brain and retina, and reduction of the risk of cardiovascular and Alzheimer's diseases. The global market for omega-3 production, particularly docosahexaenoic acid (DHA), saw a large expansion in the last decade due to the increasing use of this lipid as an important component of infant food formulae and supplements. The production of omega-3 lipids from fish and vegetable oil sources has some drawbacks, such as complex purification procedures, unwanted contamination by marine pollutants, reduction or even extinction of several species of fish, and aspects related to sustainability. A promising alternative system for the production of omega-3 lipids is from microbial metabolism of yeast, fungi, or microalgae. The aim of this review is to discuss the various omega-3 sources in the context of the global demand and market potential for these bioactive compounds. To summarize, it is clear that fish and vegetable oil sources will not be sufficient to meet the future needs of the world population. The biotechnological production of single-cell oil comes as a sustainable alternative capable of supplementing the global demand for omega-3, causing less environmental impact.

Biorefinery of corn cob for microbial lipid and bio-ethanol production: An environmental friendly process

Microbial lipid and bio-ethanol were co-generated by an integrated process using corn cob bagasse as raw material. After pretreatment, the acid hydrolysate was used as substrate for microbial lipid fermentation, while the solid residue was further enzymatic hydrolysis for bio-ethanol production. The effect of acid loading and pretreatment time on microbial lipid and ethanol production were evaluated. Under the optimized condition for ethanol production, ∼131.3g of ethanol and ∼11.5g of microbial lipid were co-generated from 1kg raw material. On this condition, ∼71.6% of the overall fermentable sugars in corn cob bagasse could be converted into valuable products. At the same time, at least 33% of the initial COD in the acid hydrolysate was depredated.

Production of Palmitoleic and Linoleic Acid in Oleaginous and Nonoleaginous Yeast Biomass

We investigated the possibility of utilizing both oleaginous yeast species accumulating large amounts of lipids (Yarrowia lipolytica, Rhodotorula glutinis, Trichosporon cutaneum, and Candida sp.) and traditional biotechnological nonoleaginous ones (Kluyveromyces polysporus, Torulaspora delbrueckii, and Saccharomyces cerevisiae) as potential producers of dietetically important major fatty acids. The main objective was to examine the cultivation conditions that would induce a high ratio of dietary fatty acids and biomass. Though genus-dependent, the type of nitrogen source had a higher influence on biomass yield than the C/N ratio. The nitrogen source leading to the highest lipid accumulation was potassium nitrate, followed by ammonium sulfate, which is an ideal nitrogen source supporting, in both oleaginous and nonoleaginous species, sufficient biomass growth with concomitantly increased lipid accumulation. All yeast strains displayed high (70–90%) content of unsaturated fatty acids in total cell lipids. The content of dietary fatty acids of interest, namely, palmitoleic acid and linoleic acid, reached in Kluyveromyces and Trichosporon strains over 50% of total fatty acids and the highest yield, over 280 mg per g of dry cell weight of these fatty acids, was observed in Trichosporon with ammonium sulfate as nitrogen source at C/N ratio 70.

Modeling of process parameters for enhanced production of coenzyme Q10 from Rhodotorula glutinis

Coenzyme Q10 (CoQ10) plays an indispensable role in ATP generation through oxidative phosphorylation and helps in scavenging superoxides generated during electron transfer reactions. It finds extensive applications specifically related to oxidative damage and metabolic dysfunctions. This article reports the use of a statistical approach to optimize the concentration of key variables for the enhanced production of CoQ10 by Rhodotorula glutinis in a lab-scale fermenter. The culture conditions that promote optimum growth and CoQ10 production were optimized and the interaction of significant variables para-hydroxybenzoic acid (PHB, 819.34 mg/L) and soybean oil (7.78% [v/v]) was studied using response surface methodology (RSM). CoQ10 production increased considerably from 10 mg/L (in control) to 39.2 mg/L in batch mode with RSM-optimized precursor concentration. In the fed-batch mode, PHB and soybean oil feeding strategy enhanced CoQ10 production to 78.2 mg/L.

Sweetpotato vines hydrolysate promotes single cell oils production of Trichosporon fermentans in high-density molasses fermentation

This study investigated the co-fermentation of molasses and sweetpotato vine hydrolysate (SVH) by Trichosporon fermentans. T. fermentans showed low lipid accumulation on pure molasses; however, its lipid content increased by 35% when 10% SVH was added. The strong influence of SVH on lipid production was further demonstrated by the result of sensitivity analysis on effects of factors based on an artificial neural network model because the relative importance value of SVH dosage for lipid production was only lower than that of fermentation time. Scanning electron microscope observation and flow cytometry of yeast cells grown in culture with and without SVH showed that less deformation cells were involved in the culture with SVH. The activity of malic enzyme, which plays a key role in fatty acid synthesis, increased from 2.4U/mg to 3.7U/mg after SVH added. All results indicated SVH is a good supplement for lipid fermentation on molasses.

Synergistic effects of oleaginous yeast Rhodotorula glutinis and microalga Chlorella vulgaris for enhancement of biomass and lipid yields

The optimal mixed culture model of oleaginous yeast Rhodotorula glutinis and microalga Chlorella vulgaris was confirmed to enhance lipid production. A double system bubble column photo-bioreactor was designed and used for demonstrating the relationship of yeast and alga in mixed culture. The results showed that using the log-phase cultures of yeast and alga as seeds for mixed culture, the improvements of biomass and lipid yields reached 17.3% and 70.9%, respectively, compared with those of monocultures. Growth curves of two species were confirmed in the double system bubble column photo-bioreactor, and the second growth of yeast was observed during 36-48 h of mixed culture. Synergistic effects of two species for cell growth and lipid accumulation were demonstrated on O2/CO2 balance, substance exchange, dissolved oxygen and pH adjustment in mixed culture. This study provided a theoretical basis and culture model for producing lipids by mixed culture in place of monoculture.

Lipid and carotenoid production by Rhodotorula glutinis under irradiation/high-temperature and dark/low-temperature cultivation

The capacity of lipid and carotenoid production by Rhodotorula glutinis was investigated under different irradiation conditions, temperatures and C/N ratios. The results showed that dark/low-temperature could enhance lipid content, while irradiation/high-temperature increased the yields of biomass and carotenoid. The optimum C/N ratio for production was between 80 and 100. A two-stage cultivation strategy was used for lipid and carotenoid production in a 5L fermenter. In the first stage, the maximum biomass reached 28.1g/L under irradiation/high-temperature. Then, the cultivation condition was changed to dark/low-temperature, and C/N ratio was adjusted to 90. After the second stage, the biomass, lipid content and carotenoid reached 86.2g/L, 26.7% and 4.2mg/L, respectively. More significantly, the yields of biomass and lipid were 43.1% and 11.5%, respectively. Lipids contained 79.7% 18C and 16.8% 16C fatty acids by GC analysis. HPLC quantified the main carotenoids were β-carotene (68.4%), torularhodin (21.5%) and torulene (10.1%).

Potential utilization of waste sweetpotato vines hydrolysate as a new source for single cell oils production by Trichosporon fermentans

The enzymatic hydrolysate of sweetpotato vines (SVH) characterized as an effective nutrients supplier with low nitrogen availability was firstly used as a substrate by Trichosporon fermentans for single cell oils (SCOs) production. Batch-fermentation experiments on various SVH based media suggested that co-fermentation of SVH and some high-sugar content substrates would be much more efficient and less-cost for SCOs production. A lipid yield of 9.6 g l(-1) with a lipid content of 35.6% was achieved on the SVH without any addition, while 27.6 and 17.7 g l(-1) lipid were respectively obtained on the fructose supplemented SVH media and the SVH mixed with acid treated wheat straw hydrolysate (WSH). The positive effect of SVH on the lipid production of T. fermentans was further demonstrated with a kinetic investigation revealing that SVH had a remarkable promoting effect on the biomass formation and the substrate uptake.

Sweetpotato vines hydrolysate induces glycerol to be an effective substrate for lipid production of Trichosporon fermentans

By co-fermented with sweetpotato vines hydrolysate (SVH), glycerol can be used as an effective substrate for Trichosporon fermentans to produce lipids. Submerged fermentation results showed that T. fermentans exhibited a maximum lipid yield of 7.45 g l(-1) with a biomass of 17.95 g l(-1) on 10% SVH added glycerol mineral medium (Glycerol MM-10% SVH), which was 4.34-fold higher than that on glycerol mineral medium. Lipids produced on glycerol based media exhibited a significantly different fatty acid composition profile from that produced on sugar based media accompanying by a sharp increase in polyunsaturated fatty acids content. Biochemical behaviors characterization further demonstrated that SVH has a remarkable promoting effect on the biomass formation and glycerol uptake. The extremely high lipid yield on Glycerol MM-10% SVH was mainly attributed to the enhancement of SVH on biomass, although SVH is an excellent nutrient supplier for lipid accumulation due to its low nitrogen availability.

Lipid production by Rhodosporidium toruloides Y2 in bioethanol wastewater and evaluation of biomass energetic yield

The oleaginous yeast Rhodosporidium toruloides Y2 was employed to remove waste nutrients from bioethanol wastewater while simultaneously producing biomass enriched in microbial lipids. Under optimal conditions, the COD degradation ratio, biomass and lipid content reached 72.3%, 3.8 g/l and 34.9%, respectively. For accelerating biomass and lipid accumulation, different feeding strategies of substrate were conducted. The biomass and lipid production increased by 39.5% and 53.8%, respectively, when glucose at 1.2g/(ld) was added during the last three days of the cultivation. An equation was established to estimate biomass energetic yield. Under optimal conditions, the biomass energetic yield was 50.9% and an increase of 26.0% was obtained by feeding glucose at 1.2g/(ld) during the last three days. The fatty acid composition of the lipids was similar to that from plant oils and other microbial lipids, and could thus be used as raw material for feed additives and biodiesel production.

Biodiesel from lignocellulosic biomass--prospects and challenges

Biodiesel can be a potential alternative to petroleum diesel, but its high production cost has impeded its commercialization in most parts of the world. One of the main drivers for the generation and use of biodiesel is energy security, because this fuel can be produced from locally available resources, thereby reducing the dependence on imported oil. Many countries are now trying to produce biodiesel from plant or vegetable oils. However, the consumption of large amounts of vegetable oils for biodiesel production could result in a shortage in edible oils and cause food prices to soar. Alternatively, the use of animal fat, used frying oils, and waste oils from restaurants as feedstock could be a good strategy to reduce the cost. However, these limited resources might not meet the increasing demand for clean, renewable fuels. Therefore, recent research has been focused the use of residual materials as renewable feedstock in order to lower the cost of producing biodiesel. Microbial oils or single cell oils (SCOs), produced by oleaginous microorganisms have been studied as promising alternatives to vegetable or seed oils. Various types of agro-industrial residues have been suggested as prospective nutritional sources for microbial cultures. Since the most abundant residue from agricultural crops is lignocellulosic biomass (LCB), this byproduct has been given top-priority consideration as a source of biomass for producing biodiesel. But the biological transformation of lignocellulosic materials is complicated due to their crystalline structure. So, pretreatment is required before they can be converted into fermentable sugar. This article compares and scrutinizes the extent to which various microbes can accumulate high levels of lipids as functions of the starting materials and the fermentation conditions. Also, the obstacles associated with the use of LCB are described, along with a potentially viable approach for overcoming the obstacles that currently preclude the commercial production of biodiesel from agricultural biomass.

Oil production on wastewaters after butanol fermentation by oleaginous yeast Trichosporon coremiiforme

From the distillation process after butanol fermentation, wastewaters mainly consisted of organic acids and residual sugars and with high COD (usually >20,000 mg/L) are generated. Without any pretreatment and adding other nutrients (nitrogen sources and trace elements), these wastewaters were used as substrate for microbial oil production by oleaginous yeast Trichosporon coremiiforme. After 5 days' lipid fermentation, all the sugars and organic acids measured were totally utilized by T. coremiiforme and a 68% of COD degradation could be obtained. The highest biomass and lipid content of T. coremiiforme on the wastewaters were 5.8 g/L and 19.1%, respectively. This work shows that T. coremiiforme is a promising strain for microbial oil production on the wastewaters after butanol fermentation.

Maximizing biodiesel production from Yarrowia lipolytica Po1g biomass using subcritical water pretreatment

The yeast Yarrowia lipolytica Po1g is one of the oleaginous microorganisms with a potential for biodiesel production. Sub-critical water (SCW) treatment has been known as an effective method for increasing the amount of extractable lipids in microorganisms. In this work, the amount of neutral lipids and fatty acid profiles in neutral lipids extracted from Y. lipolytica Po1g with and without SCW pre-treatment were investigated. The effects of temperature (125, 150 or 175°C), amount of water (20, 30 or 40 mL/g biomass) and time (10, 20 or 30 min) showed that maximum neutral lipid (42.69%, w/w) could be achieved at 175°C using 20 mL water for 20 min. The maximum neutral lipid from unpretreated samples was 23.21%. No difference in fatty acid profiles was observed, but long chain fatty acids were observed in higher amount in SCW pretreated samples. SCW pretreatment increased biodiesel yield twofold.

Microbial treatment of the monosodium glutamate wastewater by Lipomyces starkeyi to produce microbial lipid

The monosodium glutamate (MSG) wastewater as a medium was treated by Lipomyces starkeyi to produce microbial lipid in the study. The effect of related factors (initial glucose concentration, inoculation concentration, initial culture pH, and cultivation time) on biomass, lipid production and lipid content was discussed, respectively. According to the experiments, the optimal fermentation conditions were determined: addition of 80g/L glucose, 10% inoculation concentration, initial pH about 5.0, incubation time 96h. Under this condition, the biomass production reached up to 4.61g/L, lipid production and lipid content was 1.14g/L and 24.73%, respectively. Simultaneously, protein and COD removal rate was 78.60% and 74.96%, respectively. The main composition of fatty acid in the resultant lipid was analyzed by gas chromatography-mass spectrometry, which showed: oleic acid (C18:1) 35.85%, palmitic acid (C16:0) 19.91%, palmitoleic acid (C16:1) 17.65%, and myristic acid (C14:0) 16.03%.

Effect of organic acids on the growth and lipid accumulation of oleaginous yeast Trichosporon fermentans

BACKGROUND

Microbial lipids have drawn increasing attention in recent years as promising raw materials for biodiesel production, and the use of lignocellulosic hydrolysates as carbon sources seems to be a feasible strategy for cost-effective lipid fermentation with oleaginous microorganisms on a large scale. During the hydrolysis of lignocellulosic materials with dilute acid, however, various kinds of inhibitors, especially large amounts of organic acids, will be produced, which substantially decrease the fermentability of lignocellulosic hydrolysates. To overcome the inhibitory effects of organic acids, it is critical to understand their impact on the growth and lipid accumulation of oleaginous microorganisms.

RESULTS

In our present work, we investigated for the first time the effect of ten representative organic acids in lignocellulosic hydrolysates on the growth and lipid accumulation of oleaginous yeast Trichosporon fermentans cells. In contrast to previous reports, we found that the toxicity of the organic acids to the cells was not directly related to their hydrophobicity. It is worth noting that most organic acids tested were less toxic than aldehydes to the cells, and some could even stimulate the growth and lipid accumulation at a low concentration. Unlike aldehydes, most binary combinations of organic acids exerted no synergistic inhibitory effects on lipid production. The presence of organic acids decelerated the consumption of glucose, whereas it influenced the utilization of xylose in a different and complicated way. In addition, all the organic acids tested, except furoic acid, inhibited the malic activity of T. fermentans. Furthermore, the inhibition of organic acids on cell growth was dependent more on inoculum size, temperature and initial pH than on lipid content.

CONCLUSIONS

This work provides some meaningful information about the effect of organic acid in lignocellulosic hydrolysates on the lipid production of oleaginous yeast, which is helpful for optimization of biomass hydrolysis processes, detoxified pretreatment of hydrolysates and lipid production using lignocellulosic materials.

Application of fishmeal wastewater as a potential low-cost medium for lipid production by Lipomyces starkeyi HL

Due to the high organic compounds and high salinity of fishmeal wastewater (FW), it was firstly used as a novel medium to produce microbial lipid in this paper. Fermentation of FW without any additives adding showed that the broth was appropriate for the growth of strain Lipomyces starkeyi HL; however, production of 5.34 g l(-1) of biomass containing 20.8% of lipid was not satisfied. In order to enhance the accumulation of lipid and cell growth, FW was supplemented with various concentrations of glucose; meanwhile, the influence of initial pH was investigated. Biomass and lipid yield on FW were markedly affected by glucose concentration and initial pH. The addition of 20 g l(-1) glucose at initial pH 4.0 got the best results: 17.6 g l(-1) of biomass, 2.7 g l(-1) of lipid yield, 91.2% of protein removal and 43.4% of the chemical oxygen demand removal. The variation of fatty acid composition upon time course in the cellular lipid on FW or a mixture of glucose and FW was further studied.

Monitoring Rhodotorula glutinis CCMI 145 physiological response and oil production growing on xylose and glucose using multi-parameter flow cytometry

Flow cytometry was used to monitor the lipid content, viability and intrinsic light scatter properties of Rhodotorula glutinis CCMI 145 cells growing on batch cultures using xylose and glucose as carbon sources. The highest lipid content was observed for cells grown on glucose, at the end of the exponential phase (17.8% w/w). The proportion of cells stained with PI attaining 77% at the end of the glucose growth. Cells growing on xylose produced a maximum lipid content of 10.6% (w/w), at the stationary phase. An increase in the proportion of cells stained with PI was observed, reaching 29% at the end of xylose growth. Changes in the side and forward light scatter detected during the yeast batch cultures supported that R. glutinis cells grown on glucose experienced harsher conditions, resulting in a high level of cytoplasmic membrane damage, which did not occur when R. glutinis cells grew on xylose.

Lipids from heterotrophic microbes: advances in metabolism research

Heterotrophic oleaginous microorganisms are capable of producing over 20% of their weight in single cell oils (SCOs) composed of triacylglycerols (TAGs). These TAGs contain fatty acids, such as palmitic, stearic and oleic acids, that are well-suited for biodiesel applications. Although some of these microbes are able to accumulate SCOs while growing on inexpensive agro-industrial biomass, the competition with plant oil resources means that a significant increase in productivity is desired. The present review aims to summarize recent details in lipid metabolism research and engineering (e.g. direct fatty acid ethyl ester production), as well as culture condition optimization and innovations, such as solid-state or semi-solid-state fermentation, that can all contribute to higher productivity and further advancement of the field.

Improving the lipid accumulation properties of the yeast cells for biodiesel production using molasses

In this article the high lipid accumulation potential of Candida lipolytica, Candida tropicalis and Rhodotorula mucilaginosa cells were shown in molasses medium. Four different pH values were examined (4-7) to discover the optimum lipid accumulation medium. Varied concentrations of (NH₄)₂SO₄ (0.5, 1.0, 1.5 g/L) and molasses (6%, 8%, 10%) were tested to find the optimum carbon and nitrogen amounts for the highest cellular lipid production. It is shown that the maximum lipid content could be achieved in the medium containing 8% molasses solution and 1.0 g/L (NH₄)₂SO₄ at pH 5 after four days of incubation time. The maximum lipid contents and methyl ester yields were measured as 59.9% and 84.9% for C. lipolytica, 46.8% and 93.2% for C. tropicalis, 69.5% and 92.3% for R. mucilaginosa. Because of the dominant fatty acids were C16 and C18 in the lipids of yeast cells, these crude lipids could be promising feedstock for biodiesel production.