Valorisation of side streams from wheat milling and confectionery industries for consolidated production and extraction of microbial lipids

Carotenoids production by Rhodosporidium paludigenum yeasts: Characterization of chemical composition, antioxidant and antimicrobial properties

The high market potential imposed by natural carotenoids has turned the scientific interest in search for new strains, capable of synthesizing a wide spectrum of these pigments. In this study, Rhodosporidium paludigenum NCYC 2663 and 2664 were investigated for carotenoids production and lipid accumulation utilizing different carbon sources (glucose, fructose, sucrose, mixture of glucose: galactose). Strain R. paludigenum 2663 produced the highest total carotenoids titer (2.21 mg/L) when cultivated on sucrose, together with 4 g/L lipids (30% w/w content) and 7 g/L exopolysaccharides. In the case of R. paludigenum 2664, glucose favored the production of 2.93 mg/L total carotenoids and 1.57 g/L lipids (31.8% w/w content). Analysis of the chemical profile during fermentation revealed that β-carotene was the prominent carotenoid. Strain 2663 co-produced γ-carotene, torulene and torularhodin in lower amounts, whereas 2664 synthesized almost exclusively β-carotene. The produced lipids from strain 2663 were rich in oleic acid, while the presence of linoleic acid was also detected in the lipoic fraction from strain 2664. The obtained carotenoid extracts exhibited antioxidant (IC50 0.14 mg/mL) and high antimicrobial activity, against common bacterial and fungal pathogenic strains. The results of this study are promising for the utilization of biotechnologically produced carotenoids in food applications.

Unlocking the potential of spent coffee grounds via a comprehensive biorefinery approach: production of microbial oil and carotenoids under fed-batch fermentation

The valorization of renewable feedstock to produce a plethora of value-added products could promote the transition towards a circular bioeconomy. This study presents the development of cascade processes to bioconvert spent coffee grounds (SCGs) into microbial oil and carotenoids employing sustainable practices. The stepwise recovery of crude phenolic extract and coffee oil was carried out using green or recyclable solvents, i.e., aqueous ethanol and hexane. Palmitic acid (43.3%) and linoleic acid (38.9%) were the major fatty acids in the oil fraction of SCGs. The LC-MS analysis of crude phenolic extracts revealed that chlorogenic acid dominated (45.7%), while neochlorogenic acid was also detected in substantial amounts (24.0%). SCGs free of coffee oil and phenolic compounds were subjected to microwave-assisted pretreatment under different irradiations and solvents to enhance subsequent enzymatic saccharification. Microwave/water pretreatment at 400 W, followed by enzymatic hydrolysis with proteases, hemicellulases, and cellulases, at 50 g/L initial SCGs, led to satisfying overall yields of cellulose (75.4%), hemicellulose (50.3%), and holocellulose (55.3%). Mannan was the most extractable polysaccharide followed by galactan and arabinan. SCGs hydrolysate was used in fed-batch bioreactor fermentations with Rhodosporidium toruloides to produce 24.0 g/L microbial oil and carotenoids of 432.9 μg/g biomass.

Determining mating type and ploidy in Rhodotorula toruloides and its effect on growth on sugars from lignocellulosic biomass

Rhodotorula toruloides is being developed for the use in industrial biotechnology processes because of its favorable physiology. This includes its ability to produce and store large amounts of lipids in the form of intracellular lipid bodies. Nineteen strains were characterized for mating type, ploidy, robustness for growth, and accumulation of lipids on inhibitory switchgrass hydrolysate (SGH). Mating type was determined using a novel polymerase chain reaction (PCR)-based assay, which was validated using the classical microscopic test. Three of the strains were heterozygous for mating type (A1/A2). Ploidy analysis revealed a complex pattern. Two strains were triploid, eight haploid, and eight either diploid or aneuploid. Two of the A1/A2 strains were compared to their parents for growth on 75%v/v concentrated SGH. The A1/A2 strains were much more robust than the parental strains, which either did not grow or had extended lag times. The entire set was evaluated in 60%v/v SGH batch cultures for growth kinetics and biomass and lipid production. Lipid titers were 2.33-9.40 g/L with a median of 6.12 g/L, excluding the two strains that did not grow. Lipid yields were 0.032-0.131 (g/g) and lipid contents were 13.5-53.7% (g/g). Four strains had significantly higher lipid yields and contents. One of these strains, which had among the highest lipid yield in this study (0.131 ± 0.007 g/g), has not been previously described in the literature.

SUMMARY

The yeast Rhodotorula toruloides was used to produce oil using sugars extracted from a bioenergy grass.

Growth Potential of Selected Yeast Strains Cultivated on Xylose-Based Media Mimicking Lignocellulosic Wastewater Streams: High Production of Microbial Lipids by Rhodosporidium toruloides

The potential of Rhodosporidium toruloides, Candida oleophila, Metschnikowia pulcherima, and Cryptococcus curvatus species to produce single-cell-oil (SCO) and other valuable metabolites on low-cost media, based on commercial-type xylose, was investigated. Rhodosporidium strains were further evaluated in shake-flasks using different lignosulphonate (LS) concentrations, in media mimicking waste streams derived from the paper and pulp industry. Increasing the LS concentration up to 40 g/L resulted in enhanced dry cell weight (DCW) while SCO production increased up to ~5.0 g/L when R. toruloides NRRL Y-27012 and DSM 4444 were employed. The intra-cellular polysaccharide production ranged from 0.9 to 2.3 g/L in all fermentations. Subsequent fed-batch bioreactor experiments with R. toruloides NRRL Y-27012 using 20 g/L of LS and xylose, led to SCO production of 17.0 g/L with maximum lipids in DCW (YL/X) = 57.0% w/w. The fatty acid (FA) profile in cellular lipids showed that oleic (50.3–63.4% w/w) and palmitic acid (23.9–31.0%) were the major FAs. Only SCO from batch trials of R. toruloides strains contained α-linolenic acid. Media that was supplemented with various LS concentrations enhanced the unsaturation profile of SCO from R. toruloides NRRL Y-27012. SCO from R. toruloides strains could replace plant-based commodity oils in oleochemical-operations and/or it could be micro- and nano-encapsulated into novel food-based formulas offering healthier food-products.

Coproduction of Microbial Oil and Carotenoids within the Circular Bioeconomy Concept: A Sequential Solid-State and Submerged Fermentation Approach

The main objective of integrative biorefinery platforms is to propose efficient green methodologies addressed to obtain high-value compounds with low emissions through biochemical conversions. This work first screened the capacity of various oleaginous yeast to cosynthesize high-value biomolecules such as lipids and carotenoids. Selected strains were evaluated for their ability to coproduce such biocompounds in the waste-based media of agro-food (brewer’s spent grain, pasta processing waste and bakery waste). Carbon and nitrogen source feedstock was obtained through enzymatic hydrolysis of the agro-food waste, where up to 80% of total sugar/starch conversion was obtained. Then, the profitability of the bioprocess for microbial oil (MO) and carotenoids production by Sporobolomyces roseus CFGU-S005 was estimated via simulation using SuperPro Designer®. Results showed the benefits of establishing optimum equipment scheduling by identifying bottlenecks to increase profitability. Sensitivity analysis demonstrated the impact of MO price and batch throughput on process economics. A profitable process was achieved with a MO batch throughput of 3.7 kg/batch (ROI 31%, payback time 3.13 years). The results revealed areas that require further improvement to achieve a sustainable and competitive process for the microbial production of carotenoids and lipids.

Valorization of low-cost, carbon-rich substrates by edible ascomycetes and basidiomycetes grown on liquid cultures

Three ascomycetes (Morchella vulgaris AMRL 36, M. elata AMRL 63, Tuber aestivum AMRL 364) and four basidiomycetes strains (Lentinula edodes AMRL 124 and 126, Agaricus bisporus AMRL 208 and 209) were screened for their ability to grow on liquid static flask cultures of glucose, glycerol, molasses and waste flour-rich hydrolysates with C/N ratio of 20 and produce biomass, exopolysaccharides and lipids. The profile of lipid fatty acids was also assessed. Selected strains were furthermore cultivated in C/N = 50. Results showed that substrate consumption, biomass formation and secondary metabolites production were strain, substrate and C/N ratio dependent. The maximum biomass (X), lipid (L) and exopolysaccharides (EPS) values noted were Xmax = 25.2 g/L (C/N = 20; molasses) and Lmax = 6.51 g/L (C/N = 50; rice cereal hydrolysates) by T. aestivum strain AMRL 364 and EPSmax = 2.41 g/L by M. elata strain AMRL 63 (C/N = 50; molasses), respectively. When C/N ratio of 50 was applied, biomass, lipid production and substrate consumption seem to be negatively affected in most of the trials. The adaptation and capability of the mushroom strains to be cultivated on substrates based on agro-industrial waste streams and infant food of expired shelf date offers the opportunity to set a circular oriented bioprocess.

Optimization of carbon source efficiency for lipid production with the oleaginous yeast Saitozyma podzolica DSM 27192 applying automated continuous feeding

BACKGROUND

Biotechnologically produced microbial lipids are of interest as potential alternatives for crude and plant oils. Their lipid profile is similar to plant oils and can therefore be a substitute for the production of biofuels, additives for food and cosmetics industry as well as building blocks for oleochemicals. Commercial microbial lipids production, however, is still not profitable and research on process optimization and cost reduction is required. This study reports on the process optimization using glucose or xylose with the unconventional oleaginous yeast Saitozyma podzolica DSM 27192 aiming to reduce the applied carbon source amount without sacrificing lipid productivity.

RESULTS

By optimizing the process parameters temperature and pH, lipid productivity was enhanced by 40%. Thereupon, by establishing a two-phase strategy with an initial batch phase and a subsequent fed-batch phase for lipid production in which a constant sugar concentration of about 10 g/L was maintained, resulted in saving of ~ 41% of total glucose and ~ 26% of total xylose. By performing the automated continuous sugar feed the total sugar uptake was improved to ~ 91% for glucose and ~ 92% for xylose and thus, prevented waste of unused carbon source in the cultivation medium. In addition, reduced glucose cultivation resulted in to 28% higher cell growth and 19% increase of lipid titer. By using xylose, the by-product xylonic acid was identified for the first time as by-product of S. podzolica.

CONCLUSIONS

These findings provide a broad view of different cultivation process strategies with subsequent comparison and evaluation for lipid production with S. podzolica. Additionally, new biotechnological characteristics of this yeast were highlighted regarding the ability to produce valuable organic acids from sustainable and renewable sugars.

Lipid Production by Yeasts Growing on Commercial Xylose in Submerged Cultures with Process Water Being Partially Replaced by Olive Mill Wastewaters

Six yeast strains belonging to Rhodosporidium toruloides, Lipomyces starkeyi, Rhodotorula glutinis and Cryptococcus curvatus were shake-flask cultured on xylose (initial sugar—S0 = 70 ± 10 g/L) under nitrogen-limited conditions. C. curvatus ATCC 20509 and L. starkeyi DSM 70296 were further cultured in media where process waters were partially replaced by the phenol-containing olive mill wastewaters (OMWs). In flasks with S0 ≈ 100 g/L and OMWs added yielding to initial phenolic compounds concentration (PCC0) between 0.0 g/L (blank experiment) and 2.0 g/L, C. curvatus presented maximum total dry cell weight—TDCWmax ≈ 27 g/L, in all cases. The more the PCC0 increased, the fewer lipids were produced. In OMW-enriched media with PCC0 ≈ 1.2 g/L, TDCW = 20.9 g/L containing ≈ 40% w/w of lipids was recorded. In L. starkeyi cultures, when PCC0 ≈ 2.0 g/L, TDCW ≈ 25 g/L was synthesized, whereas lipids in TDCW = 24–28% w/w, similar to the experiments without OMWs, were recorded. Non-negligible dephenolization and species-dependent decolorization of the wastewater occurred. A batch-bioreactor trial by C. curvatus only with xylose (S0 ≈ 110 g/L) was performed and TDCW = 35.1 g/L (lipids in TDCW = 44.3% w/w) was produced. Yeast total lipids were composed of oleic and palmitic and to lesser extent linoleic and stearic acids. C. curvatus lipids were mainly composed of nonpolar fractions (i.e., triacylglycerols).

Production of added-value microbial metabolites during growth of yeast strains on media composed of biodiesel-derived crude glycerol and glycerol/xylose blends

A total of 11 yeast strains of Yarrowia lipolytica, Metschnikowia sp., Rhodotorula sp. and Rhodosporidium toruloides were grown under nitrogen-limited conditions with crude glycerol employed as substrate in shake flasks, presenting interesting dry cell weight (DCW) production. Three of these strains belonging to Metschnikowia sp. accumulated significant quantities of endopolysaccharides (i.e. the strain V.V.-D4 produced 11.0 g/L of endopolysaccharides, with polysaccharides in DCW ≈ 63% w/w). A total of six Y. lipolytica strains produced either citric acid or mannitol. Most of the screened yeasts presented somehow elevated lipid and polysaccharides in DCW values at the early steps of growth despite nitrogen appearance in the fermentation medium. Lipid in DCW values decreased as growth proceeded. R. toruloides DSM 4444 cultivated on media presenting higher glycerol concentrations presented interesting lipid-accumulating capacities (maximum lipid = 12.5 g/L, maximum lipid in DCW = 43.0–46.0% w/w, conversion yield on glycerol = 0.16 g/g). Replacement of crude glycerol by xylose resulted in somehow decreased lipid accumulation. In xylose/glycerol mixtures, xylose was more rapidly assimilated from glycerol. R. toruloides total lipids were mainly composed of triacylglycerols. Total cellular fatty acid composition on xylose presented some differences compared with that on glycerol. Cellular lipids contained mainly oleic and palmitic acid.

Genomic Considerations for the Modification of Saccharomyces cerevisiae for Biofuel and Metabolite Biosynthesis

The growing global population and developing world has put a strain on non-renewable natural resources, such as fuels. The shift to renewable sources will, thus, help meet demands, often through the modification of existing biosynthetic pathways or the introduction of novel pathways into non-native species. There are several useful biosynthetic pathways endogenous to organisms that are not conducive for the scale-up necessary for industrial use. The use of genetic and synthetic biological approaches to engineer these pathways in non-native organisms can help ameliorate these challenges. The budding yeast Saccharomyces cerevisiae offers several advantages for genetic engineering for this purpose due to its widespread use as a model system studied by many researchers. The focus of this review is to present a primer on understanding genomic considerations prior to genetic modification and manipulation of S. cerevisiae. The choice of a site for genetic manipulation can have broad implications on transcription throughout a region and this review will present the current understanding of position effects on transcription.

Bioprocess development for the production of novel oleogels from soybean and microbial oils

This study presents the production of novel oleogels via circular valorisation of food industry side streams. Sugarcane molasses and soybean processing side streams (i.e. soybean cake) were employed as fermentation feedstocks for the production of microbial oil. Fed-batch bioreactor fermentations carried out by the oleaginous yeast Rhodosporidium toruloides led to the production of 36.9 g/L total dry weight with an intracellular oil content of 49.8% (w/w) and 89.4 μg/g carotenoids. The carotenoid-rich microbial oil and soybean oil were evaluated as base oils for the production of wax-based oleogels. The wax esters, used as oleogelators, were produced via enzymatic catalysis, using microbial oil or soybean fatty acid distillate as raw materials. All oleogels presented a gel-like behaviour (G' > G″). However, the highest G' was determined for the oleogel produced from soybean oil and microbial oil-wax esters, which indicated a stronger network. Thermal analysis showed that this oleogel had a melting temperature profile up to 35 °C, which is favorable for applications in the confectionery industry. Also, texture analysis demonstrated that soybean oil-microbial oil wax oleogel was stable (1.9-2.2 N) within 30-days storage period. This study showed the potential of novel oleogels production through the development of bioprocesses based on the valorisation of various renewable resources.

Development of a Circular Oriented Bioprocess for Microbial Oil Production Using Diversified Mixed Confectionery Side-Streams

Diversified mixed confectionery waste streams were utilized in a two-stage bioprocess to formulate a nutrient-rich fermentation media for microbial oil production. Solid-state fermentation was conducted for the production of crude enzyme consortia to be subsequently applied in hydrolytic reactions to break down starch, disaccharides, and proteins into monosaccharides, amino acids, and peptides. Crude hydrolysates were evaluated in bioconversion processes using the red yeast Rhodosporidium toruloides DSM 4444 both in batch and fed-batch mode. Under nitrogen-limiting conditions, during fed-batch cultures, the concentration of microbial lipids reached 16.6-17 g·L-1 with the intracellular content being more than 40% (w/w) in both hydrolysates applied. R. toruloides was able to metabolize mixed carbon sources without catabolite repression. The fatty acid profile of the produced lipids was altered based on the substrate employed in the bioconversion process. Microbial lipids were rich in polyunsaturated fatty acids, with oleic acid being the major fatty acid (61.7%, w/w). This study showed that mixed food side-streams could be valorized for the production of microbial oil with high unsaturation degree, pointing towards the potential to produce tailor-made lipids for specific food applications. Likewise, the proposed process conforms unequivocally to the principles of the circular economy, as the entire quantity of confectionery by-products are implemented to generate added-value compounds that will find applications in the same original industry, thus closing the loop.

Bioprocess development for biolubricant production using microbial oil derived via fermentation from confectionery industry wastes

Microbial oil produced from confectionery and wheat milling side streams has been evaluated as novel feedstock for biolubricant production. Nutrient-rich fermentation media were produced by a two-step bioprocess involving crude enzyme production by solid state fermentation followed by enzymatic hydrolysis of confectionery industry waste. Among 5 yeast strains and 2 fungal strains cultivated on the crude hydrolysate, Rhodosporidium toruloides and Cryptococcus curvatus were selected for further evaluation for biolubricant production based on fermentation efficiency and fatty acid composition. The extracted microbial oils were enzymatically hydrolysed and the free fatty acids were esterified by Lipomod 34-MDP in a solvent-free system with trimethylolpropane (TMP) and neopentyl glycol (NPG). The highest conversion yields were 88% and 82.7% for NPG esters of R. toruloides and C. curvatus, respectively. This study also demonstrates that NPG esters produced from microbial oil have promising physicochemical properties for bio-based lubricant formulations that could substitute for conventional lubricants.

Production of wax esters via microbial oil synthesis from food industry waste and by-product streams

The production of wax esters using microbial oils was demonstrated in this study. Microbial oils produced from food waste and by-product streams by three oleaginous yeasts were converted into wax esters via enzymatic catalysis. Palm oil was initially used to evaluate the influence of temperature and enzyme activity on wax ester synthesis catalysed by Novozyme 435 and Lipozyme lipases using cetyl, oleyl and behenyl alcohols. The highest conversion yields (up to 79.6%) were achieved using 4U/g of Novozyme 435 at 70°C. Transesterification of microbial oils to behenyl and cetyl esters was achieved at conversion yields up to 87.3% and 69.1%, respectively. Novozyme 435 was efficiently reused for six and three cycles during palm esters and microbial esters synthesis, respectively. The physicochemical properties of microbial oil derived behenyl esters were comparable to natural waxes. Wax esters from microbial oils have potential applications in cosmetics, chemical and food industries.

Polyol production from waste materials by genetically modified Yarrowia lipolytica

Sugar alcohols (polyols) are sweeteners with many industrial applications. In this study, a fermentation process of polyol production based on waste substrates - raw industrial molasses and crude glycerol - was tested. The yeast strain Yarrowia lipolytica Wratislavia K1 was genetically modified by overexpression of the Saccharomyces cerevisiae SUC2 gene and overexpression of the native GUT1 gene. This process allowed for sucrose utilization and rapid glycerol assimilation by the engineered strain. In this study, the obtained strain AIB pAD-UTGut1 produced 100.65±3.75g/l of polyols, with productivity of 1.09±0.9g/lh and yield of 0.67±0.2g/g. This is the first study describing efficient polyol production by the modified Y. lipolytica strain from industrial raw molasses and crude glycerol. By process optimization, we established conditions for abundant polyol synthesis from low-value substrates.

Evaluating feeding strategies for microbial oil production from glycerol by Rhodotorula glutinis

Oil production, from biodiesel by-product glycerol, through microbial fermentation provides a promising option as part of an integrated biorefinery process. However, bioprocessing improvements are required to make the process more efficient. In the present work, different glycerol feeding strategies were evaluated under fed-batch cultivation of the oleaginous yeast Rhodotorula glutinis. Results showed that the concept of targeting first a cell proliferation stage and then a lipid accumulation stage had beneficial effects on both biomass and oil yields. Continual feeding and pulsed feedings, delivering the same total amount of nutrients, resulted in similar values of cellular biomass (∼25 g/L) and oil content (∼40%). In contrast, continual supply of nutrients at higher rates ( >0.8 g/L/h) led to an increase in both cell densities (30 g/L) and oil content (53%), attaining a high oil yield of 16.28 g/L. This suggests that a continual cultivation with two different rates for each stage constitutes an efficient approach to enhance microbial oil production.

Enhanced lipid production by Rhodosporidium toruloides using different fed-batch feeding strategies with lignocellulosic hydrolysate as the sole carbon source

BACKGROUND

Industrial biotechnology that is able to provide environmentally friendly bio-based products has attracted more attention in replacing petroleum-based industries. Currently, most of the carbon sources used for fermentation-based bioprocesses are obtained from agricultural commodities that are used as foodstuff for human beings. Lignocellulose-derived sugars as the non-food, green, and sustainable alternative carbon sources have great potential to avoid this dilemma for producing the renewable, bio-based hydrocarbon fuel precursors, such as microbial lipid. Efficient bioconversion of lignocellulose-based sugars into lipids is one of the critical parameters for industrial application. Therefore, the fed-batch cultivation, which is a common method used in industrial applications, was investigated to achieve a high cell density culture along with high lipid yield and productivity.

RESULTS

In this study, several fed-batch strategies were explored to improve lipid production using lignocellulosic hydrolysates derived from corn stover. Compared to the batch culture giving a lipid yield of 0.19 g/g, the dissolved-oxygen-stat feeding mode increased the lipid yield to 0.23 g/g and the lipid productivity to 0.33 g/L/h. The pulse feeding mode further improved lipid productivity to 0.35 g/L/h and the yield to 0.24 g/g. However, the highest lipid yield (0.29 g/g) and productivity (0.4 g/L/h) were achieved using an automated online sugar control feeding mode, which gave a dry cell weight of 54 g/L and lipid content of 59 % (w/w). The major fatty acids of the lipid derived from lignocellulosic hydrolysates were predominately palmitic acid and oleic acid, which are similar to those of conventional oilseed plants.

CONCLUSIONS

Our results suggest that the fed-batch feeding strategy can strongly influence the lipid production. The online sugar control feeding mode was the most appealing strategy for high cell density, lipid yield, and lipid productivity using lignocellulosic hydrolysates as the sole carbon source.