Utilization of lignocellulosic biomass towards the production of omega-3 fatty acids by the heterotrophic marine microalga Crypthecodinium cohnii

From lignocellulosic biomass to single cell oil for sustainable biomanufacturing: Current advances and prospects

As global temperatures rise and arid climates intensify, the reserves of Earth's resources and the future development of humankind are under unprecedented pressure. Traditional methods of food production are increasingly inadequate in meeting the demands of human life while remaining environmentally sustainable and resource-efficient. Consequently, the sustainable supply of lipids is expected to become a pivotal area for future food development. Lignocellulose biomass (LB), as the most abundant and cost-effective renewable resource, has garnered significant attention from researchers worldwide. Thus, bioprocessing based on LB is appearing as a sustainable model for mitigating the depletion of energy reserves and reducing carbon footprints. Currently, the transformation of LB primarily focuses on producing biofuels, such as bioethanol, biobutanol, and biodiesel, to address the energy crisis. However, there are limited reports on the production of single cell oil (SCO) from LB. This review, therefore, provides a comprehensive summary of the research progress in lignocellulosic pretreatment. Subsequently, it describes how the capability for lignocellulosic use can be conferred to cells through genetic engineering. Additionally, the current status of saccharification and fermentation of LB is outlined. The article also highlights the advances in synthetic biology aimed at driving the development of oil-producing microorganism (OPM), including genetic transformation, chassis modification, and metabolic pathway optimization. Finally, the limitations currently faced in SCO production from straw are discussed, and future directions for achieving high SCO yields from various perspectives are proposed. This review aims to provide a valuable reference for the industrial application of green SCO production.

Use of Residual Lignocellulosic Biomass and Algal Biomass to Produce Biofuels

Efforts are intensifying to identify new biofuel sources in response to the pressing need to mitigate environmental pollutants, such as greenhouse gases, which are key contributors to global warming and various worldwide calamities. Algae and microalgae present themselves as excellent alternatives for solid-gaseous fuel production, given their renewable nature and non-polluting characteristics. However, making biomass production from these organisms economically feasible remains a challenge. This article collates various studies on the use of lignocellulosic waste, transforming it from environmental waste to valuable organic supplements for algae and microalgae cultivation. The focus is on enhancing biomass production and the metabolites derived from these biomasses.

A novel rice hull - microalgal biorefinery for the production of natural phenolic compounds comprising of rice hull acid pretreatment and a two-stage Botryococcus braunii cultivation process

Recently, the rising demand of the industry for natural phenolic antioxidant compounds has turned to the study of microalgae as potential sources. Yet, more economic substrates for microalgal cultivation are sought to lower production costs. To this end, the present work deals with the utilization of rice hull hydrolysate (RHH) as substrate for microalgae Botryococcus braunii through a novel two-stage cultivation system. Initially, RHH was optimized to maximize the contained nutrients while minimizing its inhibitors content. The optimum point was reached under 121 °C, 60 min, 2% (v/v) H2SO4, 30% (w/v) loading. Next, B. braunii was successfully grown first heterotrophically in RHH (25%, v/v), obtaining high biomass production (6.67 g L-1) and then autotrophically to enhance phenolics accumulation. At the end, a high phenolic content of 7.44 ± 0.60 mg Gallic Acid Equivalents g-1 DW was achieved from the produced biomass, thus highlighting the potential of this novel biotechnological method.

Evaluation of Growth and Production of High-Value-Added Metabolites in Scenedesmus quadricauda and Chlorella vulgaris Grown on Crude Glycerol under Heterotrophic and Mixotrophic Conditions Using Monochromatic Light-Emitting Diodes (LEDs)

This study aimed to examine the impact of crude glycerol as the main carbon source on the growth, cell morphology, and production of high-value-added metabolites of two microalgal species, namely Chlorella vulgaris and Scenedesmus quadricauda, under heterotrophic and mixotrophic conditions, using monochromatic illumination from light-emitting diodes (LEDs) emitting blue, red, yellow, and white (control) light. The findings indicated that both microalgae strains exhibited higher biomass yield on the mixotrophic growth system when compared to the heterotrophic one, while S. quadricauda generally performed better than C. vulgaris. In mixotrophic mode, the use of different monochromatic illumination affected biomass production differently on both strains. In S. quadricauda, growth rate was higher under red light (μmax = 0.89 d-1), while the highest biomass concentration and yield per gram of consumed glycerol were achieved under yellow light, reaching 1.86 g/L and Yx/s = 0.18, respectively. On the other hand, C. vulgaris demonstrated a higher growth rate on blue light (μmax = 0.45 d-1) and a higher biomass production on white (control) lighting (1.34 g/L). Regarding the production of metabolites, higher yields were achieved during mixotrophic mode in both strains. In C. vulgaris, the highest lipid (26.5% of dry cell weight), protein (63%), and carbohydrate (20.3%) contents were obtained under blue, red, and yellow light, respectively, thus indicating that different light wavelengths probably activate different metabolic pathways. Similar results were obtained for S. quadricauda with red light leading to higher lipid content, while white lighting caused higher production of proteins and carbohydrates. Overall, the study demonstrated the potential of utilizing crude glycerol as a carbon source for the growth and metabolite production of microalgae and, furthermore, revealed that the strains' behavior varied depending on lighting conditions.

A comprehensive review on microbial lipid production from wastes: research updates and tendencies

Microbial lipids have recently attracted attention as an intriguing alternative for the biodiesel and oleochemical industries to achieve sustainable energy generation. However, large-scale lipid production remains limited due to the high processing costs. As multiple variables affect lipid synthesis, an up-to-date overview that will benefit researchers studying microbial lipids is necessary. In this review, the most studied keywords from bibliometric studies are first reviewed. Based on the results, the hot topics in the field were identified to be associated with microbiology studies that aim to enhance lipid synthesis and reduce production costs, focusing on the biological and metabolic engineering involved. The research updates and tendencies of microbial lipids were then analyzed in depth. In particular, feedstock and associated microbes, as well as feedstock and corresponding products, were analyzed in detail. Strategies for lipid biomass enhancement were also discussed, including feedstock adoption, value-added product synthesis, selection of oleaginous microbes, cultivation mode optimization, and metabolic engineering strategies. Finally, the environmental implications of microbial lipid production and possible research directions were presented.

Recent advances in enhancing the production of long chain omega-3 fatty acids in microalgae

Omega-3 fatty acids have gained attention due to numerous health benefits. Eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) are long chain omega-3 fatty acids produced from precursor ALA (α-linolenic acid) in humans but their rate of biosynthesis is low, therefore, these must be present in diet or should be taken as supplements. The commercial sources of omega-3 fatty acids are limited to vegetable oils and marine sources. The rising concern about vegan source, fish aquaculture conservation and heavy metal contamination in fish has led to the search for their alternative source. Microalgae have gained importance due to the production of high-value EPA and DHA and can thus serve as a sustainable and promising source of long chain omega-3 fatty acids. Although the bottleneck lies in the optimization for enhanced production that involves strategies viz. strain selection, optimization of cultivation conditions, media, metabolic and genetic engineering approaches; while co-cultivation, use of nanoparticles and strategic blending have emerged as innovative approaches that have made microalgae as potential candidates for EPA and DHA production. This review highlights the possible strategies for the enhancement of EPA and DHA production in microalgae. This will pave the way for their large-scale production for human health benefits.

Effect of Soybean Protein Concentrate Preparation on Copy Numbers and Structural Characteristics of DNA from Genetically Modified Soybean

To regulate the degradation of transgenic DNA and lay theoretical foundations for the rational utilization of genetically modified (GM) products, variations in copy numbers and structural characteristics of DNA from GM soybean event GTS 40-3-2 during soybean protein concentrate (SPC) preparation were evaluated. Results showed that defatting and the first ethanol extraction were key procedures inducing DNA degradation. After these two procedures, copy numbers of the lectin and cp4 epsps targets decreased by more than 4 × 10⁸, occupying 36.88-49.30% of the total copy numbers from raw soybean. Atomic force microscopy images visually revealed the degradation of DNA that thinned and shortened during SPC preparation. Circular dichroism spectra suggested a lower helicity of DNA from defatted soybean kernel flour and a conformation transition of DNA from B-type to A-type after ethanol extraction. The fluorescence intensity of DNA decreased during SPC preparation, verifying the DNA damage along this preparation chain.

Use of exogenous substrate in Chlorella cultivation: Strategy for biomass and polyhydroxybutyrate production

The aim of this study was to investigate the influence of exogenous carbon supplementation and nitrogen source reduction on Chlorella fusca LEB 111 growth, biomass composition, and polyhydroxybutyrate accumulation. First, assays were performed with 50 % and 25 % reduced nitrogen source concentrations (NaNO₃). In the second stage, the influence of culture supplementation with 10, 20, and 30 mg L^-1 D-xylose, associated with 50 and 25 % reductions in NaNO₃, was evaluated. The experiments conducted with a 25 % reduction in NaNO₃ and supplementation with 10 mg L^-1 D-xylose resulted in a positive effect on the biomass productivity of C. fusca LEB 111, with production as high as 354.4 mg L^-1 d^-1. The maximum concentration of PHB extracted from C. fusca LEB 111 was 3.7 % (w w^-1) and was obtained when the microalgae were cultivated with a 25 % of reduction in NaNO₃ and supplementation of D-xylose at 20 mg L^-1. Therefore, this study brings new perspectives regarding reducing the use of nutritional sources and using exogenous carbon sources in using microalgae to produce molecules of high biotechnological potential.

Alternative microbial-based functional ingredient source for lycopene, beta-carotene, and polyunsaturated fatty acids

The acquisition of carotenoids and polyunsaturated fatty acids (PUFAs) from plants and animals for use as functional ingredients raises concerns regarding productivity and cost; utilization of microorganisms as alternative sources is an option. We proposed to evaluate the production of carotenoids and PUFAs by Rhodopseudomonas faecalis PA2 using different vegetable oils (rice bran oil, palm oil, coconut oil, and soybean oil) as carbon source, different concentrations of yeast extract as nitrogen source at different cultivation time to ensure the best production. Cultivation with soybean oil as source of carbon led to the most significant changes in the fatty acid profile. Compared to the initial condition, the strain cultivated in the optimal conditions (4% soybean oil, 0.35% yeast extract, and 14 days of incubation) showed an increase in μ_max, biomass, carotenoid productivity, and microbial lipids by 102.5%, 52.7%, 33.82%, and 34.78%, respectively. The unsaturated fatty acids content was raised with additional types of PUFAs; omega-3 [alpha-linolenic acid and eicosapentaenoic acid] and omega-6 [linoleic acid and eicosatrienoic acid] fatty acids were identified. The results of ultra high-performance liquid chromatography-electrospray ionization-quadrupole time of flight-mass spectrometry (UHPLC-ESI-QTOF-MS/MS) indicated the molecular formula and mass of bacterial metabolites were identical to those of lycopene and beta-carotene. The untargeted metabolomics revealed functional lipids and several physiologically bioactive compounds. The outcome provides scientific reference regarding carotenoids, PUFAs, and useful metabolites that have not yet been reported in the species Rhodopseudomonas faecalis for further use as a microbial-based functional ingredient.

Facultative anaerobic conversion of lignocellulose biomass to new bioemulsifier by thermophilic Geobacillus thermodenitrificans NG80-2

Heavy oil has hindered crude oil exploitation and pollution remediation due to its high density and viscosity. Bioemulsifiers efficiently facilitate the formation and stabilization of oil-in-water emulsions in low concentrations thus eliminating the above bottleneck. Despite their potential benefits, various obstacles had still impeded the practical applications of bioemulsifiers, including high purification costs and poor adaptability to extreme environments such as high temperature and oxygen deficiency. Herein, thermophilic facultative anaerobic Geobacillus thermodenitrificans NG80-2 was proved capable of emulsifying heavy oils and reducing their viscosity. An exocelluar bioemulsifier could be produced by NG80-2 using low-cost lignocellulose components as carbon sources even under anaerobic condition. The purified bioemulsifier was proved to be polysaccharide-protein complexes, and both components contributed to its emulsifying capability. In addition, it displayed excellent stress tolerance over wide ranges of temperatures, salinities, and pHs. Meanwhile, the bioemulsifier significantly improved oil recovery and degradation efficiency. An eps gene cluster for polysaccharide biosynthesis and genes for the covalently bonded proteins was further certificated. Therefore, the bioemulsifier produced by G. thermodenitrificans NG80-2 has immense potential for applications in bioremediation and EOR, and its biosynthesis pathway revealed here provides a theoretical basis for increasing bioemulsifier output.

Microalgae Commercialization Using Renewable Lignocellulose Is Economically and Environmentally Viable

Conventional phototrophic cultivation for microalgae production suffers from low and unstable biomass productivity due to limited and unreliable light transmission outdoors. Alternatively, the use of a renewable lignocellulose-derived carbon source, cellulosic hydrolysate, offers a cost-effective and sustainable pathway to cultivate microalgae heterotrophically with high algal growth rate and terminal density. In this study, we evaluate the feasibility of cellulosic hydrolysate-mediated heterotrophic cultivation (Cel-HC) for microalgae production by performing economic and environmental comparisons with phototrophic cultivation through techno-economic analysis and life cycle assessment. We estimate a minimum selling price (MSP) of 4722 USD/t for producing high-purity microalgae through Cel-HC considering annual biomass productivity of 300 t (dry weight), which is competitive with the conventional phototrophic raceway pond system. Revenues from the lignocellulose-derived co-products, xylose and fulvic acid fertilizer, could further reduce the MSP to 2976 USD/t, highlighting the advantages of simultaneously producing high-value products and biofuels in an integrated biorefinery scheme. Further, Cel-HC exhibits lower environmental impacts, such as cumulative energy demand and greenhouse gas emissions, than phototrophic systems, revealing its potential to reduce the carbon intensity of algae-derived commodities. Our results demonstrate the economic and environmental competitiveness of heterotrophic microalgae production based on renewable bio-feedstock of lignocellulose.

Proteomics unveil a central role for peroxisomes in butyrate assimilation of the heterotrophic Chlorophyte alga Polytomella sp

Volatile fatty acids found in effluents of the dark fermentation of biowastes can be used for mixotrophic growth of microalgae, improving productivity and reducing the cost of the feedstock. Microalgae can use the acetate in the effluents very well, but butyrate is poorly assimilated and can inhibit growth above 1 gC.L-1. The non-photosynthetic chlorophyte alga Polytomella sp. SAG 198.80 was found to be able to assimilate butyrate fast. To decipher the metabolic pathways implicated in butyrate assimilation, quantitative proteomics study was developed comparing Polytomella sp. cells grown on acetate and butyrate at 1 gC.L-1. After statistical analysis, a total of 1772 proteins were retained, of which 119 proteins were found to be overaccumulated on butyrate vs. only 46 on acetate, indicating that butyrate assimilation necessitates additional metabolic steps. The data show that butyrate assimilation occurs in the peroxisome via the β-oxidation pathway to produce acetyl-CoA and further tri/dicarboxylic acids in the glyoxylate cycle. Concomitantly, reactive oxygen species defense enzymes as well as the branched amino acid degradation pathway were strongly induced. Although no clear dedicated butyrate transport mechanism could be inferred, several membrane transporters induced on butyrate are identified as potential condidates. Metabolic responses correspond globally to the increased needs for central cofactors NAD, ATP and CoA, especially in the peroxisome and the cytosol.

Emerging prospects of microbial production of omega fatty acids: Recent updates

Healthy foods containing omega-3/omega-6 polyunsaturated fatty acids (PUFAs) have been in great demand because of their unique dietary and health properties. Reduction in chronic inflammatory and autoimmune diseases has shown their therapeutic and health-promoting effects when consumed under recommended ratio 1:1-1:4, however imbalanced ratios (>1:4, high omega-6) enhance these risks. The importance of omega-6 is apparent however microbial production favors larger production of omega-3. Current research focus is prerequisite to designing omega-6 production strategies for better application prospects, for which thraustochytrids could be promising due to higher lipid productivity. This review provides recent updates on essential fatty acids production from potential microbes and their application, especially major insights on omega research, also discussed the novel possible strategies to promote omega-3 and omega-6 accumulation via engineering and omics approaches. It covers strategies to block the conversion of omega-6 into omega-3 by enzyme inhibition, nanoparticle-mediated regulation and/or metabolic flux regulation, etc.

Something to chew on: technological aspects for novel snacks

Snacks have accompanied people for a long time, meeting our needs for something fast and filling between meals. Societies and technologies have changed, and so have snacks, adapting to people's daily lives, concerns, and demands. Although traditional snacks, such as potato chips, are still ubiquitous and popular worldwide, there is not unanimity around them anymore, since many people have been looking for healthier snacks. Studies have been carried out to propose healthier snack options by changing their composition and/or techniques to produce them, minimizing contents of energy-dense components and/or maximizing the retention or bioavailability of nutrients. This mini-review presents the main trends on development of snacks and future perspectives. © 2021 Society of Chemical Industry.

Lytic polysaccharide monooxygenases as powerful tools in enzymatically assisted preparation of nano-scaled cellulose from lignocellulose: A review

Nanocellulose, either in the form of fibers or crystals, constitutes a renewable, biobased, biocompatible material with advantageous mechanical properties that can be isolated from lignocellulosic biomass. Enzyme-assisted isolation of nanocellulose is an attractive, environmentally friendly approach that leads to products of higher quality compared to their chemically prepared counterparts. Lytic polysaccharide monooxygenases (LPMOs) are enzymes that oxidatively cleave the β-1,4-glycosidic bond of polysaccharides upon activation of O₂ or H₂O₂ and presence of an electron donor. Their use for treatment of cellulose fibers towards the preparation of nano-scaled cellulose is related to the ability of LPMOs to create nicking points on the fiber surface, thus facilitating fiber disruption and separation. The aim of this review is to describe the mode of action of LPMOs on cellulose fibers towards the isolation of nanostructures, thus highlighting their great potential for the production of nanocellulose as a novel value added product from lignocellulose.

An integrated approach for the efficient separation of specialty compounds from biomass of the marine microalgae Amphidinium carterae

An amphidinol-prioritized fractioning approach was for the first time developed to isolate multiple specialty metabolites such as amphidinols, carotenoids and fatty acids using the biomass of the marine microalgae Amphidinium carterae. The biomass was produced in a raceway photobioreactor and the exhausted culture media were reused, thus fulfilling sustainability criteria employing a circular economy concept. The integrated bioactive compounds-targeted approach presented here consisted of four steps with which recovery percentages of carotenoids, fatty acids and amphidinols of 97%, 82% and 99 %, respectively, were achieved. The proposed process was proved to be a better extraction system for this microalga than another based on a sequential gradient partition with water and four water-immiscible organic solvents (hexane, carbon tetrachloride, dichloromethane and n-butanol). The proposed process could be scaled-up as a commercial solid-phase extraction technology well-established for industrial bioprocesses.

Efficient production of nutraceuticals and lactic acid from lignocellulosic biomass by combining organosolv fractionation with enzymatic/fermentative routes

The aim of this work was to investigate the use of isobutanol as organic solvent for the efficient delignification and fractionation of beechwood through the OxiOrganosolv process in the absence of any catalyst. The results demonstrate that cellulose-rich solid pulp produced after pretreatment is a source of fermentable sugars that can be easily hydrolyzed and serve as a carbon source in microbial fermentations for the production of omega-3 fatty acids and D-lactic acid. The C5 sugars are recovered in the aqueous liquid fractions and comprise a fraction rich in xylo-oligosaccharides with prebiotic potential. The maximum production of optically pure D-lactic from Lactobacillus delbrueckii sp. bulgaricus reached 51.6 g/L (0.57 g/g_biomass), following a simultaneous saccharification and fermentation strategy. Crypthecodenium cohnii accumulated up to 52.1 wt% lipids with a DHA content of 54.1 %, while up to 43.3 % hemicellulose recovery in form of oligosaccharides was achieved in the liquid fraction.

Production of Omega-3 Fatty Acids from the Microalga Crypthecodinium cohnii by Utilizing Both Pentose and Hexose Sugars from Agricultural Residues

The core objective of this work was to take advantage of the unexploited wheat straw biomass, currently considered as a broadly available waste stream from the Greek agricultural sector, towards the integrated valorization of sugar streams for the microbial production of polyunsaturated omega-3 fatty acids (PUFAs). The OxiOrganosolv pretreatment process was applied using acetone and ethanol as organic solvents without any additional catalyst. The results proved that both cellulose-rich solid pulp and hemicellulosic oligosaccharides-rich aqueous liquid fraction after pretreatment can be efficiently hydrolyzed enzymatically, thus resulting in high yields of fermentable monosaccharides. The latter were supplied as carbon sources to the heterotrophic microalga Crypthecodinium cohnii for the production of PUFAs, more specifically docosahexaenoic acid (DHA). The solid fractions consisted mainly of hexose sugars and led to higher DHA productivity than their pentose-rich liquid counterparts, which can be attributed to the different carbon source and C/N ratio in the two streams. The best performance was obtained with the solid pulp pretreated with ethanol at 160 °C for 120 min and an O2 pressure of 16 bar. The total fatty acids content reached 70.3 wt% of dried cell biomass, of which 32.2% was DHA. The total DHA produced was 7.1 mg per g of untreated wheat straw biomass.

Effect of creating a fed-batch like condition using carbon to nitrogen ratios on lipid accumulation in Rhodosporidium toruloides-1588

Utilizing the undetoxified wood hydrolysate to accumulate maximum lipids in Rhodosporidium toruloides under optimum conditions has been regarded as a renewable and cost-effective strategy. The current investigation aims to identify the best carbon to nitrogen (C/N 20, 70, and 120) ratio for maximum lipid accumulation in R. toruloides-1588 using wood hydrolysate. Additionally, a fed-batch-like condition was employed, where C/N ratios were maintained during the fermentation that inherently decreases in batch fermentation. The C/N ratio 70 has been identified as the best condition with 3 times higher lipid accumulation (43% w/w) than the control. Additionally, >95% and 70% of glucose and xylose consumption were observed, respectively. Moreover, 50% increase in polyunsaturated fatty acids compared to the control media reinforced the potential of R. toruloides-1588 to thrive on undetoxified hydrolysate, high lipid productivity (3.8 mg/g of dry weight per hour) and produce high value monosaturated and polyunsaturated fatty acids.

Comparative Life Cycle Assessment of EPA and DHA Production from Microalgae and Farmed Fish

The present study aims at comparing the life cycle environmental impacts of polyunsaturated fatty acids production (PUFA) from microalgae and farmed fish. PUFA production from microalgae cultivated via heterotrophy and photoautotrophy was assessed and compared. The primary energy demand (PED) and environmental impacts (EI) of PUFA production from microalgae via heterotrophy were significantly lower compared to PUFA produced via photoautotrophy. Furthermore, PED and EI of PUFA production from fish farmed in marine net pens were assessed. The results indicated that the PED and EI of PUFA production from farmed fish are higher than that produced from microalgae cultivated via heterotrophy. Therefore, the results suggest that PUFA produced from microalgae via heterotrophy could substitute fish oil from an environmental perspective. Furthermore, life cycle analysis results indicate that PUFA derived from microalgae could potentially replace fish oil in the fish feed, thus reducing the pressure on oceans.

Marine bioactives: from energy to nutrition

Microalgae have been evaluated as promising resource for biodiesel production, but algal biofuel production is not yet commercially viable, which reflects the high energy costs linked with cultivation, harvesting, and dewatering of algae. As crude oil processing declines, microalgae biorefineries are being considered for producing bioactives such as enzymes, proteins, omega-3 oils, pigments, recombinant products, and vitamins, to offset the costs of biofuel production. We believe that producing algal bioactives through advanced manufacturing pathways, encompassing a biorefinery approach, would be effective, profitable, and economical.

Conversion of organosolv pretreated hardwood biomass into 5-hydroxymethylfurfural (HMF) by combining enzymatic hydrolysis and isomerization with homogeneous catalysis

BACKGROUND

Over the last few years, valorization of lignocellulosic biomass has been expanded beyond the production of second-generation biofuels to the synthesis of numerous platform chemicals to be used instead of their fossil-based counterparts. One such well-researched example is 5-hydroxymethylfurfural (HMF), which is preferably produced by the dehydration of fructose. Fructose is obtained by the isomerization of glucose, which in turn is derived by the hydrolysis of cellulose. However, to avoid harsh reaction conditions with high environmental impact, an isomerization step towards fructose is necessary, as fructose can be directly dehydrated to HMF under mild conditions. This work presents an optimized process to produce fructose from beechwood biomass hydrolysate and subsequently convert it to HMF by employing homogeneous catalysis.

RESULTS

The optimal saccharification conditions were identified at 10% wt. solids loading and 15 mg enzyme/g_solids, as determined from preliminary trials on pure cellulose (Avicel® PH-101). Furthermore, since high rate glucose isomerization to fructose requires the addition of sodium tetraborate, the optimum borate to glucose molar ratio was determined to 0.28 and was used in all experiments. Among 20 beechwood solid pulps obtained from different organosolv pretreatment conditions tested, the highest fructose production was obtained with acetone (160 °C, 120 min), reaching 56.8 g/100 g pretreated biomass. A scale-up hydrolysis in high solids (25% wt.) was then conducted. The hydrolysate was subjected to isomerization eventually leading to a high-fructose solution (104.5 g/L). Dehydration of fructose to HMF was tested with 5 different catalysts (HCl, H₃PO₄, formic acid, maleic acid and H-mordenite). Formic acid was found to be the best one displaying 79.9% sugars conversion with an HMF yield and selectivity of 44.6% and 55.8%, respectively.

CONCLUSIONS

Overall, this work shows the feasibility of coupling bio- and chemo-catalytic processes to produce HMF from lignocellulose in an environmentally friendly manner. Further work for the deployment of biocatalysts for the oxidation of HMF to its derivatives could pave the way for the emergence of an integrated process to effectively produce biobased monomers from lignocellulose.

Integrating metagenetics and high-throughput screening for bioprospecting marine thraustochytrids producers of long-chain polyunsaturated fatty acids

Omega-3 produced by marine thraustochytrids has appeared as an alternative to fish oil and an eco-friendly solution to overfishing. Herein, an integrative analysis of metagenetics and high-throughput screening was used for bioprospecting marine thraustochytrids from southern Brazil mangrove and coastal seawater. All sampled environments showed biodiversity and abundance of SAR clade. Environmental samples detected with potential lipid-accumulating labyrinthulomycetes were further processed for direct plating and pollen baiting isolation. Microtiter plate system and fluorescence spectroscopy were combined for high-throughput screening of 319 isolates to accumulate lipids. Twenty isolates were selected for submerged cultivation and lipid characterization. Among them, B36 isolate, identified as Aurantiochytrium sp. by 18s rRNA sequencing, achieved the highest biomass (25.60 g/l CDW) and lipids (17.12 g/l CDW). This lipid content had a high biological value with 44.37% LC-PUFAs and 34.6% DHA, which can be used as a sustainable source in vegan, seafood-free and animal feed diets.

Food Ingredients and Nutraceuticals from Microalgae: Main Product Classes and Biotechnological Production

Microalgal products are an emerging class of food, feed, and nutraceuticals. They include dewatered or dried biomass, isolated pigments, and extracted fat. The oil, protein, and antioxidant-rich microalgal biomass is used as a feed and food supplement formulated as pastes, powders, tablets, capsules, or flakes designed for daily use. Pigments such as astaxanthin (red), lutein (yellow), chlorophyll (green), or phycocyanin (bright blue) are natural food dyes used as isolated pigments or pigment-rich biomass. Algal fat extracted from certain marine microalgae represents a vegetarian source of n-3-fatty acids (eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), γ-linolenic acid (GLA)). Gaining an overview of the production of microalgal products is a time-consuming task. Here, requirements and options of microalgae cultivation are summarized in a concise manner, including light and nutrient requirements, growth conditions, and cultivation systems. The rentability of microalgal products remains the major obstacle in industrial application. Key challenges are the high costs of commercial-scale cultivation, harvesting (and dewatering), and product quality assurance (toxin analysis). High-value food ingredients are commonly regarded as profitable despite significant capital expenditures and energy inputs. Improvements in capital and operational costs shall enable economic production of low-value food products going down to fishmeal replacement in the future economy.

Valorization of exhausted olive pomace for the production of omega-3 fatty acids by Crypthecodinium cohnii

Exhausted olive pomace (EOP) represents a potential candidate side stream to be utilized in biotechnological processes. EOP composition includes significant amounts of extractives and pectin, which are both usually discarded and are not utilized in the valorization process of the raw material. In this study, organosolv technology was optimized to remove the extractives and pectin using a Central Composite Rotatable Design. Optimal pretreatment conditions were predicted to be at 97.95 °C for 23.18 min, upon addition of 50% (v/v) EtOH in H₂O, with 0.5% (w/v) of H₂SO₄ as catalyst. The composition analysis of liquid fraction revealed a high content of total sugars (17.58 g/L), galacturonic acid (7.05 g/L) and phenolic compounds (2.97 g/L). The liquid fraction was utilized as a carbon source by the heterotrophic marine microalgae Crypthecodinium cohnii, where it was shown to promote lipid accumulation up to 38.5% wt. of cell biomass, even without any additional detoxification step. This study is the first report that shows the use of galacturonic acid as carbon source for the growth of C. cohnii, while underpinning the use of EOP as a promising substrate for the development of zero-waste bioprocesses.

Novel Routes in Transformation of Lignocellulosic Biomass to Furan Platform Chemicals: From Pretreatment to Enzyme Catalysis

The constant depletion of fossil fuels along with the increasing need for novel materials, necessitate the development of alternative routes for polymer synthesis. Lignocellulosic biomass, the most abundant carbon source on the planet, can serve as a renewable starting material for the design of environmentally-friendly processes for the synthesis of polyesters, polyamides and other polymers with significant value. The present review provides an overview of the main processes that have been reported throughout the literature for the production of bio-based monomers from lignocellulose, focusing on physicochemical procedures and biocatalysis. An extensive description of all different stages for the production of furans is presented, starting from physicochemical pretreatment of biomass and biocatalytic decomposition to monomeric sugars, coupled with isomerization by enzymes prior to chemical dehydration by acid Lewis catalysts. A summary of all biotransformations of furans carried out by enzymes is also described, focusing on galactose, glyoxal and aryl-alcohol oxidases, monooxygenases and transaminases for the production of oxidized derivatives and amines. The increased interest in these products in polymer chemistry can lead to a redirection of biomass valorization from second generation biofuels to chemical synthesis, by creating novel pathways to produce bio-based polymers.