Selective fractionation of Sugar Beet Pulp for release of fermentation and chemical feedstocks; optimisation of thermo-chemical pre-treatment

An Ionic Liquid-Based Biorefinery Approach for Duckweed Utilization

This study establishes a foundation for the ionic liquid (IL) pretreatment of duckweed biomass. An optimized IL-based process was designed to exploit the unique properties of duckweed including efficient metal removal, potential starch accumulation, and protein accumulation. Two ILs, namely, dimethylethanolammonium formate ([DMEtA][HCOO]) and N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), were investigated for the pretreatment of two duckweed species (Spirodela polyrhiza and Lemna minor). The evaluation focused on starch recovery, sugar release, protein recovery, and metal extraction capabilities. [DMEtA][HCOO] demonstrated near-quantitative starch recoveries at 120 °C, while [DMBA][HSO4] showed similar performance at 90 °C within a reaction time of 2 h. Saccharification yields for most pulps exceeded 90% after 8 h of hydrolysis, outperforming "traditional" lignocellulosic biomasses such as miscanthus or sugarcane bagasse. Approximately 50 and 80 wt % of the protein were solubilized in [DMEtA][HCOO] and [DMBA][HSO4], respectively, while the remaining protein distributed between the pulp and lignin. However, the solubilized protein in the IL could not be recovered due to its low molecular weight. Regarding metal extraction, [DMEtA][HCOO] demonstrated higher efficiency, achieving 81% removal of Ni from Lemna minor's pulps, whereas [DMBA][HSO4] extracted only 28% of Ni with slightly higher pulp concentrations. These findings indicate the need for further optimization in concurrent metal extraction using ILs.

Towards valorization of pectin-rich agro-industrial residues: Engineering of Saccharomyces cerevisiae for co-fermentation of d-galacturonic acid and glycerol

Pectin-rich plant biomass residues represent underutilized feedstocks for industrial biotechnology. The conversion of the oxidized monomer d-galacturonic acid (d-GalUA) to highly reduced fermentation products such as alcohols is impossible due to the lack of electrons. The reduced compound glycerol has therefore been considered an optimal co-substrate, and a cell factory able to efficiently co-ferment these two carbon sources is in demand. Here, we inserted the fungal d-GalUA pathway in a strain of the yeast S. cerevisiae previously equipped with an NAD-dependent glycerol catabolic pathway. The constructed strain was able to consume d-GalUA with the highest reported maximum specific rate of 0.23 g g_CDW^-1 h^-1 in synthetic minimal medium when glycerol was added. By means of a ¹³C isotope-labelling analysis, carbon from both substrates was shown to end up in pyruvate. The study delivers the proof of concept for a co-fermentation of the two 'respiratory' carbon sources to ethanol and demonstrates a fast and complete consumption of d-GalUA in crude sugar beet pulp hydrolysate under aerobic conditions. The future challenge will be to achieve co-fermentation under industrial, quasi-anaerobic conditions.

Valorization of sugar beet pulp through biotechnological approaches: recent developments

Sugar beet pulp (SBP) is a valuable by-product of the sugar beet industry and is predominantly composed of cellulose, hemicellulose, and pectin. It is commonly used as livestock feed because of its palatability, good energy levels, and highly digestible fibers such as pectins and glucans. However, the utilization of SBP for the production of value-added products via biotechnological approaches is gaining significance in recent years owing to its potential as a cost-effective nutrient source and technological advancements in its processing. SBP can be used as a substrate for bio-production of microbial enzymes, single cell protein, alcohols (e.g., ethanol), methane/biogas, hydrogen, lactic acid, ferulic acid, and pectic oligosaccharides. SBP can also be used as a carrier for cell immobilization in fermentation processes. This review focused on recent developments in biotechnological valorization of SBP.

Complete Utilization of the Major Carbon Sources Present in Sugar Beet Pulp Hydrolysates by the Oleaginous Red Yeasts Rhodotorula toruloides and R. mucilaginosa

Agro-industrial residues are low-cost carbon sources (C-sources) for microbial growth and production of value-added bioproducts. Among the agro-industrial residues available, those rich in pectin are generated in high amounts worldwide from the sugar industry or the industrial processing of fruits and vegetables. Sugar beet pulp (SBP) hydrolysates contain predominantly the neutral sugars d-glucose, l-arabinose and d-galactose, and the acidic sugar d-galacturonic acid. Acetic acid is also present at significant concentrations since the d-galacturonic acid residues are acetylated. In this study, we have examined and optimized the performance of a Rhodotorula mucilaginosa strain, isolated from SBP and identified at the molecular level during this work. This study was extended to another oleaginous red yeast species, R. toruloides, envisaging the full utilization of the C-sources from SBP hydrolysate (at pH 5.0). The dual role of acetic acid as a carbon and energy source and as a growth and metabolism inhibitor was examined. Acetic acid prevented the catabolism of d-galacturonic acid and l-arabinose after the complete use of the other C-sources. However, d-glucose and acetic acid were simultaneously and efficiently metabolized, followed by d-galactose. SBP hydrolysate supplementation with amino acids was crucial to allow d-galacturonic acid and l-arabinose catabolism. SBP valorization through the production of lipids and carotenoids by Rhodotorula strains, supported by complete catabolism of the major C-sources present, looks promising for industrial implementation.

Potential of Waste Biomass from the Sugar Industry as a Source of Furfural and Its Derivatives for Use as Fuel Additives in Poland

Poland is one of the leading producers of sugar from sugar beet in Europe. However, the production of sugar generates large amounts of lignocellulosic waste, in the form of beet pulp and leaves. Currently, this waste is not reutilized in the chemical industry, but is only used as food for farm animals. This paper assesses the potential of using bio-waste from the sugar industry as a raw material for the production of furfurals via acid hydrolysis. Further processing of furfural into derivatives such as furfuryl alcohol (FA) or tetrahydrofurfuryl alcohol (THFA) could increase the economic profitability of the initiative. Furfuryl alcohol can be used as a fuel additive in sugar factories. Tetrahydrofurfuryl alcohol can be used as a component in agricultural fertilizers, increasing the yield of sugar beet. This approach reduces the amount of post-production waste and brings the sugar industry closer to the concept of a circular economy.

Valorisation of pectin-rich agro-industrial residues by yeasts: potential and challenges

Pectin-rich agro-industrial residues are feedstocks with potential for sustainable biorefineries. They are generated in high amounts worldwide from the industrial processing of fruits and vegetables. The challenges posed to the industrial implementation of efficient bioprocesses are however manyfold and thoroughly discussed in this review paper, mainly at the biological level. The most important yeast cell factory platform for advanced biorefineries is currently Saccharomyces cerevisiae, but this yeast species cannot naturally catabolise the main sugars present in pectin-rich agro-industrial residues hydrolysates, in particular D-galacturonic acid and L-arabinose. However, there are non-Saccharomyces species (non-conventional yeasts) considered advantageous alternatives whenever they can express highly interesting metabolic pathways, natively assimilate a wider range of carbon sources or exhibit higher tolerance to relevant bioprocess-related stresses. For this reason, the interest in non-conventional yeasts for biomass-based biorefineries is gaining momentum. This review paper focuses on the valorisation of pectin-rich residues by exploring the potential of yeasts that exhibit vast metabolic versatility for the efficient use of the carbon substrates present in their hydrolysates and high robustness to cope with the multiple stresses encountered. The major challenges and the progresses made related with the isolation, selection, sugar catabolism, metabolic engineering and use of non-conventional yeasts and S. cerevisiae-derived strains for the bioconversion of pectin-rich residue hydrolysates are discussed. The reported examples of value-added products synthesised by different yeasts using pectin-rich residues are reviewed. Key Points • Review of the challenges and progresses made on the bioconversion of pectin-rich residues by yeasts. • Catabolic pathways for the main carbon sources present in pectin-rich residues hydrolysates. • Multiple stresses with potential to affect bioconversion productivity. • Yeast metabolic engineering to improve pectin-rich residues bioconversion. Graphical abstract.

A Simple Biorefinery Concept to Produce 2G-Lactic Acid from Sugar Beet Pulp (SBP): A High-Value Target Approach to Valorize a Waste Stream

Lactic acid is a high-value molecule with a vast number of applications. Its production in the biorefineries model is a possibility for this sector to aggregate value to its production chain. Thus, this investigation presents a biorefinery model based on the traditional sugar beet industry proposing an approach to produce lactic acid from a waste stream. Sugar beet is used to produce sugar and ethanol, and the remaining pulp is sent to animal feed. Using Bacillus coagulans in a continuous fermentation, 2781.01 g of lactic acid was produced from 3916.91 g of sugars from hydrolyzed sugar beet pulp, with a maximum productivity of 18.06 g L-1h-1. Without interfering in the sugar production, ethanol, or lactic acid, it is also possible to produce pectin and phenolic compounds in the biorefinery. The lactic acid produced was purified by a bipolar membrane electrodialysis and the recovery reached 788.80 g/L with 98% w/w purity.

Protein extraction from agri-food residues for integration in biorefinery: Potential techniques and current status

The biorefinery concept is attracting scientific and policy attention as a promising option for enhancing the benefits of agri-food biomass along with a reduction of the environmental impact. Obtaining bioproducts based on proteins from agri-food residues could help to diversify the revenue stream in a biorefinery. In fact, the extracted proteins can be applied as such or in the form of hydrolyzates due to their nutritional, bioactive and techno-functional properties. In this context, the present review summarizes, exemplifies and discusses conventional extraction methods and current trends to extract proteins from residues of the harvesting, post-harvesting and/or processing of important crops worldwide. Moreover, those extraction methods just integrated in a biorefinery scheme are also described. In conclusion, a plethora of methods exits but only some of them have been applied in biorefinery designs, mostly at laboratory scale. Their economic and technical feasibility at large scale requires further study.

One-Step Process for Environment-Friendly Preparation of Agar Oligosaccharides From Gracilaria lemaneiformis by the Action of Flammeovirga sp. OC4

Oligosaccharides extracted from agar Gracilaria lemaneiformis (G. lemaneiformis) have stronger physiological activities and a higher value than agar itself, but the pollution caused by the extraction process greatly restricts the sustainable use of agar. In this study, four bacterial strains with a high ability to degrade G. lemaneiformis were isolated from seawater by in situ enrichment in the deep sea. Among them, Flammeovirga sp. OC4, identified by morphological observation and its 16S rRNA sequencing (98.07% similarity to type strain JL-4 of Flammeovirga aprica), was selected. The optimum temperature and pH of crude enzyme produced by Flammeovirga sp. OC4 were 50°C and 8, respectively. More than 60% of the maximum enzyme activity remained after storage at pH 5.0-10.0 for 60 min. Both Mn²⁺ and Ba²⁺ could enhance the enzyme activity. A "one-step process" for preparation of oligosaccharides from G. lemaneiformis was established using Flammeovirga sp. OC4. After optimization of the Plackett-Burman (PB) design and response surface methodology (RSM), the yield of oligosaccharides was increased by 36.1% from 2.71 to 3.09 g L^-1 in a 250-mL fermenter with optimized parameters: 30 g L^-1 G. lemaneiformis powder, 4.84 g L^-1 (NH4)₂SO₄, 44.8-mL working medium volume at 36.7°C, and a shaking speed of 200 × g for 42 h. The extracted oligosaccharides were identified by thin layer chromatography (TLC) and ion chromatography, which consisted of neoagarobiose, agarotriose, neoagarotetraose, agaropentaose, and neoagarohexaose. These results provided an alternative approach for environment-friendly and sustainable utilization of algae.

Continuous enzymatic hydrolysis of sugar beet pectin and l-arabinose recovery within an integrated biorefinery

Sugar beet pulp (SBP) fractionated by steam explosion, released sugar beet pectin (SB-pectin) which was selectively hydrolysed using a novel α-l-arabinofuranosidase (AF), yielding monomeric l-arabinose (Ara) and a galacturonic acid rich backbone (GABB). AF was immobilised on an epoxy-functionalised resin with 70% overall immobilisation yield. Pretreatment of SB-pectin, to remove coloured compounds, improved the stability of the immobilised AF, allowing its reutilisation for up to 10 reaction cycles in a stirred tank reactor. Continuous hydrolysis of SB-pectin was subsequently performed using a packed bed reactor (PBR) with immobilised AF. Reactor performance was evaluated using a Design of Experiment approach. Pretreated SB-pectin hydrolysis was run for 7 consecutive days maintaining 73% of PBR performance. Continuous separation of Ara from GABB was achieved by tangential flow ultrafiltration with 92% Ara recovery. These results demonstrate the feasibility of establishing a continuous bioprocess to obtain Ara from the inexpensive SBP biomass.

Enzymatic Conversion of Sugar Beet Pulp: A Comparison of Simultaneous Saccharification and Fermentation and Separate Hydrolysis and Fermentation for Lactic Acid Production

This study compares the efficiency of lactic acid production by separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF) of sugar beet pulp, a byproduct of industrial sugar production. In experiments, sugar beet pulp was hydrolyzed using five commercial enzymes. A series of shake flask fermentations were conducted using five selected strains of lactic acid bacteria (LAB). The differences in the activities of the enzymes for degrading the principal sugar beet pulp components were reflected in the different yields of total reducing sugars. The highest yields after hydrolysis and the lowest quantities of insoluble residues were obtained using a mixture (1:1) of Viscozyme® and Ultraflo® Max. In the SHF process, only a portion of the soluble sugars released by the enzymes from the sugar beet pulp was assimilated by the LAB strains. In SSF, low enzyme loads led to reduction in the efficiency of sugar accumulation. The risk of carbon catabolic repression was reduced. Our results suggest that SSF has advantages over SHF, including lower processing costs and higher productivity. Lactic acid yield in SSF mode (approx. 30 g/L) was 80-90% higher than that in SHF.

Concept for Recycling Waste Biomass from the Sugar Industry for Chemical and Biotechnological Purposes

The objective of this study was to develop a method for the thermally-assisted acidic hydrolysis of waste biomass from the sugar industry (sugar beet pulp and leaves) for chemical and biotechnological purposes. The distillates, containing furfural, can be catalytically reduced directly into furfurayl alcohol or tetrahydrofurfuryl alcohol. The sugars present in the hydrolysates can be converted by lactic bacteria into lactic acid, which, by catalytic reduction, leads to propylene glycol. The sugars may also be utilized by microorganisms in the process of cell proliferation, and the biomass obtained used as a protein supplement in animal feed. Our study also considered the effects of the mode and length of preservation (fresh, ensilage, and drying) on the yields of furfural and monosaccharides. The yield of furfural in the distillates was measured using gas chromatography with flame ionization detector (GC-FID). The content of monosaccharides in the hydrolysates was measured spectrophotometrically using enzymatic kits. Biomass preserved under all tested conditions produced high yields of furfural, comparable to those for fresh material. Long-term storage of ensiled waste biomass did not result in loss of furfural productivity. However, there were significant reductions in the amounts of monosaccharides in the hydrolysates.

Centrifugal partition chromatography in a biorefinery context: Optimisation and scale-up of monosaccharide fractionation from hydrolysed sugar beet pulp

The isolation of component sugars from biomass represents an important step in the bioprocessing of sustainable feedstocks such as sugar beet pulp. Centrifugal partition chromatography (CPC) is used here, as an alternative to multiple resin chromatography steps, to fractionate component monosaccharides from crude hydrolysed sugar beet pulp pectin. CPC separation of samples, prepared in the stationary phase, was carried out using an ethanol: ammonium sulphate (300gL^-1) phase system (0.8:1.8v:v) in ascending mode. This enabled removal of crude feedstream impurities and separation of monosaccharides into three fractions (l-rhamnose, l-arabinose and d-galactose, and d-galacturonic acid) in a single step. Throughput was improved three-fold by increasing sample injection volume, from 4 to 16% of column volume, with similar separation performance maintained in all cases. Extrusion of the final galacturonic acid fraction increased the eluted solute concentration, reduced the total separation time by 24% and removed the need for further column regeneration. Reproducibility of the separation after extrusion was validated by using multiple stacked injections. Scale-up was performed linearly from a semi-preparative 250mL column to a preparative 950mL column with a scale-up ratio of 3.8 applied to mobile phase flow rate and sample injection volume. Throughputs of 9.4gL^-1h^-1 of total dissolved solids were achieved at the preparative scale with a throughput of 1.9gL^-1h^-1 of component monosaccharides. These results demonstrate the potential of CPC for both impurity removal and target fractionation within biorefinery separations.

An integrated biorefinery concept for conversion of sugar beet pulp into value-added chemicals and pharmaceutical intermediates

Over 8 million tonnes of sugar beet are grown annually in the UK. Sugar beet pulp (SBP) is the main by-product of sugar beet processing which is currently dried and sold as a low value animal feed. SBP is a rich source of carbohydrates, mainly in the form of cellulose and pectin, including d-glucose (Glu), l-arabinose (Ara) and d-galacturonic acid (GalAc). This work describes the technical feasibility of an integrated biorefinery concept for the fractionation of SBP and conversion of these monosaccharides into value-added products. SBP fractionation is initially carried out by steam explosion under mild conditions to yield soluble pectin and insoluble cellulose fractions. The cellulose is readily hydrolysed by cellulases to release Glu that can then be fermented by a commercial yeast strain to produce bioethanol at a high yield. The pectin fraction can be either fully hydrolysed, using physico-chemical methods, or selectively hydrolysed, using cloned arabinases and galacturonases, to yield Ara-rich and GalAc-rich streams. These monomers can be separated using either Centrifugal Partition Chromatography (CPC) or ultrafiltration into streams suitable for subsequent enzymatic upgrading. Building on our previous experience with transketolase (TK) and transaminase (TAm) enzymes, the conversion of Ara and GalAc into higher value products was explored. In particular the conversion of Ara into l-gluco-heptulose (GluHep), that has potential therapeutic applications in hypoglycaemia and cancer, using a mutant TK is described. Preliminary studies with TAm also suggest GluHep can be selectively aminated to the corresponding chiral aminopolyol. The current work is addressing the upgrading of the remaining SBP monomer, GalAc, and the modelling of the biorefinery concept to enable economic and Life Cycle Analysis (LCA).

Simultaneous Saccharification and Fermentation of Sugar Beet Pulp with Mixed Bacterial Cultures for Lactic Acid and Propylene Glycol Production

Research into fermentative production of lactic acid from agricultural by-products has recently concentrated on the direct conversion of biomass, whereby pure sugars are replaced with inexpensive feedstock in the process of lactic acid production. In our studies, for the first time, the source of carbon used is sugar beet pulp, generated as a by-product of industrial sugar production. In this paper, we focus on the simultaneous saccharification of lignocellulosic biomass and fermentation of lactic acid, using mixed cultures with complementary assimilation profiles. Lactic acid is one of the primary platform chemicals, and can be used to synthesize a wide variety of useful products, including green propylene glycol. A series of controlled batch fermentations was conducted under various conditions, including pretreatment with enzymatic hydrolysis. Inoculation was performed in two sequential stages, to avoid carbon catabolite repression. Biologically-synthesized lactic acid was catalytically reduced to propylene glycol over 5% Ru/C. The highest lactic acid yield was obtained with mixed cultures. The yield of propylene glycol from the biological lactic acid was similar to that obtained with a water solution of pure lactic acid. Our results show that simultaneous saccharification and fermentation enables generation of lactic acid, suitable for further chemical transformations, from agricultural residues.