Enhancement of sugar recovery and ethanol production from wheat straw through alkaline pre-extraction followed by steam pretreatment

Beauveria Bassiana Amylase-Polygalacturonase Production Using Lignocellulosic Biomass and Application in Juice Processing

Background

The search for sources of industrial biocatalysts, which are non-pathogenic and can utilise cheap nutrient sources, has been a continuous endeavour in the ~ 7 billion USD enzyme industry. Beauveria bassiana, an endophytic fungal entomopathogen, is non-pathogenic and possesses the potential to secrete various bioproducts while utilising readily available lignocellulosic biomass.

Objective

This study investigated the optimised production of two glycosyl hydrolases, amylase and polygalacturonase, by B. bassiana while utilising readily available agricultural residues. Subsequently, the industrial potential of the enzymes in the clarification of fruit juice was evaluated.

Materials and Methods

Initially, seven agro residues were screened for the concomitant production of amylase and polygalacturonase by B. bassiana SAN01. Subsequently, statistical optimisation tools, Plackett Burman Design (PBD) and Central Composite Design (CCD), were employed for the optimisation of enzyme production. The enzyme mixture was partially purified and applied in the clarification of pineapple juice.

Result

The production of B. bassiana SAN01 amylase and polygalacturonase was found to be maximal while utilising wheat bran. Subsequent to PBD and CCD optimisation, the optimal conditions for enzyme production were identified to be at 30 °C, pH 6.0 and wheat bran concentration of ~40 g.L-1. Under these optimised conditions, heightened production levels of 34.82 and 51.05 U.mL-1 were recorded for amylase and polygalacturonase, respectively, which were 179% and 187% of the initial unoptimised levels. In addition, the most effective clarification of the juice (~90%) was observed at 35 °C after an incubation time of 120 min with no significant effect on the pH and total dissolved solids.

Conclusion

B. bassiana, a well-known biocontrol agent, was shown to produce amylase and polygalacturonase using readily available agricultural residues for the first time. These enzyme production levels are the highest for these enzymes from any known endophytic fungal entomopathogen. This study further demonstrates the potential applicability of B. bassiana in other industrial processes besides its widespread use as a biopesticide.

Enhancing cellulosic digestibility of wheat straw by adding sodium lignosulfonate and sodium hydroxide to hydrothermal pretreatment

Surfactant-assisted pretreatment has been widely reported to improve the enzymatic hydrolysis of lignocellulose by promoting removal of xylan and lignin. Hence, this work innovatively proposed the use of sodium lignosulfonate (SL) as an additive of alkaline pretreatment (AP), and evaluated its influence on the cellulosic digestibility of wheat straw (WS). The results displayed that the maximum of 72-h cellulosic digestibility could reach 83.5% as 15 g/L SL was introduced to the AP process (SAP), while the cellulosic digestibility of hydrothermal and alkaline pretreated WS was only 63.6% and 70.2%, respectively. These increments were subsequently attributed to the improvement of 6.5% xylan and 26.8% lignin accelerated by SAP, resulting in positive changes in structural characteristics such as accessibility, specific surface area, and cellulosic crystalline structure. The utilization of lignin-based surfactants in pretreatment has realized the economic feasibility of lignocellulosic biorefining and broadened the application prospect of surfactants.

Agro-Food Residues and Bioethanol Potential: A Study for a Specific Area

Bioethanol obtained from agro-food wastes could contribute to decrease the dependency on fossil resources, reduce the impact of fossil fuels on the environment, and mitigate the food versus fuel debate. This study is aimed to investigate the availability of residual inexpensive agro-food biomasses that could feed a second-generation bioethanol plant located in a specific area of North Eastern Italy. After the identification of all crops in the area, more than 40 agro-food residues were analyzed for their availability and compositions in terms of water, polysaccharides, and sugars potentially convertible into bioethanol. 574,166 Mg of residual wet lignocellulosic biomass corresponding to 297,325 Mg of dry material were found available for bioethanol conversion. The most promising substrates were wheat straw and vine shoots. Based on the chemical composition of residues, the potential attainable ethanol was determined. Theoretical potential ethanol production was estimated at nearly 72,000 Mg per year. This quantity extensively exceeds the minimum yearly capacity of a sustainable bioethanol plant previously identified as around 50,000 Mg of ethanol. Taken together, these results demonstrate that, in the analyzed area, agro-food residues are available in an amount that could sustain bioethanol production in a specific and restricted district. Techno-economical evaluations are in progress to assess the actual feasibility of installing a second generation bioethanol production plant in the area of interest.

Enhanced lignin removal and enzymolysis efficiency of grass waste by hydrogen peroxide synergized dilute alkali pretreatment

Pretreatment process plays a key role in biofuel production from lignocellulosic feedstocks. A study on dilute NaOH pretreatment supplemented with H₂O₂ under mild condition was conducted to overcome the recalcitrance of grass waste (GW). The optimized process could selectively increase lignin removal (73.2%), resulting in high overall recovery of holocellulose (73.8%) as well as high enzymolysis efficiency (83.5%) compared to H₂O₂ or NaOH pretreatment. The analyses by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) revealed that supplementary H₂O₂ disrupted the structure of GW to facilitate the removal of lignin by NaOH, and exhibited synergistic effect on lignin removal and enzymolysis with dilute NaOH. Moreover, high titer of ethanol (100.7 g/L) was achieved by SSCF on 30% (w/v) pretreated GW loading. The present study suggests that the established synergistic pretreatment is a simple, efficient, and promising process for GW biorefinery.

Improving enzymatic saccharification of hardwood through lignin modification by carbocation scavengers and the underlying mechanisms

In this work, the beneficial effect of carbocation scavenger additives on hardwood pretreatment was revealed by significantly improved biomass saccharification: cellulose hydrolysis yield was increased by over 15% after steam pretreatment of poplar, while that was enhanced by more than 48% after dilute acid pretreatment. Besides, the relative contributions of lignin towards enzyme binding and physical barrier effect for proposed mechanisms were quantified. Results indicated that the addition of carbocation scavenger, 2-naphthol-7-sulfonate, resulted in acid groups incorporation of 62.36 mmol/kg to lignin, which mitigated enzyme non-productive binding. Moreover, enlarged biomass porosity and reduced surface lignin coverage were detected through BET and XPS analysis, respectively, which mostly related to the diminished physical barrier effect of lignin. As a result, the lignin inhibitions were significantly suppressed through the addition of carbocation scavenger, giving rise to significantly improved enzymatic hydrolysis of hardwood.

Integrated process for the coproduction of fermentable sugars and lignin adsorbents from hardwood

This work proposed an integrated process based on alkali-sulfite (AlkSul) pretreatment to coproduce fermentable sugars and lignin adsorbents from hardwood. Different from conventional liquid hot water (LHW) pretreatment, this pretreatment improved cellulose accessibility through selective lignin removal and modification, resulting in significantly enhanced biomass saccharification. Over 75% of the original cellulose and hemicellulose was released and could be recovered as fermentable sugars after pretreatment and subsequent enzymatic hydrolysis. Meanwhile, lignin residues from pretreatment hydrolysate and enzymatic hydrolysate showed lead ions adsorption capacities of 156.25 and 68.49 mg/g, respectively, indicating both streams of lignin residues were favorable adsorbents for heavy metal ions. The improved adsorption capacity of lignin residues was primarily due to the lignin modification as sulfur-containing functional groups incorporation during the integrated pretreatment. Results demonstrated the integrated alkali-sulfite pretreatment improved biomass saccharification, while coproducing lignin adsorbents for wastewater treatment, which can promote the sustainability of lignocellulosic biorefinery.

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.

Two-stage alkali-oxygen pretreatment capable of improving biomass saccharification for bioethanol production and enabling lignin valorization via adsorbents for heavy metal ions under the biorefinery concept

Converting lignin into value-added products in current lignocellulosic biorefineries has been challenging, which in turn restricts the commercialization of many lignocellulosic biorefineries. In this work, a two-stage alkali-oxygen assisted liquid hot water pretreatment (AlkOx) was proposed as the first step of biorefinery. This alkali-oxygen pretreatment facilitated biomass fractionation by solubilizing majority of lignin in water-soluble fraction, while remaining most of cellulose and hemicellulose in water-insoluble fraction. As a result, biomass saccharification was significantly improved by selective removal and oxidative modification of lignin through alkali-oxygen pretreatment. Moreover, lignin residues from both pretreatment hydrolysate and enzymatic hydrolysate were shown to be favorable adsorbents for Pb(II) ions, with adsorption capacity of 263.16 and 90.91 mg/g, respectively. Results demonstrated that this integrated process could not only improve biomass saccharification but also enable lignin valorization, which encouraged the holistic utilization of lignin residues as part of an integrated biorefinery.

Enhanced ethanol production from industrial lignocellulose hydrolysates by a hydrolysate-cofermenting Saccharomyces cerevisiae strain

Industrial production of lignocellulosic ethanol requires a microorganism utilizing both hexose and pentose, and tolerating inhibitors. In this study, a hydrolysate-cofermenting Saccharomyces cerevisiae strain was obtained through one step in vivo DNA assembly of pentose-metabolizing pathway genes, followed by consecutive adaptive evolution in pentose media containing acetic acid, and direct screening in biomass hydrolysate media. The strain was able to coferment glucose and xylose in synthetic media with the respective maximal specific rates of glucose and xylose consumption, and ethanol production of 3.47, 0.38 and 1.62 g/g DW/h, with an ethanol titre of 41.07 g/L and yield of 0.42 g/g. Industrial wheat straw hydrolysate fermentation resulted in maximal specific rates of glucose and xylose consumption, and ethanol production of 2.61, 0.54 and 1.38 g/g DW/h, respectively, with an ethanol titre of 54.11 g/L and yield of 0.44 g/g. These are among the best for wheat straw hydrolysate fermentation through separate hydrolysis and cofermentation.