A critical assessment on scalable technologies using high solids loadings in lignocellulose biorefinery: challenges and solutions

The pretreatment and the enzymatic saccharification are the key steps in the extraction of fermentable sugars for further valorization of lignocellulosic biomass (LCB) to biofuels and value-added products via biochemical and/or chemical conversion routes. Due to low density and high-water absorption capacity of LCB, the large volume of water is required for its processing. Integration of pretreatment, saccharification, and co-fermentation has succeeded and well-reported in the literature. However, there are only few reports on extraction of fermentable sugars from LCB with high biomass loading (>10% Total solids-TS) feasible to industrial reality. Furthermore, the development of enzymatic cocktails can overcome technology hurdles with high biomass loading. Hence, a better understanding of constraints involved in the development of technology with high biomass loading can result in an economical and efficient yield of fermentable sugars for the production of biofuels and bio-chemicals with viable titer, rate, and yield (TRY) at industrial scale. The present review aims to provide a critical assessment on the production of fermentable sugars from lignocelluloses with high solid biomass loading. The impact of inhibitors produced during both pretreatment and saccharification has been elucidated. Moreover, the limitations imposed by high solid loading on efficient mass transfer during saccharification process have been elaborated.

Analysis of Aureobasidium pullulans LB83 secretome reveals distinct carbohydrate active enzymes for biomass saccharification

Aureobasidium pullulans LB83 is a versatile biocatalyst that produces a plethora of bioactive products thriving on a variety of feedstocks under the varying culture conditions. In our last study using this microorganism, we found cellulase activity (FPase, 2.27 U/ml; CMCase, 7.42 U/ml) and other plant cell wall degrading enzyme activities grown on sugarcane bagasse and soybean meal as carbon source and nitrogen, respectively. In the present study, we provide insights on the secretome analysis of this enzymatic cocktail. The secretome analysis of A. pullulans LB83 by Liquid Chromatography coupled to Mass Spectroscopy (LC-MS/MS) revealed 38 classes of Carbohydrate Active enZymes (CAZymes) of a total of 464 identified proteins. These CAZymes consisted of 21 glycoside hydrolases (55.26%), 12 glycoside hydrolases harboring carbohydrate-binding module (31.58%), 4 carbohydrate esterases (10.53%) and one glycosyl transferase (2.63%). To the best of our knowledge, this is the first report on the secretome analysis of A. pullulans LB83.

Fermentative Production of β-Carotene from Sugarcane Bagasse Hydrolysate by Rhodotorula glutinis CCT-2186

Β-Carotene is a red-orange pigment that serves as a precursor to important pharmaceutical molecules like vitamin A and retinol, making it highly significant in the industrial sector. Consequently, there is an ongoing quest for more sustainable production methods. In this study, glucose and xylose, two primary sugars derived from sugarcane bagasse (SCB), were utilized as substrates for β-carotene production by Rhodotorula glutinis CCT-2186. To achieve this, SCB underwent pretreatment using NaOH, involved different concentrations of total solids (TS) (10%, 15%, and 20%) to remove lignin. Each sample was enzymatically hydrolyzed using two substrate loadings (5% and 10%). The pretreated SCB with 10%, 15%, and 20% TS exhibited glucose hydrolysis yields (%wt) of 93.10%, 91.88%, and 90.77%, respectively. The resulting hydrolysate was employed for β-carotene production under batch fermentation. After 72 h of fermentation, the SCB hydrolysate yielded a β-carotene concentration of 118.56 ± 3.01 mg/L. These findings showcase the robustness of R. glutinis as a biocatalyst for converting SCB into β-carotene.

Lignocellulosic biomass-based glycoconjugates for diverse biotechnological applications

Glycoconjugates are the ubiquitous components of mammalian cells, mainly synthesized by covalent bonds of carbohydrates to other biomolecules such as proteins and lipids, with a wide range of potential applications in novel vaccines, therapeutic peptides and antibodies (Ab). Considering the emerging developments in glycoscience, renewable production of glycoconjugates is of importance and lignocellulosic biomass (LCB) is a potential source of carbohydrates to produce synthetic glycoconjugates in a sustainable pathway. In this review, recent advances in glycobiology aiming on glycoconjugates production is presented together with the recent and cutting-edge advances in the therapeutic properties and application of glycoconjugates, including therapeutic glycoproteins, glycosaminoglycans (GAGs), and nutraceuticals, emphasizing the integral role of glycosylation in their function and efficacy. Special emphasis is given towards the potential exploration of carbon neutral feedstocks, in which LCB has an emerging role. Techniques for extraction and recovery of mono- and oligosaccharides from LCB are critically discussed and influence of the heterogeneous nature of the feedstocks and different methods for recovery of these sugars in the development of the customized glycoconjugates is explored. Although reports on the use of LCB for the production of glycoconjugates are scarce, this review sets clear that the potential of LCB as a source for the production of valuable glycoconjugates cannot be underestimated and encourages that future research should focus on refining the existing methodologies and exploring new approaches to fully realize the potential of LCB in glycoconjugate production.

Unlocking the potential of low FODMAPs sourdough technology for management of irritable bowel syndrome

Consumption of high FODMAP (Fermentable Oligo-, Di-, and Monosaccharides and Polyols) diet is the leading cause of alteration in the human gut microbiome, thereby, causing irritable bowel syndrome (IBS). Therefore, sourdough technology can be exploited for reduction of FODMAPs in various foods to alleviate the symptoms of IBS. Several microorganisms viz. Pichia fermentans, Lactobacillus fetmentum, Saccharomyces cerevisiae, Torulaspora delbrueckii, Kluyveromyces marxianus etc. have been identified for the production of low FODMAP type II sourdough fermented products. However, more research on regulation of end-product and volatilome profile is required for maximal exploitation of FODMAP-reducing microorganisms. Therefore, the present review is focused on utilisation of lactic acid bacteria and yeasts, alone and in synergy, for the production of low FODMAP sourdough foods. Moreover, the microbial bioprocessing of cereal and non-cereal based low FODMAP fermented sourdough products along with their nutritional and therapeutic benefits have been elaborated. The challenges and future prospects for the production of sourdough fermented low FODMAP foods, thereby, bringing out positive alterations in gut microbiome, have also been discussed.

Microbial meat: A sustainable vegan protein source produced from agri-waste to feed the world

In the modern world, animal and plant protein may not meet the sustainability criteria due to their high need for arable land and potable water consumption, among other practices. Considering the growing population and food shortage, finding alternative protein sources for human consumption is an urgent issue that needs to be solved, especially in developing countries. In this context, microbial bioconversion of valuable materials in nutritious microbial cells represent a sustainable alternative to the food chain. Microbial protein, also known as single-cell protein (SCP), consist of algae biomass, fungi or bacteria that are currently used as food source for both humans and animals. Besides contributing as a sustainable source of protein to feed the world, producing SCP, is important to reduce waste disposal problems and production costs meeting the sustainable development goals. However, for microbial protein as feed or food to become an important and sustainable alternative, addressing the challenges of raising awareness and achieving wider public regulatory acceptance is real and must be addressed with care and convenience. In this work, we critically reviewed the potential technologies for microbial protein production, its benefits, safety, and limitations associated with its uses, and perspectives for broader large-scale implementation. We argue that the information documented in this manuscript will assist in developing microbial meat as a major protein source for the vegan world.

Biotechnological advances in biomass pretreatment for bio-renewable production through nanotechnological intervention

Globally, the fossil fuel reserves are depleting rapidly and the escalating fuel prices as well as plethora of the pollutants released from the emission of burning fossil fuels cause global warming that massively disturb the ecological balance. Moreover, the unnecessary utilization of non-renewable energy sources is a genuine hazard to nature and economic stability, which demands an alternative renewable source of energy. The lignocellulosic biomass is the pillar of renewable sources of energy. Different conventional pretreatment methods of lignocellulosic feedstocks have employed for biofuel production. However, these pretreatments are associated with disadvantages such as high cost of chemical substances, high load of organic catalysts or mechanical equipment, time consuming, and production of toxic inhibitors causing the environmental pollution. Nanotechnology has shown the promised biorefinery results by overcoming the disadvantages associated with the conventional pretreatments. Recyclability of nanomaterials offers cost effective and economically viable biorefineries processes. Lignolytic and saccharolytic enzymes have immobilized onto/into the nanomaterials for the higher biocatalyst loading due to their inherent properties of high surface area to volume ratios. Nanobiocatalyst enhance the hydrolyzing process of pretreated biomass by their high penetration into the cell wall to disintegrate the complex carbohydrates for the release of high amounts of sugars towards biofuel and various by-products production. Different nanotechnological routes provide cost-effective bioenergy production from the rich repertoires of the forest and agricultural-based lignocellulosic biomass. In this article, a critical survey of diverse biomass pretreatment methods and the nanotechnological interventions for opening up the biomass structure has been carried out.

Sustainable utilization of pineapple wastes for production of bioenergy, biochemicals and value-added products: A review

Agricultural residues play a pivotal role in meeting the growing energy and bulk chemicals demand and food security of society. There is global concern about the utilization of fossil-based fuels and chemicals which create serious environmental problems. Biobased sustainable fuels can afford energy and fuels for future generations. Agro-industrial waste materials can act as the alternative way for generating bioenergy and biochemicals strengthening low carbon economy. Processing of pineapple generates about 60% of the weight of the original pineapple fruit in the form of peel, core, crown end, and pomace that can be converted into bioenergy sources like bioethanol, biobutanol, biohydrogen, and biomethane along with animal feed and vermicompost as described in this paper. This paper also explains about bioconversion process towards the production of various value-added products such as phenolic anti-oxidants, bromelain enzyme, phenolic flavour compounds, organic acids, and animal feed towards bioeconomy.

Drudgery assessment and ergonomic evaluation of pedal operated Ragi (Eleusine Coracana) thresher

BACKGROUND

Ragi (Eleusine Coracana) is a major food crop for the tribal population of India.

OBJECTIVE

This study emphasizes the need to consider ergonomics aspects in the design and development of a pedal operated ragi thresher (PORT) for tribal people, and assesses the drudgery as well as ergonomic evaluation of a developed thresher against the conventional practice.

METHODS

Thirty subjects (male = 15 and female = 15) from the tribal region were evaluated ergonomically. The physiological responses of the subjects were studied and their performance was compared.

RESULTS

The results revealed that the working heart rate, oxygen consumption rate and overall discomfort rating were significantly higher in case of traditional threshing as compared to those in case of PORT. Postural analysis identified the traditional method as the most fatigue one as the person has to lift the hand above shoulder level repeatedly and has to sit in a squatting posture for long period.

CONCLUSION

The drudgery and occupational hazards to public health involved in the traditional method of threshing was reduced by using the PORT. Furthermore, the traditional method involved continuous stressed actions across the entire body, whereas the PORT involved only the lower limbs.

Biodiesel Production From Lignocellulosic Biomass Using Oleaginous Microbes: Prospects for Integrated Biofuel Production

Biodiesel is an eco-friendly, renewable, and potential liquid biofuel mitigating greenhouse gas emissions. Biodiesel has been produced initially from vegetable oils, non-edible oils, and waste oils. However, these feedstocks have several disadvantages such as requirement of land and labor and remain expensive. Similarly, in reference to waste oils, the feedstock content is succinct in supply and unable to meet the demand. Recent studies demonstrated utilization of lignocellulosic substrates for biodiesel production using oleaginous microorganisms. These microbes accumulate higher lipid content under stress conditions, whose lipid composition is similar to vegetable oils. In this paper, feedstocks used for biodiesel production such as vegetable oils, non-edible oils, oleaginous microalgae, fungi, yeast, and bacteria have been illustrated. Thereafter, steps enumerated in biodiesel production from lignocellulosic substrates through pretreatment, saccharification and oleaginous microbe-mediated fermentation, lipid extraction, transesterification, and purification of biodiesel are discussed. Besides, the importance of metabolic engineering in ensuring biofuels and biorefinery and a brief note on integration of liquid biofuels have been included that have significant importance in terms of circular economy aspects.

Production of first- and second-generation ethanol for use in alcohol-based hand sanitizers and disinfectants in India

Emergence of "severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)" causing "COVID-19" or "coronavirus disease 19" as pandemic has got worldwide attention towards hygiene as the first line of defense for the infection control. It is first line of defense not only from COVID-19 but also from other infectious diseases caused by deadly pathogens such as cholera, hepatitis, tuberculosis, polio, etc. Absence of any particular vaccine or treatment let World Health Organization (WHO) recommend to the public to maintain social distancing along with regularly washing their hands with soap, sanitize their hands (where washing is not possible), and disinfect their belongings and buildings to avoid the infection. Out of various formulations available in the market, WHO has recommended alcohol-based hand sanitizers, which mainly comprise of ethanol, isopropyl alcohols, and hydrogen peroxides in different combinations due to their high potential to kill the broad range of pathogens including bacterial, viral, fungal, helminthes, etc. Therefore, alcohol-based sanitizers are in high demand since centuries to prevent infection from pathogenic diseases. Ethanol is the most common and popular alcohol in terms of vanishing wide range of pathogens, convenient to use and its production. Ethanol is produced worldwide and is used in various sectors, e.g., beauty and cosmetics, food and beverages, and as the most demanding gasoline additive. The present review is focused on the ethanol production in India, its diversified applications emphasizing hand sanitizers with discussions on formulation of sanitizer and disinfectants, and viability of lignocellulosic and food grain-based ethanol. The review article also emphasizes on the technological details of 1G and 2G ethanol production, their associated challenges, and inputs for the improved ethanol yields so as to strengthen the supply chain of ethanol in India, and making "Atmanirbhar Bharat" (Self-reliant India) campaign of Indian government successfully viable.

Kluyveromyces marxianus: a potential biocatalyst of renewable chemicals and lignocellulosic ethanol production

Kluyveromyces marxianus is an ascomycetous yeast which has shown promising results in cellulosic ethanol and renewable chemicals production. It can survive on a variety of carbon sources under industrially favorable conditions due to its fast growth rate, thermotolerance, and acid tolerance. K. marxianus, is generally regarded as a safe (GRAS) microorganism, is widely recognized as a powerhouse for the production of heterologous proteins and is accepted by the US Food and Drug Administration (USFDA) for its pharmaceutical and food applications. Since lignocellulosic hydrolysates are comprised of diverse monomeric sugars, oligosaccharides and potential metabolism inhibiting compounds, this microorganism can play a pivotal role as it can grow on lignocellulosic hydrolysates coping with vegetal cell wall derived inhibitors. Furthermore, advancements in synthetic biology, for example CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats with Cas9)-mediated genome editing, will enable development of an engineered yeast for the production of biochemicals and biopharmaceuticals having a myriad of industrial applications. Genetic engineering companies such as Cargill, Ginkgo Bioworks, DuPont, Global Yeast, Genomatica, and several others are actively working to develop designer yeasts. Given the important traits and properties of K. marxianus, these companies may find it to be a suitable biocatalyst for renewable chemicals and fuel production on the large scale. This paper reviews the recent progress made with K. marxianus biotechnology for sustainable production of ethanol, and other products utilizing lignocellulosic sugars.

Production of cellulases by Aureobasidium pullulans LB83: optimization, characterization, and hydrolytic potential for the production of cellulosic sugars

Aureobasidium pullulans LB83 was evaluated for cellulase production under submerged fermentation conditions. Different process variables such as carbon sources (corn cob, sugarcane bagasse, and sugarcane straw), synthetic (urea, ammonium sulfate, and peptone), and non-synthetic (soybean meal, rice, and corn meal) nitrogen sources and inoculum size were evaluated by one parameter at-a-time strategy. Aureobasidium pullulans LB83 showed maximum cellulase activity (FPase, 2.27 U/mL; CMCase, 7.42 U/mL) on sugarcane bagasse. Among the nitrogen sources, soybean meal as a non-synthetic nitrogen sources showed a maximum cellulase activity (FPase 2.45 U/mL; CMCase, 6.86 U/mL) after 60 hr. The inoculum size of 1.6 × 106 CFU/mL had the maximum FPase and CMCase activities of 3.14 and 8.74 U/mL, respectively. For the enzymatic hydrolysis, both the commercial cellulase (10 FPU/g of Cellic CTec 2 (#A) and 10 FPU/g of crude enzyme extract (CEE) (#B), and varying ratio of CTec 2 and CEE in combination #C (5 FPU/g of CTec 2 + 5 FPU/g CEE), combination #D (2.5 FPU/g of CTec 2 + 7.5 FPU/g CEE), and combination #E (7.5 FPU/g of CTec 2 + 2.5 FPU/g CEE) were assessed for enzymatic hydrolysis of delignified sugarcane bagasse. Enzyme combination #C showed maximum hydrolysis yield of 92.40%. The study shows the hydrolytic potential of cellulolytic enzymes from A. pullulans LB83 for lignocellulosic sugars production from delignified sugarcane bagasse.

Development of sustainable approaches for converting the organic waste to bioenergy

Dependence on fossil fuels such as oil, coal and natural gas are on alarming increase, thereby causing such resources to be in a depletion mode and a novel sustainable approach for bioenergy production are in demand. Successful implementation of zero waste discharge policy is one such way to attain a sustainable development of bioenergy. Zero waste discharge can be induced only through the conversion of organic wastes into bioenergy. Waste management is pivotal and considering its importance of minimizing the issue and menace of wastes, conversion strategy of organic waste is effectively recommended. Present review is concentrated on providing a keen view on the potential organic waste sources and the way in which the bioenergy is produced through efficient conversion processes. Biogas, bioethanol, biocoal, biohydrogen and biodiesel are the principal renewable energy sources. Different types of organic wastes used for bioenergy generation and its sources, anaerobic digestion-biogas production and its related process affecting parameters including fermentation, photosynthetic process and novel nano-inspired techniques are discussed. Bioenergy production from organic waste is associated with mitigation of lump waste generation and its dumping into land, specifically reducing all hazards and negativities in all sectors during waste disposal. A sustainable bioenergy sector with upgraded security for fuels, tackles the challenging climatic change problem also. Thus, intensification of organic waste conversion strategies to bioenergy, specially, biogas and biohydrogen production is elaborated and analyzed in the present article. Predominantly, persistent drawbacks of the existing organic waste conversion methods have been noted, providing consideration to economic, environmental and social development.

Comparative data on effects of alkaline pretreatments and enzymatic hydrolysis on bioemulsifier production from sugarcane straw by Cutaneotrichosporon mucoides

Bioemulsifiers are surface active compounds which could be potentially used in food processing, cosmetic sector and oil recovery. Sugarcane straw (SS), was used as the raw substrate for the production of bio-emulsifiers (BE) by Cutaneotrichosporon mucoides. Three different delignification strategies using dilute sodium hydroxide, sodium sulfite and ammonium hydroxide followed by enzymatic hydrolysis (Cellic CTec 2, 7.5% total solids, 15 FPU/g, 72 h) were studied. Enzyme hydrolysis of ammonium hydroxide pretreated SS showed a maximum of 62.19 ± 0.74 g/l total reducing sugars with 88.35% hydrolytic efficiency (HE) followed by sodium hydroxide (60.06 ± 0.33 g/l; 85.40% HE) and sodium sulfite pretreated SS (57.22 ± 0.52 g/l; 84.71% HE), respectively. The ultrastructure of SS (native and delignified) by fourier transform-infrared and near infrared spectroscopy, revealed notable structural differences. The fermentation of hydrolysates by C. mucoides into bioemulsifiers showing emulsification index (EI) of 54.33%, 48.66% and 32.66% from sodium sulfite, sodium hydroxide, and ammonium hydroxide pretreated SS, respectively.

Lignocellulose derived functional oligosaccharides: production, properties, and health benefits

Lignocellulosic biomass (LB) is the renewable feedstock for the production of fuel/energy, feed/food, chemicals, and materials. LB could also be the versatile source of the functional oligosaccharides, which are non-digestible food ingredients having numerous applications in food, cosmetics, pharmaceutical industries, and others. The burgeoning functional food demand is expected to be more than US$440 billion in 2022. Because of higher stability at low pH and high temperature, oligosaccharides stimulate the growth of prebiotic bifidobacteria and lactic acid bacteria. Xylooligosaccharides (XOS) are major constituents of oligosaccharides consisting of 2-7 xylose monomeric units linked via β-(1,4)-linkages. XOS can be obtained from various agro-residues by thermochemical pretreatment, enzymatic or chemoenzymatic methods. While thermochemical methods are fast, reproducible, enzymatic methods are substrate specific, costly, and produce minimum side products. Enzymatic methods are preferred for the production of food grade and pharmaceutically important oligosaccharides. XOS are potent prebiotics having antioxidant properties and enhance the bio-adsorption of calcium and improving bowel functions, etc. LB can cater to the increasing demand of oligosaccharides because of their foreseeable amount and the advancements in technology to recover oligosaccharides. This paper summarizes the methods for oligosaccharides production from LB, classification, and benefits of oligosaccharides on human health.

Hemicellulosic ethanol production by immobilized cells of Scheffersomyces stipitis: effect of cell concentration and stirring

Bioconversion of hemicellulosic hydrolysate into ethanol plays a pivotal role in the overall success of biorefineries. For the efficient fermentative conversion of hemicellulosic hydrolysates into ethanol, the use of immobilized cells system could provide the enhanced ethanol productivities with significant time savings. Here, we investigated the effect of 2 important factors (e.g., cell concentration and stirring) on ethanol production from sugarcane bagasse hydrolysate using the yeast Scheffersomyces stipitis immobilized in calcium alginate matrix. A 2(2) full factorial design of experiment was performed considering the process variables- immobilized cell concentration (3.0, 6.5 and 10.0 g/L) and stirring (100, 200 and 300 rpm). Statistical analysis showed that stirring has the major influence on ethanol production. Maximum ethanol production (8.90 g/l) with ethanol yield (Yp/s) of 0.33 g/g and ethanol productivity (Qp) of 0.185 g/l/h was obtained under the optimized process conditions (10.0 g/L of cells and 100 rpm).

Optimization of selective production media for enhanced production of xylanases in submerged fermentation by Thielaviopsis basicola MTCC 1467 using L16 orthogonal array

Enzymes have been the centre of attention for researchers/industrialists worldwide due to their wide range of physiological, analytical, food/feed and industrial based applications. Among the enzymes explored for industrial applications, xylanases play an instrumental role in food/feed, textile/detergent, paper and biorefinery based application sectors. This study deals with the statistical optimization of xylanase production by Thielaviopsis basicola MTCC 1467 under submerged fermentation conditions using rice straw, as sole carbon source. Different fermentation parameters such as carbon source, nitrogen source, inorganic salts like KH2PO4, MgSO4 and pH of the medium were optimized at the individual and interactive level by Taguchi orthogonal array methodology (L16). All selected fermentation parameters influenced the enzyme production. Rice straw, the major carbon source mainly influenced the production of xylanase (~34 %). After media optimization, the yield of enzyme improved from 38 to ~60 IU/ml (161.5 %) indicating the commercial production of xylanase by T. basicola MTCC 1467. This study shows the potential of T. basicola MTCC 1467 for the efficient xylanase production under the optimized set of conditions.

Multi-scale structural and chemical analysis of sugarcane bagasse in the process of sequential acid-base pretreatment and ethanol production by Scheffersomyces shehatae and Saccharomyces cerevisiae

BACKGROUND

Heavy usage of gasoline, burgeoning fuel prices, and environmental issues have paved the way for the exploration of cellulosic ethanol. Cellulosic ethanol production technologies are emerging and require continued technological advancements. One of the most challenging issues is the pretreatment of lignocellulosic biomass for the desired sugars yields after enzymatic hydrolysis. We hypothesized that consecutive dilute sulfuric acid-dilute sodium hydroxide pretreatment would overcome the native recalcitrance of sugarcane bagasse (SB) by enhancing cellulase accessibility of the embedded cellulosic microfibrils.

RESULTS

SB hemicellulosic hydrolysate after concentration by vacuum evaporation and detoxification showed 30.89 g/l xylose along with other products (0.32 g/l glucose, 2.31 g/l arabinose, and 1.26 g/l acetic acid). The recovered cellulignin was subsequently delignified by sodium hydroxide mediated pretreatment. The acid-base pretreated material released 48.50 g/l total reducing sugars (0.91 g sugars/g cellulose amount in SB) after enzymatic hydrolysis. Ultra-structural mapping of acid-base pretreated and enzyme hydrolyzed SB by microscopic analysis (scanning electron microcopy (SEM), transmitted light microscopy (TLM), and spectroscopic analysis (X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy) elucidated the molecular changes in hemicellulose, cellulose, and lignin components of bagasse. The detoxified hemicellulosic hydrolysate was fermented by Scheffersomyces shehatae (syn. Candida shehatae UFMG HM 52.2) and resulted in 9.11 g/l ethanol production (yield 0.38 g/g) after 48 hours of fermentation. Enzymatic hydrolysate when fermented by Saccharomyces cerevisiae 174 revealed 8.13 g/l ethanol (yield 0.22 g/g) after 72 hours of fermentation.

CONCLUSIONS

Multi-scale structural studies of SB after sequential acid-base pretreatment and enzymatic hydrolysis showed marked changes in hemicellulose and lignin removal at molecular level. The cellulosic material showed high saccharification efficiency after enzymatic hydrolysis. Hemicellulosic and cellulosic hydrolysates revealed moderate ethanol production by S. shehatae and S. cerevisiae under batch fermentation conditions.

Rice bran extract: an inexpensive nitrogen source for the production of 2G ethanol from sugarcane bagasse hydrolysate

Selection of the raw material and its efficient utilization are the critical factors in economization of second generation (2G) ethanol production. Fermentation of the released sugars into ethanol by a suitable ethanol producing microorganism using cheap media ingredients is the cornerstone of the overall process. This study evaluated the potential of rice bran extract (RBE) as a cheap nitrogen source for the production of 2G ethanol by Scheffersomyces (Pichia) stipitis NRRL Y-7124 using sugarcane bagasse (SB) hemicellulosic hydrolysate. Dilute acid hydrolysis of SB showed 12.45 g/l of xylose and 0.67 g/l of glucose along with inhibitors. It was concentrated by vacuum evaporation and submitted to sequential detoxification (neutralization by calcium hydroxide and charcoal adsorption). The detoxified hydrolysate revealed the removal of furfural (81 %) and 5-hydroxymethylfurfural (61 %) leading to the final concentration of glucose (1.69 g/l) and xylose (33.03 g/l). S. stipitis was grown in three different fermentation media composed of detoxified hydrolysate as carbon source supplemented with varying nitrogen sources i.e. medium #1 (RBE + ammonium sulfate + calcium chloride), medium #2 (yeast extract + peptone) and medium #3 (yeast extract + peptone + malt extract). Medium #1 showed maximum ethanol production (8.6 g/l, yield 0.22 g/g) followed by medium #2 (8.1 g/l, yield 0.19 g/g) and medium #3 (7.4 g/l, yield 0.18 g/g).

Evaluation of novel xylose-fermenting yeast strains from Brazilian forests for hemicellulosic ethanol production from sugarcane bagasse

Bioconversion of hemicellulosic hydrolysates into ethanol with the desired yields plays a pivotal role for the overall success of biorefineries. This paper aims to evaluate the ethanol production potential of four native strains of Scheffersomyces shehatae (syn. Candida shehatae) viz. S. shehatae BR6-2AI, CG8-8BY, PT1-1BASP and BR6-2AY, isolated from Brazilian forests. These strains were grown in commercial d-xylose-supplemented synthetic medium and sugarcane bagasse hemicellulose hydrolysate. S. shehatae BR6-2AY showed maximum ethanol production [0.48 ± 0.019 g g⁻¹, 95 ± 3.78 % fermentation efficiency (FE)] followed by S. shehatae CG8-8BY (0.47 ± 0.016 g g⁻¹, 93 ± 3.12 % FE), S. shehatae BR6-2AI (0.45 ± 0.01 g g⁻¹, 89 ± 1.71 % FE) and S. shehatae PT1-1BASP (0.44 ± 0.02 g g⁻¹, 86 ± 3.37 % FE) when grown in synthetic medium. During the fermentation of hemicellulose hydrolysates, S. shehatae CG8-8BY and S. shehatae BR6-2AY showed ethanol production (0.30 ± 0.05 g g⁻¹, 58 ± 0.02 % FE) and (0.21 ± 0.01 g g⁻¹, 40 ± 1.93 % FE), respectively.

Bioremediation: a genuine technology to remediate radionuclides from the environment

Radionuclides in the environment are a major human and environmental health concern. Like the Chernobyl disaster of 1986, the Fukushima Daiichi nuclear disaster in 2011 is once again causing damage to the environment: a large quantity of radioactive waste is being generated and dumped into the environment, and if the general population is exposed to it, may cause serious life-threatening disorders. Bioremediation has been viewed as the ecologically responsible alternative to environmentally destructive physical remediation. Microorganisms carry endogenous genetic, biochemical and physiological properties that make them ideal agents for pollutant remediation in soil and groundwater. Attempts have been made to develop native or genetically engineered (GE) microbes for the remediation of environmental contaminants including radionuclides. Microorganism-mediated bioremediation can affect the solubility, bioavailability and mobility of radionuclides. Therefore, we aim to unveil the microbial-mediated mechanisms for biotransformation of radionuclides under various environmental conditions as developing strategies for waste management of radionuclides. A discussion follows of '-omics'-integrated genomics and proteomics technologies, which can be used to trace the genes and proteins of interest in a given microorganism towards a cell-free bioremediation strategy.

Ultra-structural mapping of sugarcane bagasse after oxalic acid fiber expansion (OAFEX) and ethanol production by Candida shehatae and Saccharomyces cerevisiae

BACKGROUND

Diminishing supplies of fossil fuels and oil spills are rousing to explore the alternative sources of energy that can be produced from non-food/feed-based substrates. Due to its abundance, sugarcane bagasse (SB) could be a model substrate for the second-generation biofuel cellulosic ethanol. However, the efficient bioconversion of SB remains a challenge for the commercial production of cellulosic ethanol. We hypothesized that oxalic-acid-mediated thermochemical pretreatment (OAFEX) would overcome the native recalcitrance of SB by enhancing the cellulase amenability toward the embedded cellulosic microfibrils.

RESULTS

OAFEX treatment revealed the solubilization of hemicellulose releasing sugars (12.56 g/l xylose and 1.85 g/l glucose), leaving cellulignin in an accessible form for enzymatic hydrolysis. The highest hydrolytic efficiency (66.51%) of cellulignin was achieved by enzymatic hydrolysis (Celluclast 1.5 L and Novozym 188). The ultrastructure characterization of SB using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform-near infrared spectroscopy (FT-NIR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed structural differences before and after OAFEX treatment with enzymatic hydrolysis. Furthermore, fermentation mediated by C. shehatae UFMG HM52.2 and S. cerevisiae 174 showed fuel ethanol production from detoxified acid (3.2 g/l, yield 0.353 g/g; 0.52 g/l, yield, 0.246 g/g) and enzymatic hydrolysates (4.83 g/l, yield, 0.28 g/g; 6.6 g/l, yield 0.46 g/g).

CONCLUSIONS

OAFEX treatment revealed marked hemicellulose degradation, improving the cellulases' ability to access the cellulignin and release fermentable sugars from the pretreated substrate. The ultrastructure of SB after OAFEX and enzymatic hydrolysis of cellulignin established thorough insights at the molecular level.

Unraveling the structure of sugarcane bagasse after soaking in concentrated aqueous ammonia (SCAA) and ethanol production by Scheffersomyces (Pichia) stipitis

BACKGROUND

Fuel ethanol production from sustainable and largely abundant agro-residues such as sugarcane bagasse (SB) provides long term, geopolitical and strategic benefits. Pretreatment of SB is an inevitable process for improved saccharification of cell wall carbohydrates. Recently, ammonium hydroxide-based pretreatment technologies have gained significance as an effective and economical pretreatment strategy. We hypothesized that soaking in concentrated aqueous ammonia-mediated thermochemical pretreatment (SCAA) would overcome the native recalcitrance of SB by enhancing cellulase accessibility of the embedded holocellulosic microfibrils.

RESULTS

In this study, we designed an experiment considering response surface methodology (Taguchi method, L8 orthogonal array) to optimize sugar recovery from ammonia pretreated sugarcane bagasse (SB) by using the method of soaking in concentrated aqueous ammonia (SCAA-SB). Three independent variables: ammonia concentration, temperature and time, were selected at two levels with center point. The ammonia pretreated bagasse (SCAA-SB) was enzymatically hydrolysed by commercial enzymes (Celluclast 1.5 L and Novozym 188) using 15 FPU/g dry biomass and 17.5 Units of β-glucosidase/g dry biomass at 50°C, 150 rpm for 96 h. A maximum of 28.43 g/l reducing sugars corresponding to 0.57 g sugars/g pretreated bagasse was obtained from the SCAA-SB derived using a 20% v/v ammonia solution, at 70°C for 24 h after enzymatic hydrolysis. Among the tested parameters, pretreatment time showed the maximum influence (p value, 0.053282) while ammonia concentration showed the least influence (p value, 0.612552) on sugar recovery. The changes in the ultra-structure and crystallinity of native SCAA-SB and enzymatically hydrolysed SB were observed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and solid-state (13)C nuclear magnetic resonance (NMR) spectroscopy. The enzymatic hydrolysates and solid SCAA-SB were subjected to ethanol fermentation under separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) by Scheffersomyces (Pichia) stipitis NRRL Y-7124 respectively. Higher ethanol production (10.31 g/l and yield, 0.387 g/g) was obtained through SSF than SHF (3.83 g/l and yield, 0.289 g/g).

CONCLUSIONS

SCAA treatment showed marked lignin removal from SB thus improving the accessibility of cellulases towards holocellulose substrate as evidenced by efficient sugar release. The ultrastructure of SB after SCAA and enzymatic hydrolysis of holocellulose provided insights of the degradation process at the molecular level.

Bioconversion of novel substrate Saccharum spontaneum, a weedy material, into ethanol by Pichia stipitis NCIM3498

Rising fuel prices and environmental issues have paved the way for the exploration of cellulosic ethanol. However, challenges involving substrate hydrolysis and cost-effectiveness still limit the efficient bioconversion and utilization of cellulosic ethanol. We aimed to evaluate a cheaper and abundantly available wild sugarcane variety, Saccharum spontaneum, as the raw substrate for bioconversion of ethanol by Pichia stipitis NCIM3498. Three different strategies for substrate hydrolysis using acid (dilute sulfuric acid) and alkali (dilute sodium hydroxide) and aqueous ammonia (AA) treatment followed by enzymatic hydrolysis were studied. A maximum of 631.5±3.25 mg/g sugars with 89.38% hydrolytic efficiency (HE) could be achieved after enzymatic hydrolysis of AA-pretreated S. spontaneum. All the substrate hydrolysates were evaluated for ethanol conversion in batches by P. stipitis. The microbial fermentation of released sugars into ethanol showed (g/g) 0.36±0.011, 0.384±0.022, 0.391±0.02, and 0.40±0.01 yield from detoxified acid hydrolysate and acid-, NaOH- and AA-pretreated substrate S. spontaneum enzymatic hydrolysates, respectively.

Two-dimensional gel electrophoresis: discovering biomolecules for environmental bioremediation

Environmental contamination has been viewed as an ecological malaise for which bioremediation can be prescribed as a "perfect medicine." The solution to the problems with bioremediation lies in analyzing to what extent the microbes' physiological machinery contributes to the degradation process and which biomolecules and their mechanisms are responsible for regulatory factors within the degradation system, such as protein, metabolite, and enzymatic chemical transformation. In the post-genomic era, recent advances in proteomics have allowed us to elucidate many complex biological mechanisms. Two-dimensional gel electrophoresis (2DE) in conjunction with mass spectrometry (MS) can be utilized to identify the biomolecules and their molecular mechanisms in bioremediation. A set of highly abundant global proteins over a pI range 4-7 was separated and compared by size fractionation (25-100 kDa) on 2DE. We identified a set of catabolic proteins, enzymes, and heat shock molecular chaperones associated with the regulatory network that was found to be overexpressed under phenol-stressed conditions. This chapter also offers optimized ideal directions for 2DE, followed by easy-to-follow directions for a protein identification strategy using MALDI-TOF and targeting novel proteins/enzymes for a universal set of experiments.

Use of Saccharum spontaneum (wild sugarcane) as biomaterial for cell immobilization and modulated ethanol production by thermotolerant Saccharomyces cerevisiae VS3

Saccharum spontaneum is a wasteland weed consists of 45.10+/-0.35% cellulose and 22.75+/-0.28% of hemicellulose on dry solid (DS) basis. Aqueous ammonia delignified S. spontaneum yielded total reducing sugars, 53.91+/-0.44 g/L (539.10+/-0.55 mg/g of substrate) with a hydrolytic efficiency of 77.85+/-0.45%. The enzymes required for hydrolysis were prepared from culture supernatants of Aspergillus oryzae MTCC 1846. A maximum of 0.85+/-0.07 IU/mL of filter paperase (FPase), 1.25+/-0.04 IU/mL of carboxy methyl cellulase (CMCase) and 55.56+/-0.52 IU/mL of xylanase activity was obtained after 7 days of incubation at 28+/-0.5 degrees C using delignified S. spontaneum as carbon source under submerged fermentation conditions. Enzymatic hydrolysate of S. spontaneum was then tested for ethanol production under batch and repeated batch production system using "in-situ" entrapped Saccharomyces cerevisiae VS3 cells in S. spontaneum stalks (1 cm x 1 cm) size. Immobilization was confirmed by the scanning electron microscopy (SEM). Batch fermentation of VS3 free cells and immobilized cells showed ethanol production, 19.45+/-0.55 g/L (yield, 0.410+/-0.010 g/g) and 21.66+/-0.62 g/L (yield, 0.434+/-0.021 g/g), respectively. Immobilized VS3 cells showed maximum ethanol production (22.85+/-0.44 g/L, yield, 0.45+/-0.04 g/g) up to 8th cycle during repeated batch fermentation followed by a gradual reduction in subsequent cycles of fermentation.