CERES :: Browsing by Author "Agrawal, Deepti"

Browsing by Author "Agrawal, Deepti"

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Open Access
Acetate as a potential feedstock for the production of value-added chemicals: Metabolism and applications
(Elsevier, 2021-03-26) Kim, Yeonhee; Lama, Suman; Agrawal, Deepti; Kumar, Vinod; Park, Sunghoon
Acetate is regarded as a promising carbon feedstock in biological production owing to its possible derivation from C1 gases such as CO, CO2 and methane. To best use of acetate, comprehensive understanding of acetate metabolisms from genes and enzymes to pathways and regulations is needed. This review aims to provide an overview on the potential of acetate as carbon feedstock for industrial biotechnology. Biochemical, microbial and biotechnological aspects of acetate metabolism are described. Especially, the current state-of-the art in the production of value-added chemicals from acetate is summarized. Challenges and future perspectives are also provided.
Open Access
Arabinose as an overlooked sugar for microbial bioproduction of chemical building blocks
(Taylor and Francis, 2023-11-06) Kumar, Vinod; Agrawal, Deepti; Bommareddy, Rajesh Reddy; Islam, M. Ahsanul; Jacob, Samuel; Balan, Venkatesh; Singh, Vijai; Thakur, Vijay Kumar; Navani, Naveen Kumar; Scrutton, Nigel S.
The circular economy is anticipated to bring a disruptive transformation in manufacturing technologies. Robust and industrial scalable microbial strains that can simultaneously assimilate and valorize multiple carbon substrates are highly desirable, as waste bioresources contain substantial amounts of renewable and fermentable carbon, which is diverse. Lignocellulosic biomass (LCB) is identified as an inexhaustible and alternative resource to reduce global dependence on oil. Glucose, xylose, and arabinose are the major monomeric sugars in LCB. However, primary research has focused on the use of glucose. On the other hand, the valorization of pentose sugars, xylose, and arabinose, has been mainly overlooked, despite possible assimilation by vast microbial communities. The present review highlights the research efforts that have explicitly proven the suitability of arabinose as the starting feedstock for producing various chemical building blocks via biological routes. It begins by analyzing the availability of various arabinose-rich biorenewable sources that can serve as potential feedstocks for biorefineries. The subsequent section outlines the current understanding of arabinose metabolism, biochemical routes prevalent in prokaryotic and eukaryotic systems, and possible products that can be derived from this sugar. Further, currently, exemplar products from arabinose, including arabitol, 2,3-butanediol, 1,2,3-butanetriol, ethanol, lactic acid, and xylitol are discussed, which have been produced by native and non-native microbial strains using metabolic engineering and genome editing tools. The final section deals with the challenges and obstacles associated with arabinose-based production, followed by concluding remarks and prospects.
Open Access
Augmented hydrolysis of acid pretreated sugarcane bagasse by PEG 6000 addition: a case study of Cellic CTec2 with recycling and reuse
(Springer, 2019-11-08) Baral, Pratibha; Jain, Lavika; Kurmi, Akhilesh Kumar; Kumar, Vinod; Agrawal, Deepti
In an integrated lignocellulosic biorefinery, the cost associated with the “cellulases” and “longer duration of cellulose hydrolysis” represents the two most important bottlenecks. Thus, to overcome these barriers, the present study aimed towards augmented hydrolysis of acid pretreated sugarcane bagasse within a short span of 16 h using Cellic CTec2 by addition of PEG 6000. Addition of this surfactant not only enhanced glucose release by twofold within stipulated time, but aided in recovery of Cellic CTec2 which was further recycled and reused for second round of saccharification. During first round of hydrolysis, when Cellic CTec2 was loaded at 25 mg protein/g cellulose content, it resulted in 76.24 ± 2.18% saccharification with a protein recovery of 58.4 ± 1.09%. Filtration through 50KDa PES membrane retained ~ 89% protein in 4.5-fold concentrated form and leads to simultaneous fractionation of ~ 70% glucose in the permeate. Later, the saccharification potential of recycled Cellic CTec2 was assessed for the second round of saccharification using two different approaches. Unfortified enzyme effectively hydrolysed 67% cellulose, whereas 72% glucose release was observed with Cellic CTec2 fortified with 25% fresh protein top-up. Incorporating the use of the recycled enzyme in two-stage hydrolysis could effectively reduce the Cellic CTec2 loading from 25 to 16.8 mg protein/g cellulose. Furthermore, 80% ethanol conversion efficiencies were achieved when glucose-rich permeate obtained after the first and second rounds of saccharification were evaluated using Saccharomyces cerevisiae MTCC 180.
Open Access
Biovalorisation of crude glycerol and xylose into xylitol by oleaginous yeast Yarrowia lipolytica
(BMC (part of Springer Nature), 2020-06-03) Prabhu, Vinayak Ashok; Thomas, Dominic J.; Ledesma-Amaro, Rodrigo; Leeke, Gary A.; Medina, Angel; Verheecke-Vaessen, Carol; Coulon, Frederic; Agrawal, Deepti; Kumar, Vinod
Background Xylitol is a commercially important chemical with multiple applications in the food and pharmaceutical industries. According to the US Department of Energy, xylitol is one of the top twelve platform chemicals that can be produced from biomass. The chemical method for xylitol synthesis is however, expensive and energy intensive. In contrast, the biological route using microbial cell factories offers a potential cost-effective alternative process. The bioprocess occurs under ambient conditions and makes use of biocatalysts and biomass which can be sourced from renewable carbon originating from a variety of cheap waste feedstocks. Result In this study, biotransformation of xylose to xylitol was investigated using Yarrowia lipolytica, an oleaginous yeast which was firstly grown on a glycerol/glucose for screening of co-substrate, followed by media optimisation in shake flask, scale up in bioreactor and downstream processing of xylitol. A two-step medium optimization was employed using central composite design and artificial neural network coupled with genetic algorithm. The yeast amassed a concentration of 53.2 g/L xylitol using pure glycerol (PG) and xylose with a bioconversion yield of 0.97 g/g. Similar results were obtained when PG was substituted with crude glycerol (CG) from the biodiesel industry (titer: 50.5 g/L; yield: 0.92 g/g). Even when xylose from sugarcane bagasse hydrolysate was used as opposed to pure xylose, a xylitol yield of 0.54 g/g was achieved. Xylitol was successfully crystallized from PG/xylose and CG/xylose fermentation broths with a recovery of 39.5 and 35.3%, respectively. Conclusion To the best of the author’s knowledge, this study demonstrates for the first time the potential of using Y. lipolytica as a microbial cell factory for xylitol synthesis from inexpensive feedstocks. The results obtained are competitive with other xylitol producing organisms.
Open Access
Carbon emissions and decarbonisation: the role and relevance of fermentation industry in chemical sector
(Elsevier, 2023-10-07) Agrawal, Deepti; Awani, Kelvin; Nabavi, Seyed Ali; Balan, Venkatesh; Jin, Mingjie; Aminabhavi, Tejraj M.; Dubey, Kashyap Kumar; Kumar, Vinod
Fermentation industry is emerging as sustainable technological alternative to cater the production of various chemical building blocks which are commercially manufactured by petrochemical route. The primary reason for this major transition is global commitment towards decarbonisation of chemical sector, as their conventional fossil-based routes pose serious environmental threat. For instance, in 2022, the direct carbon dioxide (CO2) emission during synthesis of primary chemicals accounted for ∼ 920 Mt. CO2 is one of the prominent greenhouse gases (GHG’s), contributing majorly towards global warming effect and drastic climate change. Fermentation industry largely thrives on exploiting fermentable and organic carbon derived from edible and/or non-edible biomass and transforming them to valorised products using microbial cell factories. Therefore, the production of bio-based chemicals via this route is often associated with low or zero-carbon footprint, resulting in either carbon neutral or carbon negative products. This review focuses on different types of fermentative processes and their impact on carbon release and decarbonisation. It further discusses the relevance and contribution of fermentation industry as well as biological processes to provide a sustainable solution towards decarbonisation of chemical sector. Further, it showcases the advantages of some commercial proven and/or pipeline bio-based products over their conventional competitor fossil-based products, especially from an environmental viewpoint. Finally, advantages of biogenic CO2 from fermentation industry over other sources and CO2 removal from fermentation as a platform for carbon offsetting are covered.
Open Access
Comparative assessment of sugarcane bagacillo and bagasse at lab-scale for production of sugars and green chemicals via biochemical platform
(Springer, 2022-06-08) Baral, Pratibha; Jana, Arijit; Kumar, Vinod; Agrawal, Deepti
The sugarcane-driven industry can exemplify sustainable waste management by valorizing its lignocellulosic streams and boosting the rural economy by product diversification. In this aspect, bagacillo is a promising yet untapped carbonaceous feedstock, representing fine fraction of sugarcane bagasse (SCB) with low bulk density. It is used either as a filter aid for juice clarification, when added to mud or mixed with bagasse for cogeneration. This study explores bagacillo for the production of sugars and green chemicals using biochemical platform, with SCB as the benchmark. Its NaOH pretreatment preserved > 90 and > 70% glucan and xylan in solid fraction. Fed-batch hydrolysis with Cellic CTec3 at 1-kg scale liberated 167.4 ± 1.87 and 183.53 ± 1.23 g L−1 monomeric sugars in filtrates of bagacillo and SCB, respectively, in 48 h. Its high-ash content reduced glucan conversion yields by 16%, and led to glucan under-estimation in residual biomass during mass balance closure. Irrespective of feedstock type, within 18 h Saccharomyces cerevisiae MTCC 180 and Pachysolen tannophilus MTCC 1077 produced ~ 5% (v/v) ethanol from 1.5L glucose-rich filtrates, with a ~ 18-fold enhancement in biomass accumulation. However, when Bacillus coagulans NCIM 5648 was assessed for high-temperature 2G lactic acid production, the obtained titer from bagacillo-derived hydrolysate (33.6 ± 1.23 g L−1) was lower than SCB (43.38 ± 1.89 g L−1). The present study demonstrated that bagacillo is an equally amenable bioresource as ~ 506 g fermentable sugar was extracted from 1-kg raw biomass and its glucose-rich fraction showed feasibility for microbial transformation to bio-based platform chemicals.
Open Access
Cost reduction approaches for fermentable sugar production from sugarcane bagasse and its impact on techno-economics and the environment
(Springer, 2021-05-18) Baral, Pratibha; Munagala, Meghana; Shastri, Yogendra; Kumar, Vinod; Agrawal, Deepti
In an enzymatically driven lignocellulosic biorefinery, pretreatment and hydrolysis modules are the two most significant cost contributors for obtaining high gravity sugar solutions. The present study aimed to reduce the use of alkali and Cellic CTec2 during the bioprocessing of sugarcane bagasse (SCB). Later its impact on the overall process economics and the environment was evaluated. During pretreatment, solid loading of 15% (w/w) and use of 2% (w/v) sodium hydroxide at 121 °C for 30 min emerged as an optimum strategy. It resulted in > 65% delignification of SCB, retaining ≥ 90% and 65% of glucan and xylan fraction, respectively, in the pretreated biomass. Two approaches were evaluated in parallel to minimize the requirement of this commercial cellulase enzyme blend. The first strategy involved its partial replacement with an in-house enzyme cocktail by blending. The second route was performing hydrolysis with reduced loadings of cellulase enzyme blend above its optimum temperature, which gave more promising results. Hydrolysis of 20% alkali pretreated SCB with cellulase enzyme blend dosed at 15 mg protein g−1 glucan led to 84.13 ± 1 and 83.5 ± 2.3% glucan and xylan conversion yields respectively in 48 h at 52.5 °C. The filtrate and wash fraction contained ≥ 165 and ≥ 65 g L−1 sugar monomers representing glucose and xylose. However, in both the fractions > 75%, sugar accounted for glucose. The techno-economic analysis revealed that the sugar production cost from SCB was 1.32 US$/kg, with the optimized bioprocess. Environmental impact study showed that the process contributed to 1.57 kg CO2 eq in terms of climate change.
Open Access
Development of hypertolerant strain of Yarrowia lipolytica accumulating succinic acid using high levels of acetate
(American Chemical Society, 2022-08-09) Narisetty, Vivek; Prabhu, Ashish A.; Bommareddy, Rajesh Reddy; Cox, Rylan; Agrawal, Deepti; Misra, Ashish; Ali Haider, M.; Bhatnagar, Amit; Pandey, Ashok; Kumar, Vinod
Acetate is emerging as a promising feedstock for biorefineries as it can serve as an alternate carbon source for microbial cell factories. In this study, we expressed acetyl-CoA synthase in Yarrowia lipolytica PSA02004PP, and the recombinant strain grew on acetate as the sole carbon source and accumulated succinic acid or succinate (SA). Unlike traditional feedstocks, acetate is a toxic substrate for microorganisms; therefore, the recombinant strain was further subjected to adaptive laboratory evolution to alleviate toxicity and improve tolerance against acetate. At high acetate concentrations, the adapted strain Y. lipolytica ACS 5.0 grew rapidly and accumulated lipids and SA. Bioreactor cultivation of ACS 5.0 with 22.5 g/L acetate in a batch mode resulted in a maximum cell OD600 of 9.2, with lipid and SA accumulation being 0.84 and 5.1 g/L, respectively. However, its fed-batch cultivation yielded a cell OD600 of 23.5, SA titer of 6.5 g/L, and lipid production of 1.5 g/L with an acetate uptake rate of 0.2 g/L h, about 2.86 times higher than the parent strain. Cofermentation of acetate and glucose significantly enhanced the SA titer and lipid accumulation to 12.2 and 1.8 g/L, respectively, with marginal increment in cell growth (OD600: 26.7). Furthermore, metabolic flux analysis has drawn insights into utilizing acetate for the production of metabolites that are downstream to acetyl-CoA. To the best of our knowledge, this is the first report on SA production from acetate by Y. lipolytica and demonstrates a path for direct valorization of sugar-rich biomass hydrolysates with elevated acetate levels to SA.
Open Access
Emerging trends in high-solids enzymatic saccharification of lignocellulosic feedstocks for developing an efficient and industrially deployable sugar platform
(Taylor and Francis, 2021-09-16) Baral, Pratibha; Kumar, Vinod; Agrawal, Deepti
For the techno-commercial success of any lignocellulosic biorefinery, the cost-effective production of fermentable sugars for the manufacturing of bio-based products is indispensable. High-solids enzymatic saccharification (HSES) is a straightforward approach to develop an industrially deployable sugar platform. Economic incentives such as reduced capital and operational expenditure along with environmental benefits in the form of reduced effluent discharge makes this strategy more lucrative for exploitation. However, HSES suffers from the drawback of non-linear and disproportionate sugar yields with increased substrate loadings. To overcome this bottleneck, researchers tend to perform HSES at high enzyme loadings. Nonetheless, the production costs of cellulases are one of the key contributors that impair the entire process economics. This review highlights the relentless efforts made globally to attain a high-titer of sugars and their fermentation products by performing efficient HSES at low cellulase loadings. In this context, technical innovations such as advancements in new pretreatment strategies, next-generation cellulase cocktails, additives, accessory enzymes, novel reactor concepts and enzyme recycling studies are especially showcased. This review further covers new insights, learnings and prospects in the area of lignocellulosic bioprocessing.
Open Access
Enhanced xylitol production using non-detoxified xylose rich pre-hydrolysate from sugarcane bagasse by newly isolated Pichia fermentans
(BioMed Central / Springer Verlag, 2020-12-29) Prabhu, Ashish A.; Bosakornranut, Ekkarin; Amraoui, Yassin; Agrawal, Deepti; Coulon, Frederic; Vivekanand, Vivekanand; Thakur, Vijay Kumar; Kumar, Vinod
Background Integrated management of hemicellulosic fraction and its economical transformation to value-added products is the key driver towards sustainable lignocellulosic biorefineries. In this aspect, microbial cell factories are harnessed for the sustainable production of commercially viable biochemicals by valorising C5 and C6 sugars generated from agro-industrial waste. However, in the terrestrial ecosystem, microbial systems can efficiently consume glucose. On the contrary, pentose sugars are less preferred carbon source as most of the microbes lack metabolic pathway for their utilization. The effective utilization of both pentose and hexose sugars is key for economical biorefinery. Results Bioprospecting the food waste and selective enrichment on xylose-rich medium led to screening and isolation of yeast which was phylogenetically identified as Pichia fermentans. The newly isolated xylose assimilating yeast was explored for xylitol production. The wild type strain robustly grew on xylose and produced xylitol with > 40% conversion yield. Chemical mutagenesis of isolated yeast with ethyl methanesulphonate (EMS) yielded seven mutants. The mutant obtained after 15 min EMS exposure, exhibited best xylose bioconversion efficiency. This mutant under shake flask conditions produced maximum xylitol titer and yield of 34.0 g/L and 0.68 g/g, respectively. However, under the same conditions, the control wild type strain accumulated 27.0 g/L xylitol with a conversion yield of 0.45 g/g. Improved performance of the mutant was attributed to 34.6% activity enhancement in xylose reductase with simultaneous reduction of xylitol dehydrogenase activity by 22.9%. Later, the culture medium was optimized using statistical design and validated at shake flask and bioreactor level. Bioreactor studies affirmed the competence of the mutant for xylitol accumulation. The xylitol titer and yield obtained with pure xylose were 98.9 g/L and 0.67 g/g, respectively. In comparison, xylitol produced using non-detoxified xylose rich pre-hydrolysate from sugarcane bagasse was 79.0 g/L with an overall yield of 0.54 g/g. Conclusion This study demonstrates the potential of newly isolated P. fermentans in successfully valorising the hemicellulosic fraction for the sustainable xylitol production
Open Access
Expeditious production of concentrated glucose-rich hydrolysate from sugarcane bagasse and its fermentation to lactic acid with high productivity
(Elsevier, 2020-08-22) Baral, Pratibha; Pundir, Anushka; Kumar, Vinod; Kurmi, Akhilesh K.; Agrawal, Deepti
Sugarcane bagasse (SCB) is anticipated to emerge as a potential threat to waste management in India on account of cheap surplus energy options and lower incentives through its co-generation. Through biotechnological intervention, the efficient utilization of SCB is seen as an opportunity. The present study aimed towards expeditious production of concentrated glucose-rich hydrolysate from SCB. Alkali pretreated biomass was chosen for hydrolysis with a new generation cellulase cocktail, Cellic CTec2 dosed at 25 mg g−1 glucan content. A two-step (9% + 9%) substrate feeding strategy was adopted with a gap of an hour, and saccharification was terminated in three different ways. Irrespective of the methods employed for termination, ∼84.5% cellulose was hydrolyzed releasing ≥100 g L−1 glucose from 18% biomass. Direct use of glucose-rich filtrates yielded 69.2 ± 2.5 g L−1 of L (+) lactic acid (LA) using thermophilic Bacillus coagulans NCIM 5648. The best-attained glucose and LA productivities during separate hydrolysis and fermentation (SHF) in the present study were 5.27 and 2.88 g L−1 h−1, respectively. A green and sustainable process is demonstrated for the production of industrially relevant sugars from SCB at high productivity and its valorization to bio-based LA.
Open Access
Fermentative valorisation of xylose-rich hemicellulosic hydrolysates from agricultural waste residues for lactic acid production under non-sterile conditions
(Elsevier, 2023-05-18) Cox, Rylan; Narisetty, Vivek; Castro, Eulogio; Agrawal, Deepti; Jacob, Samuel; Kumar, Gopalakrishnan; Kumar, Deepak; Kumar, Vinod
Lactic acid (LA) is a platform chemical with diverse industrial applications. Presently, commercial production of LA is dominated by microbial fermentation using sugary or starch-based feedstocks. Research pursuits emphasizing towards sustainable production of LA using non-edible and renewable feedstocks have accelerated the use of lignocellulosic biomass (LCB). The present study focuses on the valorisation of xylose derived from sugarcane bagasse (SCB) and olive pits (OP) through hydrothermal and dilute acid pretreatment, respectively. The xylose-rich hydrolysate obtained was used for LA production by homo-fermentative and thermophilic Bacillus coagulans DSM2314 strain under non-sterile conditions. The fed-batch mode of fermentation resulted in maximum LA titers of 97.8, 52.4 and 61.3 g/L with a yield of 0.77, 0.66 and 0.71 g/g using pure xylose, xylose-rich SCB and OP hydrolysates, respectively. Further, a two-step aqueous two-phase system (ATPS) extraction technique was employed for the separation and recovery of LA accumulated on pure and crude xylose. The LA recovery was 45 – 65% in the first step and enhanced to 80–90% in the second step.The study demonstrated an efficient integrated biorefinery approach to valorising the xylose-rich stream for cost-effective LA production and recovery.
Open Access
High yield recovery of 2,3-butanediol from fermented broth accumulated on xylose rich sugarcane bagasse hydrolysate using aqueous two-phase extraction system
(Elsevier, 2021-06-26) Narisetty, Vivek; Amraoui, Yassin; Abdullah, Alamri; Ahmad, Ejaz; Agrawal, Deepti; Parameswaran, Binod; Pandey, Ashok; Goel, Saurav; Kumar, Vinod
Downstream processing of chemicals obtained from fermentative route is challenging and cost-determining factor of any bioprocess. 2,3-Butanediol (BDO) is a promising chemical building block with myriad applications in the polymer, food, pharmaceuticals, and fuel sector. The current study focuses on the recovery and purification of BDO produced (68.2 g/L) from detoxified xylose-rich sugarcane bagasse hydrolysate by a mutant strain of Enterobacter ludwigii. Studies involving screening and optimization of aqueous-two phase system (ATPS) revealed that 30% w/v (NH4)2SO4 addition to clarified fermentation broth facilitated BDO extraction in isopropanol (0.5 v/v), with maximum recovery and partition coefficient being 97.9 ± 4.6% and 45.5 ± 3.5, respectively. The optimized protocol was repeated with unfiltered broth containing 68.2 g/L BDO, cell biomass, and unspent protein, which led to the partitioning of 66.7 g/l BDO, 2.0 g/L xylose and 9.0 g/L acetic acid into organic phase with similar BDO recovery (97%) and partition coefficient (45).
Open Access
Integrated fermentative production and downstream processing of 2,3-butanediol from sugarcane bagasse-derived xylose by mutant strain of Enterobacter ludwigii
(American Chemical Society, 2021-07-16) Amraoui, Yassin; Narisetty, Vivek; Coulon, Frederic; Agrawal, Deepti; Chandel, Anuj Kumar; Maina, Sofia; Koutinas, Apostolis; Kumar, Vinod
In this study, a mutant strain of Enterobacter ludwigii developed in our previous work, was evaluated to utilize pure xylose as the sole carbon and energy source for 2,3-butanediol (BDO) production. Later, this strain was also investigated on detoxified and nondetoxified xylose-rich hydrolysate obtained from hydrothermally pretreated sugarcane bagasse (SCB) for BDO production. Supplementing the fermentation medium with 0.2% w/v yeast extract improved cell growth (31%), BDO titer (43%), and yield (41%) against the synthetic medium devoid of any complex nitrogen source. The fed-batch culture with cyclic control of pH resulted in a BDO production of 71.1 g/L from pure xylose with overall yield and productivity of 0.40 g/g and 0.94 g/L·h, respectively. While BDO titer, yield, and productivity of 63.5 g/L, 0.36 g/g, and 0.84 g/L·h, were acheived with detoxified hydrolysate, respectively. In contrast, 32.7 g/L BDO was produced from nondetoxified hydrolysate with a conversion yield of 0.33 g/g and a productivity of 0.43 g/L·h. BDO accumulated on pure xylose and detoxified SCB hydrolysate was separated by aqueous two-phase system (ATPS) method using (NH4)2SO4 as salting-out agent and isopropanol as an extractant, resulting in the BDO recovery of more than 85%. The results achieved in the current work exemplify a step toward industrial BDO production from cost-effective hemicellulosic hydrolysates by E. ludwigii.
Open Access
Recent advances in bio-based production of top platform chemical, succinic acid: an alternative to conventional chemistry
(Springer Nature, 2024-05-29) Kumar, Vinod; Kumar, Pankaj; Maity, Sunil K.; Agrawal, Deepti; Narisetty, Vivek; Jacob, Samuel; Kumar, Gopalakrishnan; Bhatia, Shashi Kant; Kumar, Dinesh; Vivekanand, Vivekanand
Succinic acid (SA) is one of the top platform chemicals with huge applications in diverse sectors. The presence of two carboxylic acid groups on the terminal carbon atoms makes SA a highly functional molecule that can be derivatized into a wide range of products. The biological route for SA production is a cleaner, greener, and promising technological option with huge potential to sequester the potent greenhouse gas, carbon dioxide. The recycling of renewable carbon of biomass (an indirect form of CO2), along with fixing CO2 in the form of SA, offers a carbon-negative SA manufacturing route to reduce atmospheric CO2 load. These attractive attributes compel a paradigm shift from fossil-based to microbial SA manufacturing, as evidenced by several commercial-scale bio-SA production in the last decade. The current review article scrutinizes the existing knowledge and covers SA production by the most efficient SA producers, including several bacteria and yeast strains. The review starts with the biochemistry of the major pathways accumulating SA as an end product. It discusses the SA production from a variety of pure and crude renewable sources by native as well as engineered strains with details of pathway/metabolic, evolutionary, and process engineering approaches for enhancing TYP (titer, yield, and productivity) metrics. The review is then extended to recent progress on separation technologies to recover SA from fermentation broth. Thereafter, SA derivatization opportunities via chemo-catalysis are discussed for various high-value products, which are only a few steps away. The last two sections are devoted to the current scenario of industrial production of bio-SA and associated challenges, along with the author's perspective.
Open Access
Recent advances in fermentative production of C4 diols and their chemo-catalytic upgrading to high-value chemicals
(Elsevier, 2023-09-01) Varma, Abhishek R.; Shrirame, Bhushan S.; Maity, Sunil K.; Agrawal, Deepti; Malys, Naglis; Rios-Solis, Leonardo; Kumar, Gopalakrishnan; Kumar, Vinod
The current era is witnessing the transition from a fossil-dominated economy towards sustainable and low-carbon green manufacturing technologies at economical prices with reduced energy usage. The biological production of chemical building blocks from biomass using cell factories is a potential alternative to fossil-based synthesis. However, microbes have their own limitations in generating the whole spectrum of petrochemical products. Therefore, there is a growing interest in an integrated/hybrid approach where products containing active functional groups obtained by biological upgrading of biomass are converted via chemo-catalytic routes. The present review focuses on the biological production of three important structural isomers of C4 diols, 2,3-, 1,3-, and 1,4-butanediol, which are currently manufactured by petrochemical route to meet the soaring global market demand. The review starts with justifications for the integrated approach and summarizes the current status of the biological production of these diols, including the substrates, microorganisms, fermentation technology and metabolic/pathway engineering. This is followed by a comprehensive review of recent advances in catalytic upgrading of C4 diols to generate a range of products. The roles of various active sites in the catalyst on catalytic activity, product selectivity, and catalyst stability are discussed. The review also covers examples of integrated approaches, addresses challenges associated with developing end-to-end processes for bio-based production of C4 diols, and underlines existing limitations for their upgrading via direct catalytic conversion. Finally, the concluding remarks and prospects emphasise the need for an integrated biocatalytic and chemo-catalytic approach to broaden the spectrum of products from biomass.
Open Access
Recent progress on sugarcane-bagasse based lactic acid production: technical advancements, potential and limitations
(Elsevier, 2022-12-20) Agrawal, Deepti; Kumar, Vinod
India is the largest producer of sugarcane in Asia and its sugar industry represents the second largest agro-based industry. Sugarcane bagasse (SCB), a major waste from sugar industries, is indisputably lignocellulosic biomass (LCB) embedding ∼60 % carbohydrates, making it a renewable source of fermentable sugars. Despite its unique chemical composition, SCB is primarily used for co-generation. The enormous potential of SCB can be unleashed, if sugar platform is created using biochemical route. Sugars serve as feedstock for fermentative production of several renewable fuels and chemicals, considered as key drivers for rapid industrialization. US Department of Energy has projected lactic acid (LA) as one of the top biomass-derived platform chemicals owing to its diverse applications and multi-billion-dollar market. Currently, the industrial production of LA is predominated by microbial fermentation (∼90 %) which principally uses the starchy or sugar-rich edible feedstocks. If its low-cost manufacturing relying on LCB is enabled, it can be a boon for emerging economies like India, strategically strengthening their socio-economic status. The present review showcases the technical advances made in exploiting the biochemical route towards commercial realization of LA production with SCB as the feedstock. It comprehensively discusses strategies developed in the area of pretreatment, saccharification and fermentation, bridging the gap between lab-scale and industrial LA production. It gives a glimpse on downstream processing of SCB-derived LA, which is still in its nascent stage and briefly talks about our perspective on LA as preferred choice for scale-up in “sugar industry” over other bio-based fuels and chemicals.
Open Access
Recycling potential of brewer's spent grains for circular biorefineries
(Elsevier, 2022-12-23) Agrawal, Deepti; Gopaliya, Deeksha; Willoughby, Nicholas; Khare, Sunil K.; Kumar, Vinod
Brewer's spent grain (BSG) is the major by-product of the brewing industry. BSG is principally composed of carbohydrates and proteins, with substantial amount of lipids. Presently, BSG usage is restricted to low-grade applications such as ruminant feed or landfills. The high volume, nutrient-rich composition, low cost (€35/ton), abundance, and around the year availability, makes it a promising and renewable feedstock for biorefinery development. The current review begins with beer production process, where BSG is produced. Further, it appraises emerging biotechnological advancements and green processes targeting BSG valorisation ensuring maximal resource recovery. Particularly, it illustrates diverse marketable products obtained by repurposing carbohydrate and protein fraction of BSG using either isolated or cascading approach. We believe that this review will encourage more research groups to work on developing innovative technologies for integrated and holistic valorisation of BSG. Inclusive efforts towards reduced water consumption and waste minimisation is further advocated, which are presently primary challenges associated with beer industry. It will leave a significant imprint on environmental sustainability and pave a way for developing circular bio-based economy.
Open Access
Salting-out assisted solvent extraction of L (+) lactic acid obtained after fermentation of sugarcane bagasse hydrolysate
(Elsevier, 2021-04-18) Baral, Pratibha; Pundir, Anushka; Kurmi, Akhilesh; Singh, Raghuvir; Kumar, Vinod; Agrawal, Deepti
Lactic acid is among the twelve platform chemicals produced from inexpensive and renewable feedstocks such as lignocellulosic biomass. The present study illustrates salting-out assisted solvent extraction of L (+) lactic acid, derived from sugarcane bagasse hydrolysate. Screening studies with various extractants and diluents revealed that a combination of tri-n-butyl phosphate and ethyl acetate yielded the best results and extracted 59.63 ± 1.28% lactic acid from the dilute fermentation broth adjusted to a pH of 1.6 ± 0.2. Various inorganic salts were screened to enhance extraction efficiency further. The addition of 60% (w/v) ammonium sulfate improved the lactic acid extraction by 36.17%. This salt concentration successfully extracted 85.95 ± 0.44% lactic acid to the organic phase under optimized conditions from the fermentation broth at a pH of ~ 2.5 containing 40–100 g L−1 lactic acid. Recovery of > 80% salt is also shown using chilled acetone, which upon reuse showed a nominal decline of 3.3% during extraction. Thus an eco-friendly approach using a green solvent like ethyl acetate with mild operating conditions is demonstrated in the present study.
Open Access
Strategies and tools for the biotechnological valorization of glycerol to 1, 3-propanediol: challenges, recent advancements and future outlook
(Elsevier, 2023-05-22) Agrawal, Deepti; Budakoti, Mridul; Kumar, Vinod
Global efforts towards decarbonization, environmental sustainability, and a growing impetus for exploiting renewable resources such as biomass have spurred the growth and usage of bio-based chemicals and fuels. In light of such developments, the biodiesel industry will likely flourish, as the transport sector is taking several initiatives to attain carbon-neutral mobility. However, this industry would inevitably generate glycerol as an abundant waste by-product. Despite being a renewable organic carbon source and assimilated by several prokaryotes, presently realizing glycerol-based biorefinery is a distant reality. Among several platform chemicals such as ethanol, lactic acid, succinic acid, 2, 3-butanediol etc., 1, 3-propanediol (1, 3-PDO) is the only chemical naturally produced by fermentation, with glycerol as a native substrate. The recent commercialization of glycerol-based 1, 3-PDO by Metabolic Explorer, France, has revived research interests in developing alternate cost-competitive, scalable and marketable bioprocesses. The current review outlines natural glycerol assimilating and 1, 3-PDO-producing microbes, their metabolic pathways, and associated genes. Later, technical barriers are carefully examined, such as the direct use of industrial glycerol as input material and genetic and metabolic issues related to microbes alleviating their industrial use. Biotechnological interventions exploited in the past five years, which can substantially circumvent these challenges, such as microbial bioprospecting, mutagenesis, metabolic, evolutionary and bioprocess engineering, including their combinations, are discussed in detail. The concluding section sheds light on some of the emerging and most promising breakthroughs which have resulted in evolving new, efficient, and robust microbial cell factories and/or bioprocesses for glycerol-based 1, 3-PDO production.