Bioconversion of sugarcane crop residue for value added ... · Bioconversion of sugarcane crop residue for value added products e An overview Raveendran Sindhu a, *, Edgard Gnansounou

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Renewable Energy xxx (2016) 1e13

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Bioconversion of sugarcane crop residue for value added products e

An overview

Raveendran Sindhu a, *, Edgard Gnansounou b, Parameswaran Binod a, Ashok Pandey a

a Biotechnology Division, National Institute for Interdisciplinary Science and Technology, CSIR, Trivandrum, 695 019, Indiab Ecole Polytechnique F�ed�erale de Lausanne, Institute of Urban and Regional Sciences, GC A3, Station 18, CH-1015, Lausanne, Switzerland

a r t i c l e i n f o

Article history:Received 8 January 2016Received in revised form16 February 2016Accepted 19 February 2016Available online xxx

Keywords:BiomassBioconversionValue added productsSugarcane crop residueBiorefinery

* Corresponding author. Tel.: þ91 471 2515426; faxE-mail addresses: [email protected], sindhuf

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a b s t r a c t

Sugarcane is a major crop cultivated globally and the residue left over after the crop harvest andextraction of juice is a good biomass source that can be used for the production of several usefulchemicals. The sugarcane bagasse is an excellent substrate for the production of various biochemicalsand enzymes through fermentation. Now major interest is focused on the utilization of these residue forbiofuel production. The sugarcane crop residue is rich in cellulose and hemicellulose, hence it can beused for the production of bioethanol and other liquid transportation fuels. The present review gives adetailed account of the availability of sugarcane residue and various commercially important productsthat can be produced from this residue. It also provides recent developments in R&D on the biocon-version of sugarcane crop residue for value added products.

© 2016 Elsevier Ltd. All rights reserved.

1. Introduction

Sugarcane is a major crop cultivated in tropical and sub-tropicalcountries like Brazil, China, India, Thailand and Australia [1]. Itbelongs to grass family, Gramineae and its botanical name is Sac-charum officinarum. It was first grown in South-East Asia andWestern India. Then the cultivation of sugarcane extended to alltropical and sub-tropical regions. Sugarcane area and productivitydiffer from country to country. It is cultivated in about 200 coun-tries and Brazil is the world's largest cane producer and contributesto 25% of world's total production. India is the second largest pro-ducer of sugar in the world.

Its distinguishing features are high biomass yield, high sucrosecontent and high efficiency in accumulating solar energy. Afterharvesting of sugarcane, leaves, tops and trash are left in the canefield while the sugarcane stalks are transported to sugar mills forthe extraction of cane juice for sugar production [2].

Bio-refinery concept of complete utilization of sugarcanebiomass will become a prime component for a sustainable sugar-cane industry. Biorefinery involves fractionation and reforming ofan input feed stock into multiple product streams. Lignocellulosic

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et al., Bioconversion of sugarcnene.2016.02.057

biomass offers tremendous biotechnological potential for use assubstrate in bioconversion processes and can be effectivelyexploited for the production of bulk chemicals and value addedproducts.

The annual global production of sugarcane is about 328 Tg. Asiais the primary production region which contributes to 44% whileSouth America is the second largest production region producing110 Tg of sugarcane which contributes to 34% [3]. Sugar productionis the major use of sugarcane consuming about 92% of sugarcane.Other uses such as animal feed and so on contribute less than 3%.Studies have indicated that sugarcane crop when harvested com-prises of 75% sugarcane stalk and 25% leaves and tops. This wasteprovides a huge potential fuel resource.

Harvesting of sugarcane lead to the production of large amountof post-harvest residues including sugarcane tops which could bean abundant, inexpensive and readily available source of lignocel-lulosic biomass. This can be used as good substrate for the pro-duction of bioethanol as well as for other value added products. InIndia, it is the most surplus available residue and is usually burnt inthe field itself and does not find any suitable application. Burning ofsugarcane tops produce fly ash, severely damages soil microbialdiversity and raises environmental concerns [4]. Roofing andcompost are some of the other uses. It can be used as an animalfodder for a few days before the leaves start rotting. Usually forevery 1 MTof sugarcane produced, 0.20e0.30 MTof sugarcane tops

ane crop residue for value added products e An overview, Renewable

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R. Sindhu et al. / Renewable Energy xxx (2016) 1e132

is generated.Sugarcane bagasse, the largest agro-industrial residue is a

fibrous residue of cane stalks left after the crushing and extractionof juice from the sugarcane. This by-product of the sugar industry ismainly used by sugar factories as fuel for boilers [5]. Comparing toother agricultural residues, bagasse can be considered as a richsolar energy reservoir due to its high yields and annual regenera-tion capacity. Currently several processes and products have beenreported using sugarcane bagasse as a raw material. This includeelectricity generation, pulp and paper production and variousproducts based on fermentation like industrially important en-zymes, bioethanol, organic acids, alkaloids, protein enriched cattlefeed, antibiotics etc. Bagasse in most case is used for co-generationof heat and power or sometimes used for manufacture of buildingmaterials. Paper plants also purchase bagasse from sugar plants.

Sugarcane molasses are a dark, viscous and sugar rich by-product of sugar extraction from sugarcane. It is used as a feedingredient, binder and as an energy source. Around 3e7 tons ofmolasses were generated from 100 tons of sugarcane. Thecomposition of the molasses varies depending on cane variety,climate and processes employed for sugar extraction. Molassescontain approximately 34% of sucrose, 11% of reducing sugars(glucose and fructose) and several minerals. It can be used as ani-mal feed, for yeast cultivation, for the production of ethanol, rum,other alcohols and organic acids.

Vinasse is a by-product of sugar-ethanol industry and is acidiccompost with a pH of 3.5e5.0 with a high organic content andunpleasant odor. On an average 10e15 L of vinasse is generatedwhile preparing each liter of ethanol [6]. Inadequate and indis-criminate use of vinasse in soils and water bodies leads to severalenvironmental hazards. Several studies have been carried out forfinding adequate uses and treatments of vinasse. It can be used forfertirrigation, yeast production, energy production and as a rawmaterial for the production of livestock and poultry feed [7]. Thechemical composition of vinasse varies depending upon the sourceused for ethanol production and distillation. The study revealedthat fertirrigation or the use of vinasse as a fertilizer is the bestalternative for vinasse reuse and disposal. Several new greenmethods need to be explored for developing novel uses of vinasse[8]. Cortez et al., 2007 [9] carried out anaerobic digestion of vinassefor the production of biogas. The anaerobic digestion was carriedout in two stages-the acidogenic phase and the methanogenicphase. In the acidogenic phase the complex chains of carbohydrate,lipids and proteins were hydrolyzed to organic acids and in themethanogenic phase these acids were converted to methane andcarbon dioxide. Laime et al., 2011 [10] utilized vinasse for theproduction of yeast. Additional supply of ammonium and magne-sium salts as well as high energy consumption for water removalfrom the process made it economically unviable.

Chemical compositions of the bagasse may vary for differentsugarcane varieties depending upon the genotype. Several otherfactors like location, age of crop, environmental and cultivationparameters also affect the composition of the biomass. A studyconducted by Benjamin et al., 2014 [2] showed wide variation inagronomic parameters, chemical composition and sugar releasedafter pretreatment of sugarcane varieties harvested for twogrowing seasons. A significant difference was observed amongvarieties over harvest years. The study revealed severe droughtnegatively influenced the performance in cane yield except forvariety containing the highest lignin.

Leaves and tops contain higher amounts of salts and nutrients.The sugar contained in the stem is 90% sucrose and small amountsof glucose and fructose. The greatest difference in composition ofsugarcane is seen in the moisture content which varies between13.5% in the dry leaves and 82.3% in the tops. The content of carbon,

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hydrogen, nitrogen and sulfur showed similar values in dry leavesand in tops.

Bagasse contains 50% of cellulose, 25% each of hemicellulose andlignin. Chemically it contains about 50% a-cellulose, 30% pentosansand 2.4% ash [5]. Bagasse offers numerous advantages over othercrop residues like rice straw and wheat straw because of its low ashcontent. Rice straw and wheat straw have 17.5% and 11.5% of ashrespectively. Bagasse is the raw material for 20% of total paperproduction.

Sugarcane tops contain 29.85% of cellulose, 18.85% of hemi-celluloses and 25.69% of lignin [11]. The composition may varydepending on the geographical location, variety etc.

The present review addresses the potential of sugarcane cropresidue for the production of various value added products.

2. General conversion methods

Native form of lignocellulosic biomass is a tough feed stock forhydrolysis due to crystallinity of cellulose and due to the compactpacking of cellulose, hemicelluloses and lignin. Due to recalcitrantnature of the lignocellulosic biomass a pretreatment process isessential for the removal of hemicelluloses and lignin and to in-crease cellulose conversion efficiency. The basic objective of thepretreatment is to make cellulose accessible by the action of cel-lulases which is achieved by removal of hemicelluloses or ligninfrom the biomass. A wide range of physical, mechanical, chemical,biological, combination and alternative strategies were reported forachieving these goals. In addition to pretreatment, an effectivecellulase cocktail, enzyme loading and hydrolysis conditions andnature of the lignocellulosic material are critical for maximumhydrolysis.

Several reports were available for the pretreatment of sugarcanetops like acid [11], alkali [12], surfactant assisted acid pretreatment[13], surfactant assisted ultrasound pretreatment [14] andsequential pretreatment [15]. Among these methods the highestreducing sugar yield was observed with sequential pretreatment(0.796 g/g) followed by alkali pretreatment (0.775 g/g). But therewere generation of inhibitors during acid and alkali pretreatment.The alternative strategies like surfactant assisted ultrasound pre-treatment and surfactant assisted acid pretreatment strategies didnot generate any inhibitors. Compared to other pretreatmentstrategies employed for sugarcane tops, sequential pretreatmentwas found to be better in terms of improved reducing sugar yieldwithout any inhibitor generation as well as better removal ofhemicelluloses and lignin from the biomass compared to conven-tional acid and alkali pretreatment as well as other alternativestrategies of pretreatment. Selection of the pretreatment strategywill be based on the economic feasibility as well as the targetedproduct.

Pretreated bagasse serves as an efficient inert support materialfor fungal cultivation in SSF. Several pretreatment strategies werereported for bagasse like acid [2], alkali [16], combined [17],organo-solvent [18], organic acids [19] and physical [20]. Thoughseveral pretreatment strategies were available only a few seemspromising. One of the most important challenges associated withpretreatment is to identify the composition of the feed stock and todevice the best pretreatment strategy of the selected item. Properpretreatment can improve the biomass digestibility and increaseaccessibility of enzymes to the materials. Cellulose crystallinity,accessible surface area, degree of cellulose polymerization, ligninand hemicelluloses seal as well as degree of acetylation of hemi-celluloses are the critical factors to be considered for developing asuitable strategy for pretreatment of a specific biomass. Composi-tion plays an important role. Hence fine tuning of specific pre-treatment strategies to be developed for each biomass which will


R. Sindhu et al. / Renewable Energy xxx (2016) 1e13 3

make the process economically as well as ecologically viable.Intensive R and D efforts are going on in this direction. Develop-ment of a proper pretreatment strategy will minimize the capitaland operating costs.

Most of the commercial plants use dilute acid pretreatment. Themain advantage of this strategy is that a separate pentose andhexose stream will be generated. The pentose stream can be uti-lized for the production of various value added products while thehexose stream can be used for the production of bioethanol. Diluteacid hydrolysis gives high reaction rates and improves the cellulosehydrolysis rate. Under optimized conditions 95% of hemicellulosescan be recovered from the lignocellulosic biomass.

3. Value added products from sugarcane crop residue

Several value added products can be produced by utilization ofvarious crop residues and by-products of sugarcane like bagasse,sugarcane tops, molasses and vinasse. This include bioethanol,biodiesel, biobutanol, 2, 3-butanediol, biohydrogen, bioelectricity,biopolymer, different enzymes, organic acids, amino acids, pig-ments, animal feed, composite, chelating agents, alkaloids etc.Table 1 shows different value added products produced from sug-arcane crop residue.

Schematic representation of value added products from sugar-cane crop residue is presented in Fig. 1.

3.1. Bioethanol

Increasing energy demand and depletion of fossil fuels leads toincrease interest on alternative fuels. The requirement to reducecarbon dioxide emissions leads to use of many types of biomass asalternative energy sources. Since the biomass is produced byphotosynthetic reduction of carbon dioxide, utilization of biofuelscan be carbon neutral with respect to build-up of atmosphericgreenhouse gases. Bioethanol is the most abundant biofuel forautomobile transportation. It is a renewable fuel and contains 37%of oxygen by weight. Oxygen enhances the combustion of petrol inengines and contributes to reductions in exhaust emissions of

Table 1Value added products from sugarcane crop residue.

Sugarcane residue Product Microor

Bagasse Bioethanol ZymomoSugarcane tops Bioethanol SaccharBagasse Bioethanol ScenedeBagasse 2,3- butanediol KlebsiellBagasse 2,3-butanediol KlebsiellBagasse Biohydrogen ClostridiBagasse Biohydrogen ThermoaMolasses Biohydrogen ClostridiBagasse Polyhydroxyalkaonates (PHA) RalstoniSugarcane tops Poly-3-hydroxybutyrate (PHB) ComomoBagasse Composite e

Bagasse Composite e

Bagasse Xylitol e

Bagasse Xylitol e

Bagasse Xylitol DebaromBagasse Xylitol WilliopsBagasse Xylitol CandidaBagasse lignin Chelating agentMolasses Carotenoides SporidioMolasses Carotenoides RhodospBagasse Modified catalystsBagasse L-glutamic acid BrevibacBagasse Animal feed PleurotuSugarcane pith bagasse Ergot alkaloides ClavicepBagasse Penicillium e


carbon monoxide. Ethanol can be produced from fermentation ofsugars obtained from lignocellulosic biomass which serves as thefuture feed stock for bioethanol production because of its low costand huge availability. Its high carbohydrate content and low lignincontent makes it a suitable substrate for bioconversion to ethanol.Sugarcane is the most efficient raw material for bioethanol pro-duction [21].

Ethanol production from sugarcane bagasse by Zymomonasmobilis using simultaneous saccharification and fermentation wasreported by dos Santos et al., 2010 [22]. The optimum conditionswere biomass loading of 30%, enzyme loading of 25 FPU/g and cellconcentration of 4 g/L. Maximum ethanol concentration and pro-ductivity were 60 g/L and 1.5 g/L/h respectively.

Few reports were available on exploitation of sugarcane tops forthe production of bioethanol [11]. Fermentation of the hydrolyzateobtained after acid pretreatment and enzymatic saccharificationwith Saccharomyces cerevisiae yielded 11.365 g/L of bioethanol witha fermentation efficiency of 50%.

3.2. Biodiesel

Depletion of petroleum reserves and the impact of environ-mental pollution lead to search for new alternative fuels for use indiesel engines. Biodiesel are monoalkyl esters of fatty acids derivedfrom vegetable oil or animal fat. Trans-esterified renewable oil hasbeen proven to be a viable alternative diesel engine fuel withcharacteristics similar to diesel. The energy density of biodiesel iscomparable to petroleum diesel. Biodiesel has a number of ad-vantages. Since it is derived from biomass it does not contribute toatmospheric CO2 emissions, low toxicity and biodegradable and canbe used in existing diesel engines blended with petroleum diesel orcan be run unblended in engines with minor modifications.

Utilization of low cost agricultural residues of pineapple peelsand sugarcane bagasse for lipid accumulation and biodiesel pro-duction in Scenedesmus acutus PPNK1 was carried out by Rattana-poltee and Kaewkannetra, 2014 [23]. The maximum biomassconcentration, productivity, lipid content and lipid yield usingsugarcane bagasse were 3.85 g/L, 160.42 mg/L/day, 40.89% and

ganism Reference

nas mobilis Santos et al., 2010omyces cerevisiae Sindhu et al., 2011smus acutus PPNK1 Rattanapoltee and Kaewkannetra, 2014a pneumoniae CGMCC 1.9131 Zhao et al., 2011a pneumoniae Song et al., 2012um butyricum TISTR 1032 Plangklang et al., 2012naerobacterium aotearoense Lai et al., 2014um butyricum Whiteman and Kane, 2014a eutropha Jian and Heiko, 2008nas sp. Prabisha et al., 2014

Acharya et al., 2011da Silva et al., 2013Sarrouh et al., 2009Branco et al., 2011

yces hansenii Prakash et al., 2011is saturnus Kamat et al., 2013tropicalis IEC5-ITV Costanon- Rodriguez et al., 2014

Goncalves et al., 2002bolus salmonicolor CBS 2636 Valduga et al., 2008oridium toruloides NCYC 921 Freitas et al., 2014

Marquez de Silva et al., 2013terium sp. Nampoothiri and Pandey, 1996s eryngii Okano et al., 2010s purpurea Hernandez et al., 1993

Dominguez et al., 2001


Fig. 1. Schematic representation of bioconversion of sugarcane crop residue to value added products.


1.24 g/L respectively. The study revealed that there was a 2.13 foldincrease in lipid content when sugarcane bagasse was used andusing agricultural residues as carbon source could lead to an in-crease in the lipid content and reduces the cost of biofuel produc-tion. FAME obtained from S. acutus PPNK1 after trans-esterificationshowed fatty acid compositions of chain lengths between C16 toC18. This indicates that agricultural residues like sugarcane bagassewere suitable for the production of good quality biodiesel. Utili-zation of agro-residue is a promising way to reduce environmentalpollution and lower cost for lipid production.

3.3. Biobutanol

Butanol is a four carbon primary alcohol with a higher energyintensity and lower volatility as compared to ethanol. It can be usedas fuel in current gasoline based engines with practically nochanges in engine [24]. It is also an important feed stock forchemical industry since it is used for paint, solvents and plasticizersproduction. Butanol production from renewable source involvesABE (acetone-butanol-ethanol) fermentation of sugars derivedfrom lignocellulosic biomass. But this method has few limitationslike low productivity and low n-butanol concentration due toproduct inhibition. Another strategy commonly adopted for n-butanol production from lignocellulosic biomass is the ethanolchemistry route where, ethanol is used as feed stock. Howeverproduction of n-butanol in the sugarcane biorefinery makes theprocess more economically viable by producing a biofuel moresuitable for use in chemical industry.

Dias et al., 2014 [25] developed a strategy for butanol productionin a sugarcane biorefinery using ethanol as feed stock. In this studynovel catalysts were used both in vapor and liquid-phase catalysis.Techno-economic analysis revealed that the best results wereobserved with n-butanol production through vapor phase catalysis.Biobutanol produced through liquid and vapor phase catalysispresents lower environmental impact.

3.4. 2, 3- butanediol

2, 3-Butanediol is used as a solvent, liquid fuel and as a precursorof many synthetic polymers, fumigant, moistening and softeningagents, explosives, plasticizers, cosmetics, printing inks, medicinesand resins. Methyl ethyl ketone produced by dehydration of 2, 3-butanediol is used as a liquid fuel additive [26]. Several microor-ganisms are known to produce 2, 3-butanediol using glucose.However major cost in most biomass conversion processes appearsto be the substrate cost. Exploitation of sugarcane bagasse for 2, 3-butanediol seems promising.

Zhao et al., 2011 [27] developed a strategy for the production of2, 3- butanediol by simultaneous saccharification and fermentationof alkali-peracetic acid pretreated sugarcane bagasse by Klebsiella


pneumoniae CGMCC 1.9131. The yield was 0.35e0.50 g/g consumedsugar depending on the fermentation time.

Production of 2, 3-butanediol by K. pneumoniae from enzymatichydrolysis of sugarcane bagasse was reported by Song et al., 2012[28]. The enzymatic hydrolyzate of alkali-peracetic acid and diluteacid pretreated samples were used for the production of 2, 3-butanediol and the yields were 0.36 and 0.42 g/g of sugarsrespectively. The enzymatic hydrolyzate of alkali-peracetic acidpretreated sugarcane bagasse contains 30.54 g/L of glucose and13.87 g/L of xylose, while the enzymatic hydrolyzate obtained fromdilute acid pretreated sugarcane bagasse contains 42.59 g/L ofglucose and 5.36 g/L of xylose. Since xylose is not utilized by thestrain for 2, 3-butanediol production, the final concentration of 2,3-butanediol was considerably higher for the dilute acid pretreatedmaterial (17.35 g/L) than that of alkali e peracetic acid pretreatedsugarcane bagasse (14.53 g/L).

3.5. Biohydrogen

Biohydrogen is considered as a future energy for its high energycontent and zero CO2 emission. Hence it is a promising alternativeto conventional fossil fuels. Currently majority of hydrogen is pro-duced from fossil fuels. Lignocellulosic biomass can serve as asource for sustainable production of hydrogen. Thermophilichydrogen conversion seems promising, since it can convert a va-riety of biomass based substrates into hydrogen at high yields.

Plangklang et al., 2012 [29] developed a strategy for enhancedbiohydrogen production from sugarcane by immobilized Clos-tridium butyricum TISTR 1032 on sugarcane bagasse. Immobilizedcells showed approximately 1.2 times improved hydrogen pro-duction rate than free cells. The optimum conditions of hydrogenproduction by immobilized C. butyricum were an initial sucroseconcentration of 25 g COD/L and pH was maintained at 6.5. Thehighest hydrogen production rate (HPR) and highest hydrogenyield (HY) were 3.5 L H2/L and 1.5 mol H2/mol hexose consumed.The study revealed that efficiency of hydrogen production fromsugarcane juice by C. butyricum was enhanced by immobilizationtechnique. The immobilized cells can tolerate harsh environmentalconditions likewider range of pH and sucrose concentrations betterthan the free cells. The immobilized cells showed same HPR and HYfor five successive cycles.

Lai et al., 2014 [30] used sugarcane bagasse as a substrate forbiohydrogen production using Thermoanaerbacterium aotearoense.Various process parameters affecting hydrogen production wereoptimized. The study revealed that dilute sulfuric acid pretreatedsugarcane bagasse hydrolyzate was suitable for hydrogen produc-tion by T. aotearoense due to the presence of glucose and xylose andlow level of inhibitors. Maximum hydrogen production wasobserved when pretreatment was carried out with 2.3% of H2SO4for 114.2 min at 115 �C. The hydrogen yield and hydrogen



production rate (HPR) under the best conditions were 1.86 mol H2/mol total sugar and 0.52 L/L respectively. Catabolite repression wasnot observed during the fermentation which would be beneficialfor higher hydrogen production and shorter retention time.

Comparative modeling efficiencies for biohydrogen productionby C. butyricum on sugarcane molasses adopting artificial neuralnetwork and response surface modeling were evaluated byWhiteman and Kana, 2014 [31]. Parameters like concentration ofmolasses, pH, incubation temperature and inoculum concentrationwere optimized. The data obtained were used to develop modelsfor ANN and RSM. The findings revealed that ANN has greater ac-curacy in modeling the relationships between the consideredprocess inputs for fermentative hydrogen production.

3.6. Biopolymers

Increase use of conventional non-biodegradable plastics leads tosevere environmental as well as ecological problems. This leads tosearch for biodegradable plastics which can serve as an alternativeto petroleum based polymers. The main competition betweenbiodegradable plastics and petroleum based plastics is based on thecost of production. One of the main limitations for the productionof biopolymer is the cost associated with the carbon source. Morethan 50% of the production cost is contributed by the carbon source[32]. Utilization of agro-residues or waste by product streammakesthe process economically viable.

Jian and Heiko, 2008 [33] utilized dilute acid pretreated sugar-cane bagasse hydrolyzate for the production of poly-hydroxyalkaonates (PHA) by Ralstonia eutropha. PHA biopolyesterswere synthesized and accumulated 57% w/w of biomass. Only fewreports are available on biopolymer production utilizing sugarcanetrash as the sole carbon source. Prabisha et al., 2014 [34] evaluatedthe ability of Comomonas sp. isolated from a dairy effluent samplefor the production of poly-3-hydroxybutyrate (PHB) using biomasshydrolyzate obtained after mild alkali pretreatment of sugarcanetops. The hydrolyzate obtained after enzymatic saccharification isdevoid of major fermentation inhibitors like furfural, 5-hydroxymethylfurfural, acetic acid, formic acid and propionicacid. The optimum conditions for PHB production were incubationtime of 96 h, pH 7.0, reducing sugar concentration of 1.25% andKH2PO4 concentration of 1.05%. The bacterium accumulated 55.85%of PHB with a productivity of 0.195 g/l.

3.7. Enzymes

Various agro-residues, especially sugarcane bagasse serve as agood substrate for the production of various industrially importantmicrobial enzymes adopting a SSF strategy. Some of the enzymesthat a produced by SSF utilizing sugarcane crop residues or by-products of sugarcane industry include a-amylases, cellulases,

Table 2Enzymes produced from sugarcane crop residues.

Sugarcane residue Product Microorganism

Bagasse a-amylase Bacillus subtilis KCBagasse Cellulase T. harzianum L04Bagasse Xylanase T. aurovirideBagasse Xylanase Trichoderma sp.Bagasse Inulinase Kluveromyces marxBagasse Protease Bacillus licheniformMolasses/Bagasse Invertase A. niger GH1Bagasse Lipase Rhizomucor pusilluBagasse Lipase Rhizopus oryzaeBagasse Lipase A. fumigatusBagasse Pectinase A. awamori


xylanases, pectinases, protease, invertase, lipase and inulinase.Table 2 presents different enzymes produced from sugarcane cropresidue.

3.7.1. a-amylasea e amylases are enzymes which convert starch to glucose and

maltose or variety of malto-oligosaccharides. Amylases play a sig-nificant role in starch, detergent, beverage and textile industries.Industrial production of enzymes can be made economical by uti-lizing low cost substrates like agro-industrial residues in the pro-duction medium.

Currently there has been an increasing effort on efficient utili-zation of sugarcane bagasse [2]. Sugarcane bagasse can be used as araw fiber in solid state fermentation or as acid hydrolyzed simplesugars in submerged fermentation. Rajagopalan and Krishnan,2008 [35] reported a-amylase production from catabolite dere-pressed Bacillus subtilis KCC103 utilizing sugarcane bagasse hy-drolyzate (SBH). Addition of SBH (1% reducing sugar w/v) to thenutrient medium supported maximum a-amylase production(67.4 U/ml). Media engineering improved a-amylase production 2.2fold by statistical optimization using response surface method.Existence of catabolite repression in this strain allowed productionof a-amylase synthesis in B. subtilis KCC103 in the presence ofsimple sugars in the SBH. The study demonstrated the economicalproduction of a-amylase using sugars derived from low cost agri-cultural byproduct sugarcane bagasse.

3.7.2. CellulasesThe conversion of cellulose to glucose involves synergistic ac-

tion of three enzymes-endo-b-1, 4-glucanases, cellobiohydrolasesand b-glucosidases. Hydrolytic enzymes contribute a major cost inbiofuel plants.

Pereira et al., 2013 [36] evaluated Penicillium echinulatum forcellulase production using sugarcane bagasse as carbon source.Highest enzyme production (3.7 FPU/ml) and productivity (25.7FPU/l/h) were observed with fed-batch cultivation. The studyrevealed that this enzyme performs better than commercial cellu-lase for biomass hydrolysis and can be used on site enzyme plat-form for bioethanol production from sugarcane lignocellulosicresidue.

A novel promising Trichoderma harzianum L04 strain for theproduction of cellulolytic enzymes using sugarcane bagasse wasreported by Benoliel et al., 2013 [37]. The study revealedT. harzianum L04 to produce significant levels of cellulase whengrown on sugarcane bagasse. Around 60% of sugar yield was ob-tained after 18 h of hydrolysis indicating the potential of cellulolyticenzymes of T. harzianum for biomass hydrolysis.

3.7.3. XylanasesMicrobial production of xylanase is gaining importance due to

Reference

C 103 Rajagopalan and Krishnan, 2008Benoliel et al., 2013Carneiro de Cunha et al., 2013Norazlina et al., 2013

ianus NRRL Y-7571 Mazutti et al., 2006is Rathakrishnan et al., 2012

Vaena et al., 2014s/Rhizopus oryzae Cordova et al., 1998

Vaseghi et al., 2013Naqvi et al., 2013Baladhandayutham and Thangavelu, 2011



its wide industrial and biotechnological applications. Xylanases arewidely used for bleaching paper and pulp to reduce the usage ofchlorine. It is also used for brewing, baking, fruit and vegetableprocessing and as feed additives in broiler and animal diets. Xylan isthe major component of hemicellulose and its complete degrada-tion takes place by the synergetic action of xylanolytic enzymes likeendoxylanase, b-xylosidase and accessory enzymes like a-arabi-nofuranosidase, acetylesterase and a-glucuronidase. Productioncost is the major factor limiting its use indicating the need for lowcost production systems. Cane molasses an important residue ofthe sugar industry serves as cost effective carbon source for theproduction of various industrially important enzymes.

Production of xylanase by filamentous fungi using sugarcaneand sugarcane bagasse as substratewas reported by da Cunha et al.,2013 [38]. Fungal species isolated from various parts of sugarcanewere evaluated for xylanase production using sugarcane bagasse assole carbon source. Trichoderma auroviride showed highest xyla-nase production (2037 U). The optimum conditions of xylanaseproduction were an incubation temperature of 35 �C, 150 rpmstirring intensity and incubation time of 120 h.

Xylanase production by Trichoderma sp. by SSF using sugarcanebagasse was carried out by Norazlina et al., 2013 [39]. Highestxylanase activity (380 U/g) were observed with 5.6 g of sugarcanebagasse, 1% of sucrose, incubation temperature at 50 �C, incubationtime of 6 days and moisture content of 70% (v/w). The studyrevealed that xylanase can be produced by Trichoderma usingsugarcane bagasse as substrate which is cheap and availablethroughout the year.

3.7.4. InulinaseInulinase are important enzymes used for the production of

high fructose syrups from inulin. It catalyzes the hydrolysis of inulininto fructose and fructo-oligosaccharides which are widely used asfood additives. Inulinase based hydrolysis of inulin can yieldproducts with 95% of fructose. Mazutti et al., 2006 [40] optimizedconditions for inulinase production by Kluveromyces marxianusNRRL Y-7571 using sugarcane bagasse as substrate for solid statefermentation. Maximum inulinase yield and productivity were390 U/g and 3.34 U/g/h and this is the highest reported value.Sugarcane bagasse seems to present a great nutritional potential forgrowth of K. marxianus NRRL Y-7571 and production of inulinase.

3.7.5. ProteasesEnzymes that hydrolyze peptide bonds are called proteases. It is

an important industrial enzyme which finds application in deter-gent, leather, food, pharmaceutical and for bioremediation pro-cesses. They regulate various metabolic processes like bloodcoagulation, fibrinolysis, complement activation, phagocytosis andblood pressure control. Rathakrishnan et al., 2012 [41] developed astrategy for protease production using sugarcane bagasse under SSFusing Bacillus licheniformis. Various process parameters affectingprotease production were optimized by adopting Plackett- Burmandesign. The results indicate that sugarcane bagasse serves as a bestsource for the production of protease. Under optimized conditions146.28 U/gds of protease activity was observed.

3.7.6. InvertasesInvertases are enzymes which catalyzes the hydrolysis of su-

crose into glucose and fructose. This enzyme is very important infood industry for the production of artificial sweetener. Thisenzyme has fructosyltransferase activity which is important for thesynthesis of short chain fructo-oligosaccharide compounds. Thisimproves intestinal microflora and prevents cardiovascular disease,colon cancer and osteoporosis [42]. Utilization of sugarcanemolasses and bagasse was evaluated for the production of fungal


invertase in solid state fermentation using Aspergillus niger GH1was reported by Veana et al., 2014 [43]. The by-products of sugarindustry molasses and bagasse were employed as substrates forinvertase production. Fermentation with A. niger GH1 yielded5231 U/L of invertase. Utilization of sugar industry by-products forinvertase production by A. niger GH1 seems promising since itlower the enzyme production cost as well as the enzyme yield ishigh since the enzymatic yield is higher than those reported byother A. niger strains under SSF using dilute acid treated bagassehydrolyzate.

3.7.7. LipasesLipase hydrolyzes fats into fatty acids and glycerol at the

waterelipid interface and can reverse the reaction in non-aqueousmedia. It finds application in different industries like food, phar-maceutical, cosmetics, oleo-chemicals, fuel and detergents. The useof solid state fermentation for the production of thermo-stable li-pases is an interesting alternative to the valorization of bagasse andolive oil cake. Lipase production by SSF using olive oil cake andsugarcane bagasse by Rhizomucor pusillus and Rhizopus rhizopodi-formis was reported by Cordova et al., 1998 [44]. The maximumlipase activity for R. pusillus and R. rhizopodiformis were 1.73 U/mland 0.97 U/ml respectively. The study revealed that when sugar-cane bagasse and olive oil cake were mixed in equal proportion, thelipase activity increased to 43.04 U/ml and 10.83 U/ml respectively.The synergetic effect of olive oil cake added to bagasse has beenconfirmed.

Vaseghi et al., 2013 [45] evaluated production of active lipase byRhizopus oryzae from sugarcane bagasse in a tray fermenter. A trayreactor was designed for the extracellular enzyme production. Theresults indicate that the newly constructed tray bioreactor had thepotential to produce lipases with high activity. Addition of olive oilresulted in a 1.6 fold increase in lipase activity. Maximum activityobserved under optimized conditions is 215 U/gds.

Lipase production using different pretreated sugarcane bagassehydrolyzate supplemented with mineral salts was evaluated for theproduction of lipase by Aspergillus fumigatus [46]. Maximum yieldof 40 U/ml was observed for 0.6 N NH4OH pretreated sugarcanebagasse medium supplemented with mineral salts in comparisonto other acid and alkali pretreated bagasse hydrolyzate. Sugarcanebagasse serves as a cheap source for the production of lipase.

3.7.8. PectinasesPectinases catalyze the hydrolysis of pectin. It finds extensive

applications in food and beverage industries. It is used for clarifi-cation of fruit juice, pulp and paper industry, coffee and teafermentation, waste management, protoplast isolation, retting offlax and vegetable fibers and haze removal from wines. SSF usingagro-industrial residues is an attractive option since it presentshigher productivity, lower capital and operating costs and easierdownstream processing compared to submerged fermentation.Baladhandayutham and Thangavelu, 2011 [47] reported pectinaseproduction by Aspergillus awamori using sugarcane bagasse andrice bran as substrate. Maximum pectinase production (103.33 U/ml) was observed when 85% of rice bran and 15% of sugarcanebagasse were used and incubation temperature of 35 �C.

3.7.9. LaccasesLaccases are multi-copper containing enzymes which catalyze

the oxidation of a wide variety of aromatic compounds withconcomitant reduction of oxygen to water. Potential applications oflaccase include biopulping and biobleaching, industrial dyedegradation, improving the digestibility of lignocellulosic biomass,delignification, removal of phenolic compounds and toxic pollut-ants. The use of inexpensive agro-residues for the economic



production of laccase seems promising. Singh et al., 2010 [48]evaluated laccase production by Aspergillus heteromorph usingdistillery spent wash and lignocellulosic biomass. The studyshowed that lignocellulosic biomass enhanced laccase production.Anaerobically treated distillery spent wash and lignocellulosicbiomasses like sugarcane bagasse are cheap and easily availableand serve as an ecofriendly and economic strategy for the pro-duction of laccase.

3.8. Composites

Natural fibers serve as emerging alternatives to glass-reinforcedcomposites. Few advantages of natural fiber composite are low cost,light weight, renewable and biodegradable. Other environmentaladvantages include lower greenhouse gas emissions and enhancedenergy recovery [49].

Alkali treatment of bagasse was carried out to increase theadhesion between the fiber and the resin matrix and the me-chanical properties of the composite samples to different envi-ronmental treatments were carried out by Acharya et al., 2011 [49].A chemical pretreatment was carried out to overcome the draw-backs associated with natural fiber-reinforced composites like highmoisture absorption, poor wettability and poor adhesion. The studyrevealed that sugarcane bagasse serves as a good raw material forthe production of composite by suitably bonding with resin for avalue added product.

da Silva et al., 2013 [50] developed a strategy for value additionof lignin extracted from sugarcane bagasse by organosolv pulpingby reacting with glutaraldehyde. The organosolv lignin-glutaraldehyde resin was used to prepare a composite reinforcedwith sugarcane bagasse fibers. The study revealed that the use ofphenolic materials originating from renewable resources forvarious industrial applications could contribute to an increase inthe profitability of bio-refineries where lignin is generated asbyproduct.

3.9. Organic acids

Fermentative production of organic acids is a promisingapproach for obtaining organic acids from renewable carbonsource. Organic acids constitute the key group among the buildingblock chemicals which can be produced by microbial processes.Biotechnological processes are favorable from a chemical as well aseconomic point of view. Table 3 shows different organic acidsproduced from sugarcane crop residue. Some of the organic acidsthat are produced using sugarcane crop residue or using by-products of sugarcane industry include itaconic acid, succinicacid, citric acid, lactic acid, butyric acid and propionic acid.

Table 3Organic acids produced from sugarcane crop residue.

Sugarcane residue Product Microorganism

Molasses Itaconic acid A. terreus/A. itaBagasse Itaconic acid A. niger/A.oryzBagasse Succinic acid ActinobacillusBagasse Succinic acid ActinobacillusBagasse Citric acid A. niger DS1Bagasse/Vinasse Citric acid A.nigerBagasse Citric acid A. nigerMolasses Lactic acid e

Bagasse Lactic acid BacillusBagasse Butyric acid C. tyrobutyricuMolasses Propionic acid PropionibacterBagasse Propionic acid PropionibacterBagasse Propionic acid Propionibacter


3.9.1. Itaconic acidThe wide spread use of itaconic acid in synthetic resins, syn-

thetic fibers, surfactants, rubbers, plastics and oil additives haveresulted in an increased demand for this product [51]. It also pro-vides possibilities for selective enzymatic transformations to createuseful poly-functional building blocks. Many researchers haveattempted to replace the expensive carbon source used for itaconicacid production with cheaper alternative substrates.

Nubel and Ratajak, 1960 [52] reported improved yield of itaconicacid by replacing refined glucose with less expensive carbohydratesource like sugarcane and sugar beet molasses. They developed astrategy for conversion of inexpensive carbohydrates to itaconicacid in high yield by submerged aerobic fermentation. Themolasses were pretreated with ion exchange resins, ferrocyanide,bentonite and lime for the removal of impurities like heavy metalsor alkaline earth substances from the molasses. The molasses me-dium was inoculated with Aspergillus terreus and A. itaconicus,which are capable of producing itaconic acid by submergedfermentation of carbohydrates. Cane molasses medium (1800 ml)was diluted to 18% w/v of sugar and mixed with beet molassesmedium (200 ml) was diluted to 18% w/v of sugar and inoculatedwith a spore suspension of A. terreus and incubated at 35e40 �C.Fermentation was carried out until the itaconic acid concentrationreached 5 g/100 ml. The fermented broth is filtered and concen-trated to crystallize the product.

Sugarcane bagasse was utilized for the production of itaconicacid from A. niger, A. oryzae, A. flavus and Penicillium sp. in solidstate fermentation by Paranthaman et al., 2014 [53]. Among thedifferent fungi screened, A. niger produced highest itaconic acid(8.24 mg/kg) in SSF. The study revealed the suitability of sugarcanebagasse powder for the fermentative production of itaconic acid.

3.9.2. Succinic acidSuccinic acid is a dicarboxylic acid and is produced by plants,

animals and microorganisms. It finds wide applications in in-dustries involved in producing food, green solvents, biodegradableplastics and ingredients used for the stimulation of plant growth[54]. Succinic acid is mostly used as surfactant, additive, foamingagent and detergent. It is also used as ion chelator which preventscorrosion and pitting in the metal industry and also as antimicro-bial and flavoring agent and also as an additive in the production ofvitamins, antibiotics and amino acids [55]. The cost of succinic acidproduction is affected by its productivity, raw material cost, andyield as well as product recovery system. Hence exploiting thepotential of cheaper and surplus available lignocellulosic biomassas carbon source will makes the process more economical.

Borges and Pereira, 2011 [56] developed a strategy for succinicacid production from sugarcane bagasse hemicellulose hydrolyzate

Reference

conicus Nubel and Ratajak, 1960ae/A. flavus/Penicillium Paranthaman et al., 2014succinogenes Borges and Pereira, 2011succinogenes Xi et al., 2013

Kumar et al., 2003Oliveira et al., 2012Amenaghawon et al., 2013Lunelli et al., 2010Peng et al., 2014

m Wei et al., 2013ium freudenreichii CCTCC M207015 Feng et al., 2011ium freudenreichii CCTCC M207015 Chen et al., 2012ium acidipropionii Zhu et al., 2012



by Actinobacillus succinogenes. The study revealed that supple-mentation of NaHCO3, MgSO4 and yeast extract played a significantrole in succinic acid production. The conversion yield of succinicacid from sugarcane bagasse hydrolyzate was relatively high andproduced 22.5 g/l.

Production of succinic acid using A. succinogenes by ultrasoundpretreatment and hydrolysis of sugarcane bagasse was reported byXi et al., 2013 [57]. Sugarcane bagasse hemicellulose hydrolyzatewas used as the carbon and nitrogen source for green andeconomical production of succinic acid. Ultrasound assisted diluteacid hydrolysis of sugarcane bagasse serves as a time saving andeconomical method for hydrolyzing sugarcane bagasse. The non-detoxified hydrolyzate produced 23.7 g/l of succinic acid with ayield of 79% and productivity of 0.99 g/l/h.

3.9.3. Citric acidCitric acid finds application in various industries. It is used as an

anti-oxidising, flavoring, preserving, chelating and buffering agentin the food, beverages, pharmaceutical and cosmetic industries[58]. Traditionally it is produced by submerged fermentation usingA. niger. The increase in demand of citric acid leads to search formore economical means for its production. Recently studies havebeen carried out by several researchers for the production of citricacid using agricultural residues.

SSF process for the production of citric acid by A. niger DS1 usingsugarcane bagasse as a carrier and sucrose or molasses based me-dium as a moistening agent was reported by Kumar et al., 2003[59]. Sugarcane bagasse serves as a good carrier since it did notshow agglomeration after moistening with the medium and helpsin better heat and mass transfer during fermentation and higherproduct yield. The citric acid yield from sucrose, clarified and non-clarified molasses medium were 69.6, 64.5 and 62.4% respectivelyafter nine days of incubation. The decrease in citric acid yield whennon-clarifiedmolasses were used is due to inhibition bymetal ions.Thoughmetal ions supported growth of the fungus it has a negativeimpact on citric acid yield.

Oliveira et al., 2012 [60] developed a strategy for the productionof citric acid using sugarcane bagasse with vinasse by A. niger. Thefermentation was carried out in a packed bed reactor with sugar-cane bagasse impregnated suspension of A. niger and vinasse with80% moisture, incubation temperature of 25 �C, aeration flow rateof 0.4L/min of water saturated air and incubation time for 6 days.The citric acid yield under these conditions was 1.45 g of total acid/gof dry bagasse/day. The study represents an alternative to con-ventional submerged processes for obtaining bio-products fromA. niger.

Amenaghawon et al., 2013 [61] carried out modeling and opti-mization of citric acid production from solid state fermentation ofsugarcane bagasse using A. niger. Various process parametersaffecting citric acid production likemedia pH, substrate loading andincubation time were optimized by adopting response surfacemethodology. The optimal fermentation conditions were media pHof 2.0, incubation time of 6 days and substrate loading, 80 g/L.Under optimized conditions the citric acid produced was 18.63 g/L.

Yadigary et al., 2013 [62] optimized conditions for citric acidproduction from sugarcane bagasse by adopting Taguchi design.The study revealed that sugarcane bagasse serves as a cost effectivesubstrate for the production of citric acid. The residue left out afterextraction of citric acid and destroying the microbes can be used asan animal feed since SSF decreases the concentration of anti-nutritional factors in bagasse.

3.9.4. Lactic acidLactic acid is used in the pharmaceutical, chemical, cosmetic and

food industries as well as for biodegradable polymer and green


solvent production. It can be produced by chemical synthesis or byfermentation. The fermentative production of lactic acid hasreceived a lot of interest in the present scenario since it offers analternative to environmental pollution caused by petrochemicalindustry and the limited supply of petrochemical resources [63].Currently lactic acid consumption has been increased a lot due to itsrole as a monomer in the production of biodegradable polymer,poly lactic acid (PLA).

Use of refined materials for the production of lactic acid in-creases the costs for production even though the cost for productpurification should be significantly reduced. Several attempts weregoing on for the economical production of lactic acid. Utilization ofcellulosic materials seems promising since they are cheap, abun-dant and renewable. Lunelli et al., 2010 [64] reported fermentativeproduction of lactic acid using sucrose obtained from sugarcanemolasses. Fermentation was carried out at pH 5.0, incubationtemperature of 34 �C, 200 rpm and sucrose concentration of 12 g/L.The yield of lactic acid obtained from diluted sugarcane molassesfermentation was 0.83 g/g.

Peng et al., 2014 [65] developed an efficient open fermentativeproduction of polymer grade lactic acid from sugarcane bagassehydrolyzate by thermotolerant Bacillus strain P38. In this study thelactic acid reached a concentration of 185 g/L with a volumetricproductivity of 1.93 g/L/h by using sugarcane bagasse hydrolyzateas the sole carbon source along with cotton seed meal as cheapnitrogen source. This is the highest reported lactic acid productionusing lignocellulosic source. The high tolerance of Bacillus strainP38 to the toxicity of fermentation inhibitors indicate that thisstrain can be used for the development of an efficient andeconomical process for lactic acid from various lignocellulosicbiomasses.

3.9.5. Butyric acidButyric acid finds applications in chemical, food and beverage,

cosmetic, plastic and textile fiber industries. Its applications asbioactive and therapeutic agents in nutraceutical market ingrowing rapidly [66]. Currently butyric acid is produced by petro-leum based oxo-synthesis of butyraldelyde from propylene. Due torising oil price, the production of butyric acid by anaerobicfermentation form natural resources has become attractive [67].

A fermentation process for the production of butyric acid fromsugarcane bagasse hydrolyzate by Clostridium tyrobutyricumimmobilized in a fibrous bed reactor was reported by Wei et al.,2013 [67]. The acid pretreated and enzymatically saccharifiedsugarcane bagasse was used as carbon source without any detoxi-fication. The butyric acid yield and productivity were 0.48 g/g and0.51 g/L/h respectively. This is the first report demonstrating thefeasibility of butyric acid production from sugarcane bagassehydrolyzate.

3.9.6. Propionic acidPropionic acid is an important short chain fatty acid with many

applications. It finds applications in industries like cellulose plastic,herbicides, perfumes and food. The traditional route of propionicacid production is by the oxidation of propane or propionaldehyde.Currently, the traditional petrochemical route faces more chal-lenges due to limited supply of petroleum. In this scenario, theproduction of propionic acid from renewable sources seemspromising. Considering the cost-efficiency of microbial fermenta-tion, the exploitation of low cost, renewable carbon sources have apositive impact. The utilization of cheap and surplus availablesugarcane bagasse as a renewable source for the production ofpropionic acid will reduce the cost considerably.

Green and economic production of propionic acid by Propioni-bacterium freudenreichii CCTCC M207015 in plant fibrous bed (PFB)



reactor was reported by Feng et al., 2011 [68]. Propionic acid pro-duction from molasses was studied in PFB reactor. With non-treated molasses yielded 12.69 g/L of propionic acid where as PFBfermentation yielded 41.22 g/L of propionic acid. When fed-batchfermentation was performed with hydrolyzed molasses in PFByielded 91.89 g/L of propionic acid after an incubation time of 254 h.The study revealed that low cost molasses can be utilized for thegreen and economical production of propionic acid byP. freudenreichii.

Chen et al., 2012 [69] evaluated propionic acid production in aplant fibrous-bed bioreactor (PFB) with immobilizedP. freudenreichii CCTCC M207015. Sugarcane bagasse was applied tothe PFB as immobilizing material. The highest propionic acid con-centration obtained was 136.23 g/L which is 1.4 times higher thanthe highest concentration previously reported (97.0 g/L). Comparedwith free cell fermentation the fluxes of propionic acid synthesisand the pentose phosphate pathway in PFB fermentation wereincreased by 84.65% and 227.62% respectively. The results suggestthat PFB is a simple and effective method for the high concentrationproduction of propionic acid.

Improving the productivity of propionic acid with fibrous bedbioreactor (FBB) e immobilized cells of an adapted acid-tolerantPropionibacterium acidipropionici was carried out by Zhu et al.,2012 [70]. A propionic acid concentration of 51.2 g/L with a highproductivity of 0.71 g/L/h was achieved via fed-batch fermentationin FBB system. The productivity was increased by supplementationof sugarcane bagasse hydrolyzate gave 58.8 g/L of propionic acid.The results revealed the potential of sugarcane bagasse as a sub-strate for the economic production of propionic acid at industrialscale.

3.9.7. Gluconic acidGluconic acid is a dehydrogenation product of D-glucose which

finds application in food, feed, pharmaceutical, textile, cement andchemical industries. The process of gluconic acid production can bemade more economic by utilization of agro-industrial residues assubstrates for SSF. Singh et al., 2003 [71] developed a strategy forgluconic acid production by A. niger in SSF, SmF, SF (surfacefermentation) and SmSF (semi solid state fermentation). The studyrevealed that overproduction of gluconic acid was observed underSSF conditions using sugarcane bagasse as substrate.

3.10. Xylitol

Xylitol is a polyol naturally found in various fruits and vegeta-bles and possess a high sweetening power which finds applicationin food and pharmaceutical industries. Being a sugar substitute it isused in dietary foods for insulin deficiency patients. Currently thelarge scale production is typically carried out by a chemical processof D-xylose hydrogenation [72]. Waste utilization for xylitol pro-duction seems promising. Hence development and optimization ofmethods for obtaining xylose from lignocellulosic biomass andconversion to xylitol seems promising.

Production of xylitol using hydrolyzate obtained after dilute acidpretreatment of sugarcane bagasse was reported by Sarrouh et al.,2009 [73]. The study revealed that post hydrolysis of the dilute acidpretreated sugarcane bagasse hydrolyzate resulted in an increase inxylose release in the hemicellulose fraction. The advantage of usingpost-treated hydrolyzate is that it requires less concentration ofsugars resulting in a lower concentration of fermentation inhibitorsand there was an increase in high xylose to xylitol conversion ef-ficiency (0.7 g xylitol/g xylose) and volumetric productivitycompared to the usage of original hemicellulosic hydrolyzate(0.65 g xylitol/g xylose). The post-hydrolysis stage resulted in anincrease of xylose concentration from 18.4 g/L to 23.5 g/L. Hence


there is no need for concentration of the hydrolyzate and resultedin lower fermentation inhibitors like phenolic compounds andacetic acid which in turn have a positive impact by increasingproductivity by 13% and xylitol yield by 7%.

Branco et al., 2011 [74] developed a strategy for enzymaticproduction of xylitol using sugarcane bagasse hydrolyzate withglucose dehydrogenase (GDH) system for NADPH in situ generationas well as to verify technical feasibility and potential of enzymaticproduction of xylitol as an alternative to traditional productionprocesses. Enzymatic strategy is a new alternative for conventionalmicrobiological process which can achieve 100% conversion. Thehigh conversion rate is due to direct transformation of xylose toxylitol which cannot be achieved in conventional fermentativeprocess. The enzymatic strategy involves the direct reduction ofxylose to xylitol by the enzyme xylose reductase assisted by thecoenzyme reduced form of nicotinamide adenine dinucleotidephosphate (NADPH). The study revealed that 40% v/v concentrationof sugarcane bagasse hemicellulosic hydrolyzate (SCBHH) does notinterfere with xylitol production but when high content of SCBHHe 80% and 100% v/v, showed a negative impact on xylitol produc-tion. Fine tuning of the various process variables affecting xylitolproduction will improve the yield.

Prakash et al., 2011 [75] exploited the potential of microbialproduction of xylitol from sugarcane bagasse hemicellulose usingfree and immobilized cells of Debaryomyces hansenii. The efficiencyfor free and immobilized cells was compared for xylitol productionin batch culture at 40 �C. Themaximum xylitol yield and volumetricproductivity produced by free cells were 0.69 g/g and 0.28 g/L/hrespectively after detoxification with activated charcoal and ionexchange resins. The maximum xylitol yield and productivity ofcalcium alginate immobilized cells of D. hansenii were 0.82/g and0.46 g/L/h respectively. As compared to free cells, immobilized cellsproduce xylitol more efficiently and can be reused for six cycleswithout any apparent loss in their fermentation capability.

Coupled production of biodiesel, xylitol and xylanase fromsugarcane bagasse in a biorefinery concept using fungi was re-ported by Kamat et al., 2013 [76]. Dilute acid pretreated sugarcanebagasse hydrolyzate was utilized for the production of xylitol byWilliopsis saturnus resulted in a yield 0.51 g/g of xylose consumedafter 72 h of incubation.

Co-cultures for simultaneous production of ethanol and xylitolunder continuous multistep versus fed-batch production modesusing Candida tropicalis IEC5-ITV and S. cerevisiae ITV01-RD in asimulated medium of sugarcane bagasse hydrolyzate was reportedby Castanon- Rodriguez et al., 2014 [77]. The study explores thebiotechnological production of ethanol and xylitol by twowild typeyeasts as a strategy for biorefinery. The best conditionwas observedfor simultaneous culture was S. cerevisiae co-culture andC. tropicalis sequential cultivation at 24 h. The xylitol productivityand yield at simultaneous culture condition were 0.10 g/L/h and0.31 g/g respectively. For fed-batch culture the xylitol productivityand yield were the same. The results suggest that the co-culture ofthese wild type yeasts has the potential for fermenting lignocel-lulosic substrates to simultaneously produce xylitol and ethanolusing continuous cultures. This is a good strategy to make completeuse of lignocellulosic residues while obtaining simultaneously twovalue added products.

3.11. Chelating agents

Chelating agents are used for removing heavy metals from in-dustrial effluents. A good chelating agent contains functionalgroups with high electronic density like carbonyl, amines, thiols,hydroxyls and aromatic rings. Since the lignocellulosic biomasscomponent, lignin contains several of these groups can be used as a



chelating material.Enzymatic systems serve as a promising strategy for oxidation of

lignin. Polyphenoloxidases (PPO) oxidizes lignin producing cresolsor quinone structures increasing the number of chelating groups inthe lignin. Goncalves et al., 2002 [78] developed a strategy for theproduction of chelating agents through the enzymatic oxidation ofacetosolv sugarcane bagasse lignin. Oxidation of lignin obtainedfrom acetosolv pulping of sugarcane bagasse was performed bypolyethylene glycol to increase the number of carbonyl and hy-droxyl groups in lignin for improving the chelating capacity. Thestudy revealed that the chelating capacity of lignin oxidized withPPO showed a 73% increase in chelating property when comparedto original lignin and is due to incorporation of vinyl hydroxylgroups. Chelating property increases with increase of molecularweight of lignin and is due to increase of polar groups in the ligninand cause an increase in hydrodynamic volume which in turnresulted in an increase in molecular weight.

3.12. Carotenoids

Carotenoids are natural pigments responsible for coloring foodsand have important biological activities. It finds application inpharmaceutical, chemical, food and feed industries. Biotechnolog-ical route for carotenoid is currently limited by the high cost ofproduction. However the cost can be minimized by using highpigment producing strains cultured in cheap industrial byproductsor agro-residues as nutrient source [79].

Bio-production of carotenoids by Sporidiobolus salmonicolor CBS2636 using pretreated agro-industrial substrate was reported byValduga et al., 2008 [80]. Fermentation was carried out with 10 g/Lof sugarcane molasses, 5 g/L of corn steep liquor, 5 g/L of yeasthydrolyzate, agitation at 180 rpm and initial pH of 4.0 produced atotal carotenoid content of 541.5 mg/L.

Freitas et al., 2014 [81] evaluated low-cost carbon sources forcarotenoid production by Rhodosporidium toruloides NCYC 921. Theyeast carotenoid productivity in sugarcane molasses was 3.85 mg/L/h. Flow cytometry analysis revealed that most of the yeast cellsgrown on sugarcanemolasses displayed permeabilised cytoplasmicmembranes.

3.13. Modified catalysts

The utilization of lignocellulosic materials as supports for theadsorption of metallic cat-ions has received much attention due totheir low cost. Several research groups have developed adsorptionmaterials based on lignocellulosic matrices as solid supports withgood chemical affinity for metallic ions [82]. Modified sugarcanebagasse can efficiently adsorb metallic cat-ions present in waterbodies and effluent, making positive impact from an economicaland environmental point of view [83].

A novel use formodified sugarcane bagasse containing adsorbedCo2þ and Cr3þ ions as heterogeneous catalysts for the auto-oxidation of monoterpenes were evaluated by Marquez da Silvaet al., 2013 [82]. They developed a process that uses agricultural by-products like sugarcane bagasse modified with organic ligands likesuccinic anhydride and EDTA dianhydride and used for the removalof Co2þ and Cr3þ ions from single metal aqueous solutions. Theseadsorbent materials containing adsorbed Co2þ and Cr3þ as het-erogeneous catalysts for the chemical transformation of naturalterpenic substrates were evaluated. The study revealed that thesematerials serve as promising catalysts for the oxidation of mono-terpenes. This is the first report in which lignocellulosic adsorbentsare applied in a catalytic oxidation process. The catalysts can bereused for three cycles without any loss of activity. The adsorptionstudies also demonstrated the potential of these adsorbents to treat


effluents in a large pH range, which is very useful in industrialprocesses.

3.14. Amino acids

Amino acids find wide range of applications as food additives,feed supplement and therapeutic agents. L-glutamic acid is a non-essential acidic amino acid. It is an important neurotransmitterand plays an important role in neural activation. Monosodiumglutamate, the sodium salt of glutamic acid is widely used as flavorenhancer.

Nampoothiri and Pandey, 1996 [84] reported L-glutamic acidproduction by solid state fermentation by Brevibacterium sp. usingsugarcane bagasse as substrate. The media was moistened to85e90% level with mineral salt solution containing glucose, ureaand vitamins. The maximum glutamic acid yield was 80 mg/g drysubstrate. This is the first report on cultivation of Brevibacterium sp.in solid cultures for the production of glutamic acid.

3.15. Animal feed

One of themajor causes of poor livestock productivity in tropicalregions of the world is due to inadequate nutrition. This is due toshortage of feed as well as high cost of feed constituents. Exploitingthe surplus available sugarcane bagasse for animal feed productionseems promising. Sugarcane bagasse has commonly been used forthe production of protein enriched animal feed. Treating of sugar-cane bagasse with fungus like Pleurotus would remove lignin fromthe bagasse and improves the nutritive value. Okano et al., 2010[85] cultivated Pleurotus eryngii on sugarcane bagasse to enhancethe digestibility of bagasse. The study revealed that cultivating P.eryngii on bagasse completely removed lignin after incubation for95 days and there is no difference in in vitro organic matter di-gestibility (IVOMD), in vitro gas production (IVGP) and in vitroNDFom digestibility (IVNDFom D). After 95 days of biologicaltreatment with P. eryngii the spent bagasse substrate could be usedas feed for ruminants.

3.16. Ergot alkaloids

Ergot alkaloids are mycotoxins produced by several species ofClaviceps. There are four main groups of ergot alkaloids e clavines,lysergic acids, lysergic acid amides and ergopeptides. The demandfor ergot alkaloids and their derivatives has increased in recentyears due to applications in the treatment of various diseases.Hernandez et al., 1993 [86] used impregnated sugarcane pithbagasse to grow a fungal culture for the production of ergot alka-loids. Sixteen different combinations of liquid nutrient mediumwere used for impregnating bagasse for the production of ergotalkaloids by Claviceps purpurea. The study revealed that it ispossible to achieve tailor made spectra of ergot alkaloids bychanging the liquid nutrient media composition used for impreg-nation. This opens a new avenue of achieving tailor made spectra ofergot alkaloids at an economical cost.

3.17. Antibiotics

Antibiotics are one of the best groups of the secondary metab-olites synthesized by microorganisms which are active againstother microorganisms. Due to its importance in human health care,demand for antibiotic is increasing worldwide. Several efforts havebeen made to decrease its production cost by process optimizationusing agricultural residues. Utilization of agro-industrial wasteproducts as substrate has opened the potential to reduce produc-tion costs up to 60% by reducing the cost of raw material during



fermentation [87]. Antibiotic production using SSF requires lowenergy, less investment cost, higher productivity and ecofriendlythan SmF. An advanced SSF system in which a liquid mediumadsorbed on an inert sugarcane bagasse support has been appliedfor antibiotic production by Dominguez et al., 2001 [88]. The maincomponents of the medium are bagasse, nutrients and water. Thestudy revealed that bagasse content strongly controls penicillinproduction in the SSF system. The bagasse content of the solidmedium affects physiology and particular idiophase. The higherbagasse content facilitates water and nutrient transport in the solidmedium. Hence, decreasing the bagasse content in the solid me-dium reduces the growth rate to a more adequate level for Peni-cillin production.

3.18. Plant growth hormone- gibberellic acid

Gibberellic acid is an important fungal secondary metaboliteand is a plant growth stimulant widely used in agriculture.Currently gibberellic acids were produced by SmF and the cost isvery high due to extremely low yield and expensive downstreamprocessing. SSF production of gibberellic acid has attracted a greatdeal of attention. Tomasini et al., 1997 [89] evaluated gibberellicacid production by Gibberella fujikuroi in SSF system using differentagroresidues. The study revealed that this phytohormone can beproduced effectively by SSF on sugarcane bagasse and cassava flour.

4. Conclusion and future perspectives

Bioconversion of crop residues is an ecofriendly biotechnolog-ical application for sustainable development. Sugarcane crop resi-dues and by-products from sugar industries like bagasse, molassesand vinasse offers great opportunities for interesting product outletincluding the production of a wide variety of value added products.Utilization of these residues for alternative energy sources and highvalue products could improve the sustainability of the bioenergychain and reduce the negative environmental impacts related toinappropriate disposal. Several R and D activities are going on inthis direction to develop an economically as well as ecofriendlystrategy for the sustainable production of bioenergy and othervalue added products. The by-products generated from agro-industrial processing of sugarcane serves as an efficient carbonsource for the production of various value added products ofcommercial interest, most of this is still in infancy and scaling up topilot scale is a necessity. Targeting on one product is not econom-ically viable, therefore alternative strategies for targeting produc-tion of some value addition like production of low volume highvalue products like amino acids seems promising and make theprocess economically viable. Though several pretreatment strate-gies were available none of them can be used as a standard methodfor the pretreatment of sugarcane crop residues or by products ofsugar industry. Several key factors like technical, economic andenvironmental considerations to be taken into account beforeselecting a technology for bioconversion. Based on the targetedproduct, the best pretreatment method has to be selected. Some-times development of an integrated approach seems promising andfine tuning of the process will make it economically viable. Lot ofopportunities are possible for the fundamental R and D for suc-cessful exploitation of the full biomass potential by fine tuningtechnological development and performance improvements toachieve economically feasible and environmentally sustainableyields of desired products.

Acknowledgments

One of the authors Raveendran Sindhu acknowledges


Department of Biotechnology for financial support under DBT Bio-CARe scheme. Raveendran Sindhu and Parameswaran Binodacknowledge Ecole Polytechnique F�ed�erale de Lausanne for finan-cial support.

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