full issue - Association of Biotechnology and Pharmacy

Current Trends in Biotechnology and PharmacyVol. 5 (1) 982-992 January 2011. ISSN 0973-8916 (Print), 2230-7303 (Online)98921). The higher β-glucosidase activity could haveresulted in releasing higher amount of total sugarsin the GS enzymatic hydrolysate. Recently, Dienet al. (5) also observed a key role of β-glucosidasein monosaccharide yields after enzymatichydrolysis of hot water treated corn fiber.Enzymatic hydrolysisEnzymatic hydrolysis of NaOH pretreatedGS was carried out using concentrated enzymaticsolution of (cellulase, 30 FPU g -1 ; β-glucosidase,55 U g -1 ; xylanase, 150 U g -1 of the dry substrate)Aspergillus sp. RCAL-5. Time course ofenzymatic saccharification of GS is shown inFigure 8. Saccharification of NaOH pretreatedGS shell yielded maximum sugars (0.64 g g -1 ) withthe hydrolysis efficiency of 63.12%. Thesefindings can be fairly compared with the reportsof Sharma et al. (22) who observed 59.8 %saccharification efficiency from sunflower hullsafter pretreatment with sodium hydroxide 0.5%(w/v). Saha and his coworkers (11) also showedan enzymatic hydrolytic efficiency of 64 % totalcarbohydrates (485 mg g -1 ) from wheat strawusing the commercial cellulases. The hydrolyticefficiency of lignocellulosic substrates alsodepends upon the substrate used. Recently,Chandel et al. (10) reported 77.85±0.45%hydrolytic efficiency from a weed material,Saccharum spontaneum using the cellulasesderived from A. oryzae MTCC 1846.Ethanol fermentationA typical fermentation profile of GSenzymatic hydrolysate using P. stipitis NCIM3498 utilizing 49 g l -1 total sugars is shown in Figure9. A regular increase in ethanol production wasobserved till 84 h of fermentation and declinedthereafter. About 86.5 % of the available sugarswere utilized within 84 h giving an ethanol yieldof 0.46 g g -1 sugar utilized. The fermentationparameters viz. ethanol yield, biomass yield,ethanol productivity etc. are summarized inTable 3.Table 3. Fermentation parameters of the P.stipitis NCIM3498 when grown in the Groundnutshell enzymatic hydrolysateParameters studiedValuesInitial sugar concentration (gs l-1 ) 49Sugar utilization (%) 86.50Ethanol (g pl -1 ) 19.4-1Ethanol yield (g pg s) 0.46Biomass (g xl -1 ) 3.4-1Biomass yield (g xg s) 0.08Volumetric ethanol 0.23productivity (g pl -1 h -1 )Biomass productivity (gx l-1 h -1 ) 0.04Sugar uptake rate (gs l-1 h -1 ) 0.50-1Specific ethanol productivity (g pg xh -1 ) 0.06Total incubation time- 84 h. The data presentedare averages of three independent analysis.Among the xylose fermenting yeasts, P.stiptis has been promising in utilizing maximumfermentable sugars present in lignocellulosehydrolysates which in turn reflects in the higherethanol production with a greater yield. In general,the fermentation performance of P. stipitis islower than the conventionally used ethanologen,Saccharomyces cerevisiae or Zymomonasmobilis. But looking the ability of P. stipitis forutilization of almost all sugars present in thelignocellulose hydrolysates, this microorganism isconsidered ideal in biorefineries. S. cerevisiae orZ. mobilis utilize C 6sugars or sucrose highlyefficiently but their inability to utilize C 5sugarsmake them inappropriate candidates forbiorefineries (3, 4). Our results were similaraccording to the earlier reports summarized inTable 4.Chandra Sekhar et al