Solid State Fermentation: An Overview - pierre

58 S. BHARGAV et al., Solid-state Fermentation: An Overview, Chem. Biochem. Eng. Q. 22 (1) 49–70 (2008)mal stability, and activity at mesophillic temperaturesare generally utilized in chemical processes. 85Some of the agro-industrial wastes used in SSFfor lipase production are babassu oil cake, wheatbran, rice bran, gingelly oil cake, almond meal,mustard meal, coconut meal, rice husk, sugarcanebagasse, cassava bagasse, coconut oil cake, olive oilcake, etc.CellulaseCellulase is an enzyme complex used for theconversion of lignocellulosic residues and used forproduction of ethanol, single-cell protein, bleachingof pulp, for treatment of waste papers and for fruitjuice extraction. In SSF, using lignocellulosicwastes as substrates can reduce the cost of cellulaseproduction. 61 Lignocellulosic materials are cheaperand pretreatment is required to improve their utilization.Pretreatment of lignocellulosic matrix increasesthe potential of cellulases to act oncellulose, hemicelluloses.The concerted action of enzymes like endoglucanases,exoglucanases and - glucosidase isused for hydrolyzing cellulose. The rate-limitingstep is the ability of endoglucanases to reach amorphousregions within the crystalline matrix and createnew ends with which endoglucanases can act. 86Ethanol production from lignocellulose biomass requireshydrolysis by cellulase and hemicellulase forconverting lignocellulosic biomass to biofuel. 87Some factors like moisture content, particlesize, pH, incubation temperature, inoculum size, incubationperiod and enrichment of medium withcarbon and nitrogen were considered optimum forcellulase production by bacterial strain Bacillussubtilis on banana fruit stalk wastes. However, totalenzyme production was 12 times higher in SSFthan in submerged fermentation under similar experimentalcondition. 88 It is necessary to considerthese factors for cellulase production from lignocellulosicwastes as their nutrients are already depleted.Water content of substrate and aeration rate arecritical factors in cellulase production using SSF.Corncob residue was used for cellulase productionwith Trichoderma reesei ZU02 in shallow tray fermentors.Xia and Cen used a deep trough fermentorwith forced aeration for cellulase production.Forced aeration enhanced the mass transfer to agreater extent, which increased cellulase activity to305 IU per g of cellulose. 61 It has been reported byFujian et al. that substrates in solid-state with continuouscirculation of air and convective diffusionwith pressure are better for fungal propagation thanstatic cultures. This periodic air circulation increasesthe looseness of substrates and enhancescellulase activity. The filter paper activity of cellulaseenzyme increased to 20.4 IU g –1 at a bed heightof h = 9cm in t = 60 h, while maximum filter paperenzyme activity was 10.8 IU g –1 in 84 h withinstatic cultures. The work was performed usingsteam-exploded wheat straw as carrier with Penicillumdecumbens in SSF. 89 However, changes inthe amplitude of air pressure increased the oxygenavailability to the cultures used and heat removal.The variations enhanced the cellulase production byTrichoderma viride in SSF. 90Co culturing of two fungi in SSF enhances theenzyme production. Co culturing of Trichodermareesei mutants with Aspergillus spp. increased thecellulase production by 50 % and improved thecellulase glucosidase ratio, by partially removingproduct inhibition and its hydrolysis. 91 Co culturingAspergillus ellipticus and Aspergillus fumigatus resultedin improved hydrolytic and -glucosidaes activity.61,71 However, some newly developed agro-industrialwastes used for cellulase production arebanana wastes, rice straw, corn cob residue, ricehusk, wheat straw, banana fruit stalk, and coconutcoir pith.PectinasePectinases are constitutive or inducible enzymesproduced by microbes for breaking pectin.Different substrates used for production of pectinaseare wheat bran, soy bran, apple pomace, cranberrypomace, strawberry pomace, beet pulp, coffeepulp & husk, cocoa, lemon & orange peel, combinationof sugarcane bagasse and orange bagasse,wheat bran etc.Production of polygalactouronase (PG) andpectinesterase (PE) was 6.4 times higher in SSFcompared to submerged fermentation. PE and PGactivity was measured to be 500 U L –1 and 350UL –1 at 24 h of incubation with pectin as the solecarbon source with SSF, but in submerged fermentationenzyme production was 127 U L –1 and 55UL –1 at t = 48 h of incubation. Supplementation ofglucose decreased the production of enzymes due tocatabolite repression in submerged fermentation.However, PE and PG enzymes increased by 30 %and 33 % respectively with addition of glucose. 92Similarly, exopectinase activity increased from 623to 7150 (IU L –1 ) in SSF, but decreased from 1714 to355 (IU L –1 ) in submerged fermentation in the presenceof sucrose at A w of 0.995. Similar results wereat A w of 0.96. Increase in water activity increasedpectinase activity in SSF. 93 Production usingdeseeded sunflower head as substrate resulted instep-up of exopectinase and endopectinase enzymeusing SSF. In SMF the endopectinase was 18.9UmL –1 , which increased to 19.8 U mL –1 in SSF.