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Optimization of xylanase production from Aspergillus terreus by using renewable agricultural lignocellulosic residues

2009-09-01
Kocabas, A.
Bakir, U.
Ögel, Zümrüt Begüm
Plant cell walls are composed mainly of cellulose (40—45%),hemicellulose (30—35%) and lignin (20—23%). Xylan is themain hemicellulolytic polysaccharide exist in plant cell wallsand constitute a remarkable renewable biomass comprising upto 20—35% dry weight of agricultural wastes. Hydrolysis ofxylan plays an important role in the breakdown process of plantmaterial in nature. The enzymes acting on the xylan backboneare classified in two groups: endo- -1,4-xylanases (E.C. 3.2.1.8,xylan xylanohydrolase) and exo- -1,4-xylanases (E.C. 3.2.1.37,D-xylan xylanohydrolase). Furthermore the complexity of xylan isresponsible for the multiplicity of xylanases produced by microor-ganisms.The aim of this research is to optimize xylanase productionfromAspergillus terreususing agricultural by-products as carbonsources in the production media. The study started with two dif-ferent media: ingredients of Medium-1 were chosen according toliterature reports where it had an inducing effect on xylanase pro-duction and the Medium-2 was used through previous studies withthe organism. In this study, media containing glucose were usedas control for microbial growth. 1% xylan containing media wereused as a control for xylanase production. Xylose was used as car-bon source to observe if the organism can utilize it as efficiently asglucose.The results showed thatA. terreuscan utilize xylose as a sub-stitution of glucose. Moreover, the xylanase activity ofA. terreus(57 IU/mL on 1% birch wood) was higher than any xylanase activ-ities reported in the literature from other strains ofA. terreus.Decreasing the initial inoculation pH and using Medium-2 resultedin the highest xylanase activity. Cotton stalk and sunflower stalkcould not induce xylanase activity and xylanase activities on theseresidues were 4 IU/mL, each. Nonetheless, xylanase activity oncorn cob was 36 IU/ml whereas cellulase activity was very low.These findings indicate that agricultural wastes can be used as sub-strate for xylanase production; furthermore it is possible to reducethe cost at industrial production scale using agricultural wastes.Therefore, it is of interest to investigate further whether the usageof agricultural waste is possible for increasing xylanase produc-tion fromA. terreus. Further research on the xylanase system ofthis organism is expected to facilitate the full realization of itscommercial potential.