Alkali pretreatment of rice straw and enhanced cellulase production by a locally isolated fungus Aspergillus fumigatus NITDGPKA3

Nibedita Sarkar, Kaustav Aikat

Abstract


Studies were conducted on the alkali pretreatment of rice straw by varying NaOH concentration from 0.1 M to 2.5 M. Cellulose content was maximum (62.19%) for 0.5 M NaOH. Lignin content showed a significant decrease on increase in NaOH concentration up to 0.5M NaOH. Significant morphological changes were detected in the rice straw structure by scanning electron microscopy after pretreatment. A locally isolated cellulolytic fungus Aspergillus fumigatus NITDGPKA3 was used for cellulase (CMCase and FPase) and xylanase production under submerged fermentation of rice straw pretreated with various NaOH concentrations. Maximum enzyme activites were obtained for 0.5 M NaOH. Culture conditions (incubation temperature, initial pH and rotational speed) for cellulase and xylanase production under submerged fermentation of thus pretreated rice straw by Aspergillus fumigatus NITDGPKA3 were statistically optimized by response surface methodology based on central composite design. The optimum conditions were found to be incubation temperature 30oC, rotational speed 120 rpm and initial pH 4.17 (CMCase and FPase) and 4.5 (xylanase). A significantly higher titre of xylanase was obtained compared to the available literature.

 

Key words: Alkali pretreatment , Cellulase , Rice straw , Submerged fermentation


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