Biobleaching of wheat straw-rich-soda pulp by the application of alkalophilic and thermophilic mannanase from <i>Streptomyces</i> sp. PG-08-3

Abstract

An alkalophilic and thermophilic mannanase from Streptomyces sp. PG-08-3 was applied to wheat straw-rich-soda pulp to check its bleaching potential. Optimum conditions for bio-bleaching of pulp were as follows: Mannanase 5 Ug^-1 of pulp at pH 8.5 with temperature 55ºC that enhanced the brightness by 7.3% and reduced the kappa number by 24.6% within 4 h of incubation. Tear index (20%) and burst index (11.2%) were also improved by mannanase-treated pulp as compared to the untreated pulp. Treatment of chemically (CEH1H2) bleached pulp with enzyme showed significant effect on release of chromophores, hydrophobic and reducing compounds. Mannanase-prebleaching of raw pulp reduced the use of hypochlorite by 16% to achieve brightness of resultant hand sheets similar to the fully chemically bleached pulp. Scanning electron microscopy of wheat straw rich soda-pulp after treatment with denatured and active mannanase was performed. There was appearance of micro-fibers on the surface of pulp that was treated with active mannanase.

Key words: Biobleaching, mannanase, wheat straw-rich-soda pulp.