Production of bacterial cellulases by solid state bioprocessing of banana wastes

Abstract

Banana fruit stalk waste, one of the abundantly available lignocellulosic agricultural wastes in tropical and subtropical countries, served as solid substrate for the production of cellulases. The effects of pretreatment of the substrate, moisture content, particle size, pH of the medium, incubation temperature, enrichment of the medium with nitrogen and carbon sources, inoculum size and the incubation period were observed for optimal production of these enzymes by the bacterial strain Bacillus subtilis (CBTK 106), isolated from banana waste. The optimal filter paper activity (FP Ase) of 2.8 IUgds −1, CMCase activity of 9.6 IUgds −1 and cellobiase activity of 4.5 IUgds −1 were obtained at 72 h incubation with media containing banana fruit stalk (autoclaved at 121°C for 60 min, particles of 400 μm size), with optimal moisture content of 70%, pH of 7.0, incubation temperature of 35°C, with minerals, and additional nutrients of (NH 4) 2SO 4 or NaNO 3 or glucose at 1.0% (w/w) and an inoculum to substrate ratio of 15% (v/w). Banana fruit stalk was found to be the most suitable substrate among a few easily available lignocellulosics tested. The total enzyme production was 12 fold higher in solid-state fermentation (SSF) than that in submerged fermentation (SmF). Results indicate the excellent scope of utilising banana fruit stalk as solid substrate for commercial production of cellulase employing Bacillus subtilis.