Comparison of sodium hydroxide and potassium hydroxide followed by heat treatment on rice straw for cellulase production under solid state fermentation

Abstract

Rice straw is the major agricultural by-product in the world. Its low digestibility made it unsuitable as livestock feed which lead to the mass disposal and burning of rice straw. The main objective of this study were to optimise the alkali concentration and soaking time on rice straw for the alkali pretreatment followed by heat treatment for cellulose production and to compare the effectiveness of both alkali used. The rice straws were subjected to two treatments, which were Treatment A and Treatment B. In Treatment A, the rice straws were treated with sodium hydroxide (NaOH) followed by heat treatment (autoclaving at 121 °C for an hour), whereas the rice straws were treated with potassium hydroxide (KOH) followed by heat in Treatment B. Four different alkali concentrations (5, 10, 15 and 20%) at four different soaking times (1, 2, 3 and 4 h) were investigated. The treated rice straws were subjected to Solid State Fermentation (SSF) with the condition of 1:1 moisture content, 1% ammonium sulphate and 1 × 107 spores mL-1 of locally isolated Aspergillus niger. The highest yield of filter paper enzyme (FPase) and carboxymethyl cellulase (CMCase) were obtained after 6 days of SSF, which were 7.85±0.18 Ug-1 substrate and 11.73±0.27 Ug-1 substrate, respectively; when the rice straw was pre-treated with 15% KOH with 1 h soaking time followed by heat. Conclusively, rice straw can be effectively bio-converted into valuable product such as cellulase in SSF. © 2010 Asian Network for Scientific Information.