Utilisation of Egyptian rice straw in production of cellulases and microbial protein: Effect of various pretreatments on yields of protein and enzyme activity

Rice straw was chosen as a cheap carbon source for SCP production using a locally isolated fungus identified as Trichoderma harzianum. The chemical constituents of the raw material were cellulose 43%, hemicellulose 26% and relatively low lignin, 16%. The effects of chemical and physical pretreatments on the protein production, cellulase activity and cell mass of T. harzianum have been investigated. Pretreatment of the raw material using a combination of NaOH and high pressure steam treatment increased its microbial digestibility from 24% to 73%. Similar results were obtained by pretreatment with sodium chlorite for holocellulose formation. However, maximum yields of cell mass and protein were obtained by the first method. The organism gave 7.18 g litre−1 cell mass and 2.50 g litre−1 mycelial protein. Treatment with sodium chlorite increased cellulase activities but gave a lower fungal yield. When the NaOH was applied with high pressure steam, the organism produced 32.8% crude protein, a yield similar to that given by the same organism cultured on soluble carboxymethylcellulose.