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Production of fungal biomass from cormel process waste-water of cocoyam (Xanthosoma sagittifolium (L) Schott) using Aspergillus oryzae obtained from cormel flour

Aspergillus oryzae obtained from spoilt cormel flour was subjected to mutation treatments using X-rays, solar radiation and bleach. Exposure of A oryzae spores to X-radiation of 50 kV at 20 mA s and other treatments induced both mutation and lethality in the organism. Following selection and screening of viable colonies on a medium containing cormel process waste-water as the only carbon source, two strains, A oryzae No 15 and A oryzae No 8, which significantly (P ≤ 0.05) produced more biomass at a higher growth rate than the wild parent, were chosen for single-cell protein production. Nutrient content of the single-cell protein produced by the mutants was comparable to that of the wild type. Addition of 3.0 g each of (NH4)2SO4, NH4NO3, NH4Cl, and urea in 1 l of Xanthosoma process waste-water increased the growth rate of mutants, with the highest increase observed with urea. Medium amended with urea also produced fungal biomass with the highest protein level of 7.97 g l−1 for A oryzae No 8 strain compared with a protein yield of 3.97 g l−1 obtained in the control. Total biomass produced after 54 h was 22.47 g l−1 for A oryzae No 15 strain when urea was added, whereas only 15.20 g l−1 was produced when no nitrogen source was added. The optimal temperature for single-cell protein production was found to be 35 °C and the optimal pH was 3.50. A speed of 100 rpm gave the largest quantity of fungal biomass for the mutants tested. Copyright © 2003 Society of Chemical Industry