Agar plate growth studies of Rhizopus oligosporus and Aspergillus oryzae to determine their suitability for solid-state fermentation

Summary Colony radial growth rates of Rhizopus oligosporus and Aspergillus oryzae were compared under various conditions on agar plates containing cassava starch. Both organisms grew well on cassava starch as their sole source of carbon and energy, although growth was stimulated by the addition of yeast extract and peptone. Neither organism utilized ungelatinized starch effectively. The optimum initial pH for R. oligosporus was 7, although good growth was obtained at pH 5 when ammonium sulfate was partially replaced by urea. A. oryzae grew well over a range of initial pH values from 5 to 8. Growth of R. oligosporus was inhibited by NaCl concentrations above 0.5% (w/v) while A. oryzae was unaffected up to 4% NaCl. The best colony radial growth rate obtained for R. oligosporus was 1.01 mm/h, which was far superior to that obtained for A. oryzae (0.29 mm/h). R. oligosporus was chosen as the more suitable organism for future studies of the protein enrichment of cassava by solid-state fermentation.