Saccharification of raw cassava starch by local strains of Aspergillus and Rhizopus

The strains investigated were 70 isolates of Aspergillus and 349 isolates of Rhizopus, of which Aspergillus W 337 and Rhizopus W 65 were found to be the most efficient strains in raw cassava starch digestion. Optimum conditions for glucoalmylase production of Aspergillus W 337 and Rhizopus W65 were obtained on a medium containing wheat bran, rice husk and cassava starch at 5:1:1 and 7:1:1 ratio, respectively, both without nitrogen source supplementation. For Aspergillus W337 initial pH and moisture content were 3.6 and 80 percent (dry weight basis), respectively and incubation was at 30 degrees centrigrade for 120 hours. For Rhizopus W65 initial pH and moisture content were 4.6 and 40 percent (dry weight basis), respectively, and incubation was at 30 degrees centigrade for 72 hours. Optimal ranges of temperature and pH for glucoamylase activity of crude enzyme obtained from Aspergillus W337 were 45 to 55 degrees centigrade and 3.0 to 5.0, respectively. The enzyme was stable up to 55 degrees centrigrade and the pH range of 3.0 to 3.6. However, optimum conditions for saccharification of raw starch by the enzyme were only at 37 to 45 degrees centigrade with pH range from 3.0 to 3.6. Optimum conditions for activity from Rhizopus W 65 ranged from 40 to 50 degrees centigrade and the pH ranged from 4.0 to 5.0. The enzyme was stable up to 45 degrees centigrade with the pH range of 3.0 to 8.0. Optimum conditions for saccharification of raw starch by the enzyme were at 37 to 45 degrees centigrade with pH range of 3.0 to 4.0. The enzyme from both cultures were fractionated with 60-80 percent saturation of ammonium sulfate solution. Activities of partially purified enzymes from Aspergillus W 337 was increased 3 folds and 1 fold for Rhizopus W 65. The chromatogram of glucoamylase and protein fractions on DE AE cellulose columns from Aspergillus W 337 appeared as two peaks while three peaks were observed from Rhizopus W 65. Elution of peak I from both strains were responsible for raw starch digestion