PRODUCTION OF RAW STARCH DIGESTING AMYLASE BY ASPERGILLUS-NIGER GROWN ON NATIVE STARCH SOURCES

Aspergillus niger isolated from rotting cassava produced raw starch degrading amylase on cassava, maize, sorghum and soluble potato-derived starch as the sole carbon source without prior gelatinisation. Maximum activity of the amylase was attained using cassava starch as substrate. The crude enzyme solution which comprised a mixture of raw and non raw starch digesting amylase degraded both cereal and tuber or root starches significantly. Source of assay starch significantly influenced raw starch digesting activity. Optimum pH for the raw starch degrading and the extracellular amylase were 6.0 and 3.5-4.0, respectively. However, both enzyme activities appeared to be uninfluenced across a relatively broad pH range 3.0-7.0. No correlation was found between the capacity of starch to induce expression of the enzyme and its susceptibility to enzyme digestion. The adsorbability of the various starches to raw starch digesting amylase was directly related to their digestibility.