Production of starch-gel digesting amyloglucosidase by Aspergillus oryzae HS-3 in solid state fermentation

Abstract

Aspergillus oryzae HS-3, isolated from local soil, produced very high levels of solid starch-gel digesting amyloglucosidase by solid state fermentation in Erlenmeyer flasks and enamel coated metallic trays. Productivity was affected by the nature of the solid substrate, nature of the moistening agent, level of moisture content, incubation temperature, presence or absence of carbon, nitrogen and mineral supplements. Maximum enzyme production of 5773 U/g fermented dry matter was obtained on wheat bran with distilled water at a ratio of 1:1.5 as the moistening agent after 96 h incubation at 30–40 °C. Enzyme production was stimulated by supplementing the wheat bran with 1% w/w each of lactose, soyabean meal and 1 mM each of CaCl 2 and MgSO 4. The enzyme showed optimum activity at 50 °C and pH 6.0. The thermal stability profile revealed a half-life of 6 h at 50 °C which improved significantly with the addition of Ca 2+. It could effectively digest the hard-gel of 15–20% corn starch without liquefying separately with α-amylase, exhibiting an overall liquefying efficiency of 98% and saccharifying efficiency of 85% after 24 h incubation at 40–60 °C.