Soluble and immobilized enzyme technology in bioconversion of barley starch

Abstract

Homogeneous and heterogeneous biocatalysis were both investigated as tools for barley starch syrup production. Barley starch was first liquefied by soluble heat-stable Bacillus sp. α-amylase EC 3.2.1.1 (1,4-α- d-glucan glucanohydrolase) Termamyl 60 L at 95°C, pH 6.5, to obtain slurries of varying DE- values up to ≈37. Alternatively, it was extruded with a Creusot-Loire BC 45 twin-screw extruder at 25% moisture, 150°C, for denaturation. After cooling and adjusting the pH to 4.5 or grinding, respectively, the pretreated starch was saccharified either by soluble or by immobilized Aspergillus niger glucoamylase EC 3.2.1.3 (1,4-α- d-glucan glucohydrolase) at 60°C, pH 4.5, to obtain glucose syrup of up to DE 96. The course of hydrolysis was followed by automated Biogel P-2 chromatographic analysis. Glucoamylase was immobilized either on a phenol-formaldehyde resin Duolite S 761 or on silanized Spherosil porous silica beads. Barley glucose syrup obtained was further continuously converted to high fructose syrup by a packed bed reactor of Actinoplanes missouriensis whole cell glucose isomerase (EC 5.3.1.5) Maxazyme entrapped within α-cellulose beads. We could conclude that barley starch may be used as an alternative raw material for biocatalytic starch syrup production.