Immobilised glucoamylase and its use in the food industry for molasses and sugar derivatives production
ALESSANDRA BASSO, BENJAMIN SUMMERS, ELIZABETH WATTON, SIMONA SERBAN*
*Corresponding author
Purolite Ltd, Unit D, Llantrisant, United Kingdom
Abstract
Dextrose syrups are used in the manufacture of a wide range of products spanning the food, beverage, and pharmaceutical industries and are typically manufactured by exploiting the hydrolytic action of glucoamylases. The covalent and ionic immobilisation of glucoamylase on methacrylic enzyme carrier beads was studied and optimised for applications in batch and flow processes, with the goal of reduction of downstream processing and reuse of the biocatalyst. The activities of the covalent (17.5 U/g) and ionic (15.5 U/g) biocatalysts against a model substrate were determined and the complete biotransformation of maltodextrin into dextrose was also demonstrated in flow conditions and the biocatalyst recycled five times with no change in productivity.
INTRODUCTION
The main application of glucoamylase (GA) is the conversion of starch into dextrose syrups for the food, beverage and pharmaceutical industries. Starch is composed of amylose and amylopectin containing α-1,4 and α-1,6 glycosidic bonds and is processed using gelatinisation and liquefaction to prepare the substrate for saccharification with GA (1). There are many choices of production methods, for example Smiley et al. (2) used a stirred reactor with GA immobilised onto DEAE cellulose. Starch solution can also be passed through a column packed with immobilised enzyme or production can be conducted in batch mode in a stirred reactor (3).
Glucoamylase (EC 3.2.1.3) is part of a family of hydrolases that acts on the non-reducing end of polysaccharides and breaks α-1,4 and α-1,6 bonds to produce glucose.(4) Hydrolysis occurs via a single displacement mechanism with residues Glu179 and Glu400 functioning as the general acid and base (Figure 1). Glucoamylase from Aspergillus niger is classified into family 20 carbohydrate-binding molecule (CBM20) for containing a starch binding domain (SBD) connected to a catalytic domain vi ...
