Abstract
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•Amyloglucosidase and glucose isomerase have been used to produce fructose syrup.•Their immobilization permit the combined use of the enzymes.•The addition of Mg2+ prevent negative effects of Ca2+.•As one biocatalyst is magnetic, it can be separated from the other biocatalyst.•They could be reused for six consecutive cycles without significant activity decrease.
High fructose syrup is a sweetener widely used as a substitute for sucrose in the food and beverage industry with its current industrial production being carried out in three sequential processes using three different enzymes that operate under different pH and temperature conditions. In this study, a single step synergistic saccharification and isomerization process has been proposed, using the commercial amyloglucosidase from Aspergillus niger immobilized by the CLEA technique (co-aggregated with magnetic nanoparticles and polyethyleneimine), and the commercial immobilized glucose isomerase (IGI) from Streptomyces murinus, Sweetzyme® IT Extra. Immobilization stabilized both enzymes, widening the operation window, thus, by applying a factorial design with a central composite rotatable design it was possible to define an optimal condition of pH and temperature of the process, as well as the best ratio between the two enzymes (pH 5.7, 50 °C and UGI/UAMG ratio of 1.56). Simultaneous saccharification and isomerization of 35 % (w/v) dextrin solution produced a Dextrose Equivalent yield over 95 %, with a glucose-to-fructose conversion around 48 % after 30 h of reaction. In addition, both biocatalysts could be reused for six consecutive cycles, maintaining glucose-to-fructose conversions without loss of activity and with easy recovery of the biocatalysts. Furthermore, because they are of different natures (magnetic CLEA of amyloglucosidase and non-magnetic IGI pellets), if one of these biocatalysts is inactivated, they can be easily separated and reloaded individually.