Improving the retention and reusability of Alpha-amylase by immobilization in nanoporous polyacrylamide-graphene oxide nanocomposites

Abstract

Alpha-amylase was immobilized inside three different polymeric matrices: polyacrylamide hydrogel (PAAm), polyacrylamide-graphene oxide nanocomposite (PAAm-GO) and alginate in order to study and compare the effect of the matrix on the catalytic performance. The morphology, swelling, mechanical properties, retention efficiency, and the catalytic behavior of these newly supported biocatalysts were studied. Nanocomposite made of PAAm-GO matrix incorporated 98% of the enzyme, likely through a cooperative effect, while alginate gels incorporated only 30%. Moreover, the enzyme retention using PAAm-GO reached a value of 97.5%. Starch hydrolysis catalyzed by the immobilized enzyme in PAAm-GO matrix showed similar kinetics profiles up to 5 cycles suggesting that the enzymatic activity is retained. These results compare very favorably with conventional immobilization in alginate where almost no activity was observed after 3 cycles. All results suggest that the PAAm matrices protect the biocatalyst allowing its reusability. Moreover, the improvements in enzyme catalytic properties via immobilization made this system as an excellent candidate in bio-industrial applications such as bioethanol production. Furthermore, the synthesized catalyst could produce a high yield of bioethanol by using enzymes and yeast immobilized in the same PAAm matrix. In this way, it is possible to produce sequential or simultaneous saccharification and fermentation.