The glucose isomerase GICA from Caldicoprobacter algeriensis was immobilized by ionic adsorption on polymethacrylate carriers (Sepabeads EC-EA and EC-HA) or covalent attachment to glyoxal agarose. The Sepabeads EC-HA yielded the highest recovery of activity (89%). The optimum temperature and pH of immobilized GICA were 90 °C and 7.0, respectively, similar to the corresponding values of free enzyme. Nevertheless, the adsorbed enzyme displayed higher relative activity at acidic pH, greater thermostability, and better storage stability, compared to the free form. Moreover, the immobilized enzyme showed an excellent operational stability, in 15 successive 3h reaction cycles at 85°C under a batch reactor, preserving 83% of its initial activity. Interestingly, a continuous process for High Fructose Syrup (HFS) production was established with the adsorbed GICA using a packed bed reactor during eleven days at 70 °C. HPAEC-PAD analysis showed a maximum bioconversion rate of 49 % after 48h of operation.

Abstract:The cyclodextrin glucanotransferase from Paenibacillus pabuli US132 (US132 CGTase) was engineered using a rational approach in an attempt to provide it with anti-staling properties comparable to those of the commercial maltogenic amylase (Novamyl). The study aimed to concurrently decrease the cyclization activity and increase the hydrolytic activity of US132 CGTase. A five-residue loop (PAGFS) was inserted, alone or with the substitution of essential residues for cyclization (G180, L194 and Y195), mimicking the case of Novamyl. The findings indicate that, unlike the case of the CGTase of Thermoanerobacterium thermosulfurigenes strain EM1 whose initial high hydrolytic activity was exceptional, these mutations completely abolished the cyclization and hydrolytic activities of the US132 CGTase. This suggests that those mutations are not able to convert conventional CGTases, whose hydrolytic activities are very weak, into hydrolases. Accordingly, and for the first time, a structural barrier at subsite −3 was advanced as an influential factor which might explain the low hydrolytic activity of conventional CGTases.