Enhancement of glucose isomerase activity by pretreatment with substrates prior to immobilization

Keratin-reinforced encapsulation of whole cells expressing glucose isomerase: Development of robust and reusable biocatalyst microbeads

Glucose isomerase (GI) is crucial in high-fructose corn syrup production. This study introduces a novel approach to enhance GI stability and reusability through whole-cell encapsulation of Streptomyces olivochromogenes PTCC 1457 in hybrid microbeads, utilizing keratin as a multifunctional stabilizer and cross-linker. Optimal bead formation was achieved using 2 % alginate, 2-3 % CaCl2, and 2.5 % keratin at pH 7.0 and 37-40 °C. Keratin played a vital role in forming a robust and flexible matrix. Immobilization in keratin-alginate-biomass beads maintained GI activity (655 GIU·g-1) comparable to free enzyme (650 GIU·g-1), while silicate incorporation reduced activity to 234 GIU·g-1. The immobilized enzyme exhibited enhanced stability over a wider pH (6-9) and temperature (4-60 °C) range compared to the free enzyme. Importantly, the immobilized GI maintained 80 % of its initial activity after 20 reaction cycles. Thermogravimetric analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and tensile testing confirmed the formation of hybrid beads with improved thermal and mechanical stability. This novel immobilization strategy, leveraging keratin's unique properties, offers a promising approach for enhancing GI stability, reusability, and storage longevity, potentially improving its industrial applicability in high-fructose corn syrup production.

Cross-linked polymer nanofibers for hyperthermophilic enzyme immobilization: approaches to improve enzyme performance

We report an enzyme immobilization method effective at elevated temperatures (up to 105 °C) and sufficiently robust for hyperthermophilic enzymes. Using a model hyperthermophilic enzyme, α-galactosidase from Thermotoga maritima, immobilization within chemically cross-linked poly(vinyl alcohol) (PVA) nanofibers to provide high specific surface area is achieved by (1) electrospinning a blend of a PVA and enzyme and (2) chemically cross-linking the polymer to entrap the enzyme within a water insoluble PVA fiber. The resulting enzyme-loaded nanofibers are water-insoluble at elevated temperatures, and enzyme leaching is not observed, indicating that the cross-linking effectively immobilizes the enzyme within the fibers. Upon immobilization, the enzyme retains its hyperthermophilic nature and shows improved thermal stability indicated by a 5.5-fold increase in apparent half-life at 90 °C, but with a significant decrease in apparent activity. The loss in apparent activity is attributed to enzyme deactivation and mass transfer limitations. Improvements in the apparent activity can be achieved by incorporating a cryoprotectant during immobilization to prevent enzyme deactivation. For example, immobilization in the presence of trehalose improved the apparent activity by 10-fold. Minimizing the mat thickness to reduce interfiber diffusion was a simple and effective method to further improve the performance of the immobilized enzyme.