Abstract
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•LU and TLL was immobilized on OC supports at two different loadings.•The loading affected the enzyme stability, LU highly loaded was always more stable than lowly loaded preparations.•All preparations were modified with PEI and/or Glu with scarce effect on enzyme activity.•Highly loaded preparations were much stabilized by the modifications that lowly loaded preparations.•The loading effect was mainly observed using Glu modification.
Phospholipase Lecitase Ultra (LU) and lipase from Thermomyces lanuginosus (TLL) have been immobilized under conditions that favor either enzyme crowding or enzyme dispersion. Highly loaded LU was more stable than low loaded biocatalyst under all studied conditions. Using TLL, the results depended on the inactivation conditions, e.g., crowding was positive at pH 5 and negative at pH 7. Then, all preparations were treated with glutaraldehyde (Glu), polyethyleneimine (PEI) or sequentially with Glu and PEI. These treatments may permit to stabilize the physically immobilized lipases by avoiding enzyme desorption via intermolecular crosslinking. Moreover, immobilizing a second enzyme on the lipase-glutaraldehyde-PEI has been proposed as a strategy without risks of PEI desorption by incubation in high ion strength solutions. The treatments altered the enzyme activity slightly but produced significant enzyme stabilization. This enzyme stabilization was more significant when using the highly loaded preparations, where intermolecular crosslinking was easier to obtain. SDS-PAGE analyses confirmed that crowded enzyme preparations were intermolecular crosslinked using Glu plus PEI, but some molecules still remained non-crosslinked. In general, PEI treatment was the most effective in increasing enzyme stability, while glutaraldehyde had a milder stabilization effect.