Polyethylenimine-glutaraldehyde modification of Novozym® 435 enhances stability and sugar ester synthesis in a xylose-based natural deep eutectic solvent

The synthesis of xylose oleate was investigated using an immobilized lipase ( Candida antarctica lipase B, Novozym® 435), further modified with polyethylenimine and glutaraldehyde. Coating the lipase with polyethylenimine enhanced its stability in tert-butyl alcohol, methyl ethyl ketone, and xylose-based-natural deep eutectic solvent (NADES). Increasing the molecular weight of polyethylenimine improved enzyme stabilization, and biocatalyst stability was enhanced by subsequent treatment with glutaraldehyde. Notably, the lipase immobilized and coated with 750 kDa polyethylenimine and crosslinked with glutaraldehyde exhibited minimal enzyme leaching during desorption tests with Triton X-100 (20 mg/mL). In the enzymatic conversion of oleic acid to xylose oleate, the modified lipase outperformed the unmodified Novozym® 435, yielding 2.3-fold higher conversions in xylose-based NADES medium. The enhanced performance of the modified biocatalyst was also evident in operational stability assays, where it retained 75 % of its relative conversion after five consecutive reaction cycles, demonstrating a threefold increase in stability compared with the untreated biocatalyst. The resulting xylose esters were purified and identified by mass spectrometry, confirming the formation of xylose mono-, di-, trioleate derivatives. The composition of the reaction products varied depending on both the solvent and the employed biocatalyst. Importantly, the synthesized esters exhibited superior emulsifying properties compared with certain commercial surfactants. • Modified N435 biocatalyst was developed for the synthesis of xylose oleate. • Polyethylenimine coating and glutaraldehyde crosslinking enhanced enzyme stability. • Peracylation of xylose into xylose mono-, di-, and trioleates by modified biocatalysts. • Xylose-based-natural deep eutectic solvent permitted to reach the best results. • Xylose esters had superior emulsifying properties to commercial sucrose monolaurate.